use super::Provider;
use super::traits::{
    ChatMessage, ChatRequest, ChatResponse, StreamChunk, StreamEvent, StreamOptions, StreamResult,
};
use async_trait::async_trait;
use futures_util::{StreamExt, stream};
use std::cell::RefCell;
use std::collections::HashMap;
use std::sync::atomic::{AtomicUsize, Ordering};
use std::time::Duration;

// ── Provider Fallback Notification ──────────────────────────────────────
// When ReliableProvider uses a fallback (different provider or model than
// requested), it records the details here so channel code can notify the user.
// Uses tokio::task_local to avoid cross-request leakage between concurrent
// users (the old global static had a race window).

/// Info about a provider fallback that occurred during a request.
#[derive(Debug, Clone)]
pub struct ProviderFallbackInfo {
    /// Provider that was originally requested.
    pub requested_provider: String,
    /// Model that was originally requested.
    pub requested_model: String,
    /// Provider that actually served the request.
    pub actual_provider: String,
    /// Model that actually served the request.
    pub actual_model: String,
}

tokio::task_local! {
    static PROVIDER_FALLBACK: RefCell<Option<ProviderFallbackInfo>>;
}

/// Take (consume) the last provider fallback info, if any.
/// Must be called within a `scope_provider_fallback` scope.
pub fn take_last_provider_fallback() -> Option<ProviderFallbackInfo> {
    PROVIDER_FALLBACK
        .try_with(|cell| cell.borrow_mut().take())
        .ok()
        .flatten()
}

/// Run the given future within a provider-fallback scope.
/// Both `record_provider_fallback` (inside ReliableProvider) and
/// `take_last_provider_fallback` (post-loop channel code) must execute
/// within this scope for the data to be visible.
pub async fn scope_provider_fallback<F: std::future::Future>(future: F) -> F::Output {
    PROVIDER_FALLBACK.scope(RefCell::new(None), future).await
}

/// Record a provider fallback event.
fn record_provider_fallback(
    requested_provider: &str,
    requested_model: &str,
    actual_provider: &str,
    actual_model: &str,
) {
    let _ = PROVIDER_FALLBACK.try_with(|cell| {
        *cell.borrow_mut() = Some(ProviderFallbackInfo {
            requested_provider: requested_provider.to_string(),
            requested_model: requested_model.to_string(),
            actual_provider: actual_provider.to_string(),
            actual_model: actual_model.to_string(),
        });
    });
}

// ── Error Classification ─────────────────────────────────────────────────
// Errors are split into retryable (transient server/network failures) and
// non-retryable (permanent client errors). This distinction drives whether
// the retry loop continues, falls back to the next provider, or aborts
// immediately — avoiding wasted latency on errors that cannot self-heal.

/// Check if an error is non-retryable (client errors that won't resolve with retries).
pub fn is_non_retryable(err: &anyhow::Error) -> bool {
    // Context window errors are NOT non-retryable — they can be recovered
    // by truncating conversation history, so let the retry loop handle them.
    if is_context_window_exceeded(err) {
        return false;
    }

    // Tool schema validation errors are NOT non-retryable — the provider's
    // built-in fallback in compatible.rs can recover by switching to
    // prompt-guided tool instructions.
    if is_tool_schema_error(err) {
        return false;
    }

    // 4xx errors are generally non-retryable (bad request, auth failure, etc.),
    // except 429 (rate-limit — transient) and 408 (timeout — worth retrying).
    if let Some(reqwest_err) = err.downcast_ref::<reqwest::Error>()
        && let Some(status) = reqwest_err.status()
    {
        let code = status.as_u16();
        return status.is_client_error() && code != 429 && code != 408;
    }
    // Fallback: parse status codes from stringified errors (some providers
    // embed codes in error messages rather than returning typed HTTP errors).
    let msg = err.to_string();
    for word in msg.split(|c: char| !c.is_ascii_digit()) {
        if let Ok(code) = word.parse::<u16>()
            && (400..500).contains(&code)
        {
            return code != 429 && code != 408;
        }
    }

    // Heuristic: detect auth/model failures by keyword when no HTTP status
    // is available (e.g. gRPC or custom transport errors).
    let msg_lower = msg.to_lowercase();
    let auth_failure_hints = [
        "invalid api key",
        "incorrect api key",
        "missing api key",
        "api key not set",
        "authentication failed",
        "auth failed",
        "unauthorized",
        "forbidden",
        "permission denied",
        "access denied",
        "invalid token",
    ];

    if auth_failure_hints
        .iter()
        .any(|hint| msg_lower.contains(hint))
    {
        return true;
    }

    msg_lower.contains("model")
        && (msg_lower.contains("not found")
            || msg_lower.contains("unknown")
            || msg_lower.contains("unsupported")
            || msg_lower.contains("does not exist")
            || msg_lower.contains("invalid"))
}

/// Check if an error indicates an authentication/authorization failure.
/// Used by channels to evict cached providers whose OAuth tokens may have
/// expired so the next request triggers a fresh credential resolution (#5219).
pub fn is_auth_error(err: &anyhow::Error) -> bool {
    if let Some(reqwest_err) = err.downcast_ref::<reqwest::Error>()
        && let Some(status) = reqwest_err.status()
    {
        let code = status.as_u16();
        return code == 401 || code == 403;
    }

    let msg_lower = err.to_string().to_lowercase();
    let hints = [
        "401 unauthorized",
        "403 forbidden",
        "invalid api key",
        "incorrect api key",
        "authentication failed",
        "auth failed",
        "unauthorized",
        "invalid token",
        "token expired",
        "access_token",
    ];

    hints.iter().any(|hint| msg_lower.contains(hint))
}

/// Check if an error is a tool schema validation failure (e.g. Groq returning
/// "tool call validation failed: attempted to call tool '...' which was not in request").
/// These errors should NOT be classified as non-retryable because the provider's
/// built-in fallback logic (`compatible.rs::is_native_tool_schema_unsupported`)
/// can recover by switching to prompt-guided tool instructions.
pub fn is_tool_schema_error(err: &anyhow::Error) -> bool {
    let lower = err.to_string().to_lowercase();
    let hints = [
        "tool call validation failed",
        "was not in request",
        "not found in tool list",
        "invalid_tool_call",
    ];
    hints.iter().any(|hint| lower.contains(hint))
}

pub fn is_context_window_exceeded(err: &anyhow::Error) -> bool {
    let lower = err.to_string().to_lowercase();
    let hints = [
        "exceeds the context window",
        "exceeds the available context size",
        "context window of this model",
        "maximum context length",
        "context length exceeded",
        "too many tokens",
        "token limit exceeded",
        "prompt is too long",
        "input is too long",
        "prompt exceeds max length",
    ];

    hints.iter().any(|hint| lower.contains(hint))
}

/// Check if an error is a rate-limit (429) error.
fn is_rate_limited(err: &anyhow::Error) -> bool {
    if let Some(reqwest_err) = err.downcast_ref::<reqwest::Error>()
        && let Some(status) = reqwest_err.status()
    {
        return status.as_u16() == 429;
    }
    let msg = err.to_string();
    msg.contains("429")
        && (msg.contains("Too Many") || msg.contains("rate") || msg.contains("limit"))
}

/// Check if a 429 is a business/quota-plan error that retries cannot fix.
///
/// Examples:
/// - plan does not include requested model
/// - insufficient balance / package not active
/// - known provider business codes (e.g. Z.AI: 1311, 1113)
fn is_non_retryable_rate_limit(err: &anyhow::Error) -> bool {
    if !is_rate_limited(err) {
        return false;
    }

    let msg = err.to_string();
    let lower = msg.to_lowercase();

    let business_hints = [
        "plan does not include",
        "doesn't include",
        "not include",
        "insufficient balance",
        "insufficient_balance",
        "insufficient quota",
        "insufficient_quota",
        "quota exhausted",
        "out of credits",
        "no available package",
        "package not active",
        "purchase package",
        "model not available for your plan",
    ];

    if business_hints.iter().any(|hint| lower.contains(hint)) {
        return true;
    }

    // Known provider business codes observed for 429 where retry is futile.
    for token in lower.split(|c: char| !c.is_ascii_digit()) {
        if let Ok(code) = token.parse::<u16>()
            && matches!(code, 1113 | 1311)
        {
            return true;
        }
    }

    false
}

/// Try to extract a Retry-After value (in milliseconds) from an error message.
/// Looks for patterns like `Retry-After: 5` or `retry_after: 2.5` in the error string.
fn parse_retry_after_ms(err: &anyhow::Error) -> Option<u64> {
    let msg = err.to_string();
    let lower = msg.to_lowercase();

    // Look for "retry-after: <number>" or "retry_after: <number>"
    for prefix in &[
        "retry-after:",
        "retry_after:",
        "retry-after ",
        "retry_after ",
    ] {
        if let Some(pos) = lower.find(prefix) {
            let after = &msg[pos + prefix.len()..];
            let num_str: String = after
                .trim()
                .chars()
                .take_while(|c| c.is_ascii_digit() || *c == '.')
                .collect();
            if let Ok(secs) = num_str.parse::<f64>()
                && secs.is_finite()
                && secs >= 0.0
            {
                let millis = Duration::from_secs_f64(secs).as_millis();
                if let Ok(value) = u64::try_from(millis) {
                    return Some(value);
                }
            }
        }
    }
    None
}

fn failure_reason(rate_limited: bool, non_retryable: bool) -> &'static str {
    if rate_limited && non_retryable {
        "rate_limited_non_retryable"
    } else if rate_limited {
        "rate_limited"
    } else if non_retryable {
        "non_retryable"
    } else {
        "retryable"
    }
}

fn compact_error_detail(err: &anyhow::Error) -> String {
    super::sanitize_api_error(&err.to_string())
        .split_whitespace()
        .collect::<Vec<_>>()
        .join(" ")
}

/// Truncate conversation history by dropping the oldest non-system messages.
/// Returns the number of messages dropped. Keeps at least the system message
/// (if any) and the most recent user message.
fn truncate_for_context(messages: &mut Vec<ChatMessage>) -> usize {
    // Find all non-system message indices
    let non_system: Vec<usize> = messages
        .iter()
        .enumerate()
        .filter(|(_, m)| m.role != "system")
        .map(|(i, _)| i)
        .collect();

    // Keep at least the last non-system message (most recent user turn)
    if non_system.len() <= 1 {
        return 0;
    }

    // Drop the oldest half of non-system messages
    let drop_count = non_system.len() / 2;
    let indices_to_remove: Vec<usize> = non_system[..drop_count].to_vec();

    // Remove in reverse order to preserve indices
    for &idx in indices_to_remove.iter().rev() {
        messages.remove(idx);
    }

    drop_count
}

fn push_failure(
    failures: &mut Vec<String>,
    provider_name: &str,
    model: &str,
    attempt: u32,
    max_attempts: u32,
    reason: &str,
    error_detail: &str,
) {
    failures.push(format!(
        "provider={provider_name} model={model} attempt {attempt}/{max_attempts}: {reason}; error={error_detail}"
    ));
}

// ── Resilient Provider Wrapper ────────────────────────────────────────────
// Three-level failover strategy: model chain → provider chain → retry loop.
//   Outer loop:  iterate model fallback chain (original model first, then
//                configured alternatives).
//   Middle loop: iterate registered providers in priority order.
//   Inner loop:  retry the same (provider, model) pair with exponential
//                backoff, rotating API keys on rate-limit errors.
// Loop invariant: `failures` accumulates every failed attempt so the final
// error message gives operators a complete diagnostic trail.

/// Provider wrapper with retry, fallback, auth rotation, and model failover.
pub struct ReliableProvider {
    providers: Vec<(String, Box<dyn Provider>)>,
    max_retries: u32,
    base_backoff_ms: u64,
    /// Extra API keys for rotation (index tracks round-robin position).
    api_keys: Vec<String>,
    key_index: AtomicUsize,
    /// Per-model fallback chains: model_name → [fallback_model_1, fallback_model_2, ...]
    model_fallbacks: HashMap<String, Vec<String>>,
}

impl ReliableProvider {
    pub fn new(
        providers: Vec<(String, Box<dyn Provider>)>,
        max_retries: u32,
        base_backoff_ms: u64,
    ) -> Self {
        Self {
            providers,
            max_retries,
            base_backoff_ms: base_backoff_ms.max(50),
            api_keys: Vec::new(),
            key_index: AtomicUsize::new(0),
            model_fallbacks: HashMap::new(),
        }
    }

    /// Set additional API keys for round-robin rotation on rate-limit errors.
    pub fn with_api_keys(mut self, keys: Vec<String>) -> Self {
        self.api_keys = keys;
        self
    }

    /// Set per-model fallback chains.
    pub fn with_model_fallbacks(mut self, fallbacks: HashMap<String, Vec<String>>) -> Self {
        self.model_fallbacks = fallbacks;
        self
    }

    /// Build the list of models to try: [original, fallback1, fallback2, ...]
    fn model_chain<'a>(&'a self, model: &'a str) -> Vec<&'a str> {
        let mut chain = vec![model];
        if let Some(fallbacks) = self.model_fallbacks.get(model) {
            chain.extend(fallbacks.iter().map(|s| s.as_str()));
        }
        chain
    }

    /// Advance to the next API key and return it, or None if no extra keys configured.
    fn rotate_key(&self) -> Option<&str> {
        if self.api_keys.is_empty() {
            return None;
        }
        let idx = self.key_index.fetch_add(1, Ordering::Relaxed) % self.api_keys.len();
        Some(&self.api_keys[idx])
    }

    /// Compute backoff duration, respecting Retry-After if present.
    fn compute_backoff(&self, base: u64, err: &anyhow::Error) -> u64 {
        if let Some(retry_after) = parse_retry_after_ms(err) {
            // Use Retry-After but cap at 30s to avoid indefinite waits
            retry_after.min(30_000).max(base)
        } else {
            base
        }
    }
}

#[async_trait]
impl Provider for ReliableProvider {
    async fn warmup(&self) -> anyhow::Result<()> {
        for (name, provider) in &self.providers {
            tracing::info!(provider = name, "Warming up provider connection pool");
            if provider.warmup().await.is_err() {
                tracing::warn!(provider = name, "Warmup failed (non-fatal)");
            }
        }
        Ok(())
    }

    async fn chat_with_system(
        &self,
        system_prompt: Option<&str>,
        message: &str,
        model: &str,
        temperature: Option<f64>,
    ) -> anyhow::Result<String> {
        let models = self.model_chain(model);
        let mut failures = Vec::new();

        // Outer: model fallback chain. Middle: provider priority. Inner: retries.
        // Each iteration: attempt one (provider, model) call. On success, return
        // immediately. On non-retryable error, break to next provider. On
        // retryable error, sleep with exponential backoff and retry.
        for current_model in &models {
            for (provider_name, provider) in &self.providers {
                let mut backoff_ms = self.base_backoff_ms;

                for attempt in 0..=self.max_retries {
                    match provider
                        .chat_with_system(system_prompt, message, current_model, temperature)
                        .await
                    {
                        Ok(resp) => {
                            if attempt > 0
                                || *current_model != model
                                || self.providers.first().map(|(n, _)| n.as_str())
                                    != Some(provider_name)
                            {
                                tracing::info!(
                                    provider = provider_name,
                                    model = *current_model,
                                    attempt,
                                    original_model = model,
                                    "Provider recovered (failover/retry)"
                                );
                                let primary = self
                                    .providers
                                    .first()
                                    .map(|(n, _)| n.as_str())
                                    .unwrap_or("");
                                record_provider_fallback(
                                    primary,
                                    model,
                                    provider_name,
                                    current_model,
                                );
                            }
                            return Ok(resp);
                        }
                        Err(e) => {
                            // Context window exceeded: no history to truncate
                            // in chat_with_system, bail immediately.
                            if is_context_window_exceeded(&e) {
                                let error_detail = compact_error_detail(&e);
                                push_failure(
                                    &mut failures,
                                    provider_name,
                                    current_model,
                                    attempt + 1,
                                    self.max_retries + 1,
                                    "non_retryable",
                                    &error_detail,
                                );
                                anyhow::bail!(
                                    "Request exceeds model context window. Attempts:\n{}",
                                    failures.join("\n")
                                );
                            }

                            let non_retryable_rate_limit = is_non_retryable_rate_limit(&e);
                            let non_retryable = is_non_retryable(&e) || non_retryable_rate_limit;
                            let rate_limited = is_rate_limited(&e);
                            let failure_reason = failure_reason(rate_limited, non_retryable);
                            let error_detail = compact_error_detail(&e);

                            push_failure(
                                &mut failures,
                                provider_name,
                                current_model,
                                attempt + 1,
                                self.max_retries + 1,
                                failure_reason,
                                &error_detail,
                            );

                            // Rate-limit with rotatable keys: cycle to the next API key
                            // so the retry hits a different quota bucket.
                            if rate_limited
                                && !non_retryable_rate_limit
                                && let Some(new_key) = self.rotate_key()
                            {
                                tracing::warn!(
                                    provider = provider_name,
                                    error = %error_detail,
                                    "Rate limited; key rotation selected key ending ...{} \
                                     but cannot apply (Provider trait has no set_api_key). \
                                     Retrying with original key.",
                                    &new_key[new_key.len().saturating_sub(4)..]
                                );
                            }

                            if non_retryable {
                                tracing::warn!(
                                    provider = provider_name,
                                    model = *current_model,
                                    error = %error_detail,
                                    "Non-retryable error, moving on"
                                );
                                break;
                            }

                            if attempt < self.max_retries {
                                let wait = self.compute_backoff(backoff_ms, &e);
                                tracing::warn!(
                                    provider = provider_name,
                                    model = *current_model,
                                    attempt = attempt + 1,
                                    backoff_ms = wait,
                                    reason = failure_reason,
                                    error = %error_detail,
                                    "Provider call failed, retrying"
                                );
                                tokio::time::sleep(Duration::from_millis(wait)).await;
                                backoff_ms = (backoff_ms.saturating_mul(2)).min(10_000);
                            }
                        }
                    }
                }

                tracing::warn!(
                    provider = provider_name,
                    model = *current_model,
                    "Exhausted retries, trying next provider/model"
                );
            }

            if *current_model != model {
                tracing::warn!(
                    original_model = model,
                    fallback_model = *current_model,
                    "Model fallback exhausted all providers, trying next fallback model"
                );
            }
        }

        anyhow::bail!(
            "All providers/models failed. Attempts:\n{}",
            failures.join("\n")
        )
    }

    async fn chat_with_history(
        &self,
        messages: &[ChatMessage],
        model: &str,
        temperature: Option<f64>,
    ) -> anyhow::Result<String> {
        let models = self.model_chain(model);
        let mut failures = Vec::new();
        let mut effective_messages = messages.to_vec();
        let mut context_truncated = false;

        for current_model in &models {
            for (provider_name, provider) in &self.providers {
                let mut backoff_ms = self.base_backoff_ms;

                for attempt in 0..=self.max_retries {
                    match provider
                        .chat_with_history(&effective_messages, current_model, temperature)
                        .await
                    {
                        Ok(resp) => {
                            if attempt > 0
                                || *current_model != model
                                || context_truncated
                                || self.providers.first().map(|(n, _)| n.as_str())
                                    != Some(provider_name)
                            {
                                tracing::info!(
                                    provider = provider_name,
                                    model = *current_model,
                                    attempt,
                                    original_model = model,
                                    context_truncated,
                                    "Provider recovered (failover/retry)"
                                );
                                let primary = self
                                    .providers
                                    .first()
                                    .map(|(n, _)| n.as_str())
                                    .unwrap_or("");
                                record_provider_fallback(
                                    primary,
                                    model,
                                    provider_name,
                                    current_model,
                                );
                            }
                            return Ok(resp);
                        }
                        Err(e) => {
                            // Context window exceeded: truncate history and retry
                            if is_context_window_exceeded(&e) && !context_truncated {
                                let dropped = truncate_for_context(&mut effective_messages);
                                if dropped > 0 {
                                    context_truncated = true;
                                    tracing::warn!(
                                        provider = provider_name,
                                        model = *current_model,
                                        dropped,
                                        remaining = effective_messages.len(),
                                        "Context window exceeded; truncated history and retrying"
                                    );
                                    continue; // Retry with truncated messages (counts as an attempt)
                                }
                                // Nothing to truncate (system prompt alone exceeds
                                // the model's context window) — bail immediately
                                // instead of wasting retry attempts.
                                let error_detail = compact_error_detail(&e);
                                push_failure(
                                    &mut failures,
                                    provider_name,
                                    current_model,
                                    attempt + 1,
                                    self.max_retries + 1,
                                    "non_retryable",
                                    &error_detail,
                                );
                                anyhow::bail!(
                                    "Request exceeds model context window and cannot be reduced further. \
                                     Try using a model with a larger context window, reducing the number \
                                     of tools/skills, or enabling compact_context in config. Attempts:\n{}",
                                    failures.join("\n")
                                );
                            }

                            let non_retryable_rate_limit = is_non_retryable_rate_limit(&e);
                            let non_retryable = is_non_retryable(&e) || non_retryable_rate_limit;
                            let rate_limited = is_rate_limited(&e);
                            let failure_reason = failure_reason(rate_limited, non_retryable);
                            let error_detail = compact_error_detail(&e);

                            push_failure(
                                &mut failures,
                                provider_name,
                                current_model,
                                attempt + 1,
                                self.max_retries + 1,
                                failure_reason,
                                &error_detail,
                            );

                            if rate_limited
                                && !non_retryable_rate_limit
                                && let Some(new_key) = self.rotate_key()
                            {
                                tracing::warn!(
                                    provider = provider_name,
                                    error = %error_detail,
                                    "Rate limited; key rotation selected key ending ...{} \
                                     but cannot apply (Provider trait has no set_api_key). \
                                     Retrying with original key.",
                                    &new_key[new_key.len().saturating_sub(4)..]
                                );
                            }

                            if non_retryable {
                                tracing::warn!(
                                    provider = provider_name,
                                    model = *current_model,
                                    error = %error_detail,
                                    "Non-retryable error, moving on"
                                );
                                break;
                            }

                            if attempt < self.max_retries {
                                let wait = self.compute_backoff(backoff_ms, &e);
                                tracing::warn!(
                                    provider = provider_name,
                                    model = *current_model,
                                    attempt = attempt + 1,
                                    backoff_ms = wait,
                                    reason = failure_reason,
                                    error = %error_detail,
                                    "Provider call failed, retrying"
                                );
                                tokio::time::sleep(Duration::from_millis(wait)).await;
                                backoff_ms = (backoff_ms.saturating_mul(2)).min(10_000);
                            }
                        }
                    }
                }

                tracing::warn!(
                    provider = provider_name,
                    model = *current_model,
                    "Exhausted retries, trying next provider/model"
                );
            }
        }

        anyhow::bail!(
            "All providers/models failed. Attempts:\n{}",
            failures.join("\n")
        )
    }

    fn supports_native_tools(&self) -> bool {
        self.providers
            .first()
            .map(|(_, p)| p.supports_native_tools())
            .unwrap_or(false)
    }

    fn supports_vision(&self) -> bool {
        self.providers
            .iter()
            .any(|(_, provider)| provider.supports_vision())
    }

    async fn chat_with_tools(
        &self,
        messages: &[ChatMessage],
        tools: &[serde_json::Value],
        model: &str,
        temperature: Option<f64>,
    ) -> anyhow::Result<ChatResponse> {
        let models = self.model_chain(model);
        let mut failures = Vec::new();
        let mut effective_messages = messages.to_vec();
        let mut context_truncated = false;

        for current_model in &models {
            for (provider_name, provider) in &self.providers {
                let mut backoff_ms = self.base_backoff_ms;

                for attempt in 0..=self.max_retries {
                    match provider
                        .chat_with_tools(&effective_messages, tools, current_model, temperature)
                        .await
                    {
                        Ok(resp) => {
                            if attempt > 0
                                || *current_model != model
                                || context_truncated
                                || self.providers.first().map(|(n, _)| n.as_str())
                                    != Some(provider_name)
                            {
                                tracing::info!(
                                    provider = provider_name,
                                    model = *current_model,
                                    attempt,
                                    original_model = model,
                                    context_truncated,
                                    "Provider recovered (failover/retry)"
                                );
                                let primary = self
                                    .providers
                                    .first()
                                    .map(|(n, _)| n.as_str())
                                    .unwrap_or("");
                                record_provider_fallback(
                                    primary,
                                    model,
                                    provider_name,
                                    current_model,
                                );
                            }
                            return Ok(resp);
                        }
                        Err(e) => {
                            // Context window exceeded: truncate history and retry
                            if is_context_window_exceeded(&e) && !context_truncated {
                                let dropped = truncate_for_context(&mut effective_messages);
                                if dropped > 0 {
                                    context_truncated = true;
                                    tracing::warn!(
                                        provider = provider_name,
                                        model = *current_model,
                                        dropped,
                                        remaining = effective_messages.len(),
                                        "Context window exceeded; truncated history and retrying"
                                    );
                                    continue; // Retry with truncated messages (counts as an attempt)
                                }
                                // Nothing to truncate (system prompt alone exceeds
                                // the model's context window) — bail immediately
                                // instead of wasting retry attempts.
                                let error_detail = compact_error_detail(&e);
                                push_failure(
                                    &mut failures,
                                    provider_name,
                                    current_model,
                                    attempt + 1,
                                    self.max_retries + 1,
                                    "non_retryable",
                                    &error_detail,
                                );
                                anyhow::bail!(
                                    "Request exceeds model context window and cannot be reduced further. \
                                     Try using a model with a larger context window, reducing the number \
                                     of tools/skills, or enabling compact_context in config. Attempts:\n{}",
                                    failures.join("\n")
                                );
                            }

                            let non_retryable_rate_limit = is_non_retryable_rate_limit(&e);
                            let non_retryable = is_non_retryable(&e) || non_retryable_rate_limit;
                            let rate_limited = is_rate_limited(&e);
                            let failure_reason = failure_reason(rate_limited, non_retryable);
                            let error_detail = compact_error_detail(&e);

                            push_failure(
                                &mut failures,
                                provider_name,
                                current_model,
                                attempt + 1,
                                self.max_retries + 1,
                                failure_reason,
                                &error_detail,
                            );

                            if rate_limited
                                && !non_retryable_rate_limit
                                && let Some(new_key) = self.rotate_key()
                            {
                                tracing::warn!(
                                    provider = provider_name,
                                    error = %error_detail,
                                    "Rate limited; key rotation selected key ending ...{} \
                                     but cannot apply (Provider trait has no set_api_key). \
                                     Retrying with original key.",
                                    &new_key[new_key.len().saturating_sub(4)..]
                                );
                            }

                            if non_retryable {
                                tracing::warn!(
                                    provider = provider_name,
                                    model = *current_model,
                                    error = %error_detail,
                                    "Non-retryable error, moving on"
                                );
                                break;
                            }

                            if attempt < self.max_retries {
                                let wait = self.compute_backoff(backoff_ms, &e);
                                tracing::warn!(
                                    provider = provider_name,
                                    model = *current_model,
                                    attempt = attempt + 1,
                                    backoff_ms = wait,
                                    reason = failure_reason,
                                    error = %error_detail,
                                    "Provider call failed, retrying"
                                );
                                tokio::time::sleep(Duration::from_millis(wait)).await;
                                backoff_ms = (backoff_ms.saturating_mul(2)).min(10_000);
                            }
                        }
                    }
                }

                tracing::warn!(
                    provider = provider_name,
                    model = *current_model,
                    "Exhausted retries, trying next provider/model"
                );
            }
        }

        anyhow::bail!(
            "All providers/models failed. Attempts:\n{}",
            failures.join("\n")
        )
    }

    async fn chat(
        &self,
        request: ChatRequest<'_>,
        model: &str,
        temperature: Option<f64>,
    ) -> anyhow::Result<ChatResponse> {
        let models = self.model_chain(model);
        let mut failures = Vec::new();
        let mut effective_messages = request.messages.to_vec();
        let mut context_truncated = false;

        for current_model in &models {
            for (provider_name, provider) in &self.providers {
                let mut backoff_ms = self.base_backoff_ms;

                for attempt in 0..=self.max_retries {
                    let req = ChatRequest {
                        messages: &effective_messages,
                        tools: request.tools,
                    };
                    match provider.chat(req, current_model, temperature).await {
                        Ok(resp) => {
                            if attempt > 0
                                || *current_model != model
                                || context_truncated
                                || self.providers.first().map(|(n, _)| n.as_str())
                                    != Some(provider_name)
                            {
                                tracing::info!(
                                    provider = provider_name,
                                    model = *current_model,
                                    attempt,
                                    original_model = model,
                                    context_truncated,
                                    "Provider recovered (failover/retry)"
                                );
                                let primary = self
                                    .providers
                                    .first()
                                    .map(|(n, _)| n.as_str())
                                    .unwrap_or("");
                                record_provider_fallback(
                                    primary,
                                    model,
                                    provider_name,
                                    current_model,
                                );
                            }
                            return Ok(resp);
                        }
                        Err(e) => {
                            // Context window exceeded: truncate history and retry
                            if is_context_window_exceeded(&e) && !context_truncated {
                                let dropped = truncate_for_context(&mut effective_messages);
                                if dropped > 0 {
                                    context_truncated = true;
                                    tracing::warn!(
                                        provider = provider_name,
                                        model = *current_model,
                                        dropped,
                                        remaining = effective_messages.len(),
                                        "Context window exceeded; truncated history and retrying"
                                    );
                                    continue; // Retry with truncated messages (counts as an attempt)
                                }
                                // Nothing to truncate (system prompt alone exceeds
                                // the model's context window) — bail immediately
                                // instead of wasting retry attempts.
                                let error_detail = compact_error_detail(&e);
                                push_failure(
                                    &mut failures,
                                    provider_name,
                                    current_model,
                                    attempt + 1,
                                    self.max_retries + 1,
                                    "non_retryable",
                                    &error_detail,
                                );
                                anyhow::bail!(
                                    "Request exceeds model context window and cannot be reduced further. \
                                     Try using a model with a larger context window, reducing the number \
                                     of tools/skills, or enabling compact_context in config. Attempts:\n{}",
                                    failures.join("\n")
                                );
                            }

                            let non_retryable_rate_limit = is_non_retryable_rate_limit(&e);
                            let non_retryable = is_non_retryable(&e) || non_retryable_rate_limit;
                            let rate_limited = is_rate_limited(&e);
                            let failure_reason = failure_reason(rate_limited, non_retryable);
                            let error_detail = compact_error_detail(&e);

                            push_failure(
                                &mut failures,
                                provider_name,
                                current_model,
                                attempt + 1,
                                self.max_retries + 1,
                                failure_reason,
                                &error_detail,
                            );

                            if rate_limited
                                && !non_retryable_rate_limit
                                && let Some(new_key) = self.rotate_key()
                            {
                                tracing::warn!(
                                    provider = provider_name,
                                    error = %error_detail,
                                    "Rate limited; key rotation selected key ending ...{} \
                                     but cannot apply (Provider trait has no set_api_key). \
                                     Retrying with original key.",
                                    &new_key[new_key.len().saturating_sub(4)..]
                                );
                            }

                            if non_retryable {
                                tracing::warn!(
                                    provider = provider_name,
                                    model = *current_model,
                                    error = %error_detail,
                                    "Non-retryable error, moving on"
                                );
                                break;
                            }

                            if attempt < self.max_retries {
                                let wait = self.compute_backoff(backoff_ms, &e);
                                tracing::warn!(
                                    provider = provider_name,
                                    model = *current_model,
                                    attempt = attempt + 1,
                                    backoff_ms = wait,
                                    reason = failure_reason,
                                    error = %error_detail,
                                    "Provider call failed, retrying"
                                );
                                tokio::time::sleep(Duration::from_millis(wait)).await;
                                backoff_ms = (backoff_ms.saturating_mul(2)).min(10_000);
                            }
                        }
                    }
                }

                tracing::warn!(
                    provider = provider_name,
                    model = *current_model,
                    "Exhausted retries, trying next provider/model"
                );
            }

            if *current_model != model {
                tracing::warn!(
                    original_model = model,
                    fallback_model = *current_model,
                    "Model fallback exhausted all providers, trying next fallback model"
                );
            }
        }

        anyhow::bail!(
            "All providers/models failed. Attempts:\n{}",
            failures.join("\n")
        )
    }

    fn supports_streaming(&self) -> bool {
        self.providers.iter().any(|(_, p)| p.supports_streaming())
    }

    fn supports_streaming_tool_events(&self) -> bool {
        self.providers
            .iter()
            .any(|(_, p)| p.supports_streaming_tool_events())
    }

    fn stream_chat(
        &self,
        request: ChatRequest<'_>,
        model: &str,
        temperature: Option<f64>,
        options: StreamOptions,
    ) -> stream::BoxStream<'static, StreamResult<StreamEvent>> {
        let needs_tool_events = request.tools.is_some_and(|tools| !tools.is_empty());

        for (provider_name, provider) in &self.providers {
            if !provider.supports_streaming() || !options.enabled {
                continue;
            }

            if needs_tool_events && !provider.supports_streaming_tool_events() {
                continue;
            }

            let provider_clone = provider_name.clone();

            let current_model = self
                .model_chain(model)
                .first()
                .copied()
                .unwrap_or(model)
                .to_string();

            let req = ChatRequest {
                messages: request.messages,
                tools: request.tools,
            };
            let stream = provider.stream_chat(req, &current_model, temperature, options);
            let (tx, rx) = tokio::sync::mpsc::channel::<StreamResult<StreamEvent>>(100);

            tokio::spawn(async move {
                let mut stream = stream;
                while let Some(event) = stream.next().await {
                    if let Err(ref e) = event {
                        tracing::warn!(
                            provider = provider_clone,
                            model = current_model,
                            "Streaming error: {e}"
                        );
                    }
                    if tx.send(event).await.is_err() {
                        break;
                    }
                }
            });

            return stream::unfold(rx, |mut rx| async move {
                rx.recv().await.map(|event| (event, rx))
            })
            .boxed();
        }

        let message = if needs_tool_events {
            "No provider supports streaming tool events".to_string()
        } else {
            "No provider supports streaming".to_string()
        };
        stream::once(async move { Err(super::traits::StreamError::Provider(message)) }).boxed()
    }

    fn stream_chat_with_system(
        &self,
        system_prompt: Option<&str>,
        message: &str,
        model: &str,
        temperature: Option<f64>,
        options: StreamOptions,
    ) -> stream::BoxStream<'static, StreamResult<StreamChunk>> {
        // Try each provider/model combination for streaming
        // For streaming, we use the first provider that supports it and has streaming enabled
        for (provider_name, provider) in &self.providers {
            if !provider.supports_streaming() || !options.enabled {
                continue;
            }

            // Clone provider data for the stream
            let provider_clone = provider_name.clone();

            // Try the first model in the chain for streaming
            let current_model = match self.model_chain(model).first() {
                Some(m) => (*m).to_string(),
                None => model.to_string(),
            };

            // For streaming, we attempt once and propagate errors
            // The caller can retry the entire request if needed
            let stream = provider.stream_chat_with_system(
                system_prompt,
                message,
                &current_model,
                temperature,
                options,
            );

            // Use a channel to bridge the stream with logging
            let (tx, rx) = tokio::sync::mpsc::channel::<StreamResult<StreamChunk>>(100);

            tokio::spawn(async move {
                let mut stream = stream;
                while let Some(chunk) = stream.next().await {
                    if let Err(ref e) = chunk {
                        tracing::warn!(
                            provider = provider_clone,
                            model = current_model,
                            "Streaming error: {e}"
                        );
                    }
                    if tx.send(chunk).await.is_err() {
                        break; // Receiver dropped
                    }
                }
            });

            // Convert channel receiver to stream
            return stream::unfold(rx, |mut rx| async move {
                rx.recv().await.map(|chunk| (chunk, rx))
            })
            .boxed();
        }

        // No streaming support available
        stream::once(async move {
            Err(super::traits::StreamError::Provider(
                "No provider supports streaming".to_string(),
            ))
        })
        .boxed()
    }

    fn stream_chat_with_history(
        &self,
        messages: &[ChatMessage],
        model: &str,
        temperature: Option<f64>,
        options: StreamOptions,
    ) -> stream::BoxStream<'static, StreamResult<StreamChunk>> {
        // Try each provider/model combination for streaming with history.
        // Mirrors stream_chat_with_system but delegates to the underlying
        // provider's stream_chat_with_history, preserving the full conversation.
        for (provider_name, provider) in &self.providers {
            if !provider.supports_streaming() || !options.enabled {
                continue;
            }

            let provider_clone = provider_name.clone();

            let current_model = match self.model_chain(model).first() {
                Some(m) => (*m).to_string(),
                None => model.to_string(),
            };

            let stream =
                provider.stream_chat_with_history(messages, &current_model, temperature, options);

            let (tx, rx) = tokio::sync::mpsc::channel::<StreamResult<StreamChunk>>(100);

            tokio::spawn(async move {
                let mut stream = stream;
                while let Some(chunk) = stream.next().await {
                    if let Err(ref e) = chunk {
                        tracing::warn!(
                            provider = provider_clone,
                            model = current_model,
                            "Streaming error: {e}"
                        );
                    }
                    if tx.send(chunk).await.is_err() {
                        break; // Receiver dropped
                    }
                }
            });

            return stream::unfold(rx, |mut rx| async move {
                rx.recv().await.map(|chunk| (chunk, rx))
            })
            .boxed();
        }

        // No streaming support available
        stream::once(async move {
            Err(super::traits::StreamError::Provider(
                "No provider supports streaming".to_string(),
            ))
        })
        .boxed()
    }
}

#[cfg(test)]
mod tests {
    use super::*;
    use futures_util::StreamExt;
    use std::sync::Arc;
    use kylinbot_api::tool::ToolSpec;

    struct MockProvider {
        calls: Arc<AtomicUsize>,
        fail_until_attempt: usize,
        response: &'static str,
        error: &'static str,
    }

    #[async_trait]
    impl Provider for MockProvider {
        async fn chat_with_system(
            &self,
            _system_prompt: Option<&str>,
            _message: &str,
            _model: &str,
            _temperature: Option<f64>,
        ) -> anyhow::Result<String> {
            let attempt = self.calls.fetch_add(1, Ordering::SeqCst) + 1;
            if attempt <= self.fail_until_attempt {
                anyhow::bail!(self.error);
            }
            Ok(self.response.to_string())
        }

        async fn chat_with_history(
            &self,
            _messages: &[ChatMessage],
            _model: &str,
            _temperature: Option<f64>,
        ) -> anyhow::Result<String> {
            let attempt = self.calls.fetch_add(1, Ordering::SeqCst) + 1;
            if attempt <= self.fail_until_attempt {
                anyhow::bail!(self.error);
            }
            Ok(self.response.to_string())
        }
    }

    /// Mock that records which model was used for each call.
    struct ModelAwareMock {
        calls: Arc<AtomicUsize>,
        models_seen: parking_lot::Mutex<Vec<String>>,
        fail_models: Vec<&'static str>,
        response: &'static str,
    }

    #[async_trait]
    impl Provider for ModelAwareMock {
        async fn chat_with_system(
            &self,
            _system_prompt: Option<&str>,
            _message: &str,
            model: &str,
            _temperature: Option<f64>,
        ) -> anyhow::Result<String> {
            self.calls.fetch_add(1, Ordering::SeqCst);
            self.models_seen.lock().push(model.to_string());
            if self.fail_models.contains(&model) {
                anyhow::bail!("500 model {} unavailable", model);
            }
            Ok(self.response.to_string())
        }
    }

    // ── Existing tests (preserved) ──

    #[tokio::test]
    async fn succeeds_without_retry() {
        let calls = Arc::new(AtomicUsize::new(0));
        let provider = ReliableProvider::new(
            vec![(
                "primary".into(),
                Box::new(MockProvider {
                    calls: Arc::clone(&calls),
                    fail_until_attempt: 0,
                    response: "ok",
                    error: "boom",
                }),
            )],
            2,
            1,
        );

        let result = provider
            .simple_chat("hello", "test", Some(0.0))
            .await
            .unwrap();
        assert_eq!(result, "ok");
        assert_eq!(calls.load(Ordering::SeqCst), 1);
    }

    #[tokio::test]
    async fn retries_then_recovers() {
        let calls = Arc::new(AtomicUsize::new(0));
        let provider = ReliableProvider::new(
            vec![(
                "primary".into(),
                Box::new(MockProvider {
                    calls: Arc::clone(&calls),
                    fail_until_attempt: 1,
                    response: "recovered",
                    error: "temporary",
                }),
            )],
            2,
            1,
        );

        let result = provider
            .simple_chat("hello", "test", Some(0.0))
            .await
            .unwrap();
        assert_eq!(result, "recovered");
        assert_eq!(calls.load(Ordering::SeqCst), 2);
    }

    #[tokio::test]
    async fn falls_back_after_retries_exhausted() {
        let primary_calls = Arc::new(AtomicUsize::new(0));
        let fallback_calls = Arc::new(AtomicUsize::new(0));

        let provider = ReliableProvider::new(
            vec![
                (
                    "primary".into(),
                    Box::new(MockProvider {
                        calls: Arc::clone(&primary_calls),
                        fail_until_attempt: usize::MAX,
                        response: "never",
                        error: "primary down",
                    }),
                ),
                (
                    "fallback".into(),
                    Box::new(MockProvider {
                        calls: Arc::clone(&fallback_calls),
                        fail_until_attempt: 0,
                        response: "from fallback",
                        error: "fallback down",
                    }),
                ),
            ],
            1,
            1,
        );

        let result = provider
            .simple_chat("hello", "test", Some(0.0))
            .await
            .unwrap();
        assert_eq!(result, "from fallback");
        assert_eq!(primary_calls.load(Ordering::SeqCst), 2);
        assert_eq!(fallback_calls.load(Ordering::SeqCst), 1);
    }

    #[tokio::test]
    async fn returns_aggregated_error_when_all_providers_fail() {
        let provider = ReliableProvider::new(
            vec![
                (
                    "p1".into(),
                    Box::new(MockProvider {
                        calls: Arc::new(AtomicUsize::new(0)),
                        fail_until_attempt: usize::MAX,
                        response: "never",
                        error: "p1 error",
                    }),
                ),
                (
                    "p2".into(),
                    Box::new(MockProvider {
                        calls: Arc::new(AtomicUsize::new(0)),
                        fail_until_attempt: usize::MAX,
                        response: "never",
                        error: "p2 error",
                    }),
                ),
            ],
            0,
            1,
        );

        let err = provider
            .simple_chat("hello", "test", Some(0.0))
            .await
            .expect_err("all providers should fail");
        let msg = err.to_string();
        assert!(msg.contains("All providers/models failed"));
        assert!(msg.contains("provider=p1 model=test"));
        assert!(msg.contains("provider=p2 model=test"));
        assert!(msg.contains("error=p1 error"));
        assert!(msg.contains("error=p2 error"));
        assert!(msg.contains("retryable"));
    }

    #[test]
    fn non_retryable_detects_common_patterns() {
        assert!(is_non_retryable(&anyhow::anyhow!("400 Bad Request")));
        assert!(is_non_retryable(&anyhow::anyhow!("401 Unauthorized")));
        assert!(is_non_retryable(&anyhow::anyhow!("403 Forbidden")));
        assert!(is_non_retryable(&anyhow::anyhow!("404 Not Found")));
        assert!(is_non_retryable(&anyhow::anyhow!(
            "invalid api key provided"
        )));
        assert!(is_non_retryable(&anyhow::anyhow!("authentication failed")));
        assert!(is_non_retryable(&anyhow::anyhow!(
            "model glm-4.7 not found"
        )));
        assert!(is_non_retryable(&anyhow::anyhow!(
            "unsupported model: glm-4.7"
        )));
        assert!(!is_non_retryable(&anyhow::anyhow!("429 Too Many Requests")));
        assert!(!is_non_retryable(&anyhow::anyhow!("408 Request Timeout")));
        assert!(!is_non_retryable(&anyhow::anyhow!(
            "500 Internal Server Error"
        )));
        assert!(!is_non_retryable(&anyhow::anyhow!("502 Bad Gateway")));
        assert!(!is_non_retryable(&anyhow::anyhow!("timeout")));
        assert!(!is_non_retryable(&anyhow::anyhow!("connection reset")));
        assert!(!is_non_retryable(&anyhow::anyhow!(
            "model overloaded, try again later"
        )));
        // Context window errors are now recoverable (not non-retryable)
        assert!(!is_non_retryable(&anyhow::anyhow!(
            "OpenAI Codex stream error: Your input exceeds the context window of this model."
        )));
    }

    #[test]
    fn auth_error_detects_common_patterns() {
        assert!(is_auth_error(&anyhow::anyhow!("401 Unauthorized")));
        assert!(is_auth_error(&anyhow::anyhow!("403 Forbidden")));
        assert!(is_auth_error(&anyhow::anyhow!("invalid api key")));
        assert!(is_auth_error(&anyhow::anyhow!("authentication failed")));
        assert!(is_auth_error(&anyhow::anyhow!("token expired")));
        assert!(!is_auth_error(&anyhow::anyhow!("400 Bad Request")));
        assert!(!is_auth_error(&anyhow::anyhow!("429 Too Many Requests")));
        assert!(!is_auth_error(&anyhow::anyhow!("timeout")));
        assert!(!is_auth_error(&anyhow::anyhow!("connection reset")));
    }

    #[tokio::test]
    async fn context_window_error_aborts_retries_and_model_fallbacks() {
        let calls = Arc::new(AtomicUsize::new(0));
        let mut model_fallbacks = std::collections::HashMap::new();
        model_fallbacks.insert(
            "gpt-5.3-codex".to_string(),
            vec!["gpt-5.2-codex".to_string()],
        );

        let provider = ReliableProvider::new(
            vec![(
                "openai-codex".into(),
                Box::new(MockProvider {
                    calls: Arc::clone(&calls),
                    fail_until_attempt: usize::MAX,
                    response: "never",
                    error: "OpenAI Codex stream error: Your input exceeds the context window of this model. Please adjust your input and try again.",
                }),
            )],
            4,
            1,
        )
        .with_model_fallbacks(model_fallbacks);

        let err = provider
            .simple_chat("hello", "gpt-5.3-codex", Some(0.0))
            .await
            .expect_err("context window overflow should fail fast");
        let msg = err.to_string();

        assert!(msg.contains("context window"));
        // chat_with_system has no history to truncate, so it bails immediately
        assert_eq!(calls.load(Ordering::SeqCst), 1);
    }

    #[tokio::test]
    async fn aggregated_error_marks_non_retryable_model_mismatch_with_details() {
        let calls = Arc::new(AtomicUsize::new(0));
        let provider = ReliableProvider::new(
            vec![(
                "custom".into(),
                Box::new(MockProvider {
                    calls: Arc::clone(&calls),
                    fail_until_attempt: usize::MAX,
                    response: "never",
                    error: "unsupported model: glm-4.7",
                }),
            )],
            3,
            1,
        );

        let err = provider
            .simple_chat("hello", "glm-4.7", Some(0.0))
            .await
            .expect_err("provider should fail");
        let msg = err.to_string();

        assert!(msg.contains("non_retryable"));
        assert!(msg.contains("error=unsupported model: glm-4.7"));
        // Non-retryable errors should not consume retry budget.
        assert_eq!(calls.load(Ordering::SeqCst), 1);
    }

    #[tokio::test]
    async fn skips_retries_on_non_retryable_error() {
        let primary_calls = Arc::new(AtomicUsize::new(0));
        let fallback_calls = Arc::new(AtomicUsize::new(0));

        let provider = ReliableProvider::new(
            vec![
                (
                    "primary".into(),
                    Box::new(MockProvider {
                        calls: Arc::clone(&primary_calls),
                        fail_until_attempt: usize::MAX,
                        response: "never",
                        error: "401 Unauthorized",
                    }),
                ),
                (
                    "fallback".into(),
                    Box::new(MockProvider {
                        calls: Arc::clone(&fallback_calls),
                        fail_until_attempt: 0,
                        response: "from fallback",
                        error: "fallback err",
                    }),
                ),
            ],
            3,
            1,
        );

        let result = provider
            .simple_chat("hello", "test", Some(0.0))
            .await
            .unwrap();
        assert_eq!(result, "from fallback");
        // Primary should have been called only once (no retries)
        assert_eq!(primary_calls.load(Ordering::SeqCst), 1);
        assert_eq!(fallback_calls.load(Ordering::SeqCst), 1);
    }

    #[tokio::test]
    async fn chat_with_history_retries_then_recovers() {
        let calls = Arc::new(AtomicUsize::new(0));
        let provider = ReliableProvider::new(
            vec![(
                "primary".into(),
                Box::new(MockProvider {
                    calls: Arc::clone(&calls),
                    fail_until_attempt: 1,
                    response: "history ok",
                    error: "temporary",
                }),
            )],
            2,
            1,
        );

        let messages = vec![ChatMessage::system("system"), ChatMessage::user("hello")];
        let result = provider
            .chat_with_history(&messages, "test", Some(0.0))
            .await
            .unwrap();
        assert_eq!(result, "history ok");
        assert_eq!(calls.load(Ordering::SeqCst), 2);
    }

    #[tokio::test]
    async fn chat_with_history_falls_back() {
        let primary_calls = Arc::new(AtomicUsize::new(0));
        let fallback_calls = Arc::new(AtomicUsize::new(0));

        let provider = ReliableProvider::new(
            vec![
                (
                    "primary".into(),
                    Box::new(MockProvider {
                        calls: Arc::clone(&primary_calls),
                        fail_until_attempt: usize::MAX,
                        response: "never",
                        error: "primary down",
                    }),
                ),
                (
                    "fallback".into(),
                    Box::new(MockProvider {
                        calls: Arc::clone(&fallback_calls),
                        fail_until_attempt: 0,
                        response: "fallback ok",
                        error: "fallback err",
                    }),
                ),
            ],
            1,
            1,
        );

        let messages = vec![ChatMessage::user("hello")];
        let result = provider
            .chat_with_history(&messages, "test", Some(0.0))
            .await
            .unwrap();
        assert_eq!(result, "fallback ok");
        assert_eq!(primary_calls.load(Ordering::SeqCst), 2);
        assert_eq!(fallback_calls.load(Ordering::SeqCst), 1);
    }

    // ── New tests: model failover ──

    #[tokio::test]
    async fn model_failover_tries_fallback_model() {
        let calls = Arc::new(AtomicUsize::new(0));
        let mock = Arc::new(ModelAwareMock {
            calls: Arc::clone(&calls),
            models_seen: parking_lot::Mutex::new(Vec::new()),
            fail_models: vec!["claude-opus"],
            response: "ok from sonnet",
        });

        let mut fallbacks = HashMap::new();
        fallbacks.insert("claude-opus".to_string(), vec!["claude-sonnet".to_string()]);

        let provider = ReliableProvider::new(
            vec![(
                "anthropic".into(),
                Box::new(mock.clone()) as Box<dyn Provider>,
            )],
            0, // no retries — force immediate model failover
            1,
        )
        .with_model_fallbacks(fallbacks);

        let result = provider
            .simple_chat("hello", "claude-opus", Some(0.0))
            .await
            .unwrap();
        assert_eq!(result, "ok from sonnet");

        let seen = mock.models_seen.lock();
        assert_eq!(seen.len(), 2);
        assert_eq!(seen[0], "claude-opus");
        assert_eq!(seen[1], "claude-sonnet");
    }

    #[tokio::test]
    async fn model_failover_all_models_fail() {
        let calls = Arc::new(AtomicUsize::new(0));
        let mock = Arc::new(ModelAwareMock {
            calls: Arc::clone(&calls),
            models_seen: parking_lot::Mutex::new(Vec::new()),
            fail_models: vec!["model-a", "model-b", "model-c"],
            response: "never",
        });

        let mut fallbacks = HashMap::new();
        fallbacks.insert(
            "model-a".to_string(),
            vec!["model-b".to_string(), "model-c".to_string()],
        );

        let provider = ReliableProvider::new(
            vec![("p1".into(), Box::new(mock.clone()) as Box<dyn Provider>)],
            0,
            1,
        )
        .with_model_fallbacks(fallbacks);

        let err = provider
            .simple_chat("hello", "model-a", Some(0.0))
            .await
            .expect_err("all models should fail");
        assert!(err.to_string().contains("All providers/models failed"));

        let seen = mock.models_seen.lock();
        assert_eq!(seen.len(), 3);
    }

    #[tokio::test]
    async fn no_model_fallbacks_behaves_like_before() {
        let calls = Arc::new(AtomicUsize::new(0));
        let provider = ReliableProvider::new(
            vec![(
                "primary".into(),
                Box::new(MockProvider {
                    calls: Arc::clone(&calls),
                    fail_until_attempt: 0,
                    response: "ok",
                    error: "boom",
                }),
            )],
            2,
            1,
        );
        // No model_fallbacks set — should work exactly as before
        let result = provider
            .simple_chat("hello", "test", Some(0.0))
            .await
            .unwrap();
        assert_eq!(result, "ok");
        assert_eq!(calls.load(Ordering::SeqCst), 1);
    }

    // ── New tests: auth rotation ──

    #[tokio::test]
    async fn auth_rotation_cycles_keys() {
        let provider = ReliableProvider::new(
            vec![(
                "p".into(),
                Box::new(MockProvider {
                    calls: Arc::new(AtomicUsize::new(0)),
                    fail_until_attempt: 0,
                    response: "ok",
                    error: "",
                }),
            )],
            0,
            1,
        )
        .with_api_keys(vec!["key-a".into(), "key-b".into(), "key-c".into()]);

        // Rotate 5 times, verify round-robin
        let keys: Vec<&str> = (0..5).map(|_| provider.rotate_key().unwrap()).collect();
        assert_eq!(keys, vec!["key-a", "key-b", "key-c", "key-a", "key-b"]);
    }

    #[tokio::test]
    async fn auth_rotation_returns_none_when_empty() {
        let provider = ReliableProvider::new(vec![], 0, 1);
        assert!(provider.rotate_key().is_none());
    }

    // ── New tests: Retry-After parsing ──

    #[test]
    fn parse_retry_after_integer() {
        let err = anyhow::anyhow!("429 Too Many Requests, Retry-After: 5");
        assert_eq!(parse_retry_after_ms(&err), Some(5000));
    }

    #[test]
    fn parse_retry_after_float() {
        let err = anyhow::anyhow!("Rate limited. retry_after: 2.5 seconds");
        assert_eq!(parse_retry_after_ms(&err), Some(2500));
    }

    #[test]
    fn parse_retry_after_missing() {
        let err = anyhow::anyhow!("500 Internal Server Error");
        assert_eq!(parse_retry_after_ms(&err), None);
    }

    #[test]
    fn rate_limited_detection() {
        assert!(is_rate_limited(&anyhow::anyhow!("429 Too Many Requests")));
        assert!(is_rate_limited(&anyhow::anyhow!(
            "HTTP 429 rate limit exceeded"
        )));
        assert!(!is_rate_limited(&anyhow::anyhow!("401 Unauthorized")));
        assert!(!is_rate_limited(&anyhow::anyhow!(
            "500 Internal Server Error"
        )));
    }

    #[test]
    fn non_retryable_rate_limit_detects_plan_restricted_model() {
        let err = anyhow::anyhow!(
            "{}",
            "API error (429 Too Many Requests): {\"code\":1311,\"message\":\"the current account plan does not include glm-5\"}"
        );
        assert!(
            is_non_retryable_rate_limit(&err),
            "plan-restricted 429 should skip retries"
        );
    }

    #[test]
    fn non_retryable_rate_limit_detects_insufficient_balance() {
        let err = anyhow::anyhow!(
            "{}",
            "API error (429 Too Many Requests): {\"code\":1113,\"message\":\"insufficient balance\"}"
        );
        assert!(
            is_non_retryable_rate_limit(&err),
            "insufficient-balance 429 should skip retries"
        );
    }

    #[test]
    fn non_retryable_rate_limit_does_not_flag_generic_429() {
        let err = anyhow::anyhow!("429 Too Many Requests: rate limit exceeded");
        assert!(
            !is_non_retryable_rate_limit(&err),
            "generic rate-limit 429 should remain retryable"
        );
    }

    #[test]
    fn compute_backoff_uses_retry_after() {
        let provider = ReliableProvider::new(vec![], 0, 500);
        let err = anyhow::anyhow!("429 Retry-After: 3");
        assert_eq!(provider.compute_backoff(500, &err), 3_000);
    }

    #[test]
    fn compute_backoff_caps_at_30s() {
        let provider = ReliableProvider::new(vec![], 0, 500);
        let err = anyhow::anyhow!("429 Retry-After: 120");
        assert_eq!(provider.compute_backoff(500, &err), 30_000);
    }

    #[test]
    fn compute_backoff_falls_back_to_base() {
        let provider = ReliableProvider::new(vec![], 0, 500);
        let err = anyhow::anyhow!("500 Server Error");
        assert_eq!(provider.compute_backoff(500, &err), 500);
    }

    // ── §2.1 API auth error (401/403) tests ──────────────────

    #[test]
    fn non_retryable_detects_401() {
        let err = anyhow::anyhow!("API error (401 Unauthorized): invalid api key");
        assert!(
            is_non_retryable(&err),
            "401 errors must be detected as non-retryable"
        );
    }

    #[test]
    fn non_retryable_detects_403() {
        let err = anyhow::anyhow!("API error (403 Forbidden): access denied");
        assert!(
            is_non_retryable(&err),
            "403 errors must be detected as non-retryable"
        );
    }

    #[test]
    fn non_retryable_detects_404() {
        let err = anyhow::anyhow!("API error (404 Not Found): model not found");
        assert!(
            is_non_retryable(&err),
            "404 errors must be detected as non-retryable"
        );
    }

    #[test]
    fn non_retryable_does_not_flag_429() {
        let err = anyhow::anyhow!("429 Too Many Requests");
        assert!(
            !is_non_retryable(&err),
            "429 must NOT be treated as non-retryable (it is retryable with backoff)"
        );
    }

    #[test]
    fn non_retryable_does_not_flag_408() {
        let err = anyhow::anyhow!("408 Request Timeout");
        assert!(
            !is_non_retryable(&err),
            "408 must NOT be treated as non-retryable (it is retryable)"
        );
    }

    #[test]
    fn non_retryable_does_not_flag_500() {
        let err = anyhow::anyhow!("500 Internal Server Error");
        assert!(
            !is_non_retryable(&err),
            "500 must NOT be treated as non-retryable (server errors are retryable)"
        );
    }

    #[test]
    fn non_retryable_does_not_flag_502() {
        let err = anyhow::anyhow!("502 Bad Gateway");
        assert!(
            !is_non_retryable(&err),
            "502 must NOT be treated as non-retryable"
        );
    }

    // ── §2.2 Rate limit Retry-After edge cases ───────────────

    #[test]
    fn parse_retry_after_zero() {
        let err = anyhow::anyhow!("429 Too Many Requests, Retry-After: 0");
        assert_eq!(
            parse_retry_after_ms(&err),
            Some(0),
            "Retry-After: 0 should parse as 0ms"
        );
    }

    #[test]
    fn parse_retry_after_with_underscore_separator() {
        let err = anyhow::anyhow!("rate limited, retry_after: 10");
        assert_eq!(
            parse_retry_after_ms(&err),
            Some(10_000),
            "retry_after with underscore must be parsed"
        );
    }

    #[test]
    fn parse_retry_after_space_separator() {
        let err = anyhow::anyhow!("Retry-After 7");
        assert_eq!(
            parse_retry_after_ms(&err),
            Some(7000),
            "Retry-After with space separator must be parsed"
        );
    }

    #[test]
    fn rate_limited_false_for_generic_error() {
        let err = anyhow::anyhow!("Connection refused");
        assert!(
            !is_rate_limited(&err),
            "generic errors must not be flagged as rate-limited"
        );
    }

    // ── §2.3 Malformed API response error classification ─────

    #[tokio::test]
    async fn non_retryable_skips_retries_for_401() {
        let calls = Arc::new(AtomicUsize::new(0));
        let provider = ReliableProvider::new(
            vec![(
                "primary".into(),
                Box::new(MockProvider {
                    calls: Arc::clone(&calls),
                    fail_until_attempt: usize::MAX,
                    response: "never",
                    error: "API error (401 Unauthorized): invalid key",
                }),
            )],
            5,
            1,
        );

        let result = provider.simple_chat("hello", "test", Some(0.0)).await;
        assert!(result.is_err(), "401 should fail without retries");
        assert_eq!(
            calls.load(Ordering::SeqCst),
            1,
            "must not retry on 401 — should be exactly 1 call"
        );
    }

    #[tokio::test]
    async fn non_retryable_rate_limit_skips_retries_for_plan_errors() {
        let calls = Arc::new(AtomicUsize::new(0));
        let provider = ReliableProvider::new(
            vec![(
                "primary".into(),
                Box::new(MockProvider {
                    calls: Arc::clone(&calls),
                    fail_until_attempt: usize::MAX,
                    response: "never",
                    error: "API error (429 Too Many Requests): {\"code\":1311,\"message\":\"plan does not include glm-5\"}",
                }),
            )],
            5,
            1,
        );

        let result = provider.simple_chat("hello", "test", Some(0.0)).await;
        assert!(
            result.is_err(),
            "plan-restricted 429 should fail quickly without retrying"
        );
        assert_eq!(
            calls.load(Ordering::SeqCst),
            1,
            "must not retry non-retryable 429 business errors"
        );
    }

    // Arc<ModelAwareMock> Provider impl provided by blanket impl in kylinbot-types.

    /// Mock provider that implements `chat()` with native tool support.
    struct NativeToolMock {
        calls: Arc<AtomicUsize>,
        fail_until_attempt: usize,
        response_text: &'static str,
        tool_calls: Vec<super::super::traits::ToolCall>,
        error: &'static str,
    }

    #[async_trait]
    impl Provider for NativeToolMock {
        async fn chat_with_system(
            &self,
            _system_prompt: Option<&str>,
            _message: &str,
            _model: &str,
            _temperature: Option<f64>,
        ) -> anyhow::Result<String> {
            Ok(self.response_text.to_string())
        }

        fn supports_native_tools(&self) -> bool {
            true
        }

        async fn chat(
            &self,
            _request: ChatRequest<'_>,
            _model: &str,
            _temperature: Option<f64>,
        ) -> anyhow::Result<ChatResponse> {
            let attempt = self.calls.fetch_add(1, Ordering::SeqCst) + 1;
            if attempt <= self.fail_until_attempt {
                anyhow::bail!(self.error);
            }
            Ok(ChatResponse {
                text: Some(self.response_text.to_string()),
                tool_calls: self.tool_calls.clone(),
                usage: None,
                reasoning_content: None,
            })
        }
    }

    #[tokio::test]
    async fn chat_delegates_to_inner_provider() {
        let calls = Arc::new(AtomicUsize::new(0));
        let tool_call = super::super::traits::ToolCall {
            id: "call_1".to_string(),
            name: "shell".to_string(),
            arguments: r#"{"command":"date"}"#.to_string(),
            extra_content: None,
        };
        let provider = ReliableProvider::new(
            vec![(
                "primary".into(),
                Box::new(NativeToolMock {
                    calls: Arc::clone(&calls),
                    fail_until_attempt: 0,
                    response_text: "ok",
                    tool_calls: vec![tool_call.clone()],
                    error: "boom",
                }) as Box<dyn Provider>,
            )],
            2,
            1,
        );

        let messages = vec![ChatMessage::user("what time is it?")];
        let request = ChatRequest {
            messages: &messages,
            tools: None,
        };
        let result = provider
            .chat(request, "test-model", Some(0.0))
            .await
            .unwrap();

        assert_eq!(result.text.as_deref(), Some("ok"));
        assert_eq!(result.tool_calls.len(), 1);
        assert_eq!(result.tool_calls[0].name, "shell");
        assert_eq!(calls.load(Ordering::SeqCst), 1);
    }

    #[tokio::test]
    async fn chat_retries_and_recovers() {
        let calls = Arc::new(AtomicUsize::new(0));
        let tool_call = super::super::traits::ToolCall {
            id: "call_1".to_string(),
            name: "shell".to_string(),
            arguments: r#"{"command":"date"}"#.to_string(),
            extra_content: None,
        };
        let provider = ReliableProvider::new(
            vec![(
                "primary".into(),
                Box::new(NativeToolMock {
                    calls: Arc::clone(&calls),
                    fail_until_attempt: 2,
                    response_text: "recovered",
                    tool_calls: vec![tool_call],
                    error: "temporary failure",
                }) as Box<dyn Provider>,
            )],
            3,
            1,
        );

        let messages = vec![ChatMessage::user("test")];
        let request = ChatRequest {
            messages: &messages,
            tools: None,
        };
        let result = provider
            .chat(request, "test-model", Some(0.0))
            .await
            .unwrap();

        assert_eq!(result.text.as_deref(), Some("recovered"));
        assert!(
            calls.load(Ordering::SeqCst) > 1,
            "should have retried at least once"
        );
    }

    #[tokio::test]
    async fn chat_preserves_native_tools_support() {
        let calls = Arc::new(AtomicUsize::new(0));
        let provider = ReliableProvider::new(
            vec![(
                "primary".into(),
                Box::new(NativeToolMock {
                    calls: Arc::clone(&calls),
                    fail_until_attempt: 0,
                    response_text: "ok",
                    tool_calls: vec![],
                    error: "boom",
                }) as Box<dyn Provider>,
            )],
            2,
            1,
        );

        assert!(
            provider.supports_native_tools(),
            "ReliableProvider must propagate supports_native_tools from inner provider"
        );
    }

    // ── Gap 2-4: Parity tests for chat() ────────────────────────

    /// Gap 2: `chat()` returns an aggregated error when all providers fail,
    /// matching behavior of `returns_aggregated_error_when_all_providers_fail`.
    #[tokio::test]
    async fn chat_returns_aggregated_error_when_all_providers_fail() {
        let provider = ReliableProvider::new(
            vec![
                (
                    "p1".into(),
                    Box::new(NativeToolMock {
                        calls: Arc::new(AtomicUsize::new(0)),
                        fail_until_attempt: usize::MAX,
                        response_text: "never",
                        tool_calls: vec![],
                        error: "p1 chat error",
                    }) as Box<dyn Provider>,
                ),
                (
                    "p2".into(),
                    Box::new(NativeToolMock {
                        calls: Arc::new(AtomicUsize::new(0)),
                        fail_until_attempt: usize::MAX,
                        response_text: "never",
                        tool_calls: vec![],
                        error: "p2 chat error",
                    }) as Box<dyn Provider>,
                ),
            ],
            0,
            1,
        );

        let messages = vec![ChatMessage::user("hello")];
        let request = ChatRequest {
            messages: &messages,
            tools: None,
        };
        let err = provider
            .chat(request, "test", Some(0.0))
            .await
            .expect_err("all providers should fail");
        let msg = err.to_string();
        assert!(msg.contains("All providers/models failed"));
        assert!(msg.contains("provider=p1 model=test"));
        assert!(msg.contains("provider=p2 model=test"));
        assert!(msg.contains("error=p1 chat error"));
        assert!(msg.contains("error=p2 chat error"));
        assert!(msg.contains("retryable"));
    }

    /// Mock that records model names and can fail specific models,
    /// implementing `chat()` for native tool calling parity tests.
    struct NativeModelAwareMock {
        calls: Arc<AtomicUsize>,
        models_seen: parking_lot::Mutex<Vec<String>>,
        fail_models: Vec<&'static str>,
        response_text: &'static str,
    }

    #[async_trait]
    impl Provider for NativeModelAwareMock {
        async fn chat_with_system(
            &self,
            _system_prompt: Option<&str>,
            _message: &str,
            _model: &str,
            _temperature: Option<f64>,
        ) -> anyhow::Result<String> {
            Ok(self.response_text.to_string())
        }

        fn supports_native_tools(&self) -> bool {
            true
        }

        async fn chat(
            &self,
            _request: ChatRequest<'_>,
            model: &str,
            _temperature: Option<f64>,
        ) -> anyhow::Result<ChatResponse> {
            self.calls.fetch_add(1, Ordering::SeqCst);
            self.models_seen.lock().push(model.to_string());
            if self.fail_models.contains(&model) {
                anyhow::bail!("500 model {} unavailable", model);
            }
            Ok(ChatResponse {
                text: Some(self.response_text.to_string()),
                tool_calls: vec![],
                usage: None,
                reasoning_content: None,
            })
        }
    }

    // Arc<NativeModelAwareMock> Provider impl provided by blanket impl in kylinbot-types.

    /// Gap 3: `chat()` tries fallback models on failure,
    /// matching behavior of `model_failover_tries_fallback_model`.
    #[tokio::test]
    async fn chat_tries_model_failover_on_failure() {
        let calls = Arc::new(AtomicUsize::new(0));
        let mock = Arc::new(NativeModelAwareMock {
            calls: Arc::clone(&calls),
            models_seen: parking_lot::Mutex::new(Vec::new()),
            fail_models: vec!["claude-opus"],
            response_text: "ok from sonnet",
        });

        let mut fallbacks = HashMap::new();
        fallbacks.insert("claude-opus".to_string(), vec!["claude-sonnet".to_string()]);

        let provider = ReliableProvider::new(
            vec![(
                "anthropic".into(),
                Box::new(mock.clone()) as Box<dyn Provider>,
            )],
            0, // no retries — force immediate model failover
            1,
        )
        .with_model_fallbacks(fallbacks);

        let messages = vec![ChatMessage::user("hello")];
        let request = ChatRequest {
            messages: &messages,
            tools: None,
        };
        let result = provider
            .chat(request, "claude-opus", Some(0.0))
            .await
            .unwrap();
        assert_eq!(result.text.as_deref(), Some("ok from sonnet"));

        let seen = mock.models_seen.lock();
        assert_eq!(seen.len(), 2);
        assert_eq!(seen[0], "claude-opus");
        assert_eq!(seen[1], "claude-sonnet");
    }

    /// Gap 4: `chat()` skips retries on non-retryable errors (401, 403, etc.),
    /// matching behavior of `skips_retries_on_non_retryable_error`.
    #[tokio::test]
    async fn chat_skips_non_retryable_errors() {
        let primary_calls = Arc::new(AtomicUsize::new(0));
        let fallback_calls = Arc::new(AtomicUsize::new(0));

        let provider = ReliableProvider::new(
            vec![
                (
                    "primary".into(),
                    Box::new(NativeToolMock {
                        calls: Arc::clone(&primary_calls),
                        fail_until_attempt: usize::MAX,
                        response_text: "never",
                        tool_calls: vec![],
                        error: "401 Unauthorized",
                    }) as Box<dyn Provider>,
                ),
                (
                    "fallback".into(),
                    Box::new(NativeToolMock {
                        calls: Arc::clone(&fallback_calls),
                        fail_until_attempt: 0,
                        response_text: "from fallback",
                        tool_calls: vec![],
                        error: "fallback err",
                    }) as Box<dyn Provider>,
                ),
            ],
            3,
            1,
        );

        let messages = vec![ChatMessage::user("hello")];
        let request = ChatRequest {
            messages: &messages,
            tools: None,
        };
        let result = provider.chat(request, "test", Some(0.0)).await.unwrap();
        assert_eq!(result.text.as_deref(), Some("from fallback"));
        // Primary should have been called only once (no retries)
        assert_eq!(primary_calls.load(Ordering::SeqCst), 1);
        assert_eq!(fallback_calls.load(Ordering::SeqCst), 1);
    }

    // ── Context window truncation tests ─────────────────────────

    #[test]
    fn context_window_error_is_not_non_retryable() {
        // Context window errors should be recoverable via truncation
        assert!(!is_non_retryable(&anyhow::anyhow!(
            "exceeds the context window"
        )));
        assert!(!is_non_retryable(&anyhow::anyhow!(
            "maximum context length exceeded"
        )));
        assert!(!is_non_retryable(&anyhow::anyhow!(
            "too many tokens in the request"
        )));
        assert!(!is_non_retryable(&anyhow::anyhow!("token limit exceeded")));
    }

    #[test]
    fn is_context_window_exceeded_detects_llamacpp() {
        assert!(is_context_window_exceeded(&anyhow::anyhow!(
            "request (8968 tokens) exceeds the available context size (8448 tokens), try increasing it"
        )));
    }

    #[test]
    fn truncate_for_context_drops_oldest_non_system() {
        let mut messages = vec![
            ChatMessage::system("sys"),
            ChatMessage::user("msg1"),
            ChatMessage::assistant("resp1"),
            ChatMessage::user("msg2"),
            ChatMessage::assistant("resp2"),
            ChatMessage::user("msg3"),
        ];

        let dropped = truncate_for_context(&mut messages);

        // 5 non-system messages, drop oldest half = 2
        assert_eq!(dropped, 2);
        // System message preserved
        assert_eq!(messages[0].role, "system");
        // Remaining messages should be the newer ones
        assert_eq!(messages.len(), 4); // system + 3 remaining non-system
        // The last message should still be the most recent user message
        assert_eq!(messages.last().unwrap().content, "msg3");
    }

    #[test]
    fn truncate_for_context_preserves_system_and_last_message() {
        // Only one non-system message: nothing to drop
        let mut messages = vec![ChatMessage::system("sys"), ChatMessage::user("only")];
        let dropped = truncate_for_context(&mut messages);
        assert_eq!(dropped, 0);
        assert_eq!(messages.len(), 2);

        // No system message, only one user message
        let mut messages = vec![ChatMessage::user("only")];
        let dropped = truncate_for_context(&mut messages);
        assert_eq!(dropped, 0);
        assert_eq!(messages.len(), 1);
    }

    /// Mock that fails with context error on first N calls, then succeeds.
    /// Tracks the number of messages received on each call.
    struct ContextOverflowMock {
        calls: Arc<AtomicUsize>,
        fail_until_attempt: usize,
        message_counts: parking_lot::Mutex<Vec<usize>>,
    }

    #[async_trait]
    impl Provider for ContextOverflowMock {
        async fn chat_with_system(
            &self,
            _system_prompt: Option<&str>,
            _message: &str,
            _model: &str,
            _temperature: Option<f64>,
        ) -> anyhow::Result<String> {
            Ok("ok".to_string())
        }

        async fn chat_with_history(
            &self,
            messages: &[ChatMessage],
            _model: &str,
            _temperature: Option<f64>,
        ) -> anyhow::Result<String> {
            let attempt = self.calls.fetch_add(1, Ordering::SeqCst) + 1;
            self.message_counts.lock().push(messages.len());
            if attempt <= self.fail_until_attempt {
                anyhow::bail!(
                    "request (8968 tokens) exceeds the available context size (8448 tokens), try increasing it"
                );
            }
            Ok("recovered after truncation".to_string())
        }
    }

    #[tokio::test]
    async fn chat_with_history_truncates_on_context_overflow() {
        let calls = Arc::new(AtomicUsize::new(0));
        let mock = ContextOverflowMock {
            calls: Arc::clone(&calls),
            fail_until_attempt: 1, // fail first call, succeed after truncation
            message_counts: parking_lot::Mutex::new(Vec::new()),
        };

        let provider = ReliableProvider::new(
            vec![("local".into(), Box::new(mock) as Box<dyn Provider>)],
            3,
            1,
        );

        let messages = vec![
            ChatMessage::system("system prompt"),
            ChatMessage::user("old message 1"),
            ChatMessage::assistant("old response 1"),
            ChatMessage::user("old message 2"),
            ChatMessage::assistant("old response 2"),
            ChatMessage::user("current question"),
        ];

        let result = provider
            .chat_with_history(&messages, "local-model", Some(0.0))
            .await
            .unwrap();
        assert_eq!(result, "recovered after truncation");
        // Should have been called twice: once with full messages, once with truncated
        assert_eq!(calls.load(Ordering::SeqCst), 2);
    }

    #[tokio::test]
    async fn context_overflow_with_no_history_to_truncate_bails_immediately() {
        let calls = Arc::new(AtomicUsize::new(0));
        let mock = ContextOverflowMock {
            calls: Arc::clone(&calls),
            fail_until_attempt: 999, // always fail
            message_counts: parking_lot::Mutex::new(Vec::new()),
        };

        let provider = ReliableProvider::new(
            vec![("local".into(), Box::new(mock) as Box<dyn Provider>)],
            3,
            1,
        );

        // Only system + one user message — nothing to truncate
        let messages = vec![
            ChatMessage::system("huge system prompt that exceeds context window"),
            ChatMessage::user("hello"),
        ];

        let result = provider
            .chat_with_history(&messages, "local-model", Some(0.0))
            .await;
        assert!(result.is_err());
        let err_msg = result.unwrap_err().to_string();
        assert!(
            err_msg.contains("cannot be reduced further"),
            "Should bail with actionable message, got: {err_msg}"
        );
        // Should only be called once — no useless retries
        assert_eq!(
            calls.load(Ordering::SeqCst),
            1,
            "Should not retry when truncation is impossible"
        );
    }

    // ── Tool schema error detection tests ───────────────────────────────

    #[test]
    fn tool_schema_error_detects_groq_validation_failure() {
        let msg = r#"Groq API error (400 Bad Request): {"error":{"message":"tool call validation failed: attempted to call tool 'memory_recall' which was not in request"}}"#;
        let err = anyhow::anyhow!("{}", msg);
        assert!(is_tool_schema_error(&err));
    }

    #[test]
    fn tool_schema_error_detects_not_in_request() {
        let err = anyhow::anyhow!("tool 'search' was not in request");
        assert!(is_tool_schema_error(&err));
    }

    #[test]
    fn tool_schema_error_detects_not_found_in_tool_list() {
        let err = anyhow::anyhow!("function 'foo' not found in tool list");
        assert!(is_tool_schema_error(&err));
    }

    #[test]
    fn tool_schema_error_detects_invalid_tool_call() {
        let err = anyhow::anyhow!("invalid_tool_call: no matching function");
        assert!(is_tool_schema_error(&err));
    }

    #[test]
    fn tool_schema_error_ignores_unrelated_errors() {
        let err = anyhow::anyhow!("invalid api key");
        assert!(!is_tool_schema_error(&err));

        let err = anyhow::anyhow!("model not found");
        assert!(!is_tool_schema_error(&err));
    }

    #[test]
    fn non_retryable_returns_false_for_tool_schema_400() {
        // A 400 error with tool schema validation text should NOT be non-retryable.
        let msg = "400 Bad Request: tool call validation failed: attempted to call tool 'x' which was not in request";
        let err = anyhow::anyhow!("{}", msg);
        assert!(!is_non_retryable(&err));
    }

    #[test]
    fn non_retryable_returns_true_for_other_400_errors() {
        // A regular 400 error (e.g. invalid API key) should still be non-retryable.
        let err = anyhow::anyhow!("400 Bad Request: invalid api key provided");
        assert!(is_non_retryable(&err));
    }

    struct StreamingToolEventMock {
        stream_calls: Arc<AtomicUsize>,
        supports_tool_events: bool,
    }

    impl StreamingToolEventMock {
        fn new(supports_tool_events: bool) -> Self {
            Self {
                stream_calls: Arc::new(AtomicUsize::new(0)),
                supports_tool_events,
            }
        }
    }

    #[async_trait]
    impl Provider for StreamingToolEventMock {
        async fn chat_with_system(
            &self,
            _system_prompt: Option<&str>,
            _message: &str,
            _model: &str,
            _temperature: Option<f64>,
        ) -> anyhow::Result<String> {
            Ok("ok".to_string())
        }

        fn supports_streaming(&self) -> bool {
            true
        }

        fn supports_streaming_tool_events(&self) -> bool {
            self.supports_tool_events
        }

        fn stream_chat(
            &self,
            _request: ChatRequest<'_>,
            _model: &str,
            _temperature: Option<f64>,
            _options: StreamOptions,
        ) -> stream::BoxStream<'static, StreamResult<StreamEvent>> {
            self.stream_calls.fetch_add(1, Ordering::SeqCst);
            stream::iter(vec![
                Ok(StreamEvent::ToolCall(super::super::traits::ToolCall {
                    id: "call_1".to_string(),
                    name: "shell".to_string(),
                    arguments: r#"{"command":"date"}"#.to_string(),
                    extra_content: None,
                })),
                Ok(StreamEvent::Final),
            ])
            .boxed()
        }
    }

    // Arc<StreamingToolEventMock> Provider impl provided by blanket impl in kylinbot-types.

    #[tokio::test]
    async fn stream_chat_prefers_provider_with_tool_event_support() {
        let primary = Arc::new(StreamingToolEventMock::new(false));
        let fallback = Arc::new(StreamingToolEventMock::new(true));
        let provider = ReliableProvider::new(
            vec![
                (
                    "primary".into(),
                    Box::new(Arc::clone(&primary)) as Box<dyn Provider>,
                ),
                (
                    "fallback".into(),
                    Box::new(Arc::clone(&fallback)) as Box<dyn Provider>,
                ),
            ],
            0,
            1,
        );

        let messages = vec![ChatMessage::user("hello")];
        let tools = vec![ToolSpec {
            name: "shell".to_string(),
            description: "run shell".to_string(),
            parameters: serde_json::json!({
                "type": "object",
                "properties": {
                    "command": { "type": "string" }
                }
            }),
        }];
        let mut stream = provider.stream_chat(
            ChatRequest {
                messages: &messages,
                tools: Some(&tools),
            },
            "model",
            Some(0.0),
            StreamOptions::new(true),
        );

        let first = stream.next().await.unwrap().unwrap();
        let second = stream.next().await.unwrap().unwrap();
        assert!(stream.next().await.is_none());

        match first {
            StreamEvent::ToolCall(call) => assert_eq!(call.name, "shell"),
            other => panic!("expected tool-call event, got {other:?}"),
        }
        assert!(matches!(second, StreamEvent::Final));
        assert_eq!(primary.stream_calls.load(Ordering::SeqCst), 0);
        assert_eq!(fallback.stream_calls.load(Ordering::SeqCst), 1);
    }

    #[tokio::test]
    async fn stream_chat_errors_when_no_provider_supports_tool_events() {
        let primary = Arc::new(StreamingToolEventMock::new(false));
        let provider = ReliableProvider::new(
            vec![(
                "primary".into(),
                Box::new(Arc::clone(&primary)) as Box<dyn Provider>,
            )],
            0,
            1,
        );

        let messages = vec![ChatMessage::user("hello")];
        let tools = vec![ToolSpec {
            name: "shell".to_string(),
            description: "run shell".to_string(),
            parameters: serde_json::json!({"type": "object"}),
        }];
        let mut stream = provider.stream_chat(
            ChatRequest {
                messages: &messages,
                tools: Some(&tools),
            },
            "model",
            Some(0.0),
            StreamOptions::new(true),
        );

        let first = stream.next().await.unwrap();
        let err = first.expect_err("stream should fail without tool-event support");
        assert!(
            err.to_string()
                .contains("No provider supports streaming tool events"),
            "unexpected stream error: {err}"
        );
        assert!(stream.next().await.is_none());
        assert_eq!(primary.stream_calls.load(Ordering::SeqCst), 0);
    }

    // ── stream_chat_with_history failover tests ──────────────────────

    /// Mock provider that supports streaming via stream_chat_with_history.
    struct StreamingHistoryMock {
        stream_calls: Arc<AtomicUsize>,
        supports: bool,
    }

    #[async_trait]
    impl Provider for StreamingHistoryMock {
        async fn chat_with_system(
            &self,
            _system_prompt: Option<&str>,
            _message: &str,
            _model: &str,
            _temperature: Option<f64>,
        ) -> anyhow::Result<String> {
            Ok("ok".to_string())
        }

        fn supports_streaming(&self) -> bool {
            self.supports
        }

        fn stream_chat_with_history(
            &self,
            messages: &[ChatMessage],
            _model: &str,
            _temperature: Option<f64>,
            _options: StreamOptions,
        ) -> stream::BoxStream<'static, StreamResult<StreamChunk>> {
            self.stream_calls.fetch_add(1, Ordering::SeqCst);
            // Echo the number of messages as the delta to verify history was passed through
            let msg_count = messages.len().to_string();
            stream::iter(vec![
                Ok(StreamChunk::delta(msg_count)),
                Ok(StreamChunk::final_chunk()),
            ])
            .boxed()
        }
    }

    #[tokio::test]
    async fn stream_chat_with_history_delegates_to_streaming_provider() {
        let calls = Arc::new(AtomicUsize::new(0));
        let provider = ReliableProvider::new(
            vec![(
                "primary".into(),
                Box::new(StreamingHistoryMock {
                    stream_calls: Arc::clone(&calls),
                    supports: true,
                }) as Box<dyn Provider>,
            )],
            0,
            1,
        );

        let messages = vec![
            ChatMessage::system("system"),
            ChatMessage::user("msg1"),
            ChatMessage::assistant("resp1"),
            ChatMessage::user("msg2"),
        ];
        let mut stream = provider.stream_chat_with_history(
            &messages,
            "model",
            Some(0.0),
            StreamOptions::new(true),
        );

        let first = stream.next().await.unwrap().unwrap();
        assert_eq!(first.delta, "4", "should pass all 4 messages to provider");
        let second = stream.next().await.unwrap().unwrap();
        assert!(second.is_final);
        assert!(stream.next().await.is_none());
        assert_eq!(calls.load(Ordering::SeqCst), 1);
    }

    #[tokio::test]
    async fn stream_chat_with_history_skips_non_streaming_providers() {
        let non_streaming_calls = Arc::new(AtomicUsize::new(0));
        let streaming_calls = Arc::new(AtomicUsize::new(0));

        let provider = ReliableProvider::new(
            vec![
                (
                    "non-streaming".into(),
                    Box::new(StreamingHistoryMock {
                        stream_calls: Arc::clone(&non_streaming_calls),
                        supports: false,
                    }) as Box<dyn Provider>,
                ),
                (
                    "streaming".into(),
                    Box::new(StreamingHistoryMock {
                        stream_calls: Arc::clone(&streaming_calls),
                        supports: true,
                    }) as Box<dyn Provider>,
                ),
            ],
            0,
            1,
        );

        let messages = vec![ChatMessage::user("hello")];
        let mut stream = provider.stream_chat_with_history(
            &messages,
            "model",
            Some(0.0),
            StreamOptions::new(true),
        );

        let first = stream.next().await.unwrap().unwrap();
        assert_eq!(first.delta, "1");
        assert_eq!(
            non_streaming_calls.load(Ordering::SeqCst),
            0,
            "non-streaming provider should be skipped"
        );
        assert_eq!(
            streaming_calls.load(Ordering::SeqCst),
            1,
            "streaming provider should be used"
        );
    }

    #[tokio::test]
    async fn stream_chat_with_history_errors_when_no_provider_supports_streaming() {
        let provider = ReliableProvider::new(
            vec![(
                "non-streaming".into(),
                Box::new(StreamingHistoryMock {
                    stream_calls: Arc::new(AtomicUsize::new(0)),
                    supports: false,
                }) as Box<dyn Provider>,
            )],
            0,
            1,
        );

        let messages = vec![ChatMessage::user("hello")];
        let mut stream = provider.stream_chat_with_history(
            &messages,
            "model",
            Some(0.0),
            StreamOptions::new(true),
        );

        let first = stream.next().await.unwrap();
        let err = first.expect_err("should fail when no provider supports streaming");
        assert!(
            err.to_string().contains("No provider supports streaming"),
            "unexpected error: {err}"
        );
        assert!(stream.next().await.is_none());
    }

    #[tokio::test]
    async fn fallback_records_provider_fallback_info() {
        scope_provider_fallback(async {
            let provider = ReliableProvider::new(
                vec![
                    (
                        "broken".into(),
                        Box::new(MockProvider {
                            calls: Arc::new(AtomicUsize::new(0)),
                            fail_until_attempt: 99, // always fail
                            response: "unused",
                            error: "401 Unauthorized",
                        }),
                    ),
                    (
                        "working".into(),
                        Box::new(MockProvider {
                            calls: Arc::new(AtomicUsize::new(0)),
                            fail_until_attempt: 0,
                            response: "hello from working",
                            error: "unused",
                        }),
                    ),
                ],
                2,
                1,
            );

            let resp = provider
                .simple_chat("hi", "test-model", Some(0.0))
                .await
                .unwrap();
            assert_eq!(resp, "hello from working");

            let fb = take_last_provider_fallback();
            assert!(fb.is_some(), "fallback info should be recorded");
            let fb = fb.unwrap();
            assert_eq!(fb.requested_provider, "broken");
            assert_eq!(fb.actual_provider, "working");
            assert_eq!(fb.actual_model, "test-model");

            // Second take should be None.
            assert!(take_last_provider_fallback().is_none());
        })
        .await;
    }
}
