use super::types::{BudgetCheck, CostRecord, CostSummary, ModelStats, TokenUsage, UsagePeriod};
use crate::schema::CostConfig;
use anyhow::{Context, Result, anyhow};
use chrono::{Datelike, NaiveDate, Utc};
use parking_lot::{Mutex, MutexGuard};
use std::collections::HashMap;
use std::fs::{self, File, OpenOptions};
use std::io::{BufRead, BufReader, Write};
use std::path::{Path, PathBuf};
use std::sync::{Arc, OnceLock};

/// Cost tracker for API usage monitoring and budget enforcement.
pub struct CostTracker {
    config: CostConfig,
    storage: Arc<Mutex<CostStorage>>,
    session_id: String,
    session_costs: Arc<Mutex<Vec<CostRecord>>>,
}

impl CostTracker {
    /// Create a new cost tracker.
    pub fn new(config: CostConfig, workspace_dir: &Path) -> Result<Self> {
        let storage_path = resolve_storage_path(workspace_dir)?;

        let storage = CostStorage::new(&storage_path).with_context(|| {
            format!("Failed to open cost storage at {}", storage_path.display())
        })?;

        Ok(Self {
            config,
            storage: Arc::new(Mutex::new(storage)),
            session_id: uuid::Uuid::new_v4().to_string(),
            session_costs: Arc::new(Mutex::new(Vec::new())),
        })
    }

    /// Get the session ID.
    pub fn session_id(&self) -> &str {
        &self.session_id
    }

    fn lock_storage(&self) -> MutexGuard<'_, CostStorage> {
        self.storage.lock()
    }

    fn lock_session_costs(&self) -> MutexGuard<'_, Vec<CostRecord>> {
        self.session_costs.lock()
    }

    /// Check if a request is within budget.
    pub fn check_budget(&self, estimated_cost_usd: f64) -> Result<BudgetCheck> {
        if !self.config.enabled {
            return Ok(BudgetCheck::Allowed);
        }

        if !estimated_cost_usd.is_finite() || estimated_cost_usd < 0.0 {
            return Err(anyhow!(
                "Estimated cost must be a finite, non-negative value"
            ));
        }

        let mut storage = self.lock_storage();
        let (daily_cost, monthly_cost) = storage.get_aggregated_costs()?;

        // Check daily limit
        let projected_daily = daily_cost + estimated_cost_usd;
        if projected_daily > self.config.daily_limit_usd {
            return Ok(BudgetCheck::Exceeded {
                current_usd: daily_cost,
                limit_usd: self.config.daily_limit_usd,
                period: UsagePeriod::Day,
            });
        }

        // Check monthly limit
        let projected_monthly = monthly_cost + estimated_cost_usd;
        if projected_monthly > self.config.monthly_limit_usd {
            return Ok(BudgetCheck::Exceeded {
                current_usd: monthly_cost,
                limit_usd: self.config.monthly_limit_usd,
                period: UsagePeriod::Month,
            });
        }

        // Check warning thresholds
        let warn_threshold = f64::from(self.config.warn_at_percent.min(100)) / 100.0;
        let daily_warn_threshold = self.config.daily_limit_usd * warn_threshold;
        let monthly_warn_threshold = self.config.monthly_limit_usd * warn_threshold;

        if projected_daily >= daily_warn_threshold {
            return Ok(BudgetCheck::Warning {
                current_usd: daily_cost,
                limit_usd: self.config.daily_limit_usd,
                period: UsagePeriod::Day,
            });
        }

        if projected_monthly >= monthly_warn_threshold {
            return Ok(BudgetCheck::Warning {
                current_usd: monthly_cost,
                limit_usd: self.config.monthly_limit_usd,
                period: UsagePeriod::Month,
            });
        }

        Ok(BudgetCheck::Allowed)
    }

    /// Record a usage event.
    pub fn record_usage(&self, usage: TokenUsage) -> Result<()> {
        if !self.config.enabled {
            return Ok(());
        }

        if !usage.cost_usd.is_finite() || usage.cost_usd < 0.0 {
            return Err(anyhow!(
                "Token usage cost must be a finite, non-negative value"
            ));
        }

        let record = CostRecord::new(&self.session_id, usage);

        // Persist first for durability guarantees.
        {
            let mut storage = self.lock_storage();
            storage.add_record(record.clone())?;
        }

        // Then update in-memory session snapshot.
        let mut session_costs = self.lock_session_costs();
        session_costs.push(record);

        Ok(())
    }

    /// Get the current cost summary.
    pub fn get_summary(&self) -> Result<CostSummary> {
        let (daily_cost, monthly_cost) = {
            let mut storage = self.lock_storage();
            storage.get_aggregated_costs()?
        };

        let session_costs = self.lock_session_costs();
        let session_cost: f64 = session_costs
            .iter()
            .map(|record| record.usage.cost_usd)
            .sum();
        let total_tokens: u64 = session_costs
            .iter()
            .map(|record| record.usage.total_tokens)
            .sum();
        let request_count = session_costs.len();
        let by_model = build_session_model_stats(&session_costs);

        Ok(CostSummary {
            session_cost_usd: session_cost,
            daily_cost_usd: daily_cost,
            monthly_cost_usd: monthly_cost,
            total_tokens,
            request_count,
            by_model,
        })
    }

    /// Get the daily cost for a specific date.
    pub fn get_daily_cost(&self, date: NaiveDate) -> Result<f64> {
        let storage = self.lock_storage();
        storage.get_cost_for_date(date)
    }

    /// Get the monthly cost for a specific month.
    pub fn get_monthly_cost(&self, year: i32, month: u32) -> Result<f64> {
        let storage = self.lock_storage();
        storage.get_cost_for_month(year, month)
    }
}

// ── Process-global singleton ────────────────────────────────────────
// Both the gateway and the channels supervisor share a single CostTracker
// so that budget enforcement is consistent across all paths.

static GLOBAL_COST_TRACKER: OnceLock<Option<Arc<CostTracker>>> = OnceLock::new();

impl CostTracker {
    /// Return the process-global `CostTracker`, creating it on first call.
    /// Subsequent calls (from gateway or channels, whichever starts second)
    /// receive the same `Arc`.  Returns `None` when cost tracking is disabled
    /// or initialisation fails.
    pub fn get_or_init_global(config: CostConfig, workspace_dir: &Path) -> Option<Arc<Self>> {
        GLOBAL_COST_TRACKER
            .get_or_init(|| {
                if !config.enabled {
                    return None;
                }
                match Self::new(config, workspace_dir) {
                    Ok(ct) => Some(Arc::new(ct)),
                    Err(e) => {
                        tracing::warn!("Failed to initialize global cost tracker: {e}");
                        None
                    }
                }
            })
            .clone()
    }
}

fn resolve_storage_path(workspace_dir: &Path) -> Result<PathBuf> {
    let storage_path = workspace_dir.join("state").join("costs.jsonl");
    let legacy_path = workspace_dir.join(".kylinbot").join("costs.db");

    if !storage_path.exists() && legacy_path.exists() {
        if let Some(parent) = storage_path.parent() {
            fs::create_dir_all(parent)
                .with_context(|| format!("Failed to create directory {}", parent.display()))?;
        }

        if let Err(error) = fs::rename(&legacy_path, &storage_path) {
            tracing::warn!(
                "Failed to move legacy cost storage from {} to {}: {error}; falling back to copy",
                legacy_path.display(),
                storage_path.display()
            );
            fs::copy(&legacy_path, &storage_path).with_context(|| {
                format!(
                    "Failed to copy legacy cost storage from {} to {}",
                    legacy_path.display(),
                    storage_path.display()
                )
            })?;
        }
    }

    Ok(storage_path)
}

fn build_session_model_stats(session_costs: &[CostRecord]) -> HashMap<String, ModelStats> {
    let mut by_model: HashMap<String, ModelStats> = HashMap::new();

    for record in session_costs {
        let entry = by_model
            .entry(record.usage.model.clone())
            .or_insert_with(|| ModelStats {
                model: record.usage.model.clone(),
                cost_usd: 0.0,
                total_tokens: 0,
                request_count: 0,
            });

        entry.cost_usd += record.usage.cost_usd;
        entry.total_tokens += record.usage.total_tokens;
        entry.request_count += 1;
    }

    by_model
}

/// Persistent storage for cost records.
struct CostStorage {
    path: PathBuf,
    daily_cost_usd: f64,
    monthly_cost_usd: f64,
    cached_day: NaiveDate,
    cached_year: i32,
    cached_month: u32,
}

impl CostStorage {
    /// Create or open cost storage.
    fn new(path: &Path) -> Result<Self> {
        if let Some(parent) = path.parent() {
            fs::create_dir_all(parent)
                .with_context(|| format!("Failed to create directory {}", parent.display()))?;
        }

        let now = Utc::now();
        let mut storage = Self {
            path: path.to_path_buf(),
            daily_cost_usd: 0.0,
            monthly_cost_usd: 0.0,
            cached_day: now.date_naive(),
            cached_year: now.year(),
            cached_month: now.month(),
        };

        storage.rebuild_aggregates(
            storage.cached_day,
            storage.cached_year,
            storage.cached_month,
        )?;

        Ok(storage)
    }

    fn for_each_record<F>(&self, mut on_record: F) -> Result<()>
    where
        F: FnMut(CostRecord),
    {
        if !self.path.exists() {
            return Ok(());
        }

        let file = File::open(&self.path)
            .with_context(|| format!("Failed to read cost storage from {}", self.path.display()))?;
        let reader = BufReader::new(file);

        for (line_number, line) in reader.lines().enumerate() {
            let raw_line = line.with_context(|| {
                format!(
                    "Failed to read line {} from cost storage {}",
                    line_number + 1,
                    self.path.display()
                )
            })?;

            let trimmed = raw_line.trim();
            if trimmed.is_empty() {
                continue;
            }

            match serde_json::from_str::<CostRecord>(trimmed) {
                Ok(record) => on_record(record),
                Err(error) => {
                    tracing::warn!(
                        "Skipping malformed cost record at {}:{}: {error}",
                        self.path.display(),
                        line_number + 1
                    );
                }
            }
        }

        Ok(())
    }

    fn rebuild_aggregates(&mut self, day: NaiveDate, year: i32, month: u32) -> Result<()> {
        let mut daily_cost = 0.0;
        let mut monthly_cost = 0.0;

        self.for_each_record(|record| {
            let timestamp = record.usage.timestamp.naive_utc();

            if timestamp.date() == day {
                daily_cost += record.usage.cost_usd;
            }

            if timestamp.year() == year && timestamp.month() == month {
                monthly_cost += record.usage.cost_usd;
            }
        })?;

        self.daily_cost_usd = daily_cost;
        self.monthly_cost_usd = monthly_cost;
        self.cached_day = day;
        self.cached_year = year;
        self.cached_month = month;

        Ok(())
    }

    fn ensure_period_cache_current(&mut self) -> Result<()> {
        let now = Utc::now();
        let day = now.date_naive();
        let year = now.year();
        let month = now.month();

        if day != self.cached_day || year != self.cached_year || month != self.cached_month {
            self.rebuild_aggregates(day, year, month)?;
        }

        Ok(())
    }

    /// Add a new record.
    fn add_record(&mut self, record: CostRecord) -> Result<()> {
        let mut file = OpenOptions::new()
            .create(true)
            .append(true)
            .open(&self.path)
            .with_context(|| format!("Failed to open cost storage at {}", self.path.display()))?;

        writeln!(file, "{}", serde_json::to_string(&record)?)
            .with_context(|| format!("Failed to write cost record to {}", self.path.display()))?;
        file.sync_all()
            .with_context(|| format!("Failed to sync cost storage at {}", self.path.display()))?;

        self.ensure_period_cache_current()?;

        let timestamp = record.usage.timestamp.naive_utc();
        if timestamp.date() == self.cached_day {
            self.daily_cost_usd += record.usage.cost_usd;
        }
        if timestamp.year() == self.cached_year && timestamp.month() == self.cached_month {
            self.monthly_cost_usd += record.usage.cost_usd;
        }

        Ok(())
    }

    /// Get aggregated costs for current day and month.
    fn get_aggregated_costs(&mut self) -> Result<(f64, f64)> {
        self.ensure_period_cache_current()?;
        Ok((self.daily_cost_usd, self.monthly_cost_usd))
    }

    /// Get cost for a specific date.
    fn get_cost_for_date(&self, date: NaiveDate) -> Result<f64> {
        let mut cost = 0.0;

        self.for_each_record(|record| {
            if record.usage.timestamp.naive_utc().date() == date {
                cost += record.usage.cost_usd;
            }
        })?;

        Ok(cost)
    }

    /// Get cost for a specific month.
    fn get_cost_for_month(&self, year: i32, month: u32) -> Result<f64> {
        let mut cost = 0.0;

        self.for_each_record(|record| {
            let timestamp = record.usage.timestamp.naive_utc();
            if timestamp.year() == year && timestamp.month() == month {
                cost += record.usage.cost_usd;
            }
        })?;

        Ok(cost)
    }
}

#[cfg(test)]
mod tests {
    use super::*;
    use tempfile::TempDir;

    fn enabled_config() -> CostConfig {
        CostConfig {
            enabled: true,
            ..Default::default()
        }
    }

    #[test]
    fn cost_tracker_initialization() {
        let tmp = TempDir::new().unwrap();
        let tracker = CostTracker::new(enabled_config(), tmp.path()).unwrap();
        assert!(!tracker.session_id().is_empty());
    }

    #[test]
    fn budget_check_when_disabled() {
        let tmp = TempDir::new().unwrap();
        let config = CostConfig {
            enabled: false,
            ..Default::default()
        };

        let tracker = CostTracker::new(config, tmp.path()).unwrap();
        let check = tracker.check_budget(1000.0).unwrap();
        assert!(matches!(check, BudgetCheck::Allowed));
    }

    #[test]
    fn record_usage_and_get_summary() {
        let tmp = TempDir::new().unwrap();
        let tracker = CostTracker::new(enabled_config(), tmp.path()).unwrap();

        let usage = TokenUsage::new("test/model", 1000, 500, 1.0, 2.0);
        tracker.record_usage(usage).unwrap();

        let summary = tracker.get_summary().unwrap();
        assert_eq!(summary.request_count, 1);
        assert!(summary.session_cost_usd > 0.0);
        assert_eq!(summary.by_model.len(), 1);
    }

    #[test]
    fn budget_exceeded_daily_limit() {
        let tmp = TempDir::new().unwrap();
        let config = CostConfig {
            enabled: true,
            daily_limit_usd: 0.01, // Very low limit
            ..Default::default()
        };

        let tracker = CostTracker::new(config, tmp.path()).unwrap();

        // Record a usage that exceeds the limit
        let usage = TokenUsage::new("test/model", 10000, 5000, 1.0, 2.0); // ~0.02 USD
        tracker.record_usage(usage).unwrap();

        let check = tracker.check_budget(0.01).unwrap();
        assert!(matches!(check, BudgetCheck::Exceeded { .. }));
    }

    #[test]
    fn summary_by_model_is_session_scoped() {
        let tmp = TempDir::new().unwrap();
        let storage_path = resolve_storage_path(tmp.path()).unwrap();
        if let Some(parent) = storage_path.parent() {
            fs::create_dir_all(parent).unwrap();
        }

        let old_record = CostRecord::new(
            "old-session",
            TokenUsage::new("legacy/model", 500, 500, 1.0, 1.0),
        );
        let mut file = OpenOptions::new()
            .create(true)
            .append(true)
            .open(storage_path)
            .unwrap();
        writeln!(file, "{}", serde_json::to_string(&old_record).unwrap()).unwrap();
        file.sync_all().unwrap();

        let tracker = CostTracker::new(enabled_config(), tmp.path()).unwrap();
        tracker
            .record_usage(TokenUsage::new("session/model", 1000, 1000, 1.0, 1.0))
            .unwrap();

        let summary = tracker.get_summary().unwrap();
        assert_eq!(summary.by_model.len(), 1);
        assert!(summary.by_model.contains_key("session/model"));
        assert!(!summary.by_model.contains_key("legacy/model"));
    }

    #[test]
    fn malformed_lines_are_ignored_while_loading() {
        let tmp = TempDir::new().unwrap();
        let storage_path = resolve_storage_path(tmp.path()).unwrap();
        if let Some(parent) = storage_path.parent() {
            fs::create_dir_all(parent).unwrap();
        }

        let valid_usage = TokenUsage::new("test/model", 1000, 0, 1.0, 1.0);
        let valid_record = CostRecord::new("session-a", valid_usage.clone());

        let mut file = OpenOptions::new()
            .create(true)
            .append(true)
            .open(storage_path)
            .unwrap();
        writeln!(file, "{}", serde_json::to_string(&valid_record).unwrap()).unwrap();
        writeln!(file, "not-a-json-line").unwrap();
        writeln!(file).unwrap();
        file.sync_all().unwrap();

        let tracker = CostTracker::new(enabled_config(), tmp.path()).unwrap();
        let today_cost = tracker.get_daily_cost(Utc::now().date_naive()).unwrap();
        assert!((today_cost - valid_usage.cost_usd).abs() < f64::EPSILON);
    }

    #[test]
    fn invalid_budget_estimate_is_rejected() {
        let tmp = TempDir::new().unwrap();
        let tracker = CostTracker::new(enabled_config(), tmp.path()).unwrap();

        let err = tracker.check_budget(f64::NAN).unwrap_err();
        assert!(
            err.to_string()
                .contains("Estimated cost must be a finite, non-negative value")
        );
    }
}
