package cron

import (
	"context"
	"encoding/json"
	"log/slog"
	"time"

	"github.com/ez-api/ez-api/internal/model"
	"gorm.io/gorm"
)

// DailyStatsJob aggregates log_records into daily_stats for efficient dashboard queries.
// Runs at 00:05 UTC daily to aggregate the previous day's data.
// Design principles:
// - Idempotent: skip if date already exists
// - Immutable: once generated, rows are never modified
// - T-1 aggregation: aggregates yesterday's data (ensures completeness)
type DailyStatsJob struct {
	db    *gorm.DB // main database (writes daily_stats)
	logDB *gorm.DB // log database (reads log_records)
}

// NewDailyStatsJob creates a new DailyStatsJob.
func NewDailyStatsJob(db, logDB *gorm.DB) *DailyStatsJob {
	return &DailyStatsJob{
		db:    db,
		logDB: logDB,
	}
}

// RunOnce executes a single daily stats aggregation. Called by scheduler.
func (j *DailyStatsJob) RunOnce(ctx context.Context) {
	if j == nil || j.db == nil || j.logDB == nil {
		return
	}
	if err := j.aggregateYesterday(ctx); err != nil {
		slog.Default().Warn("daily stats aggregation failed", "err", err)
	}
}

func (j *DailyStatsJob) aggregateYesterday(ctx context.Context) error {
	yesterday := time.Now().UTC().AddDate(0, 0, -1)
	dateStr := yesterday.Format("2006-01-02")

	// Idempotent check: skip if already exists
	var count int64
	if err := j.db.Model(&model.DailyStat{}).Where("date = ?", dateStr).Count(&count).Error; err != nil {
		return err
	}
	if count > 0 {
		slog.Default().Debug("daily stats already exists, skipping", "date", dateStr)
		return nil
	}

	// Calculate time window for yesterday (UTC)
	startOfDay := time.Date(yesterday.Year(), yesterday.Month(), yesterday.Day(), 0, 0, 0, 0, time.UTC)
	endOfDay := startOfDay.Add(24 * time.Hour)

	// Aggregate basic stats from log_records
	var stats struct {
		Requests     int64
		Success      int64
		Failed       int64
		TokensIn     int64
		TokensOut    int64
		LatencySumMs int64
	}

	if err := j.logDB.Model(&model.LogRecord{}).
		Select(`
			COUNT(*) as requests,
			SUM(CASE WHEN status_code >= 200 AND status_code < 400 THEN 1 ELSE 0 END) as success,
			SUM(CASE WHEN status_code >= 400 OR status_code = 0 THEN 1 ELSE 0 END) as failed,
			COALESCE(SUM(tokens_in), 0) as tokens_in,
			COALESCE(SUM(tokens_out), 0) as tokens_out,
			COALESCE(SUM(latency_ms), 0) as latency_sum_ms
		`).
		Where("created_at >= ? AND created_at < ?", startOfDay, endOfDay).
		Scan(&stats).Error; err != nil {
		return err
	}

	// Skip if no data for this day
	if stats.Requests == 0 {
		slog.Default().Debug("no log records for date, skipping daily stats", "date", dateStr)
		return nil
	}

	// Aggregate top models
	topModels, err := j.aggregateTopModels(startOfDay, endOfDay)
	if err != nil {
		slog.Default().Warn("failed to aggregate top models", "date", dateStr, "err", err)
		topModels = "[]"
	}

	// Create daily stat record
	dailyStat := model.DailyStat{
		Date:         dateStr,
		Requests:     stats.Requests,
		Success:      stats.Success,
		Failed:       stats.Failed,
		TokensIn:     stats.TokensIn,
		TokensOut:    stats.TokensOut,
		LatencySumMs: stats.LatencySumMs,
		TopModels:    topModels,
		CreatedAt:    time.Now().UTC(),
	}

	if err := j.db.Create(&dailyStat).Error; err != nil {
		return err
	}

	slog.Default().Info("daily stats aggregated",
		"date", dateStr,
		"requests", stats.Requests,
		"tokens_in", stats.TokensIn,
		"tokens_out", stats.TokensOut,
	)

	return nil
}

func (j *DailyStatsJob) aggregateTopModels(startOfDay, endOfDay time.Time) (string, error) {
	type modelStat struct {
		Model    string
		Requests int64
		Tokens   int64
	}

	var results []modelStat
	if err := j.logDB.Model(&model.LogRecord{}).
		Select(`
			model_name as model,
			COUNT(*) as requests,
			COALESCE(SUM(tokens_in), 0) + COALESCE(SUM(tokens_out), 0) as tokens
		`).
		Where("created_at >= ? AND created_at < ?", startOfDay, endOfDay).
		Group("model_name").
		Order("requests DESC").
		Limit(10).
		Scan(&results).Error; err != nil {
		return "", err
	}

	// Convert to TopModelStat format
	topModels := make([]model.TopModelStat, 0, len(results))
	for _, r := range results {
		topModels = append(topModels, model.TopModelStat{
			Model:    r.Model,
			Requests: r.Requests,
			Tokens:   r.Tokens,
		})
	}

	data, err := json.Marshal(topModels)
	if err != nil {
		return "", err
	}

	return string(data), nil
}

// BackfillRange aggregates daily stats for a date range (inclusive).
// Useful for initial population or recovery. Skips dates that already exist.
func (j *DailyStatsJob) BackfillRange(ctx context.Context, startDate, endDate time.Time) error {
	current := startDate
	for !current.After(endDate) {
		select {
		case <-ctx.Done():
			return ctx.Err()
		default:
		}

		if err := j.aggregateDate(ctx, current); err != nil {
			slog.Default().Warn("backfill failed for date", "date", current.Format("2006-01-02"), "err", err)
		}
		current = current.AddDate(0, 0, 1)
	}
	return nil
}

func (j *DailyStatsJob) aggregateDate(ctx context.Context, date time.Time) error {
	dateStr := date.Format("2006-01-02")

	// Idempotent check
	var count int64
	if err := j.db.Model(&model.DailyStat{}).Where("date = ?", dateStr).Count(&count).Error; err != nil {
		return err
	}
	if count > 0 {
		return nil
	}

	startOfDay := time.Date(date.Year(), date.Month(), date.Day(), 0, 0, 0, 0, time.UTC)
	endOfDay := startOfDay.Add(24 * time.Hour)

	var stats struct {
		Requests     int64
		Success      int64
		Failed       int64
		TokensIn     int64
		TokensOut    int64
		LatencySumMs int64
	}

	if err := j.logDB.Model(&model.LogRecord{}).
		Select(`
			COUNT(*) as requests,
			SUM(CASE WHEN status_code >= 200 AND status_code < 400 THEN 1 ELSE 0 END) as success,
			SUM(CASE WHEN status_code >= 400 OR status_code = 0 THEN 1 ELSE 0 END) as failed,
			COALESCE(SUM(tokens_in), 0) as tokens_in,
			COALESCE(SUM(tokens_out), 0) as tokens_out,
			COALESCE(SUM(latency_ms), 0) as latency_sum_ms
		`).
		Where("created_at >= ? AND created_at < ?", startOfDay, endOfDay).
		Scan(&stats).Error; err != nil {
		return err
	}

	if stats.Requests == 0 {
		return nil
	}

	topModels, err := j.aggregateTopModels(startOfDay, endOfDay)
	if err != nil {
		topModels = "[]"
	}

	dailyStat := model.DailyStat{
		Date:         dateStr,
		Requests:     stats.Requests,
		Success:      stats.Success,
		Failed:       stats.Failed,
		TokensIn:     stats.TokensIn,
		TokensOut:    stats.TokensOut,
		LatencySumMs: stats.LatencySumMs,
		TopModels:    topModels,
		CreatedAt:    time.Now().UTC(),
	}

	return j.db.Create(&dailyStat).Error
}