package service

import (
	"context"
	"errors"
	"sync"
	"time"

	"with_you/internal/config"
	"with_you/internal/pkg/s3"
	"with_you/internal/repository"

	redislib "github.com/redis/go-redis/v9"
	"go.uber.org/zap"
)

// FileCleanupWorker 聊天文件 TTL 过期清理 worker
// 周期性扫描 uploaded_files 表，将超过保留期的文件从 S3 删除并标记 expired。
// 多实例部署时通过 Redis 分布式锁保证仅主实例执行清理。
type FileCleanupWorker struct {
	cfg          *config.Config
	uploadedRepo repository.UploadedFileRepository
	s3Client     *s3.Client
	rdb          *redislib.Client // 用于分布式锁（可为 nil，降级为本地运行）
	stopOnce     sync.Once
	stopCh       chan struct{}
	doneCh       chan struct{}
}

const (
	// fileCleanupLockKey Redis 分布式锁键
	fileCleanupLockKey = "file_cleanup:leader_lock"
	// fileCleanupLockTTL 锁持有时间（略大于扫描间隔，确保单实例持有）
	fileCleanupLockTTL = 7 * time.Hour
	// fileCleanupLockRetryInterval 竞争锁的重试间隔
	fileCleanupLockRetryInterval = 1 * time.Minute
)

// NewFileCleanupWorker 创建文件清理 worker
func NewFileCleanupWorker(
	cfg *config.Config,
	uploadedRepo repository.UploadedFileRepository,
	s3Client *s3.Client,
	rdb *redislib.Client,
) *FileCleanupWorker {
	return &FileCleanupWorker{
		cfg:          cfg,
		uploadedRepo: uploadedRepo,
		s3Client:     s3Client,
		rdb:          rdb,
		stopCh:       make(chan struct{}),
		doneCh:       make(chan struct{}),
	}
}

// tryAcquireLock 尝试获取分布式锁，返回是否成功
func (w *FileCleanupWorker) tryAcquireLock(ctx context.Context) bool {
	if w.rdb == nil {
		return true // 无 Redis 时降级为本地运行
	}
	ok, err := w.rdb.SetNX(ctx, fileCleanupLockKey, "1", fileCleanupLockTTL).Result()
	if err != nil {
		zap.L().Warn("file cleanup: failed to acquire leader lock, running locally", zap.Error(err))
		return true
	}
	return ok
}

// keepLockAlive 周期性续期分布式锁
func (w *FileCleanupWorker) keepLockAlive(ctx context.Context) {
	if w.rdb == nil {
		return
	}
	ticker := time.NewTicker(fileCleanupLockTTL / 2)
	defer ticker.Stop()
	for {
		select {
		case <-ctx.Done():
			return
		case <-w.stopCh:
			return
		case <-ticker.C:
			w.rdb.Expire(ctx, fileCleanupLockKey, fileCleanupLockTTL)
		}
	}
}

// releaseLock 释放分布式锁
func (w *FileCleanupWorker) releaseLock() {
	if w.rdb == nil {
		return
	}
	w.rdb.Del(context.Background(), fileCleanupLockKey)
}

// Start 启动清理 worker
func (w *FileCleanupWorker) Start(ctx context.Context) {
	if w == nil || w.cfg == nil || !w.cfg.FileCleanup.Enabled {
		close(w.doneCh)
		return
	}
	if w.uploadedRepo == nil || w.s3Client == nil {
		zap.L().Warn("file cleanup: missing dependencies, worker disabled")
		close(w.doneCh)
		return
	}

	// 扫描间隔，默认 6 小时，最小 5 分钟
	interval := time.Duration(w.cfg.FileCleanup.IntervalMinutes) * time.Minute
	if interval < 5*time.Minute {
		interval = 6 * time.Hour
	}

	go func() {
		defer close(w.doneCh)

		isLeader := false
		lockCtx, lockCancel := context.WithCancel(ctx)

		for {
			select {
			case <-w.stopCh:
				if isLeader {
					w.releaseLock()
				}
				lockCancel()
				return
			default:
			}

			acquired := w.tryAcquireLock(ctx)
			if acquired {
				if !isLeader {
					zap.L().Info("file cleanup: acquired leader lock, becoming primary")
					isLeader = true
					go w.keepLockAlive(lockCtx)

					// 主实例启动后立即执行一次清理
					w.runOnce(ctx)

					ticker := time.NewTicker(interval)
					for {
						select {
						case <-w.stopCh:
							ticker.Stop()
							lockCancel()
							w.releaseLock()
							return
						case <-ticker.C:
							w.runOnce(ctx)
						}
					}
				}
			} else {
				zap.L().Debug("file cleanup: another instance holds leader lock, retrying later")
			}

			select {
			case <-w.stopCh:
				lockCancel()
				return
			case <-time.After(fileCleanupLockRetryInterval):
			}
		}
	}()
}

// Stop 停止 worker
func (w *FileCleanupWorker) Stop() {
	if w == nil {
		return
	}
	w.stopOnce.Do(func() {
		close(w.stopCh)
	})
	<-w.doneCh
	w.releaseLock()
}

// runOnce 执行一次清理扫描
func (w *FileCleanupWorker) runOnce(ctx context.Context) {
	cfg := w.cfg.FileCleanup
	retentionDays := cfg.RetentionDays
	if retentionDays <= 0 {
		retentionDays = 7
	}
	batchSize := cfg.BatchSize
	if batchSize <= 0 {
		batchSize = 100
	}

	before := time.Now().Add(-time.Duration(retentionDays) * 24 * time.Hour)
	totalDeleted := 0
	totalFailed := 0

	for {
		select {
		case <-w.stopCh:
			return
		default:
		}

		files, err := w.uploadedRepo.ListPendingCleanup(ctx, before, batchSize)
		if err != nil {
			zap.L().Warn("file cleanup: list pending failed", zap.Error(err))
			break
		}
		if len(files) == 0 {
			break
		}

		for _, f := range files {
			select {
			case <-w.stopCh:
				return
			default:
			}

			// 删除 S3 对象
			if derr := w.s3Client.Delete(ctx, f.ObjectName); derr != nil {
				// 删除失败不标记，下次重试
				totalFailed++
				zap.L().Warn("file cleanup: delete object failed, will retry",
					zap.String("object", f.ObjectName),
					zap.String("url", f.URL),
					zap.Error(derr),
				)
				continue
			}

			// 标记已清理
			now := time.Now()
			if merr := w.uploadedRepo.MarkExpired(ctx, f.ID, now); merr != nil {
				zap.L().Warn("file cleanup: mark expired failed",
					zap.Uint("id", f.ID),
					zap.String("url", f.URL),
					zap.Error(merr),
				)
				totalFailed++
			} else {
				totalDeleted++
			}
		}

		// 本批次不足 batchSize，说明已无待清理记录
		if len(files) < batchSize {
			break
		}
	}

	if totalDeleted > 0 || totalFailed > 0 {
		zap.L().Info("file cleanup sweep done",
			zap.Int("deleted", totalDeleted),
			zap.Int("failed", totalFailed),
			zap.Int("retention_days", retentionDays),
		)
	}
}

// 兜底：保证 errors 包被引用（若未来 runOnce 增加错误判断）
var _ = errors.Is