package service

import (
	"context"
	"sync"
	"time"

	"with_you/internal/config"
	"with_you/internal/repository"

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

// DeviceCleanupWorker 设备 registration_id 清理 worker
// 周期性清理超过保留期未使用的设备 token（按 last_used_at 判断）。
// 多实例部署时通过 Redis 分布式锁保证仅主实例执行清理。
type DeviceCleanupWorker struct {
	cfg        *config.Config
	deviceRepo repository.DeviceTokenRepository
	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 (
	// deviceCleanupLockKey Redis 分布式锁键
	deviceCleanupLockKey = "device_cleanup:leader_lock"
	// deviceCleanupLockTTL 锁持有时间（略大于扫描间隔，确保单实例持有）
	deviceCleanupLockTTL = 7 * time.Hour
	// deviceCleanupLockRetryInterval 竞争锁的重试间隔
	deviceCleanupLockRetryInterval = 1 * time.Minute
)

// NewDeviceCleanupWorker 创建设备清理 worker
func NewDeviceCleanupWorker(
	cfg *config.Config,
	deviceRepo repository.DeviceTokenRepository,
	rdb *redislib.Client,
) *DeviceCleanupWorker {
	return &DeviceCleanupWorker{
		cfg:        cfg,
		deviceRepo: deviceRepo,
		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 *DeviceCleanupWorker) 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, deviceCleanupLockKey, "1", deviceCleanupLockTTL).Result()
	if err != nil {
		zap.L().Warn("device 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 *DeviceCleanupWorker) keepLockAlive(ctx context.Context) {
	if w.rdb == nil {
		return
	}
	ticker := time.NewTicker(deviceCleanupLockTTL / 2)
	defer ticker.Stop()
	for {
		select {
		case <-ctx.Done():
			return
		case <-w.stopCh:
			return
		case <-ticker.C:
			w.rdb.Expire(ctx, deviceCleanupLockKey, deviceCleanupLockTTL)
		}
	}
}

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

// Start 启动清理 worker
func (w *DeviceCleanupWorker) Start(ctx context.Context) {
	if w == nil || w.cfg == nil || !w.cfg.DeviceCleanup.Enabled {
		close(w.doneCh)
		return
	}
	if w.deviceRepo == nil {
		zap.L().Warn("device 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.DeviceCleanup.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("device 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("device cleanup: another instance holds leader lock, retrying later")
			}

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

// Stop 停止 worker
func (w *DeviceCleanupWorker) 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 *DeviceCleanupWorker) runOnce(ctx context.Context) {
	cfg := w.cfg.DeviceCleanup
	retentionDays := cfg.RetentionDays
	if retentionDays <= 0 {
		retentionDays = 3
	}

	before := time.Now().Add(-time.Duration(retentionDays) * 24 * time.Hour)
	if err := w.deviceRepo.DeleteStaleDevices(before); err != nil {
		zap.L().Warn("device cleanup: delete stale devices failed", zap.Error(err))
		return
	}

	zap.L().Info("device cleanup sweep done",
		zap.Int("retention_days", retentionDays),
		zap.Time("before", before),
	)
}