package service

import (
	"context"
	"errors"
	"fmt"
	"log"
	"strconv"
	"time"

	"sub2api/internal/model"
	"sub2api/internal/repository"

	"github.com/redis/go-redis/v9"
)

// 缓存Key前缀和TTL
const (
	billingBalanceKeyPrefix = "billing:balance:"
	billingSubKeyPrefix     = "billing:sub:"
	billingCacheTTL         = 5 * time.Minute
)

// 订阅缓存Hash字段
const (
	subFieldStatus       = "status"
	subFieldExpiresAt    = "expires_at"
	subFieldDailyUsage   = "daily_usage"
	subFieldWeeklyUsage  = "weekly_usage"
	subFieldMonthlyUsage = "monthly_usage"
	subFieldVersion      = "version"
)

// 错误定义
// 注：ErrInsufficientBalance在redeem_service.go中定义
// 注：ErrDailyLimitExceeded/ErrWeeklyLimitExceeded/ErrMonthlyLimitExceeded在subscription_service.go中定义
var (
	ErrSubscriptionInvalid = errors.New("subscription is invalid or expired")
)

// 预编译的Lua脚本
var (
	// deductBalanceScript: 扣减余额缓存，key不存在则忽略
	deductBalanceScript = redis.NewScript(`
		local current = redis.call('GET', KEYS[1])
		if current == false then
			return 0
		end
		local newVal = tonumber(current) - tonumber(ARGV[1])
		redis.call('SET', KEYS[1], newVal)
		redis.call('EXPIRE', KEYS[1], ARGV[2])
		return 1
	`)

	// updateSubUsageScript: 更新订阅用量缓存，key不存在则忽略
	updateSubUsageScript = redis.NewScript(`
		local exists = redis.call('EXISTS', KEYS[1])
		if exists == 0 then
			return 0
		end
		local cost = tonumber(ARGV[1])
		redis.call('HINCRBYFLOAT', KEYS[1], 'daily_usage', cost)
		redis.call('HINCRBYFLOAT', KEYS[1], 'weekly_usage', cost)
		redis.call('HINCRBYFLOAT', KEYS[1], 'monthly_usage', cost)
		redis.call('EXPIRE', KEYS[1], ARGV[2])
		return 1
	`)
)

// subscriptionCacheData 订阅缓存数据结构（内部使用）
type subscriptionCacheData struct {
	Status       string
	ExpiresAt    time.Time
	DailyUsage   float64
	WeeklyUsage  float64
	MonthlyUsage float64
	Version      int64
}

// BillingCacheService 计费缓存服务
// 负责余额和订阅数据的缓存管理，提供高性能的计费资格检查
type BillingCacheService struct {
	rdb      *redis.Client
	userRepo *repository.UserRepository
	subRepo  *repository.UserSubscriptionRepository
}

// NewBillingCacheService 创建计费缓存服务
func NewBillingCacheService(rdb *redis.Client, userRepo *repository.UserRepository, subRepo *repository.UserSubscriptionRepository) *BillingCacheService {
	return &BillingCacheService{
		rdb:      rdb,
		userRepo: userRepo,
		subRepo:  subRepo,
	}
}

// ============================================
// 余额缓存方法
// ============================================

// GetUserBalance 获取用户余额（优先从缓存读取）
func (s *BillingCacheService) GetUserBalance(ctx context.Context, userID int64) (float64, error) {
	if s.rdb == nil {
		// Redis不可用，直接查询数据库
		return s.getUserBalanceFromDB(ctx, userID)
	}

	key := fmt.Sprintf("%s%d", billingBalanceKeyPrefix, userID)

	// 尝试从缓存读取
	val, err := s.rdb.Get(ctx, key).Result()
	if err == nil {
		balance, parseErr := strconv.ParseFloat(val, 64)
		if parseErr == nil {
			return balance, nil
		}
	}

	// 缓存未命中或解析错误，从数据库读取
	balance, err := s.getUserBalanceFromDB(ctx, userID)
	if err != nil {
		return 0, err
	}

	// 异步建立缓存
	go func() {
		cacheCtx, cancel := context.WithTimeout(context.Background(), 2*time.Second)
		defer cancel()
		s.setBalanceCache(cacheCtx, userID, balance)
	}()

	return balance, nil
}

// getUserBalanceFromDB 从数据库获取用户余额
func (s *BillingCacheService) getUserBalanceFromDB(ctx context.Context, userID int64) (float64, error) {
	user, err := s.userRepo.GetByID(ctx, userID)
	if err != nil {
		return 0, fmt.Errorf("get user balance: %w", err)
	}
	return user.Balance, nil
}

// setBalanceCache 设置余额缓存
func (s *BillingCacheService) setBalanceCache(ctx context.Context, userID int64, balance float64) {
	if s.rdb == nil {
		return
	}
	key := fmt.Sprintf("%s%d", billingBalanceKeyPrefix, userID)
	if err := s.rdb.Set(ctx, key, balance, billingCacheTTL).Err(); err != nil {
		log.Printf("Warning: set balance cache failed for user %d: %v", userID, err)
	}
}

// DeductBalanceCache 扣减余额缓存（异步调用，用于扣费后更新缓存）
func (s *BillingCacheService) DeductBalanceCache(ctx context.Context, userID int64, amount float64) error {
	if s.rdb == nil {
		return nil
	}

	key := fmt.Sprintf("%s%d", billingBalanceKeyPrefix, userID)

	// 使用预编译的Lua脚本原子性扣减，如果key不存在则忽略
	_, err := deductBalanceScript.Run(ctx, s.rdb, []string{key}, amount, int(billingCacheTTL.Seconds())).Result()
	if err != nil && !errors.Is(err, redis.Nil) {
		log.Printf("Warning: deduct balance cache failed for user %d: %v", userID, err)
	}
	return nil
}

// InvalidateUserBalance 失效用户余额缓存
func (s *BillingCacheService) InvalidateUserBalance(ctx context.Context, userID int64) error {
	if s.rdb == nil {
		return nil
	}

	key := fmt.Sprintf("%s%d", billingBalanceKeyPrefix, userID)
	if err := s.rdb.Del(ctx, key).Err(); err != nil {
		log.Printf("Warning: invalidate balance cache failed for user %d: %v", userID, err)
		return err
	}
	return nil
}

// ============================================
// 订阅缓存方法
// ============================================

// GetSubscriptionStatus 获取订阅状态（优先从缓存读取）
func (s *BillingCacheService) GetSubscriptionStatus(ctx context.Context, userID, groupID int64) (*subscriptionCacheData, error) {
	if s.rdb == nil {
		return s.getSubscriptionFromDB(ctx, userID, groupID)
	}

	key := fmt.Sprintf("%s%d:%d", billingSubKeyPrefix, userID, groupID)

	// 尝试从缓存读取
	result, err := s.rdb.HGetAll(ctx, key).Result()
	if err == nil && len(result) > 0 {
		data, parseErr := s.parseSubscriptionCache(result)
		if parseErr == nil {
			return data, nil
		}
	}

	// 缓存未命中，从数据库读取
	data, err := s.getSubscriptionFromDB(ctx, userID, groupID)
	if err != nil {
		return nil, err
	}

	// 异步建立缓存
	go func() {
		cacheCtx, cancel := context.WithTimeout(context.Background(), 2*time.Second)
		defer cancel()
		s.setSubscriptionCache(cacheCtx, userID, groupID, data)
	}()

	return data, nil
}

// getSubscriptionFromDB 从数据库获取订阅数据
func (s *BillingCacheService) getSubscriptionFromDB(ctx context.Context, userID, groupID int64) (*subscriptionCacheData, error) {
	sub, err := s.subRepo.GetActiveByUserIDAndGroupID(ctx, userID, groupID)
	if err != nil {
		return nil, fmt.Errorf("get subscription: %w", err)
	}

	return &subscriptionCacheData{
		Status:       sub.Status,
		ExpiresAt:    sub.ExpiresAt,
		DailyUsage:   sub.DailyUsageUSD,
		WeeklyUsage:  sub.WeeklyUsageUSD,
		MonthlyUsage: sub.MonthlyUsageUSD,
		Version:      sub.UpdatedAt.Unix(),
	}, nil
}

// parseSubscriptionCache 解析订阅缓存数据
func (s *BillingCacheService) parseSubscriptionCache(data map[string]string) (*subscriptionCacheData, error) {
	result := &subscriptionCacheData{}

	result.Status = data[subFieldStatus]
	if result.Status == "" {
		return nil, errors.New("invalid cache: missing status")
	}

	if expiresStr, ok := data[subFieldExpiresAt]; ok {
		expiresAt, err := strconv.ParseInt(expiresStr, 10, 64)
		if err == nil {
			result.ExpiresAt = time.Unix(expiresAt, 0)
		}
	}

	if dailyStr, ok := data[subFieldDailyUsage]; ok {
		result.DailyUsage, _ = strconv.ParseFloat(dailyStr, 64)
	}

	if weeklyStr, ok := data[subFieldWeeklyUsage]; ok {
		result.WeeklyUsage, _ = strconv.ParseFloat(weeklyStr, 64)
	}

	if monthlyStr, ok := data[subFieldMonthlyUsage]; ok {
		result.MonthlyUsage, _ = strconv.ParseFloat(monthlyStr, 64)
	}

	if versionStr, ok := data[subFieldVersion]; ok {
		result.Version, _ = strconv.ParseInt(versionStr, 10, 64)
	}

	return result, nil
}

// setSubscriptionCache 设置订阅缓存
func (s *BillingCacheService) setSubscriptionCache(ctx context.Context, userID, groupID int64, data *subscriptionCacheData) {
	if s.rdb == nil || data == nil {
		return
	}

	key := fmt.Sprintf("%s%d:%d", billingSubKeyPrefix, userID, groupID)

	fields := map[string]interface{}{
		subFieldStatus:       data.Status,
		subFieldExpiresAt:    data.ExpiresAt.Unix(),
		subFieldDailyUsage:   data.DailyUsage,
		subFieldWeeklyUsage:  data.WeeklyUsage,
		subFieldMonthlyUsage: data.MonthlyUsage,
		subFieldVersion:      data.Version,
	}

	pipe := s.rdb.Pipeline()
	pipe.HSet(ctx, key, fields)
	pipe.Expire(ctx, key, billingCacheTTL)
	if _, err := pipe.Exec(ctx); err != nil {
		log.Printf("Warning: set subscription cache failed for user %d group %d: %v", userID, groupID, err)
	}
}

// UpdateSubscriptionUsage 更新订阅用量缓存（异步调用，用于扣费后更新缓存）
func (s *BillingCacheService) UpdateSubscriptionUsage(ctx context.Context, userID, groupID int64, costUSD float64) error {
	if s.rdb == nil {
		return nil
	}

	key := fmt.Sprintf("%s%d:%d", billingSubKeyPrefix, userID, groupID)

	// 使用预编译的Lua脚本原子性增加用量，如果key不存在则忽略
	_, err := updateSubUsageScript.Run(ctx, s.rdb, []string{key}, costUSD, int(billingCacheTTL.Seconds())).Result()
	if err != nil && !errors.Is(err, redis.Nil) {
		log.Printf("Warning: update subscription usage cache failed for user %d group %d: %v", userID, groupID, err)
	}
	return nil
}

// InvalidateSubscription 失效指定订阅缓存
func (s *BillingCacheService) InvalidateSubscription(ctx context.Context, userID, groupID int64) error {
	if s.rdb == nil {
		return nil
	}

	key := fmt.Sprintf("%s%d:%d", billingSubKeyPrefix, userID, groupID)
	if err := s.rdb.Del(ctx, key).Err(); err != nil {
		log.Printf("Warning: invalidate subscription cache failed for user %d group %d: %v", userID, groupID, err)
		return err
	}
	return nil
}

// ============================================
// 统一检查方法
// ============================================

// CheckBillingEligibility 检查用户是否有资格发起请求
// 余额模式：检查缓存余额 > 0
// 订阅模式：检查缓存用量未超过限额（Group限额从参数传入）
func (s *BillingCacheService) CheckBillingEligibility(ctx context.Context, user *model.User, apiKey *model.ApiKey, group *model.Group, subscription *model.UserSubscription) error {
	// 判断计费模式
	isSubscriptionMode := group != nil && group.IsSubscriptionType() && subscription != nil

	if isSubscriptionMode {
		return s.checkSubscriptionEligibility(ctx, user.ID, group, subscription)
	}

	return s.checkBalanceEligibility(ctx, user.ID)
}

// checkBalanceEligibility 检查余额模式资格
func (s *BillingCacheService) checkBalanceEligibility(ctx context.Context, userID int64) error {
	balance, err := s.GetUserBalance(ctx, userID)
	if err != nil {
		// 缓存/数据库错误，允许通过（降级处理）
		log.Printf("Warning: get user balance failed, allowing request: %v", err)
		return nil
	}

	if balance <= 0 {
		return ErrInsufficientBalance
	}

	return nil
}

// checkSubscriptionEligibility 检查订阅模式资格
func (s *BillingCacheService) checkSubscriptionEligibility(ctx context.Context, userID int64, group *model.Group, subscription *model.UserSubscription) error {
	// 获取订阅缓存数据
	subData, err := s.GetSubscriptionStatus(ctx, userID, group.ID)
	if err != nil {
		// 缓存/数据库错误，降级使用传入的subscription进行检查
		log.Printf("Warning: get subscription cache failed, using fallback: %v", err)
		return s.checkSubscriptionLimitsFallback(subscription, group)
	}

	// 检查订阅状态
	if subData.Status != model.SubscriptionStatusActive {
		return ErrSubscriptionInvalid
	}

	// 检查是否过期
	if time.Now().After(subData.ExpiresAt) {
		return ErrSubscriptionInvalid
	}

	// 检查限额（使用传入的Group限额配置）
	if group.HasDailyLimit() && subData.DailyUsage >= *group.DailyLimitUSD {
		return ErrDailyLimitExceeded
	}

	if group.HasWeeklyLimit() && subData.WeeklyUsage >= *group.WeeklyLimitUSD {
		return ErrWeeklyLimitExceeded
	}

	if group.HasMonthlyLimit() && subData.MonthlyUsage >= *group.MonthlyLimitUSD {
		return ErrMonthlyLimitExceeded
	}

	return nil
}

// checkSubscriptionLimitsFallback 降级检查订阅限额
func (s *BillingCacheService) checkSubscriptionLimitsFallback(subscription *model.UserSubscription, group *model.Group) error {
	if subscription == nil {
		return ErrSubscriptionInvalid
	}

	if !subscription.IsActive() {
		return ErrSubscriptionInvalid
	}

	if !subscription.CheckDailyLimit(group, 0) {
		return ErrDailyLimitExceeded
	}

	if !subscription.CheckWeeklyLimit(group, 0) {
		return ErrWeeklyLimitExceeded
	}

	if !subscription.CheckMonthlyLimit(group, 0) {
		return ErrMonthlyLimitExceeded
	}

	return nil
}