package service

import (
	"context"
	"crypto/rand"
	"encoding/hex"
	"errors"
	"fmt"
	"strings"
	"sub2api/internal/model"
	"sub2api/internal/repository"
	"time"

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

var (
	ErrRedeemCodeNotFound  = errors.New("redeem code not found")
	ErrRedeemCodeUsed      = errors.New("redeem code already used")
	ErrRedeemCodeInvalid   = errors.New("invalid redeem code")
	ErrInsufficientBalance = errors.New("insufficient balance")
	ErrRedeemRateLimited   = errors.New("too many failed attempts, please try again later")
	ErrRedeemCodeLocked    = errors.New("redeem code is being processed, please try again")
)

const (
	redeemRateLimitKeyPrefix = "redeem:rate_limit:"
	redeemLockKeyPrefix      = "redeem:lock:"
	redeemMaxErrorsPerHour   = 20
	redeemRateLimitDuration  = time.Hour
	redeemLockDuration       = 10 * time.Second // 锁超时时间，防止死锁
)

// GenerateCodesRequest 生成兑换码请求
type GenerateCodesRequest struct {
	Count int     `json:"count"`
	Value float64 `json:"value"`
	Type  string  `json:"type"`
}

// RedeemCodeResponse 兑换码响应
type RedeemCodeResponse struct {
	Code      string    `json:"code"`
	Value     float64   `json:"value"`
	Status    string    `json:"status"`
	CreatedAt time.Time `json:"created_at"`
}

// RedeemService 兑换码服务
type RedeemService struct {
	redeemRepo          *repository.RedeemCodeRepository
	userRepo            *repository.UserRepository
	subscriptionService *SubscriptionService
	rdb                 *redis.Client
	billingCacheService *BillingCacheService
}

// NewRedeemService 创建兑换码服务实例
func NewRedeemService(redeemRepo *repository.RedeemCodeRepository, userRepo *repository.UserRepository, subscriptionService *SubscriptionService, rdb *redis.Client) *RedeemService {
	return &RedeemService{
		redeemRepo:          redeemRepo,
		userRepo:            userRepo,
		subscriptionService: subscriptionService,
		rdb:                 rdb,
	}
}

// SetBillingCacheService 设置计费缓存服务（用于缓存失效）
func (s *RedeemService) SetBillingCacheService(billingCacheService *BillingCacheService) {
	s.billingCacheService = billingCacheService
}

// GenerateRandomCode 生成随机兑换码
func (s *RedeemService) GenerateRandomCode() (string, error) {
	// 生成16字节随机数据
	bytes := make([]byte, 16)
	if _, err := rand.Read(bytes); err != nil {
		return "", fmt.Errorf("generate random bytes: %w", err)
	}

	// 转换为十六进制字符串
	code := hex.EncodeToString(bytes)

	// 格式化为 XXXX-XXXX-XXXX-XXXX 格式
	parts := []string{
		strings.ToUpper(code[0:8]),
		strings.ToUpper(code[8:16]),
		strings.ToUpper(code[16:24]),
		strings.ToUpper(code[24:32]),
	}

	return strings.Join(parts, "-"), nil
}

// GenerateCodes 批量生成兑换码
func (s *RedeemService) GenerateCodes(ctx context.Context, req GenerateCodesRequest) ([]model.RedeemCode, error) {
	if req.Count <= 0 {
		return nil, errors.New("count must be greater than 0")
	}

	if req.Value <= 0 {
		return nil, errors.New("value must be greater than 0")
	}

	if req.Count > 1000 {
		return nil, errors.New("cannot generate more than 1000 codes at once")
	}

	codeType := req.Type
	if codeType == "" {
		codeType = model.RedeemTypeBalance
	}

	codes := make([]model.RedeemCode, 0, req.Count)
	for i := 0; i < req.Count; i++ {
		code, err := s.GenerateRandomCode()
		if err != nil {
			return nil, fmt.Errorf("generate code: %w", err)
		}

		codes = append(codes, model.RedeemCode{
			Code:   code,
			Type:   codeType,
			Value:  req.Value,
			Status: model.StatusUnused,
		})
	}

	// 批量插入
	if err := s.redeemRepo.CreateBatch(ctx, codes); err != nil {
		return nil, fmt.Errorf("create batch codes: %w", err)
	}

	return codes, nil
}

// checkRedeemRateLimit 检查用户兑换错误次数是否超限
func (s *RedeemService) checkRedeemRateLimit(ctx context.Context, userID int64) error {
	if s.rdb == nil {
		return nil
	}

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

	count, err := s.rdb.Get(ctx, key).Int()
	if err != nil && !errors.Is(err, redis.Nil) {
		// Redis 出错时不阻止用户操作
		return nil
	}

	if count >= redeemMaxErrorsPerHour {
		return ErrRedeemRateLimited
	}

	return nil
}

// incrementRedeemErrorCount 增加用户兑换错误计数
func (s *RedeemService) incrementRedeemErrorCount(ctx context.Context, userID int64) {
	if s.rdb == nil {
		return
	}

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

	pipe := s.rdb.Pipeline()
	pipe.Incr(ctx, key)
	pipe.Expire(ctx, key, redeemRateLimitDuration)
	_, _ = pipe.Exec(ctx)
}

// acquireRedeemLock 尝试获取兑换码的分布式锁
// 返回 true 表示获取成功，false 表示锁已被占用
func (s *RedeemService) acquireRedeemLock(ctx context.Context, code string) bool {
	if s.rdb == nil {
		return true // 无 Redis 时降级为不加锁
	}

	key := redeemLockKeyPrefix + code
	ok, err := s.rdb.SetNX(ctx, key, "1", redeemLockDuration).Result()
	if err != nil {
		// Redis 出错时不阻止操作，依赖数据库层面的状态检查
		return true
	}
	return ok
}

// releaseRedeemLock 释放兑换码的分布式锁
func (s *RedeemService) releaseRedeemLock(ctx context.Context, code string) {
	if s.rdb == nil {
		return
	}

	key := redeemLockKeyPrefix + code
	s.rdb.Del(ctx, key)
}

// Redeem 使用兑换码
func (s *RedeemService) Redeem(ctx context.Context, userID int64, code string) (*model.RedeemCode, error) {
	// 检查限流
	if err := s.checkRedeemRateLimit(ctx, userID); err != nil {
		return nil, err
	}

	// 获取分布式锁，防止同一兑换码并发使用
	if !s.acquireRedeemLock(ctx, code) {
		return nil, ErrRedeemCodeLocked
	}
	defer s.releaseRedeemLock(ctx, code)

	// 查找兑换码
	redeemCode, err := s.redeemRepo.GetByCode(ctx, code)
	if err != nil {
		if errors.Is(err, gorm.ErrRecordNotFound) {
			s.incrementRedeemErrorCount(ctx, userID)
			return nil, ErrRedeemCodeNotFound
		}
		return nil, fmt.Errorf("get redeem code: %w", err)
	}

	// 检查兑换码状态
	if !redeemCode.CanUse() {
		s.incrementRedeemErrorCount(ctx, userID)
		return nil, ErrRedeemCodeUsed
	}

	// 验证兑换码类型的前置条件
	if redeemCode.Type == model.RedeemTypeSubscription && redeemCode.GroupID == nil {
		return nil, errors.New("invalid subscription redeem code: missing group_id")
	}

	// 获取用户信息
	user, err := s.userRepo.GetByID(ctx, userID)
	if err != nil {
		if errors.Is(err, gorm.ErrRecordNotFound) {
			return nil, ErrUserNotFound
		}
		return nil, fmt.Errorf("get user: %w", err)
	}
	_ = user // 使用变量避免未使用错误

	// 【关键】先标记兑换码为已使用，确保并发安全
	// 利用数据库乐观锁（WHERE status = 'unused'）保证原子性
	if err := s.redeemRepo.Use(ctx, redeemCode.ID, userID); err != nil {
		if errors.Is(err, gorm.ErrRecordNotFound) {
			// 兑换码已被其他请求使用
			return nil, ErrRedeemCodeUsed
		}
		return nil, fmt.Errorf("mark code as used: %w", err)
	}

	// 执行兑换逻辑（兑换码已被锁定，此时可安全操作）
	switch redeemCode.Type {
	case model.RedeemTypeBalance:
		// 增加用户余额
		if err := s.userRepo.UpdateBalance(ctx, userID, redeemCode.Value); err != nil {
			return nil, fmt.Errorf("update user balance: %w", err)
		}
		// 失效余额缓存
		if s.billingCacheService != nil {
			go func() {
				cacheCtx, cancel := context.WithTimeout(context.Background(), 5*time.Second)
				defer cancel()
				s.billingCacheService.InvalidateUserBalance(cacheCtx, userID)
			}()
		}

	case model.RedeemTypeConcurrency:
		// 增加用户并发数
		if err := s.userRepo.UpdateConcurrency(ctx, userID, int(redeemCode.Value)); err != nil {
			return nil, fmt.Errorf("update user concurrency: %w", err)
		}

	case model.RedeemTypeSubscription:
		validityDays := redeemCode.ValidityDays
		if validityDays <= 0 {
			validityDays = 30
		}
		_, _, err := s.subscriptionService.AssignOrExtendSubscription(ctx, &AssignSubscriptionInput{
			UserID:       userID,
			GroupID:      *redeemCode.GroupID,
			ValidityDays: validityDays,
			AssignedBy:   0, // 系统分配
			Notes:        fmt.Sprintf("通过兑换码 %s 兑换", redeemCode.Code),
		})
		if err != nil {
			return nil, fmt.Errorf("assign or extend subscription: %w", err)
		}
		// 失效订阅缓存
		if s.billingCacheService != nil {
			groupID := *redeemCode.GroupID
			go func() {
				cacheCtx, cancel := context.WithTimeout(context.Background(), 5*time.Second)
				defer cancel()
				s.billingCacheService.InvalidateSubscription(cacheCtx, userID, groupID)
			}()
		}

	default:
		return nil, fmt.Errorf("unsupported redeem type: %s", redeemCode.Type)
	}

	// 重新获取更新后的兑换码
	redeemCode, err = s.redeemRepo.GetByID(ctx, redeemCode.ID)
	if err != nil {
		return nil, fmt.Errorf("get updated redeem code: %w", err)
	}

	return redeemCode, nil
}

// GetByID 根据ID获取兑换码
func (s *RedeemService) GetByID(ctx context.Context, id int64) (*model.RedeemCode, error) {
	code, err := s.redeemRepo.GetByID(ctx, id)
	if err != nil {
		if errors.Is(err, gorm.ErrRecordNotFound) {
			return nil, ErrRedeemCodeNotFound
		}
		return nil, fmt.Errorf("get redeem code: %w", err)
	}
	return code, nil
}

// GetByCode 根据Code获取兑换码
func (s *RedeemService) GetByCode(ctx context.Context, code string) (*model.RedeemCode, error) {
	redeemCode, err := s.redeemRepo.GetByCode(ctx, code)
	if err != nil {
		if errors.Is(err, gorm.ErrRecordNotFound) {
			return nil, ErrRedeemCodeNotFound
		}
		return nil, fmt.Errorf("get redeem code: %w", err)
	}
	return redeemCode, nil
}

// List 获取兑换码列表（管理员功能）
func (s *RedeemService) List(ctx context.Context, params repository.PaginationParams) ([]model.RedeemCode, *repository.PaginationResult, error) {
	codes, pagination, err := s.redeemRepo.List(ctx, params)
	if err != nil {
		return nil, nil, fmt.Errorf("list redeem codes: %w", err)
	}
	return codes, pagination, nil
}

// Delete 删除兑换码（管理员功能）
func (s *RedeemService) Delete(ctx context.Context, id int64) error {
	// 检查兑换码是否存在
	code, err := s.redeemRepo.GetByID(ctx, id)
	if err != nil {
		if errors.Is(err, gorm.ErrRecordNotFound) {
			return ErrRedeemCodeNotFound
		}
		return fmt.Errorf("get redeem code: %w", err)
	}

	// 不允许删除已使用的兑换码
	if code.IsUsed() {
		return errors.New("cannot delete used redeem code")
	}

	if err := s.redeemRepo.Delete(ctx, id); err != nil {
		return fmt.Errorf("delete redeem code: %w", err)
	}

	return nil
}

// GetStats 获取兑换码统计信息
func (s *RedeemService) GetStats(ctx context.Context) (map[string]interface{}, error) {
	// TODO: 实现统计逻辑
	// 统计未使用、已使用的兑换码数量
	// 统计总面值等

	stats := map[string]interface{}{
		"total_codes":  0,
		"unused_codes": 0,
		"used_codes":   0,
		"total_value":  0.0,
	}

	return stats, nil
}

// GetUserHistory 获取用户的兑换历史
func (s *RedeemService) GetUserHistory(ctx context.Context, userID int64, limit int) ([]model.RedeemCode, error) {
	codes, err := s.redeemRepo.ListByUser(ctx, userID, limit)
	if err != nil {
		return nil, fmt.Errorf("get user redeem history: %w", err)
	}
	return codes, nil
}