sub2api/backend/internal/repository/billing_cache.go

package repository

import (
	"context"
	"errors"
	"fmt"
	"log"
	"math/rand/v2"
	"strconv"
	"time"

	"github.com/Wei-Shaw/sub2api/internal/service"
	"github.com/redis/go-redis/v9"
)

const (
	billingBalanceKeyPrefix = "billing:balance:"
	billingSubKeyPrefix     = "billing:sub:"
	billingCacheTTL         = 5 * time.Minute
	billingCacheJitter      = 30 * time.Second
)

// jitteredTTL 返回带随机抖动的 TTL，防止缓存雪崩
func jitteredTTL() time.Duration {
	// 只做“减法抖动”，确保实际 TTL 不会超过 billingCacheTTL（避免上界预期被打破）。
	if billingCacheJitter <= 0 {
		return billingCacheTTL
	}
	jitter := time.Duration(rand.IntN(int(billingCacheJitter)))
	return billingCacheTTL - jitter
}

// billingBalanceKey generates the Redis key for user balance cache.
func billingBalanceKey(userID int64) string {
	return fmt.Sprintf("%s%d", billingBalanceKeyPrefix, userID)
}

// billingSubKey generates the Redis key for subscription cache.
func billingSubKey(userID, groupID int64) string {
	return fmt.Sprintf("%s%d:%d", billingSubKeyPrefix, userID, groupID)
}

const (
	subFieldStatus       = "status"
	subFieldExpiresAt    = "expires_at"
	subFieldDailyUsage   = "daily_usage"
	subFieldWeeklyUsage  = "weekly_usage"
	subFieldMonthlyUsage = "monthly_usage"
	subFieldVersion      = "version"
)

var (
	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 = 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
	`)
)

type billingCache struct {
	rdb *redis.Client
}

func NewBillingCache(rdb *redis.Client) service.BillingCache {
	return &billingCache{rdb: rdb}
}

func (c *billingCache) GetUserBalance(ctx context.Context, userID int64) (float64, error) {
	key := billingBalanceKey(userID)
	val, err := c.rdb.Get(ctx, key).Result()
	if err != nil {
		return 0, err
	}
	return strconv.ParseFloat(val, 64)
}

func (c *billingCache) SetUserBalance(ctx context.Context, userID int64, balance float64) error {
	key := billingBalanceKey(userID)
	return c.rdb.Set(ctx, key, balance, jitteredTTL()).Err()
}

func (c *billingCache) DeductUserBalance(ctx context.Context, userID int64, amount float64) error {
	key := billingBalanceKey(userID)
	_, err := deductBalanceScript.Run(ctx, c.rdb, []string{key}, amount, int(jitteredTTL().Seconds())).Result()
	if err != nil && !errors.Is(err, redis.Nil) {
		log.Printf("Warning: deduct balance cache failed for user %d: %v", userID, err)
		return err
	}
	return nil
}

func (c *billingCache) InvalidateUserBalance(ctx context.Context, userID int64) error {
	key := billingBalanceKey(userID)
	return c.rdb.Del(ctx, key).Err()
}

func (c *billingCache) GetSubscriptionCache(ctx context.Context, userID, groupID int64) (*service.SubscriptionCacheData, error) {
	key := billingSubKey(userID, groupID)
	result, err := c.rdb.HGetAll(ctx, key).Result()
	if err != nil {
		return nil, err
	}
	if len(result) == 0 {
		return nil, redis.Nil
	}
	return c.parseSubscriptionCache(result)
}

func (c *billingCache) parseSubscriptionCache(data map[string]string) (*service.SubscriptionCacheData, error) {
	result := &service.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
}

func (c *billingCache) SetSubscriptionCache(ctx context.Context, userID, groupID int64, data *service.SubscriptionCacheData) error {
	if data == nil {
		return nil
	}

	key := billingSubKey(userID, groupID)

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

	pipe := c.rdb.Pipeline()
	pipe.HSet(ctx, key, fields)
	pipe.Expire(ctx, key, jitteredTTL())
	_, err := pipe.Exec(ctx)
	return err
}

func (c *billingCache) UpdateSubscriptionUsage(ctx context.Context, userID, groupID int64, cost float64) error {
	key := billingSubKey(userID, groupID)
	_, err := updateSubUsageScript.Run(ctx, c.rdb, []string{key}, cost, int(jitteredTTL().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 err
	}
	return nil
}

func (c *billingCache) InvalidateSubscriptionCache(ctx context.Context, userID, groupID int64) error {
	key := billingSubKey(userID, groupID)
	return c.rdb.Del(ctx, key).Err()
}