package stocklock

import (
	"context"
	"fmt"
	"sync/atomic"
	"time"

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

// 滑动窗口：ZSET 里存每次请求的时间戳（毫秒），先删掉窗口外的，再数窗口内的
var slidingScript = redis.NewScript(`
local key, now, window, limit, member = KEYS[1], tonumber(ARGV[1]), tonumber(ARGV[2]), tonumber(ARGV[3]), ARGV[4]
redis.call("ZREMRANGEBYSCORE", key, 0, now - window)
if redis.call("ZCARD", key) >= limit then
  return 0
end
redis.call("ZADD", key, now, member)
redis.call("PEXPIRE", key, window)
return 1`)

type SlidingWindow struct {
	rdb    *redis.Client
	limit  int
	window time.Duration
	seq    func() string // 生成唯一成员，避免同一毫秒的请求互相覆盖
}

func NewSlidingWindow(rdb *redis.Client, limit int, window time.Duration) *SlidingWindow {
	var n atomic.Uint64 // 并发安全的序号；多实例部署时成员里再加上实例标识或用 UUID
	return &SlidingWindow{rdb: rdb, limit: limit, window: window, seq: func() string {
		return fmt.Sprintf("%d-%d", time.Now().UnixNano(), n.Add(1))
	}}
}

// Allow 判断 key（如 "rl:user:42"）在当前窗口内是否还能通过
func (s *SlidingWindow) Allow(ctx context.Context, key string, now time.Time) (bool, error) {
	n, err := slidingScript.Run(ctx, s.rdb, []string{key},
		now.UnixMilli(), s.window.Milliseconds(), s.limit, s.seq()).Int()
	return n == 1, err
}