package middleware

import (
	"net/http"
	"sync"
	"time"

	"github.com/gin-gonic/gin"
)

// RateLimiter is a simple per-IP sliding-window rate limiter that runs
// entirely in-process. It is intended for auth endpoints (login, register)
// where brute-force protection is critical.
type RateLimiter struct {
	mu       sync.Mutex
	window   time.Duration
	max      int
	requests map[string][]time.Time
	stop     chan struct{}
	stopped  sync.Once
}

// NewRateLimiter creates a rate limiter allowing max requests per window
// per client IP.
func NewRateLimiter(max int, window time.Duration) *RateLimiter {
	rl := &RateLimiter{
		window:   window,
		max:      max,
		requests: make(map[string][]time.Time),
		stop:     make(chan struct{}),
	}
	go rl.cleanup()
	return rl
}

// Close 停止后台清理 goroutine：清理循环此前无停止机制，每建一个实例
// 就永久滞留一条 goroutine（测试场景会随实例创建不断累积）。
func (rl *RateLimiter) Close() {
	rl.stopped.Do(func() { close(rl.stop) })
}

func (rl *RateLimiter) cleanup() {
	ticker := time.NewTicker(5 * time.Minute)
	defer ticker.Stop()
	for {
		select {
		case <-rl.stop:
			return
		case <-ticker.C:
		}
		rl.mu.Lock()
		now := time.Now()
		for ip, times := range rl.requests {
			var valid []time.Time
			for _, t := range times {
				if now.Sub(t) <= rl.window {
					valid = append(valid, t)
				}
			}
			if len(valid) == 0 {
				delete(rl.requests, ip)
			} else {
				rl.requests[ip] = valid
			}
		}
		rl.mu.Unlock()
	}
}

// Allow returns true if the request from ip is within the rate limit.
func (rl *RateLimiter) Allow(ip string) bool {
	rl.mu.Lock()
	defer rl.mu.Unlock()
	now := time.Now()
	times := rl.requests[ip]
	var valid []time.Time
	for _, t := range times {
		if now.Sub(t) <= rl.window {
			valid = append(valid, t)
		}
	}
	if len(valid) >= rl.max {
		rl.requests[ip] = valid
		return false
	}
	rl.requests[ip] = append(valid, now)
	return true
}

// RateLimit returns a Gin middleware that rejects requests exceeding the
// per-IP rate limit with 429 Too Many Requests.
func RateLimit(limiter *RateLimiter) gin.HandlerFunc {
	return func(c *gin.Context) {
		if !limiter.Allow(c.ClientIP()) {
			c.AbortWithStatusJSON(http.StatusTooManyRequests, gin.H{
				"code":    42901,
				"message": "too many requests, please try again later",
			})
			return
		}
		c.Next()
	}
}