package middleware

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

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

type rateLimitBucket struct {
	count    int
	resetAt  time.Time
	lastSeen time.Time
}

type rateLimiter struct {
	mu      sync.Mutex
	limit   int
	window  time.Duration
	buckets map[string]rateLimitBucket
}

func RateLimitPerMinute(limit int) gin.HandlerFunc {
	if limit <= 0 {
		return func(c *gin.Context) {
			c.Next()
		}
	}
	limiter := &rateLimiter{
		limit:   limit,
		window:  time.Minute,
		buckets: make(map[string]rateLimitBucket),
	}
	return limiter.handle
}

func (l *rateLimiter) handle(c *gin.Context) {
	now := time.Now()
	key := c.ClientIP()
	allowed, resetAt := l.allow(key, now)
	if !allowed {
		c.Header("Retry-After", retryAfterSeconds(now, resetAt))
		c.AbortWithStatusJSON(http.StatusTooManyRequests, gin.H{
			"code":    "rate_limited",
			"message": "请求过于频繁，请稍后再试",
		})
		return
	}
	c.Next()
}

func (l *rateLimiter) allow(key string, now time.Time) (bool, time.Time) {
	l.mu.Lock()
	defer l.mu.Unlock()

	l.cleanup(now)
	bucket := l.buckets[key]
	if bucket.resetAt.IsZero() || !now.Before(bucket.resetAt) {
		bucket = rateLimitBucket{resetAt: now.Add(l.window)}
	}
	bucket.count++
	bucket.lastSeen = now
	l.buckets[key] = bucket
	return bucket.count <= l.limit, bucket.resetAt
}

func (l *rateLimiter) cleanup(now time.Time) {
	for key, bucket := range l.buckets {
		if now.Sub(bucket.lastSeen) > 2*l.window {
			delete(l.buckets, key)
		}
	}
}

func retryAfterSeconds(now time.Time, resetAt time.Time) string {
	seconds := int(resetAt.Sub(now).Seconds())
	if seconds < 1 {
		seconds = 1
	}
	return strconv.Itoa(seconds)
}