package api

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

	"github.com/gin-gonic/gin"
	"golang.org/x/time/rate"

	"oci-portal/internal/service"
)

// ipEvictInterval 是陈旧限速条目的回收周期。
const ipEvictInterval = 10 * time.Minute

// ipRateLimiter 维护每 IP 令牌桶;速率与突发取安全设置快照,
// 设置变更后既有桶就地调参;陈旧条目由后台 ticker 惰性回收。
type ipRateLimiter struct {
	mu       sync.RWMutex
	limiters map[string]*ipEntry
}

type ipEntry struct {
	limiter *rate.Limiter
	// lastSeen 是 UnixNano 时间戳;请求路径无锁写、回收循环无锁读
	lastSeen atomic.Int64
}

func newIPRateLimiter() *ipRateLimiter {
	l := &ipRateLimiter{limiters: make(map[string]*ipEntry)}
	go l.evictLoop()
	return l
}

// get 返回 ip 对应的令牌桶,参数与当前配置不一致时就地调整。
// lastSeen 用原子时间戳:并发请求与回收循环两侧无锁读写,避免数据竞态。
func (l *ipRateLimiter) get(ip string, rps, burst int) *rate.Limiter {
	l.mu.RLock()
	entry, ok := l.limiters[ip]
	l.mu.RUnlock()
	if !ok {
		l.mu.Lock()
		if entry, ok = l.limiters[ip]; !ok {
			entry = &ipEntry{limiter: rate.NewLimiter(rate.Limit(rps), burst)}
			l.limiters[ip] = entry
		}
		l.mu.Unlock()
	}
	entry.lastSeen.Store(time.Now().UnixNano())
	if entry.limiter.Limit() != rate.Limit(rps) || entry.limiter.Burst() != burst {
		entry.limiter.SetLimit(rate.Limit(rps))
		entry.limiter.SetBurst(burst)
	}
	return entry.limiter
}

func (l *ipRateLimiter) evictLoop() {
	ticker := time.NewTicker(ipEvictInterval)
	defer ticker.Stop()
	for range ticker.C {
		l.mu.Lock()
		cutoff := time.Now().Add(-ipEvictInterval).UnixNano()
		for ip, e := range l.limiters {
			if e.lastSeen.Load() < cutoff {
				delete(l.limiters, ip)
			}
		}
		l.mu.Unlock()
	}
}

// IPRateMiddleware 返回全局 IP 限速中间件;超限返回 429,参数随安全设置热更新。
func IPRateMiddleware(settings *service.SettingService) gin.HandlerFunc {
	lm := newIPRateLimiter()
	return func(c *gin.Context) {
		sec := settings.SecurityCached()
		if !lm.get(requestIP(c), sec.IPRateRPS, sec.IPRateBurst).Allow() {
			c.AbortWithStatusJSON(http.StatusTooManyRequests, gin.H{"error": "rate limit exceeded"})
			return
		}
		c.Next()
	}
}