package ratelimit

import (
	"net"
	"sync"
	"time"

	"github.com/sirupsen/logrus"
)

// RateLimiter 速率限制器
type RateLimiter struct {
	logger          *logrus.Logger
	globalLimit     *TokenBucket
	perIPLimiters   map[string]*TokenBucket
	cleanupInterval time.Duration
	mu              sync.RWMutex
	stopCh          chan struct{}
}

// TokenBucket Token桶算法实现
type TokenBucket struct {
	capacity   int64
	tokens     int64
	refillRate int64 // tokens per second
	lastRefill time.Time
	mu         sync.Mutex
}

// Config 速率限制配置
type Config struct {
	Enabled             bool          `json:"enabled"`
	RequestsPerSecond   int           `json:"requestsPerSecond"`
	BurstSize           int           `json:"burstSize"`
	PerIPRequestsPerSec int           `json:"perIPRequestsPerSec"`
	PerIPBurstSize      int           `json:"perIPBurstSize"`
	CleanupInterval     time.Duration `json:"cleanupInterval"`
}

// NewRateLimiter 创建新的速率限制器
func NewRateLimiter(config Config, logger *logrus.Logger) *RateLimiter {
	if !config.Enabled {
		return &RateLimiter{
			logger: logger,
		}
	}

	// 默认值
	if config.BurstSize == 0 {
		config.BurstSize = config.RequestsPerSecond * 2
	}
	if config.PerIPBurstSize == 0 {
		config.PerIPBurstSize = config.PerIPRequestsPerSec * 2
	}
	if config.CleanupInterval == 0 {
		config.CleanupInterval = 5 * time.Minute
	}

	rl := &RateLimiter{
		logger:          logger,
		globalLimit:     NewTokenBucket(int64(config.BurstSize), int64(config.RequestsPerSecond)),
		perIPLimiters:   make(map[string]*TokenBucket),
		cleanupInterval: config.CleanupInterval,
		stopCh:          make(chan struct{}),
	}

	// 启动清理goroutine
	go rl.cleanup()

	return rl
}

// Allow 检查是否允许请求
func (rl *RateLimiter) Allow(remoteAddr string) bool {
	if rl.globalLimit == nil {
		return true // 未启用速率限制
	}

	// 全局速率限制
	if !rl.globalLimit.Allow() {
		rl.logger.WithField("type", "global").Debug("Rate limit exceeded")
		return false
	}

	// 获取客户端IP
	host, _, err := net.SplitHostPort(remoteAddr)
	if err != nil {
		host = remoteAddr
	}

	// 单IP速率限制
	rl.mu.RLock()
	bucket, exists := rl.perIPLimiters[host]
	rl.mu.RUnlock()

	if !exists {
		rl.mu.Lock()
		bucket, exists = rl.perIPLimiters[host]
		if !exists {
			bucket = NewTokenBucket(20, 10) // 默认每IP 10 rps, burst 20
			rl.perIPLimiters[host] = bucket
		}
		rl.mu.Unlock()
	}

	if !bucket.Allow() {
		rl.logger.WithFields(logrus.Fields{
			"type": "per_ip",
			"ip":   host,
		}).Debug("Per-IP rate limit exceeded")
		return false
	}

	return true
}

// Stop 停止速率限制器
func (rl *RateLimiter) Stop() {
	if rl.stopCh != nil {
		close(rl.stopCh)
	}
}

// GetStats 获取统计信息
func (rl *RateLimiter) GetStats() map[string]interface{} {
	if rl.globalLimit == nil {
		return map[string]interface{}{
			"enabled": false,
		}
	}

	rl.mu.RLock()
	perIPCount := len(rl.perIPLimiters)
	rl.mu.RUnlock()

	return map[string]interface{}{
		"enabled":        true,
		"global_tokens":  rl.globalLimit.GetTokens(),
		"per_ip_buckets": perIPCount,
	}
}

// cleanup 清理过期的IP限制器
func (rl *RateLimiter) cleanup() {
	ticker := time.NewTicker(rl.cleanupInterval)
	defer ticker.Stop()

	for {
		select {
		case <-rl.stopCh:
			return
		case <-ticker.C:
			rl.cleanupExpiredBuckets()
		}
	}
}

// cleanupExpiredBuckets 清理过期的IP桶
func (rl *RateLimiter) cleanupExpiredBuckets() {
	rl.mu.Lock()
	defer rl.mu.Unlock()

	now := time.Now()
	expiredIPs := make([]string, 0)

	for ip, bucket := range rl.perIPLimiters {
		// 如果桶超过10分钟没有活动，清理掉
		if now.Sub(bucket.lastRefill) > 10*time.Minute {
			expiredIPs = append(expiredIPs, ip)
		}
	}

	for _, ip := range expiredIPs {
		delete(rl.perIPLimiters, ip)
	}

	if len(expiredIPs) > 0 {
		rl.logger.WithField("count", len(expiredIPs)).Debug("Cleaned up expired rate limit buckets")
	}
}

// NewTokenBucket 创建新的Token桶
func NewTokenBucket(capacity, refillRate int64) *TokenBucket {
	return &TokenBucket{
		capacity:   capacity,
		tokens:     capacity,
		refillRate: refillRate,
		lastRefill: time.Now(),
	}
}

// Allow 检查是否允许请求（消耗一个token）
func (tb *TokenBucket) Allow() bool {
	tb.mu.Lock()
	defer tb.mu.Unlock()

	tb.refill()

	if tb.tokens > 0 {
		tb.tokens--
		return true
	}

	return false
}

// refill 补充tokens
func (tb *TokenBucket) refill() {
	now := time.Now()
	elapsed := now.Sub(tb.lastRefill)

	// 计算应该补充的tokens
	tokensToAdd := int64(elapsed.Seconds()) * tb.refillRate

	if tokensToAdd > 0 {
		tb.tokens += tokensToAdd
		if tb.tokens > tb.capacity {
			tb.tokens = tb.capacity
		}
		tb.lastRefill = now
	}
}

// GetTokens 获取当前token数量
func (tb *TokenBucket) GetTokens() int64 {
	tb.mu.Lock()
	defer tb.mu.Unlock()

	tb.refill()
	return tb.tokens
}