package event

import (
	"sync"
	"time"
)

// SessionUserCache 会话-用户映射缓存，支持TTL过期
type SessionUserCache struct {
	mu       sync.RWMutex
	cache    map[string]cacheEntry
	ttl      time.Duration
	stopChan chan struct{}
}

// cacheEntry 缓存条目
type cacheEntry struct {
	userID    string
	expiresAt time.Time
}

// NewSessionUserCache 创建新的会话-用户缓存
func NewSessionUserCache(ttl time.Duration) *SessionUserCache {
	cache := &SessionUserCache{
		cache:    make(map[string]cacheEntry),
		ttl:      ttl,
		stopChan: make(chan struct{}),
	}

	// 启动清理协程
	go cache.cleanupWorker()

	return cache
}

// Set 设置会话-用户映射
func (c *SessionUserCache) Set(sessionID, userID string) {
	c.mu.Lock()
	defer c.mu.Unlock()

	c.cache[sessionID] = cacheEntry{
		userID:    userID,
		expiresAt: time.Now().Add(c.ttl),
	}
}

// Get 获取用户ID，如果不存在或已过期返回空字符串
func (c *SessionUserCache) Get(sessionID string) string {
	c.mu.RLock()
	entry, exists := c.cache[sessionID]
	c.mu.RUnlock()

	if !exists {
		return ""
	}

	// 检查是否过期
	if time.Now().After(entry.expiresAt) {
		// 异步删除过期条目
		go c.deleteIfExpired(sessionID)
		return ""
	}

	return entry.userID
}

// Delete 删除指定会话的缓存
func (c *SessionUserCache) Delete(sessionID string) {
	c.mu.Lock()
	defer c.mu.Unlock()

	delete(c.cache, sessionID)
}

// deleteIfExpired 检查并删除过期条目
func (c *SessionUserCache) deleteIfExpired(sessionID string) {
	c.mu.Lock()
	defer c.mu.Unlock()

	if entry, exists := c.cache[sessionID]; exists {
		if time.Now().After(entry.expiresAt) {
			delete(c.cache, sessionID)
		}
	}
}

// cleanupWorker 定期清理过期条目的工作协程
func (c *SessionUserCache) cleanupWorker() {
	ticker := time.NewTicker(c.ttl / 2)
	defer ticker.Stop()

	for {
		select {
		case <-ticker.C:
			c.cleanupExpired()
		case <-c.stopChan:
			return
		}
	}
}

// cleanupExpired 清理所有过期条目
func (c *SessionUserCache) cleanupExpired() {
	c.mu.Lock()
	defer c.mu.Unlock()

	now := time.Now()
	for sessionID, entry := range c.cache {
		if now.After(entry.expiresAt) {
			delete(c.cache, sessionID)
		}
	}
}

// Stop 停止缓存清理协程
func (c *SessionUserCache) Stop() {
	close(c.stopChan)
}