package cache

import (
	"crypto/md5"
	"encoding/hex"
	"sync"
	"time"

	"github.com/subconverter-go/internal/conversion"
	"github.com/subconverter-go/internal/logging"
)

// CacheEntry 缓存条目
type CacheEntry struct {
	Response    *conversion.ConversionResponse `json:"response"`
	Expiration  time.Time                      `json:"expiration"`
	AccessCount int                            `json:"accessCount"`
	LastAccess  time.Time                      `json:"lastAccess"`
}

// CacheManager 缓存管理器
// 提供转换结果的缓存功能，提高性能和减少重复计算
type CacheManager struct {
	logger      *logging.Logger
	entries     map[string]*CacheEntry
	mutex       sync.RWMutex
	ttl         time.Duration
	maxSize     int
	enabled     bool
	stats       *CacheStats
	cleanupChan chan struct{}
}

// CacheStats 缓存统计信息
type CacheStats struct {
	Hits      int64   `json:"hits"`
	Misses    int64   `json:"misses"`
	Evictions int64   `json:"evictions"`
	Size      int64   `json:"size"`
	TotalSize int64   `json:"totalSize"`
	HitRate   float64 `json:"hitRate"`
}

// CacheConfig 缓存配置
type CacheConfig struct {
	Enabled bool          `json:"enabled" yaml:"enabled"`
	TTL     time.Duration `json:"ttl" yaml:"ttl"`
	MaxSize int           `json:"maxSize" yaml:"maxSize"`
	Cleanup time.Duration `json:"cleanup" yaml:"cleanup"`
}

// NewCacheManager 创建新的缓存管理器
func NewCacheManager(config *CacheConfig, logger *logging.Logger) *CacheManager {
	if config == nil {
		// 默认配置
		config = &CacheConfig{
			Enabled: true,
			TTL:     5 * time.Minute,
			MaxSize: 1000,
			Cleanup: 1 * time.Minute,
		}
	}

	cm := &CacheManager{
		logger:      logger,
		entries:     make(map[string]*CacheEntry),
		ttl:         config.TTL,
		maxSize:     config.MaxSize,
		enabled:     config.Enabled,
		stats:       &CacheStats{},
		cleanupChan: make(chan struct{}),
	}

	if cm.enabled {
		go cm.cleanupTask(config.Cleanup)
		logger.Infof("Cache manager initialized with TTL=%v, maxSize=%d", cm.ttl, cm.maxSize)
	} else {
		logger.Info("Cache manager disabled")
	}

	return cm
}

// Get 获取缓存的转换结果
func (cm *CacheManager) Get(key string) (*conversion.ConversionResponse, bool) {
	if !cm.enabled {
		return nil, false
	}

	cm.mutex.RLock()
	defer cm.mutex.RUnlock()

	entry, exists := cm.entries[key]
	if !exists {
		cm.stats.Misses++
		return nil, false
	}

	// 检查是否过期
	if time.Now().After(entry.Expiration) {
		cm.stats.Misses++
		go cm.removeExpiredEntry(key)
		return nil, false
	}

	// 更新访问统计
	entry.AccessCount++
	entry.LastAccess = time.Now()
	cm.stats.Hits++

	cm.logger.Debugf("Cache hit for key: %s", key)
	return entry.Response, true
}

// Set 设置缓存条目
func (cm *CacheManager) Set(key string, response *conversion.ConversionResponse) error {
	if !cm.enabled {
		return nil
	}

	cm.mutex.Lock()
	defer cm.mutex.Unlock()

	// 检查缓存大小限制
	if len(cm.entries) >= cm.maxSize {
		cm.evictEntries()
	}

	entry := &CacheEntry{
		Response:    response,
		Expiration:  time.Now().Add(cm.ttl),
		AccessCount: 1,
		LastAccess:  time.Now(),
	}

	cm.entries[key] = entry
	cm.stats.Size++
	cm.stats.TotalSize++

	cm.logger.Debugf("Cache entry set for key: %s, expires at: %v", key, entry.Expiration)
	return nil
}

// GenerateKey 生成缓存键
func (cm *CacheManager) GenerateKey(request *conversion.ConversionRequest) string {
	if request == nil {
		return ""
	}

	signature := request.CacheSignature()

	// 使用MD5生成固定长度的键
	hash := md5.Sum([]byte(signature))
	return hex.EncodeToString(hash[:])
}

// Remove 移除指定的缓存条目
func (cm *CacheManager) Remove(key string) {
	if !cm.enabled {
		return
	}

	cm.mutex.Lock()
	defer cm.mutex.Unlock()

	if _, exists := cm.entries[key]; exists {
		delete(cm.entries, key)
		cm.stats.Size--
		cm.logger.Debugf("Cache entry removed for key: %s", key)
	}
}

// Clear 清空所有缓存
func (cm *CacheManager) Clear() {
	if !cm.enabled {
		return
	}

	cm.mutex.Lock()
	defer cm.mutex.Unlock()

	cm.entries = make(map[string]*CacheEntry)
	cm.stats.Size = 0
	cm.logger.Info("Cache cleared")
}

// GetStats 获取缓存统计信息
func (cm *CacheManager) GetStats() *CacheStats {
	if !cm.enabled {
		return &CacheStats{}
	}

	cm.mutex.RLock()
	defer cm.mutex.RUnlock()

	// 计算命中率
	total := cm.stats.Hits + cm.stats.Misses
	if total > 0 {
		cm.stats.HitRate = float64(cm.stats.Hits) / float64(total)
	}

	// 返回统计信息的副本
	statsCopy := *cm.stats
	return &statsCopy
}

// Close 关闭缓存管理器
func (cm *CacheManager) Close() {
	if !cm.enabled {
		return
	}

	// 停止清理任务
	close(cm.cleanupChan)

	// 清空缓存
	cm.Clear()

	cm.logger.Info("Cache manager closed")
}

// removeExpiredEntry 移除过期条目（异步）
func (cm *CacheManager) removeExpiredEntry(key string) {
	cm.mutex.Lock()
	defer cm.mutex.Unlock()

	if entry, exists := cm.entries[key]; exists && time.Now().After(entry.Expiration) {
		delete(cm.entries, key)
		cm.stats.Size++
		cm.stats.Evictions++
		cm.logger.Debugf("Expired cache entry removed for key: %s", key)
	}
}

// evictEntries 执行缓存淘汰策略
func (cm *CacheManager) evictEntries() {
	// LRU (Least Recently Used) 淘汰策略
	var oldestKey string
	var oldestTime time.Time

	for key, entry := range cm.entries {
		if oldestKey == "" || entry.LastAccess.Before(oldestTime) {
			oldestKey = key
			oldestTime = entry.LastAccess
		}
	}

	if oldestKey != "" {
		delete(cm.entries, oldestKey)
		cm.stats.Size--
		cm.stats.Evictions++
		cm.logger.Debugf("Cache entry evicted (LRU) for key: %s", oldestKey)
	}
}

// cleanupTask 定期清理过期条目
func (cm *CacheManager) cleanupTask(interval time.Duration) {
	// 如果间隔为0，不启动清理任务
	if interval <= 0 {
		return
	}

	ticker := time.NewTicker(interval)
	defer ticker.Stop()

	for {
		select {
		case <-ticker.C:
			cm.cleanupExpired()
		case <-cm.cleanupChan:
			return
		}
	}
}

// cleanupExpired 清理所有过期条目
func (cm *CacheManager) cleanupExpired() {
	cm.mutex.Lock()
	defer cm.mutex.Unlock()

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

	for key, entry := range cm.entries {
		if now.After(entry.Expiration) {
			expiredKeys = append(expiredKeys, key)
		}
	}

	for _, key := range expiredKeys {
		delete(cm.entries, key)
		cm.stats.Evictions++
	}

	cm.stats.Size = int64(len(cm.entries))

	if len(expiredKeys) > 0 {
		cm.logger.Debugf("Cleaned up %d expired cache entries", len(expiredKeys))
	}
}

// IsEnabled 检查缓存是否启用
func (cm *CacheManager) IsEnabled() bool {
	return cm.enabled
}

// GetSize 获取当前缓存大小
func (cm *CacheManager) GetSize() int {
	if !cm.enabled {
		return 0
	}

	cm.mutex.RLock()
	defer cm.mutex.RUnlock()
	return len(cm.entries)
}

// GetTTTL 获取缓存TTL
func (cm *CacheManager) GetTTL() time.Duration {
	return cm.ttl
}

// SetTTTL 设置缓存TTL
func (cm *CacheManager) SetTTL(ttl time.Duration) {
	cm.mutex.Lock()
	defer cm.mutex.Unlock()

	cm.ttl = ttl
	cm.logger.Infof("Cache TTL updated to: %v", ttl)
}

// GetMaxSize 获取最大缓存大小
func (cm *CacheManager) GetMaxSize() int {
	return cm.maxSize
}

// SetMaxSize 设置最大缓存大小
func (cm *CacheManager) SetMaxSize(maxSize int) {
	cm.mutex.Lock()
	defer cm.mutex.Unlock()

	cm.maxSize = maxSize
	cm.logger.Infof("Cache max size updated to: %d", maxSize)
}

// GetEntry 获取缓存条目详细信息（用于调试）
func (cm *CacheManager) GetEntry(key string) (*CacheEntry, bool) {
	if !cm.enabled {
		return nil, false
	}

	cm.mutex.RLock()
	defer cm.mutex.RUnlock()

	entry, exists := cm.entries[key]
	if !exists {
		return nil, false
	}

	// 返回副本
	entryCopy := *entry
	return &entryCopy, true
}

// GetAllKeys 获取所有缓存键
func (cm *CacheManager) GetAllKeys() []string {
	if !cm.enabled {
		return nil
	}

	cm.mutex.RLock()
	defer cm.mutex.RUnlock()

	keys := make([]string, 0, len(cm.entries))
	for key := range cm.entries {
		keys = append(keys, key)
	}

	return keys
}