package cache

import (
	"crypto/sha256"
	"encoding/hex"
	"fmt"
	"hash/fnv"
	"log"
	"net/http"
	"os"
	"path/filepath"
	"sort"
	"strings"
	"sync"
	"sync/atomic"
	"time"
)

// CacheKey 用于标识缓存项的唯一键
type CacheKey struct {
	URL           string
	AcceptHeaders string
	UserAgent     string
}

// String 实现 Stringer 接口，用于生成唯一的字符串表示
func (k CacheKey) String() string {
	return fmt.Sprintf("%s|%s|%s", k.URL, k.AcceptHeaders, k.UserAgent)
}

// Equal 比较两个 CacheKey 是否相等
func (k CacheKey) Equal(other CacheKey) bool {
	return k.URL == other.URL &&
		k.AcceptHeaders == other.AcceptHeaders &&
		k.UserAgent == other.UserAgent
}

// Hash 生成 CacheKey 的哈希值
func (k CacheKey) Hash() uint64 {
	h := fnv.New64a()
	h.Write([]byte(k.String()))
	return h.Sum64()
}

// CacheItem 表示一个缓存项
type CacheItem struct {
	FilePath    string
	ContentType string
	Size        int64
	LastAccess  time.Time
	Hash        string
	CreatedAt   time.Time
	AccessCount int64
}

// CacheStats 缓存统计信息
type CacheStats struct {
	TotalItems int     `json:"total_items"` // 缓存项数量
	TotalSize  int64   `json:"total_size"`  // 总大小
	HitCount   int64   `json:"hit_count"`   // 命中次数
	MissCount  int64   `json:"miss_count"`  // 未命中次数
	HitRate    float64 `json:"hit_rate"`    // 命中率
	BytesSaved int64   `json:"bytes_saved"` // 节省的带宽
	Enabled    bool    `json:"enabled"`     // 缓存开关状态
}

// CacheManager 缓存管理器
type CacheManager struct {
	cacheDir     string
	items        sync.Map
	maxAge       time.Duration
	cleanupTick  time.Duration
	maxCacheSize int64
	enabled      atomic.Bool  // 缓存开关
	hitCount     atomic.Int64 // 命中计数
	missCount    atomic.Int64 // 未命中计数
	bytesSaved   atomic.Int64 // 节省的带宽
}

// NewCacheManager 创建新的缓存管理器
func NewCacheManager(cacheDir string) (*CacheManager, error) {
	if err := os.MkdirAll(cacheDir, 0755); err != nil {
		return nil, fmt.Errorf("failed to create cache directory: %v", err)
	}

	cm := &CacheManager{
		cacheDir:     cacheDir,
		maxAge:       30 * time.Minute,
		cleanupTick:  5 * time.Minute,
		maxCacheSize: 10 * 1024 * 1024 * 1024, // 10GB
	}

	cm.enabled.Store(true) // 默认启用缓存

	// 启动清理协程
	go cm.cleanup()

	return cm, nil
}

// GenerateCacheKey 生成缓存键
func (cm *CacheManager) GenerateCacheKey(r *http.Request) CacheKey {
	// 处理 Vary 头部
	varyHeaders := make([]string, 0)
	for _, vary := range strings.Split(r.Header.Get("Vary"), ",") {
		vary = strings.TrimSpace(vary)
		if vary != "" {
			value := r.Header.Get(vary)
			varyHeaders = append(varyHeaders, vary+"="+value)
		}
	}
	sort.Strings(varyHeaders)

	return CacheKey{
		URL:           r.URL.String(),
		AcceptHeaders: r.Header.Get("Accept"),
		UserAgent:     r.Header.Get("User-Agent"),
	}
}

// Get 获取缓存项
func (cm *CacheManager) Get(key CacheKey, r *http.Request) (*CacheItem, bool, bool) {
	if !cm.enabled.Load() {
		return nil, false, false
	}

	// 检查缓存项是否存在
	value, ok := cm.items.Load(key)
	if !ok {
		cm.missCount.Add(1)
		return nil, false, false
	}

	item := value.(*CacheItem)

	// 验证文件是否存在
	if _, err := os.Stat(item.FilePath); err != nil {
		cm.items.Delete(key)
		cm.missCount.Add(1)
		return nil, false, false
	}

	// 只检查基本的缓存过期
	if time.Since(item.CreatedAt) > cm.maxAge {
		cm.items.Delete(key)
		os.Remove(item.FilePath)
		cm.missCount.Add(1)
		return nil, false, false
	}

	// 更新访问信息
	item.LastAccess = time.Now()
	atomic.AddInt64(&item.AccessCount, 1)
	cm.hitCount.Add(1)
	cm.bytesSaved.Add(item.Size)

	return item, true, false
}

// Put 添加缓存项
func (cm *CacheManager) Put(key CacheKey, resp *http.Response, body []byte) (*CacheItem, error) {
	// 只检查基本的响应状态
	if resp.StatusCode != http.StatusOK {
		return nil, fmt.Errorf("response status not OK")
	}

	// 计算内容哈希
	contentHash := sha256.Sum256(body)
	hashStr := hex.EncodeToString(contentHash[:])

	// 检查是否存在相同哈希的缓存项
	var existingItem *CacheItem
	cm.items.Range(func(k, v interface{}) bool {
		if item := v.(*CacheItem); item.Hash == hashStr {
			if _, err := os.Stat(item.FilePath); err == nil {
				existingItem = item
				return false
			}
			cm.items.Delete(k)
		}
		return true
	})

	if existingItem != nil {
		cm.items.Store(key, existingItem)
		log.Printf("[Cache] Reusing existing cache for %s", key.URL)
		return existingItem, nil
	}

	// 生成文件名并存储
	fileName := hashStr
	filePath := filepath.Join(cm.cacheDir, fileName)

	if err := os.WriteFile(filePath, body, 0600); err != nil {
		return nil, fmt.Errorf("failed to write cache file: %v", err)
	}

	item := &CacheItem{
		FilePath:    filePath,
		ContentType: resp.Header.Get("Content-Type"),
		Size:        int64(len(body)),
		LastAccess:  time.Now(),
		Hash:        hashStr,
		CreatedAt:   time.Now(),
		AccessCount: 1,
	}

	cm.items.Store(key, item)
	log.Printf("[Cache] Cached %s (%s)", key.URL, formatBytes(item.Size))
	return item, nil
}

// cleanup 定期清理过期的缓存项
func (cm *CacheManager) cleanup() {
	ticker := time.NewTicker(cm.cleanupTick)
	for range ticker.C {
		var totalSize int64
		var keysToDelete []CacheKey

		// 收集需要删除的键和计算总大小
		cm.items.Range(func(k, v interface{}) bool {
			key := k.(CacheKey)
			item := v.(*CacheItem)
			totalSize += item.Size

			if time.Since(item.LastAccess) > cm.maxAge {
				keysToDelete = append(keysToDelete, key)
			}
			return true
		})

		// 如果总大小超过限制，按最后访问时间排序删除
		if totalSize > cm.maxCacheSize {
			var items []*CacheItem
			cm.items.Range(func(k, v interface{}) bool {
				items = append(items, v.(*CacheItem))
				return true
			})

			// 按最后访问时间排序
			sort.Slice(items, func(i, j int) bool {
				return items[i].LastAccess.Before(items[j].LastAccess)
			})

			// 删除最旧的项直到总大小小于限制
			for _, item := range items {
				if totalSize <= cm.maxCacheSize {
					break
				}
				cm.items.Range(func(k, v interface{}) bool {
					if v.(*CacheItem) == item {
						keysToDelete = append(keysToDelete, k.(CacheKey))
						totalSize -= item.Size
						return false
					}
					return true
				})
			}
		}

		// 删除过期和超出大小限制的缓存项
		for _, key := range keysToDelete {
			if item, ok := cm.items.Load(key); ok {
				cacheItem := item.(*CacheItem)
				os.Remove(cacheItem.FilePath)
				cm.items.Delete(key)
				log.Printf("[Cache] Removed expired item: %s", key.URL)
			}
		}
	}
}

// formatBytes 格式化字节大小
func formatBytes(bytes int64) string {
	const (
		KB = 1024
		MB = 1024 * KB
		GB = 1024 * MB
	)

	switch {
	case bytes >= GB:
		return fmt.Sprintf("%.2f GB", float64(bytes)/float64(GB))
	case bytes >= MB:
		return fmt.Sprintf("%.2f MB", float64(bytes)/float64(MB))
	case bytes >= KB:
		return fmt.Sprintf("%.2f KB", float64(bytes)/float64(KB))
	default:
		return fmt.Sprintf("%d B", bytes)
	}
}

// GetStats 获取缓存统计信息
func (cm *CacheManager) GetStats() CacheStats {
	var totalItems int
	var totalSize int64

	cm.items.Range(func(_, value interface{}) bool {
		item := value.(*CacheItem)
		totalItems++
		totalSize += item.Size
		return true
	})

	hitCount := cm.hitCount.Load()
	missCount := cm.missCount.Load()
	totalRequests := hitCount + missCount
	hitRate := float64(0)
	if totalRequests > 0 {
		hitRate = float64(hitCount) / float64(totalRequests) * 100
	}

	return CacheStats{
		TotalItems: totalItems,
		TotalSize:  totalSize,
		HitCount:   hitCount,
		MissCount:  missCount,
		HitRate:    hitRate,
		BytesSaved: cm.bytesSaved.Load(),
		Enabled:    cm.enabled.Load(),
	}
}

// SetEnabled 设置缓存开关状态
func (cm *CacheManager) SetEnabled(enabled bool) {
	cm.enabled.Store(enabled)
}

// ClearCache 清空缓存
func (cm *CacheManager) ClearCache() error {
	// 删除所有缓存文件
	var keysToDelete []CacheKey
	cm.items.Range(func(key, value interface{}) bool {
		cacheKey := key.(CacheKey)
		item := value.(*CacheItem)
		os.Remove(item.FilePath)
		keysToDelete = append(keysToDelete, cacheKey)
		return true
	})

	// 清除缓存项
	for _, key := range keysToDelete {
		cm.items.Delete(key)
	}

	// 重置统计信息
	cm.hitCount.Store(0)
	cm.missCount.Store(0)
	cm.bytesSaved.Store(0)

	return nil
}

// CreateTemp 创建临时缓存文件
func (cm *CacheManager) CreateTemp(key CacheKey, resp *http.Response) (*os.File, error) {
	if !cm.enabled.Load() {
		return nil, fmt.Errorf("cache is disabled")
	}

	// 创建临时文件
	tempFile, err := os.CreateTemp(cm.cacheDir, "temp-*")
	if err != nil {
		return nil, fmt.Errorf("failed to create temp file: %v", err)
	}

	return tempFile, nil
}

// Commit 提交缓存文件
func (cm *CacheManager) Commit(key CacheKey, tempPath string, resp *http.Response, size int64) error {
	if !cm.enabled.Load() {
		os.Remove(tempPath)
		return fmt.Errorf("cache is disabled")
	}

	// 生成最终的缓存文件名
	h := sha256.New()
	h.Write([]byte(key.String()))
	hashStr := hex.EncodeToString(h.Sum(nil))
	ext := filepath.Ext(key.URL)
	if ext == "" {
		ext = ".bin"
	}
	filePath := filepath.Join(cm.cacheDir, hashStr+ext)

	// 重命名临时文件
	if err := os.Rename(tempPath, filePath); err != nil {
		os.Remove(tempPath)
		return fmt.Errorf("failed to rename temp file: %v", err)
	}

	// 创建缓存项
	item := &CacheItem{
		FilePath:    filePath,
		ContentType: resp.Header.Get("Content-Type"),
		Size:        size,
		LastAccess:  time.Now(),
		Hash:        hashStr,
		CreatedAt:   time.Now(),
		AccessCount: 1,
	}

	cm.items.Store(key, item)
	cm.bytesSaved.Add(size)
	log.Printf("[Cache] Cached %s (%s)", key.URL, formatBytes(size))
	return nil
}