package handler

import (
	"context"
	"fmt"
	"io"
	"log"
	"net"
	"net/http"
	"net/url"
	"proxy-go/internal/cache"
	"proxy-go/internal/config"
	"proxy-go/internal/metrics"
	"proxy-go/internal/utils"
	"strings"
	"time"

	"golang.org/x/net/http2"
)

const (
	// 超时时间常量
	clientConnTimeout   = 10 * time.Second
	proxyRespTimeout    = 60 * time.Second
	backendServTimeout  = 40 * time.Second
	idleConnTimeout     = 120 * time.Second
	tlsHandshakeTimeout = 10 * time.Second
)

// 添加 hop-by-hop 头部映射
var hopHeadersBase = map[string]bool{
	"Connection":          true,
	"Keep-Alive":          true,
	"Proxy-Authenticate":  true,
	"Proxy-Authorization": true,
	"Proxy-Connection":    true,
	"Te":                  true,
	"Trailer":             true,
	"Transfer-Encoding":   true,
	"Upgrade":             true,
}

// ErrorHandler 定义错误处理函数类型
type ErrorHandler func(w http.ResponseWriter, r *http.Request, err error)

type ProxyHandler struct {
	pathMap      map[string]config.PathConfig
	client       *http.Client
	startTime    time.Time
	config       *config.Config
	auth         *authManager
	errorHandler ErrorHandler
	Cache        *cache.CacheManager
}

// NewProxyHandler 创建新的代理处理器
func NewProxyHandler(cfg *config.Config) *ProxyHandler {
	dialer := &net.Dialer{
		Timeout:   clientConnTimeout,
		KeepAlive: 30 * time.Second,
	}

	transport := &http.Transport{
		DialContext:            dialer.DialContext,
		MaxIdleConns:           1000,
		MaxIdleConnsPerHost:    100,
		IdleConnTimeout:        idleConnTimeout,
		TLSHandshakeTimeout:    tlsHandshakeTimeout,
		ExpectContinueTimeout:  1 * time.Second,
		MaxConnsPerHost:        200,
		DisableKeepAlives:      false,
		DisableCompression:     false,
		ForceAttemptHTTP2:      true,
		WriteBufferSize:        64 * 1024,
		ReadBufferSize:         64 * 1024,
		ResponseHeaderTimeout:  backendServTimeout,
		MaxResponseHeaderBytes: 64 * 1024,
	}

	// 设置HTTP/2传输配置
	http2Transport, err := http2.ConfigureTransports(transport)
	if err == nil && http2Transport != nil {
		http2Transport.ReadIdleTimeout = 10 * time.Second
		http2Transport.PingTimeout = 5 * time.Second
		http2Transport.AllowHTTP = false
		http2Transport.MaxReadFrameSize = 32 * 1024
		http2Transport.StrictMaxConcurrentStreams = true
	}

	// 初始化缓存管理器
	cacheManager, err := cache.NewCacheManager("data/cache")
	if err != nil {
		log.Printf("[Cache] Failed to initialize cache manager: %v", err)
	}

	handler := &ProxyHandler{
		pathMap: cfg.MAP,
		client: &http.Client{
			Transport: transport,
			Timeout:   proxyRespTimeout,
			CheckRedirect: func(req *http.Request, via []*http.Request) error {
				if len(via) >= 10 {
					return fmt.Errorf("stopped after 10 redirects")
				}
				return nil
			},
		},
		startTime: time.Now(),
		config:    cfg,
		auth:      newAuthManager(),
		Cache:     cacheManager,
		errorHandler: func(w http.ResponseWriter, r *http.Request, err error) {
			log.Printf("[Error] %s %s -> %v from %s", r.Method, r.URL.Path, err, utils.GetRequestSource(r))
			w.WriteHeader(http.StatusInternalServerError)
			w.Write([]byte("Internal Server Error"))
		},
	}

	// 注册配置更新回调
	config.RegisterUpdateCallback(func(newCfg *config.Config) {
		// 确保所有路径配置的processedExtMap都已更新
		for _, pathConfig := range newCfg.MAP {
			pathConfig.ProcessExtensionMap()
		}

		handler.pathMap = newCfg.MAP
		handler.config = newCfg
		log.Printf("[Config] 代理处理器配置已更新: %d 个路径映射", len(newCfg.MAP))
	})

	return handler
}

func (h *ProxyHandler) ServeHTTP(w http.ResponseWriter, r *http.Request) {
	// 添加 panic 恢复
	defer func() {
		if err := recover(); err != nil {
			log.Printf("[Panic] %s %s -> %v from %s", r.Method, r.URL.Path, err, utils.GetRequestSource(r))
			h.errorHandler(w, r, fmt.Errorf("panic: %v", err))
		}
	}()

	collector := metrics.GetCollector()
	collector.BeginRequest()
	defer collector.EndRequest()

	start := time.Now()

	// 创建带超时的上下文
	ctx, cancel := context.WithTimeout(r.Context(), proxyRespTimeout)
	defer cancel()
	r = r.WithContext(ctx)

	// 处理根路径请求
	if r.URL.Path == "/" {
		w.WriteHeader(http.StatusOK)
		fmt.Fprint(w, "Welcome to CZL proxy.")
		log.Printf("[Proxy] %s %s -> %d (%s) from %s", r.Method, r.URL.Path, http.StatusOK, utils.GetClientIP(r), utils.GetRequestSource(r))
		return
	}

	// 查找匹配的代理路径
	var matchedPrefix string
	var pathConfig config.PathConfig

	// 首先尝试完全匹配路径段
	for prefix, cfg := range h.pathMap {
		// 检查是否是完整的路径段匹配
		if strings.HasPrefix(r.URL.Path, prefix) {
			// 确保匹配的是完整的路径段
			restPath := r.URL.Path[len(prefix):]
			if restPath == "" || restPath[0] == '/' {
				matchedPrefix = prefix
				pathConfig = cfg
				break
			}
		}
	}

	// 如果没有找到完全匹配，返回404
	if matchedPrefix == "" {
		// 返回 404
		http.NotFound(w, r)
		return
	}

	// 构建目标 URL
	targetPath := strings.TrimPrefix(r.URL.Path, matchedPrefix)

	// URL 解码，然后重新编码，确保特殊字符被正确处理
	decodedPath, err := url.QueryUnescape(targetPath)
	if err != nil {
		h.errorHandler(w, r, fmt.Errorf("error decoding path: %v", err))
		return
	}

	// 使用统一的路由选择逻辑
	targetBase, usedAltTarget := utils.GetTargetURL(h.client, r, pathConfig, decodedPath)

	// 重新编码路径，保留 '/'
	parts := strings.Split(decodedPath, "/")
	for i, part := range parts {
		parts[i] = url.PathEscape(part)
	}
	encodedPath := strings.Join(parts, "/")
	targetURL := targetBase + encodedPath

	// 解析目标 URL 以获取 host
	parsedURL, err := url.Parse(targetURL)
	if err != nil {
		h.errorHandler(w, r, fmt.Errorf("error parsing URL: %v", err))
		return
	}

	// 创建新的请求时使用带超时的上下文
	proxyReq, err := http.NewRequestWithContext(ctx, r.Method, targetURL, r.Body)
	if err != nil {
		h.errorHandler(w, r, fmt.Errorf("error creating request: %v", err))
		return
	}

	// 复制并处理请求头
	copyHeader(proxyReq.Header, r.Header)

	// 添加常见浏览器User-Agent
	if ua := r.Header.Get("User-Agent"); ua != "" {
		proxyReq.Header.Set("User-Agent", ua)
	} else {
		proxyReq.Header.Set("User-Agent", "Mozilla/5.0 (Windows NT 10.0; Win64; x64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/120.0.0.0 Safari/537.36")
	}

	// 添加Origin
	proxyReq.Header.Set("Origin", fmt.Sprintf("%s://%s", parsedURL.Scheme, parsedURL.Host))

	// 设置Referer为源站的完整域名（带上斜杠）
	proxyReq.Header.Set("Referer", fmt.Sprintf("%s://%s/", parsedURL.Scheme, parsedURL.Host))

	// 设置Host头和proxyReq.Host
	proxyReq.Header.Set("Host", parsedURL.Host)
	proxyReq.Host = parsedURL.Host

	// 确保设置适当的Accept头
	if accept := r.Header.Get("Accept"); accept != "" {
		proxyReq.Header.Set("Accept", accept)
	} else {
		proxyReq.Header.Set("Accept", "text/html,application/xhtml+xml,application/xml;q=0.9,image/avif,image/webp,image/apng,*/*;q=0.8,application/signed-exchange;v=b3;q=0.7")
	}

	// 确保设置Accept-Encoding
	if acceptEncoding := r.Header.Get("Accept-Encoding"); acceptEncoding != "" {
		proxyReq.Header.Set("Accept-Encoding", acceptEncoding)
	} else {
		proxyReq.Header.Set("Accept-Encoding", "gzip, deflate, br")
	}

	// 特别处理图片请求
	if utils.IsImageRequest(r.URL.Path) {
		// 获取 Accept 头
		accept := r.Header.Get("Accept")

		// 根据 Accept 头设置合适的图片格式
		if strings.Contains(accept, "image/avif") {
			proxyReq.Header.Set("Accept", "image/avif")
		} else if strings.Contains(accept, "image/webp") {
			proxyReq.Header.Set("Accept", "image/webp")
		}

		// 设置 Cloudflare 特定的头部
		proxyReq.Header.Set("CF-Image-Format", "auto") // 让 Cloudflare 根据 Accept 头自动选择格式
	}

	// 设置最小必要的代理头部
	proxyReq.Header.Set("X-Real-IP", utils.GetClientIP(r))

	// 如果源站不严格要求Host匹配，可以保留以下头部
	// 否则可能需要注释掉这些头部
	// proxyReq.Header.Set("X-Forwarded-Host", r.Host)
	// proxyReq.Header.Set("X-Forwarded-Proto", r.URL.Scheme)

	// 添加或更新 X-Forwarded-For
	if clientIP := utils.GetClientIP(r); clientIP != "" {
		if prior := proxyReq.Header.Get("X-Forwarded-For"); prior != "" {
			proxyReq.Header.Set("X-Forwarded-For", prior+", "+clientIP)
		} else {
			proxyReq.Header.Set("X-Forwarded-For", clientIP)
		}
	}

	// 处理 Cookie 安全属性
	if r.TLS != nil && len(proxyReq.Cookies()) > 0 {
		cookies := proxyReq.Cookies()
		for _, cookie := range cookies {
			if !cookie.Secure {
				cookie.Secure = true
			}
			if !cookie.HttpOnly {
				cookie.HttpOnly = true
			}
		}
	}

	// 检查是否可以使用缓存
	if r.Method == http.MethodGet && h.Cache != nil {
		cacheKey := h.Cache.GenerateCacheKey(r)
		if item, hit, notModified := h.Cache.Get(cacheKey, r); hit {
			// 从缓存提供响应
			w.Header().Set("Content-Type", item.ContentType)
			if item.ContentEncoding != "" {
				w.Header().Set("Content-Encoding", item.ContentEncoding)
			}
			w.Header().Set("Proxy-Go-Cache", "HIT")

			// 如果使用了扩展名映射的备用目标，添加标记响应头
			if usedAltTarget {
				w.Header().Set("Proxy-Go-AltTarget", "true")
			}

			if notModified {
				w.WriteHeader(http.StatusNotModified)
				return
			}
			http.ServeFile(w, r, item.FilePath)
			collector.RecordRequest(r.URL.Path, http.StatusOK, time.Since(start), item.Size, utils.GetClientIP(r), r)
			return
		}
	}

	// 发送代理请求
	resp, err := h.client.Do(proxyReq)
	if err != nil {
		if ctx.Err() == context.DeadlineExceeded {
			h.errorHandler(w, r, fmt.Errorf("request timeout after %v", proxyRespTimeout))
			log.Printf("[Proxy] ERR %s %s -> 408 (%s) timeout from %s", r.Method, r.URL.Path, utils.GetClientIP(r), utils.GetRequestSource(r))
		} else {
			h.errorHandler(w, r, fmt.Errorf("proxy error: %v", err))
			log.Printf("[Proxy] ERR %s %s -> 502 (%s) proxy error from %s", r.Method, r.URL.Path, utils.GetClientIP(r), utils.GetRequestSource(r))
		}
		return
	}
	defer resp.Body.Close()

	// 复制响应头
	copyHeader(w.Header(), resp.Header)
	w.Header().Set("Proxy-Go-Cache", "MISS")

	// 如果使用了扩展名映射的备用目标，添加标记响应头
	if usedAltTarget {
		w.Header().Set("Proxy-Go-AltTarget", "true")
	}

	// 设置响应状态码
	w.WriteHeader(resp.StatusCode)

	var written int64
	// 如果是GET请求且响应成功，使用TeeReader同时写入缓存
	if r.Method == http.MethodGet && resp.StatusCode == http.StatusOK && h.Cache != nil {
		cacheKey := h.Cache.GenerateCacheKey(r)
		if cacheFile, err := h.Cache.CreateTemp(cacheKey, resp); err == nil {
			defer cacheFile.Close()
			teeReader := io.TeeReader(resp.Body, cacheFile)
			written, err = io.Copy(w, teeReader)
			if err == nil {
				h.Cache.Commit(cacheKey, cacheFile.Name(), resp, written)
			}
		} else {
			written, err = io.Copy(w, resp.Body)
			if err != nil && !isConnectionClosed(err) {
				log.Printf("[Proxy] ERR %s %s -> write error (%s) from %s", r.Method, r.URL.Path, utils.GetClientIP(r), utils.GetRequestSource(r))
				return
			}
		}
	} else {
		written, err = io.Copy(w, resp.Body)
		if err != nil && !isConnectionClosed(err) {
			log.Printf("[Proxy] ERR %s %s -> write error (%s) from %s", r.Method, r.URL.Path, utils.GetClientIP(r), utils.GetRequestSource(r))
			return
		}
	}

	// 记录统计信息
	collector.RecordRequest(r.URL.Path, resp.StatusCode, time.Since(start), written, utils.GetClientIP(r), r)
}

func copyHeader(dst, src http.Header) {
	// 创建一个新的局部 map，复制基础 hop headers
	hopHeaders := make(map[string]bool, len(hopHeadersBase))
	for k, v := range hopHeadersBase {
		hopHeaders[k] = v
	}

	// 处理 Connection 头部指定的其他 hop-by-hop 头部
	if connection := src.Get("Connection"); connection != "" {
		for _, h := range strings.Split(connection, ",") {
			hopHeaders[strings.TrimSpace(h)] = true
		}
	}

	// 使用局部 map 快速查找，跳过 hop-by-hop 头部
	for k, vv := range src {
		if !hopHeaders[k] {
			for _, v := range vv {
				dst.Add(k, v)
			}
		}
	}
}

// 添加辅助函数判断是否是连接关闭错误
func isConnectionClosed(err error) bool {
	if err == nil {
		return false
	}
	return strings.Contains(err.Error(), "broken pipe") ||
		strings.Contains(err.Error(), "connection reset by peer") ||
		strings.Contains(err.Error(), "protocol wrong type for socket")
}