package middleware

import (
	"bytes"
	"context"
	"fmt"
	"io"
	"net/http"
	"runtime/debug"
	"strings"
	"time"

	"github.com/zeromicro/go-zero/core/logx"
)

// LoggerConfig 日志配置
type LoggerConfig struct {
	EnableRequestBody    bool          // 是否记录请求体
	EnableResponseBody   bool          // 是否记录响应体
	MaxBodySize         int64         // 最大记录的请求/响应体大小
	SkipPaths           []string      // 跳过记录的路径
	SlowRequestDuration time.Duration // 慢请求阈值
	EnablePanicRecover  bool          // 是否启用panic恢复
}

// DefaultLoggerConfig 默认日志配置
func DefaultLoggerConfig() LoggerConfig {
	return LoggerConfig{
		EnableRequestBody:    false, // 默认不记录请求体 (可能包含敏感信息)
		EnableResponseBody:   false, // 默认不记录响应体 (减少日志量)
		MaxBodySize:         1024,   // 最大记录1KB
		SkipPaths:           []string{"/health", "/metrics", "/favicon.ico"},
		SlowRequestDuration: 1 * time.Second,
		EnablePanicRecover:  true,
	}
}

// LoggerMiddleware 日志中间件
type LoggerMiddleware struct {
	config LoggerConfig
}

// NewLoggerMiddleware 创建日志中间件
func NewLoggerMiddleware(config LoggerConfig) *LoggerMiddleware {
	return &LoggerMiddleware{
		config: config,
	}
}

// responseWriter 包装 http.ResponseWriter 用于记录响应
type responseWriter struct {
	http.ResponseWriter
	status int
	size   int64
	body   *bytes.Buffer
}

// newResponseWriter 创建响应写入器
func newResponseWriter(w http.ResponseWriter) *responseWriter {
	return &responseWriter{
		ResponseWriter: w,
		status:         http.StatusOK,
		body:          &bytes.Buffer{},
	}
}

// Write 写入响应数据
func (rw *responseWriter) Write(b []byte) (int, error) {
	size, err := rw.ResponseWriter.Write(b)
	rw.size += int64(size)
	
	// 记录响应体 (如果启用)
	if rw.body.Len() < int(1024) { // 限制缓存大小
		rw.body.Write(b)
	}
	
	return size, err
}

// WriteHeader 写入响应头
func (rw *responseWriter) WriteHeader(statusCode int) {
	rw.status = statusCode
	rw.ResponseWriter.WriteHeader(statusCode)
}

// Handle 处理请求日志
func (m *LoggerMiddleware) Handle(next http.HandlerFunc) http.HandlerFunc {
	return http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
		// 检查是否跳过此路径
		if m.shouldSkipPath(r.URL.Path) {
			next(w, r)
			return
		}

		// 记录请求开始时间
		start := time.Now()

		// 生成请求ID
		requestID := m.generateRequestID(r)
		ctx := context.WithValue(r.Context(), "request_id", requestID)
		r = r.WithContext(ctx)

		// 添加请求ID到响应头
		w.Header().Set("X-Request-ID", requestID)

		// 包装响应写入器
		rw := newResponseWriter(w)

		// 记录请求体 (如果启用)
		var requestBody string
		if m.config.EnableRequestBody && r.Body != nil {
			requestBody = m.readRequestBody(r)
		}

		// 设置panic恢复
		if m.config.EnablePanicRecover {
			defer func() {
				if err := recover(); err != nil {
					m.logPanic(r, err, string(debug.Stack()))
					http.Error(rw, "Internal Server Error", http.StatusInternalServerError)
				}
			}()
		}

		// 记录请求开始
		m.logRequestStart(r, requestID, requestBody)

		// 执行下一个处理器
		next(rw, r)

		// 计算处理时间
		duration := time.Since(start)

		// 记录响应体 (如果启用)
		var responseBody string
		if m.config.EnableResponseBody && rw.body.Len() > 0 {
			responseBody = m.truncateString(rw.body.String(), int(m.config.MaxBodySize))
		}

		// 记录请求完成
		m.logRequestComplete(r, requestID, rw.status, rw.size, duration, responseBody)

		// 记录慢请求
		if duration > m.config.SlowRequestDuration {
			m.logSlowRequest(r, requestID, duration)
		}
	})
}

// shouldSkipPath 检查是否应该跳过此路径
func (m *LoggerMiddleware) shouldSkipPath(path string) bool {
	for _, skipPath := range m.config.SkipPaths {
		if strings.HasPrefix(path, skipPath) {
			return true
		}
	}
	return false
}

// generateRequestID 生成请求ID
func (m *LoggerMiddleware) generateRequestID(r *http.Request) string {
	// 优先使用现有的请求ID
	if requestID := r.Header.Get("X-Request-ID"); requestID != "" {
		return requestID
	}
	
	// 生成新的请求ID
	return fmt.Sprintf("%d-%s", time.Now().UnixNano(), randomString(8))
}

// readRequestBody 读取请求体
func (m *LoggerMiddleware) readRequestBody(r *http.Request) string {
	if r.Body == nil {
		return ""
	}

	// 读取请求体
	body, err := io.ReadAll(io.LimitReader(r.Body, m.config.MaxBodySize))
	if err != nil {
		return fmt.Sprintf("error reading body: %v", err)
	}

	// 恢复请求体 (以便后续处理器可以读取)
	r.Body = io.NopCloser(bytes.NewBuffer(body))

	return string(body)
}

// logRequestStart 记录请求开始
func (m *LoggerMiddleware) logRequestStart(r *http.Request, requestID, requestBody string) {
	fields := map[string]interface{}{
		"request_id":     requestID,
		"method":         r.Method,
		"path":           r.URL.Path,
		"query":          r.URL.RawQuery,
		"user_agent":     r.UserAgent(),
		"remote_addr":    getClientIP(r),
		"content_length": r.ContentLength,
	}

	if requestBody != "" {
		fields["request_body"] = requestBody
	}

	logx.WithContext(r.Context()).Infof("Request started: %+v", fields)
}

// logRequestComplete 记录请求完成
func (m *LoggerMiddleware) logRequestComplete(r *http.Request, requestID string, status int, size int64, duration time.Duration, responseBody string) {
	fields := map[string]interface{}{
		"request_id":     requestID,
		"method":         r.Method,
		"path":           r.URL.Path,
		"status":         status,
		"response_size":  size,
		"duration_ms":    duration.Milliseconds(),
		"duration":       duration.String(),
	}

	if responseBody != "" {
		fields["response_body"] = responseBody
	}

	// 根据状态码选择日志级别
	switch {
	case status >= 500:
		logx.WithContext(r.Context()).Errorf("Request completed with server error: %+v", fields)
	case status >= 400:
		logx.WithContext(r.Context()).Infof("Request completed with client error: %+v", fields)
	default:
		logx.WithContext(r.Context()).Infof("Request completed: %+v", fields)
	}
}

// logSlowRequest 记录慢请求
func (m *LoggerMiddleware) logSlowRequest(r *http.Request, requestID string, duration time.Duration) {
	fields := map[string]interface{}{
		"request_id":  requestID,
		"method":      r.Method,
		"path":        r.URL.Path,
		"duration":    duration.String(),
		"duration_ms": duration.Milliseconds(),
	}
	logx.WithContext(r.Context()).Infof("Slow request detected: %+v", fields)
}

// logPanic 记录panic
func (m *LoggerMiddleware) logPanic(r *http.Request, err interface{}, stack string) {
	fields := map[string]interface{}{
		"method":      r.Method,
		"path":        r.URL.Path,
		"error":       err,
		"stack_trace": stack,
	}
	logx.WithContext(r.Context()).Errorf("Panic recovered: %+v", fields)
}

// getClientIP 获取客户端IP
func getClientIP(r *http.Request) string {
	// 检查各种可能的IP头部
	for _, header := range []string{"X-Forwarded-For", "X-Real-IP", "X-Client-IP"} {
		if ip := r.Header.Get(header); ip != "" {
			// X-Forwarded-For 可能包含多个IP，取第一个
			if strings.Contains(ip, ",") {
				return strings.TrimSpace(strings.Split(ip, ",")[0])
			}
			return ip
		}
	}
	
	// 使用 RemoteAddr
	if ip := r.RemoteAddr; ip != "" {
		// 移除端口号
		if strings.Contains(ip, ":") {
			return strings.Split(ip, ":")[0]
		}
		return ip
	}
	
	return "unknown"
}

// truncateString 截断字符串
func (m *LoggerMiddleware) truncateString(s string, maxLen int) string {
	if len(s) <= maxLen {
		return s
	}
	return s[:maxLen] + "..."
}

// randomString 生成随机字符串
func randomString(length int) string {
	const charset = "abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ0123456789"
	result := make([]byte, length)
	for i := range result {
		result[i] = charset[time.Now().UnixNano()%int64(len(charset))]
	}
	return string(result)
}