package middleware

import (
	"crypto/rand"
	"encoding/hex"

	"github.com/gin-gonic/gin"
)

// RequestIDHeader 请求 ID 的响应头名称
const RequestIDHeader = "X-Request-ID"

// RequestIDContextKey 上下文中存储请求 ID 的键
const RequestIDContextKey = "request_id"

// RequestID 为每个请求生成唯一 ID，写入上下文和响应头
func RequestID() gin.HandlerFunc {
	return func(c *gin.Context) {
		// 优先从请求头读取上游传入的 request_id
		rid := c.GetHeader(RequestIDHeader)
		if rid == "" {
			rid = generateRequestID()
		}
		c.Set(RequestIDContextKey, rid)
		c.Header(RequestIDHeader, rid)
		c.Next()
	}
}

// GetRequestID 从 gin.Context 中获取请求 ID
func GetRequestID(c *gin.Context) string {
	if rid, exists := c.Get(RequestIDContextKey); exists {
		if s, ok := rid.(string); ok {
			return s
		}
	}
	return ""
}

// generateRequestID 生成 16 字节随机 hex 请求 ID
func generateRequestID() string {
	b := make([]byte, 16)
	_, _ = rand.Read(b)
	return hex.EncodeToString(b)
}