package middleware

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

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

var traceParentPattern = regexp.MustCompile(`^00-([0-9a-f]{32})-([0-9a-f]{16})-[0-9a-f]{2}$`)

func randomHex(bytes int) string {
	value := make([]byte, bytes)
	_, _ = rand.Read(value)
	return hex.EncodeToString(value)
}

func RequestMeta() gin.HandlerFunc {
	return func(c *gin.Context) {
		requestID := c.GetHeader("X-Request-Id")
		if requestID == "" || len(requestID) > 128 || strings.ContainsAny(requestID, "\r\n") {
			requestID = uuid.NewString()
		}
		traceID, parentSpanID := "", ""
		if match := traceParentPattern.FindStringSubmatch(strings.ToLower(c.GetHeader("traceparent"))); len(match) == 3 {
			traceID, parentSpanID = match[1], match[2]
		} else if candidate := c.GetHeader("X-Trace-Id"); len(candidate) <= 128 && !strings.ContainsAny(candidate, "\r\n") {
			traceID = candidate
		}
		if traceID == "" {
			traceID = randomHex(16)
		}
		spanID := randomHex(8)
		c.Header("X-Request-Id", requestID)
		c.Header("X-Trace-Id", traceID)
		if len(traceID) == 32 {
			c.Header("traceparent", "00-"+traceID+"-"+spanID+"-01")
		}
		c.Set("request_id", requestID)
		c.Set("trace_id", traceID)
		c.Set("span_id", spanID)
		c.Set("parent_span_id", parentSpanID)
		c.Next()
	}
}