package main

import (
	"encoding/binary"
	"fmt"
)

const sridFlag = 0x20000000

func wkbToEwkbWithSrid(geometry []byte, srid int) []byte {
	if len(geometry) < 5 {
		return geometry
	}

	var byteOrder binary.ByteOrder
	if geometry[0] == 0 {
		byteOrder = binary.BigEndian
	} else {
		byteOrder = binary.LittleEndian
	}

	wkbType := byteOrder.Uint32(geometry[1:5])
	if wkbType&sridFlag != 0 {
		return geometry
	}

	ewkbType := wkbType | sridFlag

	result := make([]byte, len(geometry)+4)

	result[0] = geometry[0]

	byteOrder.PutUint32(result[1:5], ewkbType)

	byteOrder.PutUint32(result[5:9], uint32(srid))

	copy(result[9:], geometry[5:])

	return result
}

func main() {
	shape := []byte{
		1, 3, 0, 0, 0, 1, 0, 0, 0, 5, 0, 0, 0, 217, 61, 121, 88, 168, 57, 83, 192,
		60, 78, 209, 145, 92, 222, 39, 192, 232, 106, 43, 246, 151, 57, 83, 192,
		60, 78, 209, 145, 92, 222, 39, 192, 232, 106, 43, 246, 151, 57, 83, 192,
		174, 182, 98, 127, 217, 221, 39, 192, 217, 61, 121, 88, 168, 57, 83, 192,
		174, 182, 98, 127, 217, 221, 39, 192, 217, 61, 121, 88, 168, 57, 83, 192,
		60, 78, 209, 145, 92, 222, 39, 192,
	}

	srid := 4326
	result := wkbToEwkbWithSrid(shape, srid)

	fmt.Printf("WKB Original (len): %d\n", len(shape))
	fmt.Printf("EWKB Result   (len): %d\n", len(result))
	fmt.Printf("Primeros bytes (original): %v\n", shape[:10])
	fmt.Printf("Primeros bytes (resultado): %v\n", result[:10])
}