package client

import (
	"encoding/binary"
	"net"
)

// proxyV2Signature is the fixed 12-byte HAProxy v2 signature.
var proxyV2Signature = []byte{
	0x0D, 0x0A, 0x0D, 0x0A, 0x00, 0x0D, 0x0A, 0x51, 0x55, 0x49, 0x54, 0x0A,
}

// BuildProxyV2 builds a HAProxy protocol v2 PROXY header conveying the real
// source (player) and destination addresses (PROTOCOL.md §8).
func BuildProxyV2(srcIP net.IP, srcPort int, dstIP net.IP, dstPort int) []byte {
	s4, d4 := srcIP.To4(), dstIP.To4()
	out := make([]byte, 0, 16+36)
	out = append(out, proxyV2Signature...)
	out = append(out, 0x21) // version 2, PROXY command

	var addr []byte
	if s4 != nil && d4 != nil {
		out = append(out, 0x11) // TCP over IPv4
		addr = make([]byte, 0, 12)
		addr = append(addr, s4...)
		addr = append(addr, d4...)
	} else {
		out = append(out, 0x21) // TCP over IPv6
		addr = make([]byte, 0, 36)
		addr = append(addr, srcIP.To16()...)
		addr = append(addr, dstIP.To16()...)
	}
	var ports [4]byte
	binary.BigEndian.PutUint16(ports[0:], uint16(srcPort))
	binary.BigEndian.PutUint16(ports[2:], uint16(dstPort))
	addr = append(addr, ports[:]...)

	var lenField [2]byte
	binary.BigEndian.PutUint16(lenField[:], uint16(len(addr)))
	out = append(out, lenField[:]...)
	out = append(out, addr...)
	return out
}