package udp

import (
	"bytes"
	"encoding/binary"
)

// Sending WSJT-X UDP messages, as opposed to parsing them (wsjt.go).
//
// This exists for Logger32, and for anything else that listens on the WSJT-X
// interface rather than for plain text. Logger32's "additional WSJT/JTDX UDP
// sockets" receivers — ports 2250, 2251, 2252 — are documented as receiving
// "UDP logging packets": they speak the WSJT-X v2 protocol, and a raw ADIF
// record posted to them is discarded without a word.
//
// That is a real distinction and not a detail: an operator can watch OpsLog
// report "sent 1153 bytes to 127.0.0.1:2250" and see nothing whatsoever appear
// in Logger32, because both statements are true.

// buildQString encodes a Qt QString/QByteArray as QDataStream writes it: a
// big-endian int32 length followed by the UTF-8 bytes. A negative length means
// null, which is not what we ever want here — an empty string is length 0.
func buildQString(s string) []byte {
	out := make([]byte, 4, 4+len(s))
	binary.BigEndian.PutUint32(out, uint32(len(s)))
	return append(out, s...)
}

// BuildWSJTLoggedADIF frames a WSJT-X "Logged ADIF" datagram (message type 12).
//
//	uint32  magic   0xadbccbda
//	uint32  schema  2
//	uint32  type    12
//	QString id      the sending program's name
//	QString adif    the ADIF record
//
// id matters more than it looks: a receiver uses it to tell instances apart, and
// some show it in their log. "OpsLog" is honest — pretending to be WSJT-X would
// make a second instance of the real thing indistinguishable from us.
func BuildWSJTLoggedADIF(id, adif string) []byte {
	var b bytes.Buffer
	var hdr [12]byte
	binary.BigEndian.PutUint32(hdr[0:4], wsjtMagic)
	binary.BigEndian.PutUint32(hdr[4:8], 2) // schema 2 — what WSJT-X 2.x speaks
	binary.BigEndian.PutUint32(hdr[8:12], wsjtMsgLoggedADIF)
	b.Write(hdr[:])
	b.Write(buildQString(id))
	b.Write(buildQString(adif))
	return b.Bytes()
}