package node

import (
	"errors"
	"net/netip"
)

var (
	errMalformedPacket   = errors.New("malformed packet")
	errUnknownPacketType = errors.New("unknown packet type")
)

const (
	packetTypeSyn = iota + 1
	packetTypeSynAck
	packetTypeAck
	packetTypeProbe
	packetTypeAddrDiscovery
)

// ----------------------------------------------------------------------------

type controlPacket struct {
	SrcIP   byte
	SrcAddr netip.AddrPort
	Payload any
}

func (p *controlPacket) ParsePayload(buf []byte) (err error) {
	switch buf[0] {
	case packetTypeSyn:
		p.Payload, err = parseSynPacket(buf)
	case packetTypeSynAck:
		p.Payload, err = parseSynAckPacket(buf)
	case packetTypeProbe:
		p.Payload, err = parseProbePacket(buf)
	case packetTypeAddrDiscovery:
		p.Payload, err = parseAddrDiscoveryPacket(buf)
	default:
		return errUnknownPacketType
	}
	return err
}

// ----------------------------------------------------------------------------

type synPacket struct {
	TraceID   uint64   // TraceID to match response w/ request.
	SharedKey [32]byte // Our shared key.
	Direct    bool
	FromAddr  netip.AddrPort // The client's sending address.
}

func (p synPacket) Marshal(buf []byte) []byte {
	return newBinWriter(buf).
		Byte(packetTypeSyn).
		Uint64(p.TraceID).
		SharedKey(p.SharedKey).
		Bool(p.Direct).
		AddrPort(p.FromAddr).
		Build()
}

func parseSynPacket(buf []byte) (p synPacket, err error) {
	err = newBinReader(buf[1:]).
		Uint64(&p.TraceID).
		SharedKey(&p.SharedKey).
		Bool(&p.Direct).
		AddrPort(&p.FromAddr).
		Error()
	return
}

// ----------------------------------------------------------------------------

type synAckPacket struct {
	TraceID  uint64
	FromAddr netip.AddrPort
}

func (p synAckPacket) Marshal(buf []byte) []byte {
	return newBinWriter(buf).
		Byte(packetTypeSynAck).
		Uint64(p.TraceID).
		AddrPort(p.FromAddr).
		Build()
}

func parseSynAckPacket(buf []byte) (p synAckPacket, err error) {
	err = newBinReader(buf[1:]).
		Uint64(&p.TraceID).
		AddrPort(&p.FromAddr).
		Error()
	return
}

// ----------------------------------------------------------------------------

type addrDiscoveryPacket struct {
	TraceID uint64
	ToAddr  netip.AddrPort
}

func (p addrDiscoveryPacket) Marshal(buf []byte) []byte {
	return newBinWriter(buf).
		Byte(packetTypeAddrDiscovery).
		Uint64(p.TraceID).
		AddrPort(p.ToAddr).
		Build()
}

func parseAddrDiscoveryPacket(buf []byte) (p addrDiscoveryPacket, err error) {
	err = newBinReader(buf[1:]).
		Uint64(&p.TraceID).
		AddrPort(&p.ToAddr).
		Error()
	return
}

// ----------------------------------------------------------------------------

// A probeReqPacket is sent from a client to a server to determine if direct
// UDP communication can be used.
type probePacket struct {
	TraceID uint64
}

func (p probePacket) Marshal(buf []byte) []byte {
	return newBinWriter(buf).
		Byte(packetTypeProbe).
		Uint64(p.TraceID).
		Build()
}

func parseProbePacket(buf []byte) (p probePacket, err error) {
	err = newBinReader(buf[1:]).
		Uint64(&p.TraceID).
		Error()
	return
}