package node

import (
	"errors"
	"net/netip"
	"time"
	"unsafe"
)

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

const (
	packetTypeSyn = iota + 1
	packetTypeSynAck
	packetTypeAck
	packetTypePing
	packetTypePong
	packetTypeRelayed
)

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

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

func (p *controlPacket) ParsePayload(buf []byte) (err error) {
	switch buf[0] {
	case packetTypePing:
		p.Payload, err = parsePingPacket(buf)
	case packetTypePong:
		p.Payload, err = parsePongPacket(buf)
	case packetTypeSyn:
		p.Payload, err = parseSynPacket(buf)
	default:
		return errUnknownPacketType
	}
	return err
}

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

type synPacket struct {
	TraceID    uint64         // TraceID to match response w/ request.
	SharedKey  [32]byte       // Our shared key.
	ServerAddr netip.AddrPort // The address we're sending to.
	Direct     bool           // True if this is request isn't relayed.
}

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

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

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

type synAckPacket struct {
	TraceID uint64
}

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

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

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

type ackPacket struct {
	TraceID uint64
}

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

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

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

// A pingPacket is sent from a node acting as a client, to a node acting
// as a server. It always contains the shared key the client is expecting
// to use for data encryption with the server.
type pingPacket struct {
	SentAt    int64 // UnixMilli. // Not used. Use traceID.
	SharedKey [32]byte
}

func newPingPacket(sharedKey [32]byte) (pp pingPacket) {
	pp.SentAt = time.Now().UnixMilli()
	pp.SharedKey = sharedKey
	return
}

func (p pingPacket) Marshal(buf []byte) []byte {
	return newBinWriter(buf).
		Byte(packetTypePing).
		Int64(p.SentAt).
		SharedKey(p.SharedKey).
		Build()
}

func parsePingPacket(buf []byte) (p pingPacket, err error) {
	err = newBinReader(buf[1:]).
		Int64(&p.SentAt).
		SharedKey(&p.SharedKey).
		Error()
	return
}

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

// A pongPacket is sent by a node in a server role in response to a pingPacket.
type pongPacket struct {
	SentAt  int64 // UnixMilli.
	RecvdAt int64 // UnixMilli.
}

func newPongPacket(sentAt int64) (pp pongPacket) {
	pp.SentAt = sentAt
	pp.RecvdAt = time.Now().UnixMilli()
	return
}

func (p pongPacket) Marshal(buf []byte) []byte {
	buf = buf[:17]
	buf[0] = packetTypePong
	*(*uint64)(unsafe.Pointer(&buf[1])) = uint64(p.SentAt)
	*(*uint64)(unsafe.Pointer(&buf[9])) = uint64(p.RecvdAt)

	return buf
}

func parsePongPacket(buf []byte) (p pongPacket, err error) {
	if len(buf) != 17 {
		return p, errMalformedPacket
	}
	p.SentAt = *(*int64)(unsafe.Pointer(&buf[1]))
	p.RecvdAt = *(*int64)(unsafe.Pointer(&buf[9]))
	return
}