package hopp

import "io"
import "net"
import "context"
import "git.tebibyte.media/sashakoshka/hopp/tape"

// B implements METADAPT-B over a multiplexed stream-oriented transport such as
// QUIC.
type b struct {
	underlying MultiConn
}

// AdaptB returns a connection implementing METADAPT-B over a singular stream-
// oriented transport such as TCP or UNIX domain stream sockets.
func AdaptB(underlying MultiConn) Conn {
	return &b {
		underlying: underlying,
	}
}

func (this *b) Close() error {
	return this.underlying.Close()
}

func (this *b) OpenTrans() (Trans, error) {
	stream, err := this.underlying.OpenStream()
	if err != nil { return nil, err }
	return transB { underlying: stream }, nil
}

func (this *b) AcceptTrans(ctx context.Context) (Trans, error) {
	stream, err := this.underlying.AcceptStream(ctx)
	if err != nil { return nil, err }
	return transB { underlying: stream }, nil
}

type transB struct {
	underlying Stream
}

func (trans transB) Close() error {
	return trans.underlying.Close()
}

func (trans transB) ID() int64 {
	return trans.underlying.ID()
}

func (trans transB) Send(method uint16, data []byte) error {
	buffer := make([]byte, 4 + len(data))
	tape.EncodeI16(buffer[:2], method)
	length, ok := tape.U16CastSafe(len(data))
	if !ok { return ErrPayloadTooLarge }
	tape.EncodeI16(data[2:4], length)
	copy(buffer[4:], data)
	_, err := trans.underlying.Write(buffer)
	return err
}

func (trans transB) Receive() (uint16, []byte, error) {
	headerBuffer := [4]byte { }
	_, err := io.ReadFull(trans.underlying, headerBuffer[:])
	if err != nil { return 0, nil, err }
	method, err := tape.DecodeI16[uint16](headerBuffer[:2])
	if err != nil { return 0, nil, err }
	length, err := tape.DecodeI16[uint16](headerBuffer[2:4])
	if err != nil { return 0, nil, err }
	payloadBuffer := make([]byte, int(length))
	_, err = io.ReadFull(trans.underlying, payloadBuffer)
	if err != nil { return 0, nil, err }
	return method, payloadBuffer, nil
}

// MultiConn represens a multiplexed stream-oriented transport for use in [B].
type MultiConn interface {
	// See documentation for [net.Conn].
	io.Closer
	LocalAddr() net.Addr
	RemoteAddr() net.Addr
	// AcceptStream accepts the next incoming stream from the other party.
	AcceptStream(context.Context) (Stream, error)
	// OpenStream opens a new stream.
	OpenStream() (Stream, error)
}

// Stream represents a single stream returned by a [MultiConn].
type Stream interface {
	// See documentation for [net.Conn].
	io.ReadWriteCloser
	// ID returns the stream ID
	ID() int64
}