package gortsplib

import (
	"bufio"
	"encoding/binary"
	"fmt"
	"io"
)

const (
	_INTERLEAVED_FRAME_MAX_SIZE         = 2048
	_INTERLEAVED_FRAME_MAX_CONTENT_SIZE = (_INTERLEAVED_FRAME_MAX_SIZE - 4)
)

// InterleavedFrame is a structure that allows to send and receive binary data
// with RTSP connections.
// It is usually used to send RTP and RTCP with RTSP.
type InterleavedFrame struct {
	Channel uint8
	Content []byte
}

func readInterleavedFrame(r io.Reader) (*InterleavedFrame, error) {
	var header [4]byte
	_, err := io.ReadFull(r, header[:])
	if err != nil {
		return nil, err
	}

	if header[0] != 0x24 {
		return nil, fmt.Errorf("wrong magic byte (0x%.2x)", header[0])
	}

	framelen := binary.BigEndian.Uint16(header[2:])
	if int(framelen) > _INTERLEAVED_FRAME_MAX_SIZE {
		return nil, fmt.Errorf("frame length greater than maximum allowed")
	}

	f := &InterleavedFrame{
		Channel: header[1],
		Content: make([]byte, framelen),
	}

	_, err = io.ReadFull(r, f.Content)
	if err != nil {
		return nil, err
	}

	return f, nil
}

func (f *InterleavedFrame) write(bw *bufio.Writer) error {
	_, err := bw.Write([]byte{0x24, f.Channel})
	if err != nil {
		return err
	}

	buf := make([]byte, 2)
	binary.BigEndian.PutUint16(buf, uint16(len(f.Content)))
	_, err = bw.Write(buf)
	if err != nil {
		return err
	}

	_, err = bw.Write(f.Content)
	if err != nil {
		return err
	}

	return bw.Flush()
}