package flv

import (
	"io"
	"os/exec"
	"encoding/binary"
)

type FLVWriter struct {
	w io.WriteCloser
}

func NewFLVWriter(stream_dir string) (*FLVWriter, error) {
	writer := new(FLVWriter)
	transcoder := exec.Command(
		"ffmpeg",
		"-probesize", "5000",
		"-i", "pipe:0",
		"-c:a", "aac",
		"-c:v", "h264",
		"-b:v", "1M",
		"-hls_time", "6",
		"-hls_list_size", "10",
		"-hls_flags", "delete_segments",
		"stream.m3u8",
	)
	transcoder.Dir = stream_dir
	flvpipe, err := transcoder.StdinPipe()
	transcoder.Start()
	if err != nil {
		return nil, err
	}
	writer.w = flvpipe
	if err = writer.write_flv_header(); err != nil {
		return nil, err
	}
	return writer, nil
}

func (writer *FLVWriter) Close() (error) {
	return writer.w.Close()
}

func (writer *FLVWriter) WriteMetadataTag(data *[]byte) (err error) {
	uint24_buf := make([]byte, 4)
	tag_header := make([]byte, 11)
	tag_header[0] = 18
	binary.BigEndian.PutUint32(uint24_buf, uint32(len((*data)[16:])))
	copy(tag_header[1:4], uint24_buf[1:])

	if _, err = writer.w.Write(tag_header); err != nil {
		return
	}
	if _, err = writer.w.Write((*data)[16:]); err != nil {
		return
	}


	tag_len_buf := make([]byte, 4)
	binary.BigEndian.PutUint32(tag_len_buf, uint32(len((*data)[16:]) + 11))
	_, err = writer.w.Write(tag_len_buf)
	return	
}

func (writer *FLVWriter) WriteMediaTag(data *[]byte, timestamp uint32, media_type uint8) (err error) {
	uint24_buf := make([]byte, 4)
	tag_header := make([]byte, 11)
	tag_header[0] = media_type
	data_len := uint32(len(*data))
	binary.BigEndian.PutUint32(uint24_buf, data_len)
	copy(tag_header[1:4], uint24_buf[1:])

	binary.BigEndian.PutUint32(uint24_buf, timestamp)
	copy(tag_header[4:7], uint24_buf[1:])
	tag_header[7] = uint24_buf[0]

	if _, err = writer.w.Write(tag_header); err != nil {
		return
	}
	if _, err = writer.w.Write(*data); err != nil {
		return
	}

	tag_len_buf := make([]byte, 4)
	binary.BigEndian.PutUint32(tag_len_buf, data_len + 11)
	_, err = writer.w.Write(tag_len_buf)
	return 
}

func (writer *FLVWriter) write_flv_header() (err error) {
	header := make([]byte, 13)
	copy(header[:3], "FLV")
	header[3] = 1
	header[4] = 5
	header[8] = 9
	
	_, err = writer.w.Write(header)
	return
}