#!/usr/bin/nodejs
const { spawn } = require('child_process'),
  filename = process.argv[2],
  child = spawn('ffmpeg', [
    '-i', filename
  ]),
  streams = [],
  basename = filename.replace(/\.[^.]+$/, "");

let output = [];

child.stdout.on('data', (data) => {
});

child.stderr.on('data', (data) => {
  output += data;
});

/*
    Stream #0:2(eng): Subtitle: ass (default)
    Metadata:
      title           : English
      BPS-eng         : 130
      DURATION-eng    : 00:47:44.040000000
...
    Stream #0:4(eng): Subtitle: hdmv_pgs_subtitle
    Metadata:
      BPS             : 3072
      BPS-eng         : 3072
      DURATION        : 00:21:51.602000000
      DURATION-eng    : 00:21:51.602000000
     
*/

let stream = undefined;

child.on('close', code => {
  output.toString().split('\n').forEach(line => {
    const parts = line.match(/^\s*Stream\s+#([^ ]+) Subtitle:\s*([^ ]+).*$/);
    if (parts && parts.length > 0) {
      /* parts[1] = '0:2(eng):'
         parts[2] = 'srt'
      */
      if (stream) {
        streams.push(stream);
      }
      stream = {
        extension: parts[2].replace(/hdmv_pgs_subtitle/, 'sup'), /* srt, sup */
        number: parts[1].replace(/^.*([^(]+).*$/, '$1'),         /* 0:2 -- not used */
        language: parts[1].replace(/^[^(]*\((.*)\).*$/, '$1')    /* eng */
      };
      return;
    }
    /* We tried parsing out 'title' for the langauge title, however
     * that is not a consistent standard and title seems to be used 
     * arbitrarily. Instead, we will rely on the 'language' we parse
     * from the stream name, which is specified inISO 639-1:
 
       https://en.wikipedia.org/wiki/List_of_ISO_639-1_codes
 
    */
    if (stream) {
      if (!stream.metadata) {
        if (/^\s*Metadata:.*/.exec(line)) {    
          stream.metadata = true;
        } else {
          streams.push(stream);
          stream = undefined;
        }
        return;
      }
      const language = line.match(/^\s*title\s*:\s*([^\s]+)/);
      if (language && language.length > 0) {
        stream.language = language[1].toLowerCase();
        streams.push(stream);
        stream = undefined;
      }
    }
  });
  streams.forEach((stream, index) => {
    const target = `${basename}.${index}_${stream.language}.${stream.extension}`,
      ffmpeg = spawn('ffmpeg', [
      '-i', filename,
      '-c:s', 'copy',
      '-map', `0:s:${index}`,
      '-y',
      target
    ]);
    console.log(`0:s:${index} => ${target}`);

    ffmpeg.stdout.on('data', (data) => {
      console.log(data.toString());
    });

    ffmpeg.stderr.on('data', (data) => {
      console.error(data.toString());
    });
 
    ffmpeg.on('close', code => {
      console.log(`Completed: ${target} ${code}`);
    });
  });
  console.log(JSON.stringify(streams));
});