// recover from audacity crash
// usage:
// node audacity_rescue.js [sourcedir] [result_file.wav] [mono|stereo]

// the mono or stereo option is optional, the default is mono.
// 
// Description:
// This script will sort all files on modification date.
// If you create a backup, make sure you use `cp -a` to preserve the modification date
// or create a zip.
// The resulting file will pretend to be a wave file (because of the .wav extension), but 
// is in fact a Audacity simple block file. You will have to open the resulting file with 
// audacity and then export it as a normal file.

const fs = require('fs');
const pathLib = require('path');
const pj = pathLib.join;


const srcdirname = process.argv[2];
const result_file = process.argv[3];
const type = process.argv[4];

if (!(srcdirname && result_file)) {
  console.log("Need both a source dir and a target file");
  process.exit(1);
}

if (!type) type = 'mono';
if (! (type === 'mono' || type === 'stereo')) {
  console.log('invalid audio format');
}

console.log('source dir name: ', srcdirname);
console.log('result_file', result_file);

// we need all files in the subdirectories of dirname
// sorted by date
const allFiles = [];

function readFiles (dir) {
  const names = fs.readdirSync(dir);
  names.forEach(n => {
    const fullPath = pj(dir, n);
    const stats = fs.statSync(fullPath);
    if (stats.isDirectory()) {
      readFiles(fullPath);
    }
    else {
      if (pathLib.extname(n) === ".au") {
        allFiles.push({ name: fullPath, time: stats.mtime.getTime()})
      }
    }
  });
}

console.log('searching and sorting files by date');
readFiles(srcdirname);
allFiles.sort( (a, b) => {
  return a.time - b.time;
});

if (type === 'stereo') {
  console.log('writing result files');
  const f = pathLib.parse(result_file);
  const left_fn = pathLib.join(f.root, f.dir, f.base + '_L' + f.ext);
  const right_fn = pathLib.join(f.root, f.dir, f.base + '_R' + f.ext);
  const fhL = fs.openSync(left_fn, 'w');
  const fhR = fs.openSync(right_fn, 'w');
  let targetPosL = 0;
  let targetPosR = 0;
  const numFiles = allFiles.length;
  allFiles.forEach( (f, i) => {
    console.log(`reading ${f.name} (${i} of ${numFiles})`);
    const buf = fs.readFileSync(f.name);
    const offset = (i === 0 || i === 1) ? 0: buf.readUInt16LE(4);
    if (i % 2 === 0) { // assume left
      targetPosL += fs.writeSync(fhL, buf, offset, buf.length-offset, targetPosL);
    }
    else {
      // assume right
      targetPosR += fs.writeSync(fhR, buf, offset, buf.length-offset, targetPosR);
    }
  })
  fs.closeSync(fhL);
  fs.closeSync(fhR);
}
else {
  // now merge all files in the result
  console.log('writing result file');
  const fh = fs.openSync(result_file, 'w');
  let targetPos = 0;
  const numFiles = allFiles.length;
  allFiles.forEach( (f, i) => {
    console.log(`reading ${f.name} (${i} of ${numFiles})`);
    const buf = fs.readFileSync(f.name);
    const offset = i === 0? 0: buf.readUInt16LE(4);
    targetPos += fs.writeSync(fh, buf, offset, buf.length-offset, targetPos);
  });
  fs.closeSync(fh);
}


console.log('Done');