(function() {
  const checkboxes = document.querySelectorAll('input[type="checkbox"]');
  const button = document.querySelector('#export');
  const selectedTracks = [];
  checkboxes.forEach((box) => {
    const meta = [
      box.getAttribute('data-file'), box.getAttribute('data-spotify')
    ];
    function clickBox() {
      if (box.checked) {
        selectedTracks.push(meta);
      } else {
        const i = selectedTracks.indexOf(meta);
        if (i > -1) {
          selectedTracks.splice(i, 1);
        }
      }
    }
    box.addEventListener('change', ($ev) => clickBox());
    box.parentElement.parentElement.addEventListener('click', () => box.click());
    clickBox();
  });

  button.addEventListener('click', ($ev) => {
    $ev.preventDefault();
    var dataStr = "data:text/json;charset=utf-8," + encodeURIComponent(JSON.stringify(selectedTracks));
    var downloadAnchorNode = document.createElement('a');
    downloadAnchorNode.setAttribute("href", dataStr);
    downloadAnchorNode.setAttribute("download", "track-selection.json");
    document.body.appendChild(downloadAnchorNode);
    downloadAnchorNode.click();
    downloadAnchorNode.remove();
  });
})();