// Progressive enhancement for the upload form. With JavaScript off the plain
// multipart POST still works; everything here is additive.
(function () {
  'use strict';

  // Copy buttons appear on the server-rendered result page too, which has no
  // upload form, so they are wired before anything form-specific bails out.
  // They ship hidden so that without this script there is no dead button.
  function wireCopy() {
    var buttons = document.querySelectorAll('button.copy[data-copy]');
    Array.prototype.forEach.call(buttons, function (button) {
      var target = document.getElementById(button.dataset.copy);
      if (!target) return;
      button.hidden = false;
      button.addEventListener('click', function () {
        target.select();
        var done = function () {
          var was = button.textContent;
          button.textContent = 'Copied';
          setTimeout(function () { button.textContent = was; }, 1500);
        };
        if (navigator.clipboard) navigator.clipboard.writeText(target.value).then(done, function () {});
        else { document.execCommand('copy'); done(); }
      });
    });
  }
  wireCopy();

  // Destructive buttons ask first. The attribute carries the question, so the
  // markup decides what is worth confirming and this stays generic.
  Array.prototype.forEach.call(document.querySelectorAll('[data-confirm]'), function (button) {
    button.addEventListener('click', function (e) {
      if (!window.confirm(button.dataset.confirm)) e.preventDefault();
    });
  });

  var form = document.getElementById('upload');
  if (!form) return;

  var fileInput = document.getElementById('file');
  var drop = document.getElementById('drop');
  var dropHint = document.getElementById('drop-hint');
  var progress = document.getElementById('progress');
  var barFill = document.getElementById('bar-fill');
  var progressText = document.getElementById('progress-text');
  var submit = document.getElementById('submit');
  var errorBox = document.getElementById('error');

  // The session's limits are rendered by the server, so this script never has
  // to ask who the visitor is. Zero means unlimited.
  var maxSize = parseInt(form.dataset.maxSize, 10) || 0;

  function formatSize(n) {
    var units = ['B', 'KiB', 'MiB', 'GiB', 'TiB'], i = 0;
    while (n >= 1024 && i < units.length - 1) { n /= 1024; i++; }
    return (i === 0 ? n : n.toFixed(2).replace(/\.00$/, '')) + ' ' + units[i];
  }

  function showError(msg) {
    errorBox.textContent = msg;
    errorBox.hidden = !msg;
  }

  // --- drag and drop ------------------------------------------------------
  function describeSelection() {
    var f = fileInput.files[0];
    dropHint.textContent = f ? f.name + ' - ' + formatSize(f.size)
                             : 'Choose a file, or drop one here.';
  }

  ['dragenter', 'dragover'].forEach(function (name) {
    drop.addEventListener(name, function (e) {
      e.preventDefault();
      drop.classList.add('over');
    });
  });
  ['dragleave', 'drop'].forEach(function (name) {
    drop.addEventListener(name, function () { drop.classList.remove('over'); });
  });
  drop.addEventListener('drop', function (e) {
    e.preventDefault();
    if (!e.dataTransfer.files.length) return;
    // DataTransfer is the only way to put a dropped file into a file input.
    var dt = new DataTransfer();
    dt.items.add(e.dataTransfer.files[0]);
    fileInput.files = dt.files;
    describeSelection();
  });
  fileInput.addEventListener('change', describeSelection);

  // --- upload -------------------------------------------------------------
  form.addEventListener('submit', function (e) {
    var file = fileInput.files[0];
    if (!file) return; // let the browser's own validation speak

    if (maxSize && file.size > maxSize) {
      e.preventDefault();
      showError('That file is ' + formatSize(file.size) + '; your limit is ' +
                formatSize(maxSize) + '.');
      return;
    }

    e.preventDefault();
    showError('');
    submit.disabled = true;
    progress.hidden = false;

    // FormData follows markup order, not painted order, so the options and the
    // token precede the file part exactly as the server requires. The drop
    // zone only looks like it comes first; see the order rules in style.css.
    var data = new FormData(form);
    var started = Date.now();

    var xhr = new XMLHttpRequest();
    xhr.open('POST', form.action);
    // Ask for the page a plain form post would have been given. What a
    // finished upload looks like is the server's business, and it already
    // renders it; this script only adds the progress bar on the way there.
    xhr.setRequestHeader('Accept', 'text/html');

    xhr.upload.onprogress = function (ev) {
      if (!ev.lengthComputable) return;
      var pct = ev.loaded / ev.total;
      barFill.style.width = (pct * 100).toFixed(1) + '%';
      var elapsed = (Date.now() - started) / 1000;
      var rate = elapsed > 0 ? ev.loaded / elapsed : 0;
      var eta = rate > 0 ? (ev.total - ev.loaded) / rate : 0;
      progressText.textContent =
        (pct * 100).toFixed(0) + '% - ' + formatSize(ev.loaded) + ' of ' +
        formatSize(ev.total) + ' - ' + formatSize(rate) + '/s' +
        (eta > 1 ? ', ' + formatTime(eta) + ' left' : '');
    };

    xhr.onload = function () {
      // Whatever came back, the result page or an error page, is the page the
      // browser should be showing now. Writing it into this document rather
      // than navigating leaves the address on the form's own URL, so a reload
      // offers a fresh form instead of posting the file a second time.
      document.open();
      document.write(xhr.responseText);
      document.close();
    };
    xhr.onerror = function () {
      submit.disabled = false;
      progress.hidden = true;
      showError('Upload failed: the connection was lost.');
    };

    xhr.send(data);
  });

  function formatTime(s) {
    s = Math.round(s);
    if (s < 60) return s + 's';
    var m = Math.floor(s / 60);
    if (m < 60) return m + 'm ' + (s % 60) + 's';
    return Math.floor(m / 60) + 'h ' + (m % 60) + 'm';
  }
})();