/* Paste / drop image uploading for the topic body editor.
 *
 * Why this exists: Quill 2's built-in `uploader` module turns a pasted or
 * dropped image into a base64 `data:` URL. That looks right in the editor but
 * sanitize_html() drops `data:` sources on save (bleach restricts img src to
 * http/https/mailto), so the image would silently vanish — and base64 would
 * bloat the row anyway. So we override the uploader to POST the file to
 * /admin/upload and embed the returned /static/uploads/... path instead.
 *
 * Two entry points are needed because Quill routes pasted content two ways:
 *   - uploader handler  -> paste/drop of an image FILE (a screenshot, a file
 *                          dragged from the desktop)
 *   - the data: sweep   -> paste of HTML that embeds base64 images (Word,
 *                          Google Docs, another web page). Those never reach
 *                          the uploader; they arrive through the clipboard as
 *                          markup, so we rehost them after the fact.
 *
 * Everything degrades safely: topic_form.html guards on window.JQCImageUpload,
 * and a failed upload leaves a visible notice rather than a silent loss.
 */
(function () {
  'use strict';

  var MIME = ['image/png', 'image/jpeg', 'image/gif', 'image/webp'];
  var MAX_BYTES = 8 * 1024 * 1024;      // matches MAX_UPLOAD_BYTES in admin.py
  var SWEEP_DELAY = 250;

  /* ------------------------------------------------------------- notices */
  var toast = null;
  var toastTimer = null;

  function notify(message, kind) {
    if (!toast) {
      toast = document.createElement('div');
      toast.className = 'jqc-toast';
      document.body.appendChild(toast);
    }
    toast.textContent = message;
    toast.className = 'jqc-toast is-visible' + (kind ? ' jqc-toast--' + kind : '');
    clearTimeout(toastTimer);
    if (kind !== 'busy') {
      toastTimer = setTimeout(function () {
        toast.className = 'jqc-toast';
      }, 4000);
    }
  }

  function clearNotice() {
    if (toast) toast.className = 'jqc-toast';
  }

  /* -------------------------------------------------------------- upload */
  function makeUploader(opts) {
    var url = opts.url;
    var csrf = opts.csrf;

    /* POST one file, resolve with its public URL. */
    function upload(file) {
      if (MIME.indexOf(file.type) === -1) {
        return Promise.reject(new Error('Only PNG, JPEG, GIF and WebP images can be uploaded.'));
      }
      if (file.size > MAX_BYTES) {
        return Promise.reject(new Error('That image is larger than the 8 MB limit.'));
      }
      var fd = new FormData();
      // The server re-checks the extension, so give the blob a plausible name:
      // a pasted screenshot arrives as a nameless Blob.
      fd.append('file', file, file.name || ('pasted.' + file.type.split('/')[1]));
      return fetch(url, {
        method: 'POST', headers: { 'X-CSRFToken': csrf }, body: fd
      }).then(function (res) {
        return res.json().catch(function () { return {}; }).then(function (body) {
          if (!res.ok || !body.url) {
            throw new Error(body.error || 'Upload failed.');
          }
          return body.url;
        });
      });
    }

    /* Upload files one at a time and embed them at `index`, in order. */
    function insertFiles(quill, index, files) {
      var images = files.filter(function (f) { return MIME.indexOf(f.type) !== -1; });
      if (!images.length) return Promise.resolve(0);

      notify(images.length > 1 ? 'Uploading ' + images.length + ' images…'
                               : 'Uploading image…', 'busy');

      var at = index;
      var done = 0;
      return images.reduce(function (chain, file) {
        return chain.then(function () {
          return upload(file).then(function (link) {
            quill.insertEmbed(at, 'image', link, 'user');
            at += 1;
            done += 1;
          });
        });
      }, Promise.resolve()).then(function () {
        quill.setSelection(at, 'silent');
        clearNotice();
        return done;
      }).catch(function (err) {
        notify(err.message || 'Upload failed.', 'error');
        return done;
      });
    }

    /* Quill calls this as the uploader module (`this` is the module, so
       `this.quill` is the editor) for both paste and drag-and-drop. */
    function handler(range, files) {
      var quill = this.quill;
      var index = range && typeof range.index === 'number'
        ? range.index
        : quill.getLength();
      insertFiles(quill, index, Array.prototype.slice.call(files));
    }

    /* ------------------------------------------------- base64 -> uploads */
    function dataUrlToFile(dataUrl) {
      // fetch() parses data: URLs for us — no manual atob/Uint8Array juggling.
      return fetch(dataUrl).then(function (r) { return r.blob(); }).then(function (blob) {
        return new File([blob], 'pasted.' + (blob.type.split('/')[1] || 'png'),
                        { type: blob.type });
      });
    }

    /* Replace an inline base64 image with an uploaded copy. The embed is
       swapped (delete + insert) rather than having its src poked directly, so
       the change goes through the document instead of behind Quill's back. */
    function rehost(quill, img) {
      var width = img.getAttribute('width');
      return dataUrlToFile(img.src).then(upload).then(function (link) {
        var blot = Quill.find(img);
        if (!blot) return;
        var index = quill.getIndex(blot);
        quill.deleteText(index, 1, 'user');
        quill.insertEmbed(index, 'image', link, 'user');
        if (width) quill.formatText(index, 1, { width: width }, 'user');
      });
    }

    /* Watch for base64 images arriving via a pasted-HTML fragment and rehost
       them one by one. Re-entrancy is guarded: our own edits fire text-change. */
    function watch(quill) {
      var timer = null;
      var busy = false;

      function sweep() {
        if (busy) return;
        var img = quill.root.querySelector('img[src^="data:image/"]');
        if (!img) { clearNotice(); return; }
        busy = true;
        notify('Uploading pasted image…', 'busy');
        rehost(quill, img).catch(function (err) {
          // Leave the image in place — deleting the admin's content would be
          // worse — but say plainly that it will not survive the save.
          notify((err.message || 'Upload failed.') +
                 " The pasted image can't be saved; upload it with the image button.",
                 'error');
          img.setAttribute('data-upload-failed', '1');   // don't retry forever
        }).then(function () {
          busy = false;
          schedule();
        });
      }

      function schedule() {
        clearTimeout(timer);
        timer = setTimeout(function () {
          // Skip images already known to be unuploadable (e.g. SVG).
          var pending = quill.root.querySelector(
            'img[src^="data:image/"]:not([data-upload-failed])');
          if (pending) sweep();
        }, SWEEP_DELAY);
      }

      quill.on('text-change', function (delta, old, source) {
        if (busy || source !== 'user') return;
        schedule();
      });
      schedule();   // in case content was pasted before this ran
    }

    return {
      mimetypes: MIME,
      upload: upload,
      insertFiles: insertFiles,
      handler: handler,
      watch: watch,
      notify: notify
    };
  }

  window.JQCImageUpload = { create: makeUploader };
})();