discourse/app/assets/javascripts/pretty-text/engines/discourse-markdown/onebox.js.es6

import { lookupCache } from 'pretty-text/oneboxer';

//  Given a node in the document and its parent, determine whether it is on its own line or not.
function isOnOneLine(link, parent) {
  if (!parent) { return false; }

  const siblings = parent.slice(1);
  if ((!siblings) || (siblings.length < 1)) { return false; }

  const idx = siblings.indexOf(link);
  if (idx === -1) { return false; }

  if (idx > 0) {
    const prev = siblings[idx-1];
    if (prev[0] !== 'br') { return false; }
  }

  if (idx < siblings.length) {
    const next = siblings[idx+1];
    if (next && (!((next[0] === 'br') || (typeof next === 'string' && next.trim() === "")))) { return false; }
  }

  return true;
}

//  We only onebox stuff that is on its own line.
export function setup(helper) {
  helper.onParseNode(event => {
    const node = event.node,
    path = event.path;

    // We only care about links
    if (node[0] !== 'a')  { return; }

    const parent = path[path.length - 1];

    // We don't onebox bbcode
    if (node[1]['data-bbcode']) {
      delete node[1]['data-bbcode'];
      return;
    }

    // We don't onebox mentions
    if (node[1]['class'] === 'mention') { return; }

    // Don't onebox links within a list
    for (var i=0; i<path.length; i++) {
      if (path[i][0] === 'li') { return; }
    }

    // If the link has a different label text than the link itself, don't onebox it.
    const label = node[node.length-1];
    if (label !== node[1]['href']) { return; }

    if (isOnOneLine(node, parent)) {

      node[1]['class'] = 'onebox';
      node[1].target = '_blank';

      const contents = lookupCache(node[1].href);
      if (contents) {
        node[0] = '__RAW';
        node[1] = contents;
        node.length = 2;
      }
    }
  });
}