/**
 * Copyright (c) 2017-present, Facebook, Inc.
 *
 * This source code is licensed under the MIT license found in the
 * LICENSE file in the root directory of this source tree.
 */

const hljs = require('highlight.js');
const Markdown = require('remarkable');
const toSlug = require('./toSlug.js');

const CWD = process.cwd();

/**
 * The anchors plugin adds GFM-style anchors to headings.
 */
function anchors(md) {
  md.renderer.rules.heading_open = function(tokens, idx /*, options, env */) {
    const textToken = tokens[idx + 1];
    return (
      '<h' +
      tokens[idx].hLevel +
      '><a class="anchor" aria-hidden="true" id="' +
      toSlug(textToken.content) +
      '"></a><a href="#' +
      toSlug(textToken.content) +
      '" aria-hidden="true" class="hash-link" ><svg aria-hidden="true" height="16" version="1.1" viewBox="0 0 16 16" width="16"><path fill-rule="evenodd" d="M4 9h1v1H4c-1.5 0-3-1.69-3-3.5S2.55 3 4 3h4c1.45 0 3 1.69 3 3.5 0 1.41-.91 2.72-2 3.25V8.59c.58-.45 1-1.27 1-2.09C10 5.22 8.98 4 8 4H4c-.98 0-2 1.22-2 2.5S3 9 4 9zm9-3h-1v1h1c1 0 2 1.22 2 2.5S13.98 12 13 12H9c-.98 0-2-1.22-2-2.5 0-.83.42-1.64 1-2.09V6.25c-1.09.53-2 1.84-2 3.25C6 11.31 7.55 13 9 13h4c1.45 0 3-1.69 3-3.5S14.5 6 13 6z"></path></svg></a>'
    );
  };
}

class MarkdownRenderer {
  constructor() {
    const siteConfig = require(CWD + '/siteConfig.js');

    const md = new Markdown({
      // Highlight.js expects hljs css classes on the code element.
      // This results in <pre><code class="hljs css javascript">
      langPrefix: 'hljs css ',
      highlight: function(str, lang) {
        lang =
          lang || (siteConfig.highlight && siteConfig.highlight.defaultLang);
        if (lang && hljs.getLanguage(lang)) {
          try {
            return hljs.highlight(lang, str).value;
          } catch (err) {}
        }

        try {
          return hljs.highlightAuto(str).value;
        } catch (err) {}

        return '';
      },
      html: true,
      linkify: true,
    });

    // Register anchors plugin
    md.use(anchors);

    // Allow client sites to register their own plugins
    if (siteConfig.markdownPlugins) {
      siteConfig.markdownPlugins.forEach(function(plugin) {
        md.use(plugin);
      });
    }

    this._md = md;
  }

  toHtml(source) {
    const html = this._md.render(source);

    // Ensure fenced code blocks use Highlight.js hljs class
    // https://github.com/jonschlinkert/remarkable/issues/224
    return html.replace(/<pre><code>/g, '<pre><code class="hljs">');
  }
}

const renderMarkdown = new MarkdownRenderer();

module.exports = source => {
  return renderMarkdown.toHtml(source);
};
