/*
  Copyright 2020 the JSDoc Authors.

  Licensed under the Apache License, Version 2.0 (the "License");
  you may not use this file except in compliance with the License.
  You may obtain a copy of the License at

      https://www.apache.org/licenses/LICENSE-2.0

  Unless required by applicable law or agreed to in writing, software
  distributed under the License is distributed on an "AS IS" BASIS,
  WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
  See the License for the specific language governing permissions and
  limitations under the License.
*/
import MarkdownIt from 'markdown-it';
import mdAnchor from 'markdown-it-anchor';

const inlineTagRegExp = /\{@[^}\r\n]+\}/g;

/**
 * Escape characters in text within a code block.
 *
 * @param {string} source - The source text to escape.
 * @return {string} The escaped source text.
 */
function escapeCode(source) {
  return source.replace(/</g, '&lt;').replace(/"/g, '&quot;').replace(/'/g, '&#39;');
}

/**
 * Escapes backslashes within inline tags, so that the Markdown renderer does not treat them as
 * formatting characters.
 *
 * @param {string} text - The text to escape.
 * @return {string} The escaped text.
 */
function escapeInlineTagBackslashes(text) {
  return text.replace(inlineTagRegExp, (wholeMatch) => wholeMatch.replace(/\\/g, '\\\\'));
}

/**
 * Converts `&quot;` to `"` within inline tags.
 *
 * @param {string} text - The text to unencode.
 * @return {string} The modified text, with standard double quotes in inline tags.
 */
function unencodeQuotes(text) {
  return text.replace(inlineTagRegExp, (wholeMatch) => wholeMatch.replace(/&quot;/g, '"'));
}

/**
 * Wrap a code snippet in HTML tags that enable syntax highlighting.
 *
 * @param {string} code - The code snippet.
 * @param {string?} language - The language of the code snippet.
 * @return {string} The wrapped code snippet.
 */
function highlight(code, language) {
  let classString;
  let langClass = '';

  if (language && language !== 'plain') {
    langClass = ` lang-${language}`;
  }

  if (language !== 'plain') {
    classString = ` class="prettyprint source${langClass}"`;
  } else {
    classString = ' class="source"';
  }

  return `<pre${classString}><code>${escapeCode(code)}</code></pre>`;
}

/**
 * Gets a Markdown rendering function. The function accepts a string containing Markdown source. The
 * function converts the Markdown source to HTML, then returns the HTML as a string.
 *
 * @returns {function} A function that converts Markdown to HTML.
 */
export function getRenderer() {
  let renderer;

  renderer = new MarkdownIt({
    highlight,
    html: true,
  });
  renderer.use(mdAnchor, { tabIndex: false });

  return (source) => {
    let result;

    source = escapeInlineTagBackslashes(source);

    result = renderer.render(source).replace(/\s+$/, '').replace(/&#39;/g, "'");
    result = unencodeQuotes(result);

    return result;
  };
}