parsedown_filter.module

<?php
/**
 * @file
 * Provides a Markdown Extra input filter.
 */

/**
 * Implements hook_filter_info().
 */
function parsedown_filter_filter_info() {
  $filters['filter_parsedown_filter'] = array(
    'title' => t('Parsedown'),
    'description' => t('Allows content to be submitted using Markdown , a simple plain-text syntax that is filtered into valid XHTML.'),
    'process callback' => '_filter_parsedown_filter',
    'settings callback' => '_filter_parsedown_settings',
    'tips callback' => '_filter_parsedown_filter_tips',
  );

  return $filters;
}

/**
 * Implements hook_autoload_info().
 */
function parsedown_filter_autoload_info() {
  return array(
    'Parsedown' => 'libraries/Parsedown/Parsedown.php',
    'ParsedownExtra' => 'libraries/ParsedownExtra/ParsedownExtra.php',
  );
}


/**
 * Returns the parsedown_filter input filter tips.
 */
function _filter_parsedown_filter_tips($format, $long = FALSE) {
  if ($long) {
    return t('Quick Tips:<ul>
      <li>Two or more spaces at a line\'s end = Line break</li>
      <li>Double returns = Paragraph</li>
      <li>*Single asterisks* or _single underscores_ = <em>Emphasis</em></li>
      <li>**Double** or __double__ = <strong>Strong</strong></li>
      <li>This is [a link](http://the.link.example.com "The optional title text")</li>
      <li>This is a image ![alt](http://the.link.example.com/example.png)</li>
      </ul>');
  }
  else {
    return t('You can use <a href="@filter_tips">Markdown syntax</a> to format and style the text.');
  }
}

/**
 * Implements callback_filter_settings().
 *
 * Filter settings callback for the Markdown content filter.
 */
function _filter_parsedown_settings($form, &$form_state, $filter, $format) {
  $settings['filter_parsedown_extra'] = array(
    '#type' => 'checkbox',
    '#title' => t('Enable Markdown Extra'),
    '#default_value' => isset($filter->settings['filter_parsedown_extra']) ? $filter->settings['filter_parsedown_extra'] : FALSE,
  );
  return $settings;
}

/**
 * Implements hook_block_view().
 */
function parsedown_filter_block_view($delta = '') {
  $block = array();
  switch ($delta) {
    case 'parsedown_filter_help':
      $block['title'] = t('Markdown filter tips');
      $block['content'] = _parsedown_filter_help_block();
      break;
  }

  return $block;
}

/**
 * Implements hook_block_info().
 */
function parsedown_filter_block_info() {
  $blocks = array();
  $blocks['parsedown_filter_help'] = array(
    'info' => t('Markdown filter tips'),
  );

  return $blocks;
}

/**
 * Provides content for the parsedown_filter help block.
 */
function _parsedown_filter_help_block() {
  return '<pre>' . t("
## Header 2 ##
### Header 3 ###
#### Header 4 ####
##### Header 5 #####
(Hashes on right are optional)

Link [Backdrop CMS](https://backdropcms.org/)

Inline markup like _italics_,
 **bold**, and `code()`.

> Blockquote. Like email replies
>> And, they can be nested

* Bullet lists are easy too
- Another one
+ Another one

1. A numbered list
2. Which is numbered
3. With periods and a space

And now some code:
```php
phpinfo();

```") . '</pre>';
}

/**
 * Implements callback_filter_process().
 *
 * Provides filtering of input into accepted HTML based on Markdown syntax.
 */
function _filter_parsedown_filter($text, $filter) {
  if (!empty($text)) {
    if ($filter->settings['filter_parsedown_extra']) {
      $Extra = new ParsedownExtra();
      $text = $Extra->text($text);
    }
    else {
      $Parsedown = new Parsedown();
      $text = $Parsedown->text($text);
    }
  }

  return $text;
}