md.php

<?php

namespace Roots\Bedrock;

use League\CommonMark\CommonMarkConverter;

class MarkdownPosts {
  const POST_OPTION = 'roots/bedrock/markdown_posts';
  const IS_MD_META = 'roots/bedrock/is_markdown';

  private static $instance;
  private $converter;
  private $monitoring = ['post' => [], 'parent' => []];

  public function __construct() {
    $this->converter = new CommonMarkConverter();
  }

  public static function getInstance() {
    if (!self::$instance) {
      self::$instance = new self();
    }

    return self::$instance;
  }

  public function init() {
    add_action('admin_init', [$this, 'registerSetting']);
    add_filter('wp_insert_post_data', [$this, 'insertPostData'], 10, 2);
    add_action('wp_insert_post', [$this, 'insertPost']);
    add_filter('edit_post_content', [$this, 'editPostContent'], 10, 2);
    add_filter('edit_post_content_filtered', [$this, 'editPostContentFiltered'], 10, 2);
  }

  private function convertMarkdownToHTML($text) {
    return $this->converter->convertToHtml($text);
  }

  public function editPostContent($content, $id) {
    if (!$this->isMarkdown($id)) { return $content; }

    $post = get_post($id);

    if ($post && !empty($post->post_content_filtered)) {
      $post = $this->swapContent($post);
      return $post->post_content;
    }

    return $content;
  }

  public function editPostContentFiltered($content, $id) {
    if (!$this->isPostMarkdownEnabled() && $this->isMarkdown($id)) {
      $post = get_post($id);

      if ($post && !empty($post->post_content_filtered)) {
        $content = '';
      }
    }

    return $content;
  }

  public function insertPost($post_id) {
    $post_parent = get_post_field('post_parent', $post_id);

    if (isset( $this->monitoring['content']) && $this->monitoring['content'] === get_post_field('post_content', $post_id)) {
      unset($this->monitoring['content']);
      $this->setAsMarkdown($post_id);
    }

    if (isset($this->monitoring['post'][$post_id])) {
      unset($this->monitoring['post'][$post_id]);
      $this->setAsMarkdown($post_id);
    } elseif (isset($this->monitoring['parent'][$post_parent])) {
      unset($this->monitoring['parent'][$post_parent]);
      $this->setAsMarkdown($post_id);
    }
  }

  public function insertPostData($post_data, $post) {
    $post_id = isset($post['ID']) ? $post['ID'] : false;

    // bail early if markdown is disabled or this post type is unsupported.
    if (!$this->isPostMarkdownEnabled()) {
      if ($this->isMarkdown($post_id) && !empty($post_data['post_content_filtered'])) {
        $post_data['post_content_filtered'] = '';
      }

      return $post_data;
    }

    if (!$this->isPostRevision($post)) {
      $post_data['post_content'] = $this->convertMarkdownToHTML($post_data['post_content']);
      $post_data['post_content'] = apply_filters('content_save_pre', $post_data['post_content']);
    } elseif (strpos($post_data['post_name'], $post_data['post_parent'] . '-autosave') === 0) {
      $post_data['post_content'] = $this->convertMarkdownToHTML($post_data['post_content']);
      $post_data['post_content'] = apply_filters('content_save_pre', $post_data['post_content']);
    }

    if ($post_id) {
      $this->monitoring['post'][$post_id] = true;
    } else {
      $this->monitoring['content'] = wp_unslash($post_data['post_content']);
    }

    if ($this->isPostRevision($post) && $this->isMarkdown($post['post_parent'])) {
      $this->monitoring['parent'][$post['post_parent']] = true;
    }

    return $post_data;
  }

  private function isMarkdown($post_id) {
    return get_metadata('post', $post_id, self::IS_MD_META, true);
  }

  public function isPostMarkdownEnabled() {
    return (bool) get_option(self::POST_OPTION, '');
  }

  private function isPostRevision($post) {
    return $post['post_type'] === 'revision';
  }

  public function registerSetting() {
    add_settings_field(self::POST_OPTION, 'Markdown', [$this, 'postField'], 'writing');
    register_setting('writing', self::POST_OPTION, [$this, 'sanitizeSetting']);
  }

  public function sanitizeSetting($input) {
    return (bool) $input;
  }

  public function postField() {
    printf(
      '<label><input name="%s" id="%s" type="checkbox"%s> %s</label>',
      self::POST_OPTION,
      self::POST_OPTION,
      checked($this->isPostMarkdownEnabled(), true, false),
      esc_html('Use Markdown for posts and pages.')
    );
  }

  private function setAsMarkdown($post_id) {
    return update_metadata('post', $post_id, self::IS_MD_META, true);
  }

  private function swapContent($post) {
    $markdown = $post->post_content_filtered;
    $post->post_content_filtered = $post->post_content;
    $post->post_content = $markdown;
    return $post;
  }
}

add_action('init', [MarkdownPosts::getInstance(), 'init']);