skins.php

<?php 
/*
Plugin Name: Skins
Plugin URI: http://github.com/ryanve/skins
Description: Add custom CSS classes to your markup for usage in your CSS.
Version: 1.0.3
Author: Ryan Van Etten
Author URI: http://ryanve.com
License: MIT
*/

call_user_func(function() {

  $plugin = array('name' => 'Skins');
  $plugin['option'] = 'plugin:skins';
  $plugin['prefix'] = 'plugin:skins:';
  $plugin['get'] = function() use (&$plugin) {
    return (array) get_option($plugin['option']);
  };
  
  $plugin['set'] = function($data) use (&$plugin) {
    return (null === $data 
      ? delete_option($plugin['option'])
      : update_option($plugin['option'], $data)
    ) ? $data : false;
  };

  $plugin['hooks'] = array('body_class', 'post_class', 'comment_class');
  $plugin['hooks'] = array_unique(apply_filters($plugin['prefix'] . 'hooks', $plugin['hooks']));

  is_admin() ? add_action('admin_menu', function() use (&$plugin) {
  
    register_deactivation_hook(__FILE__, function() use (&$plugin) {
      $plugin['set'](null); # removes all data
    }); #wp 2.0+
    
    $page = (array) apply_filters($plugin['prefix'] . 'page', array(
      'capability' => 'manage_options',
      'name' => $plugin['name'],
      'slug' => basename(__FILE__, '.php'),
      'add' => 'add_theme_page',
      'parent' => 'themes.php',
      'sections' => array('default')
    ));

    empty($page['fn']) and $page['fn'] = function() use (&$plugin, &$page) {
      echo '<div class="wrap">';
      function_exists('screen_icon') and screen_icon(); #wp 2.7.0+
      echo '<h2>' . $plugin['name'] . '</h2>';
      echo '<p>' . __('List space-separated CSS classes for usage in your CSS:') . '</p>';
      echo '<form method="post" action="options.php">';
      settings_fields($page['slug']); #wp 2.7.0+
      do_settings_fields($page['slug'], $page['sections'][0]); #wp 2.7.0+
      submit_button(__('Update')); #wp 3.1.0+
      echo '</form></div>';
    };
    
    # Create "Settings" link to appear on /wp-admin/plugins.php
    add_filter('plugin_action_links_' . plugin_basename(__FILE__), function($links) use (&$page) {
      $href = $page['parent'] ? $page['parent'] . '?page=' . $page['slug'] : $page['slug'];
      $href = admin_url($href); #wp 3.0.0+
      array_unshift($links, '<a href="' . $href . '">' . __('Settings') . '</a>');
      return $links;
    }, 10, 2);
    
    # add_theme_page or add_options_page
    call_user_func_array($page['add'], array(
      $page['name'],
      $page['name'],
      $page['capability'],
      $page['slug'],
      $page['fn']
    ));
    
    $curr = $plugin['get']();
    foreach ($plugin['hooks'] as $hook) {
      register_setting($page['slug'], $hook, function($str) use (&$plugin, &$curr, $hook) {
        $curr[$hook] = $str ? esc_attr(normalize_whitespace($str)) : ''; #wp 2.8.0+
        $plugin['set']($curr);
        return $curr[$hook];
      }); #wp 2.7.0+

      add_settings_field($hook, "<code>'$hook'</code> classes:", function() use ($curr, $hook) {
        $value = is_string($value = !isset($curr[$hook]) ?: $curr[$hook]) ? trim($value) : '';
        $style = 'max-width:100%;min-width:20%';
        $place = 'layout-example color-example';
        echo "<div><textarea style='$style' placeholder='$place' name='$hook'>$value</textarea></div>";
      }, $page['slug'], $page['sections'][0]); #wp 2.7.0+ 
    }
  
  }) : array_reduce($plugin['hooks'], function($curr, $hook) {
      $hook and add_filter($hook, function($arr) use ($curr, $hook) {
        return isset($curr[$hook]) ? array_unique(array_filter(array_merge($arr,
          is_string($curr[$hook]) ? preg_split('#\s+#', $curr[$hook]) : (array) $curr[$hook]
        ), 'strlen')) : $arr;
      });
      return $curr;
  }, $plugin['get']());
});