source: theme-switcher/trunk/theme-switcher.php @ 324274

<?php

/*
Plugin Name: Theme Switcher
Plugin URI: http://wordpress.org/extend/plugins/theme-switcher/
Description: Allow your readers to switch themes.
Version: 1.0
Author: Ryan Boren
Author URI: http://ryan.boren.me/

Adapted from Alex King's style switcher.
http://www.alexking.org/software/wordpress/

To use, add the "Theme Switcher" widget to your sidebar, 
or call wp_theme_switcher() directly, like so:

  <li>Themes:
        <?php wp_theme_switcher(); ?>
  </li>

This will create a list of themes for your readers to select.

If you would like a dropdown box rather than a list, add this:

  <li>Themes:
        <?php wp_theme_switcher('dropdown'); ?>
  </li>


*/ 

class ThemeSwitcherWidget extends WP_Widget {
        function ThemeSwitcherWidget()
        {
                return $this->WP_Widget('theme-switcher-widget', __('Theme Switcher Widget', 'theme-switcher'), array('description' => __('A widget with options for switching themes.', 'theme-switcher')));
        }

        function widget($args, $instance)
        {
                global $theme_switcher;
                $type = isset( $instance['displaytype'] ) ? $instance['displaytype'] : '';
                $title = empty( $instance['title'] ) ? __('Theme Switcher', 'theme-switcher') : $instance['title'];
                echo $args['before_widget'];
                echo $args['before_title'] . $title . $args['after_title'];
                echo $theme_switcher->theme_switcher_markup($type, $instance);
                echo $args['after_widget'];
        }

        function update($new_instance) 
        {
                return $new_instance;
        }

        function form($instance) 
        {
                $type = isset( $instance['displaytype'] ) ? $instance['displaytype'] : '';
                $title = isset( $instance['title'] ) ? $instance['title'] : '';
                ?>
                <p>
                        <label for="<?php echo $this->get_field_id('title'); ?>">
                                <span><?php _e('Title:', 'theme-switcher'); ?></span>
                                <input type="text" name="<?php echo $this->get_field_name('title'); ?>" id="<?php echo $this->get_field_id('title'); ?>" value="<?php echo esc_attr($title); ?>" />
                        </label>
                </p>
                        
                <p><label for="<?php echo $this->get_field_id('displaytype'); ?>"><?php _e('Display themes as:', 'theme-switcher'); ?></label></p>
                <p>
                        <span><input type="radio" name="<?php echo $this->get_field_name('displaytype'); ?>" value="list" <?php
                                if ( 'list' == $type ) {
                                        echo ' checked="checked"';
                                }
                        ?> /> <?php _e('List', 'theme-switcher'); ?></span>
                        <span><input type="radio" name="<?php echo $this->get_field_name('displaytype'); ?>" value="dropdown" <?php 
                                if ( 'dropdown' == $type ) {
                                        echo ' checked="checked"';
                                }
                        ?>/> <?php _e('Dropdown', 'theme-switcher'); ?></span>
                </p>
                <?php
        }
}

class ThemeSwitcher {

        function ThemeSwitcher()
        {
                add_action('init', array(&$this, 'set_theme_cookie'));
                add_action('widgets_init', array(&$this, 'event_widgets_init'));
                
                add_filter('stylesheet', array(&$this, 'get_stylesheet'));
                add_filter('template', array(&$this, 'get_template'));
        }

        function event_widgets_init()
        {
                register_widget('ThemeSwitcherWidget');
        }
        
        function get_stylesheet($stylesheet = '') {
                $theme = $this->get_theme();

                if (empty($theme)) {
                        return $stylesheet;
                }

                $theme = get_theme($theme);

                // Don't let people peek at unpublished themes.
                if (isset($theme['Status']) && $theme['Status'] != 'publish')
                        return $template;               
                
                if (empty($theme)) {
                        return $stylesheet;
                }

                return $theme['Stylesheet'];
        }

        function get_template($template) {
                $theme = $this->get_theme();

                if (empty($theme)) {
                        return $template;
                }

                $theme = get_theme($theme);
                
                if ( empty( $theme ) ) {
                        return $template;
                }

                // Don't let people peek at unpublished themes.
                if (isset($theme['Status']) && $theme['Status'] != 'publish')
                        return $template;               

                return $theme['Template'];
        }

        function get_theme() {
                if ( ! empty($_COOKIE["wptheme" . COOKIEHASH] ) ) {
                        return $_COOKIE["wptheme" . COOKIEHASH];
                } else {
                        return '';
                }
        }

        function set_theme_cookie() {
                load_plugin_textdomain('theme-switcher');
                $expire = time() + 30000000;
                if ( ! empty($_GET["wptheme"] ) ) {
                        setcookie(
                                "wptheme" . COOKIEHASH,
                                stripslashes($_GET["wptheme"]),
                                $expire,
                                COOKIEPATH
                        );
                        $redirect = remove_query_arg('wptheme');
                        wp_redirect($redirect);
                        exit;
                }
        }
        
        function theme_switcher_markup($style = "text", $instance = array()) {
                if ( ! $theme_data = wp_cache_get('themes-data', 'theme-switcher') ) {
                        $themes = (array) get_themes();
                        if ( function_exists('is_site_admin') ) {
                                $allowed_themes = (array) get_site_option( 'allowedthemes' );
                                foreach( $themes as $key => $theme ) {
                                    if( isset( $allowed_themes[ wp_specialchars( $theme[ 'Stylesheet' ] ) ] ) == false ) {
                                                unset( $themes[ $key ] );
                                    }
                                }
                        }

                        $default_theme = get_current_theme();

                        $theme_data = array();
                        foreach ((array) $themes as $theme_name => $data) {
                                // Skip unpublished themes.
                                if (empty($theme_name) || isset($themes[$theme_name]['Status']) && $themes[$theme_name]['Status'] != 'publish')
                                        continue;
                                $theme_data[add_query_arg('wptheme', $theme_name, get_option('home'))] = $theme_name;
                        }
                        
                        asort($theme_data);

                        wp_cache_set('themes-data', $theme_data, 'theme-switcher');
                }

                $ts = '<ul id="themeswitcher">'."\n";           

                if ( $style == 'dropdown' ) {
                        $ts .= '<li>' . "\n\t" . '<select name="themeswitcher" onchange="location.href=this.options[this.selectedIndex].value;">'."\n";
                }

                foreach ($theme_data as $url => $theme_name) {
                        if (
                                ! empty($_COOKIE["wptheme" . COOKIEHASH]) && $_COOKIE["wptheme" . COOKIEHASH] == $theme_name ||
                                empty($_COOKIE["wptheme" . COOKIEHASH]) && ($theme_name == $default_theme)
                        ) {
                                $pattern = 'dropdown' == $style ? '<option value="%1$s" selected="selected">%2$s</option>' : '<li>%2$s</li>';
                        } else {
                                $pattern = 'dropdown' == $style ? '<option value="%1$s">%2$s</option>' : '<li><a href="%1$s">%2$s</a></li>';
                        }                               
                        $ts .= sprintf($pattern,
                                esc_attr($url),
                                esc_html($theme_name)
                        );

                }

                if ( 'dropdown' == $style ) {
                        $ts .= "</select>\n</li>\n";
                }
                $ts .= '</ul>';
                return $ts;
        }
}

$theme_switcher = new ThemeSwitcher();

function wp_theme_switcher($type = '')
{
        global $theme_switcher;
        echo $theme_switcher->theme_switcher_markup($type);
}