Wordpress: Custom fields in Category

category-color-field.php

<table class="form-table">
<tr class="form-field">
    <th><label for="category_color">Category color</label></th>

    <td>
        <input id="category_color" type="text" name="category_color" value="<?php echo $current_color ?>" />
        <span class="description">
            Category Color.</span>
    </td>
</tr>
</table>

category-custom-fields.php

<?php
/*
Plugin Name: JAB: Products post type
Description: Plugin for products custom post type
Author: Luis Abarca
Author Uri: http://luisabarca.com
Plugin Uri: http://justoalblanco.com
*/

/*
 * Template functions
 */ 
function the_category_color($term_id = null)
{    
    if ( is_null($term_id) ) {
        global $post;
        
        $terms = wp_get_object_terms($post->ID, Product::TAXONOMY_NAME);
    
        if ( !empty($terms) ) {
            foreach ($terms as $term) {
                $term_id = $term->term_id;
            }
        }
    }
        
    the_product_category_field($term_id, 'category_color');
}

function the_product_category_field($term_id, $field)
{
    echo get_product_category_field($term_id, $field);
}

function get_product_category_field($term_id, $field)
{    
    return Product::get_taxonomy_field($term_id, $field);
}

// end template functions


$product = Product::instance();

/** 
 * create tables for taxonomies
 * Inspired by http://shibashake.com/wordpress-theme/add-term-or-taxonomy-meta-data
 */
function _create_metadata_table($type) 
{
    global $wpdb;
    
    $table_name = $wpdb->prefix . $type . 'meta';
     
	if (!empty ($wpdb->charset)) {
		$charset_collate = "DEFAULT CHARACTER SET {$wpdb->charset}";
    }
    
	if (!empty ($wpdb->collate)) {
		$charset_collate .= " COLLATE {$wpdb->collate}";
    }
    
    $sql = "CREATE TABLE IF NOT EXISTS {$table_name} (
	  	    meta_id bigint(20) NOT NULL AUTO_INCREMENT,
	  	    {$type}_id bigint(20) NOT NULL default 0,
	  	    meta_key varchar(255) DEFAULT NULL,
	  	    meta_value longtext DEFAULT NULL,
	  	    UNIQUE KEY meta_id (meta_id)
	) {$charset_collate};";

	require_once(ABSPATH . 'wp-admin/includes/upgrade.php');
	dbDelta($sql);	
}

class Product {
    const POST_TYPE_NAME = 'products';
    const POST_TYPE_REWRITE = 'products';
    const PLURAL_NAME = 'Products';
    const SINGULAR_NAME = 'Product';
    
    const TAXONOMY_NAME = 'product-category';
    const TAXONOMY_SLUG_NAME = 'product_category';
    
    private static $instance;
    
    /***************************************************************************
     * Static functions
     **************************************************************************/
	public static function instance () {

    	if ( ! isset( self::$instance ) ) {
            $class_name = __CLASS__;
            self::$instance = new $class_name;
        }

        return self::$instance;
        
    }
    
    private function __construct()
    {
        //if ( function_exists('add_term_thumbnails_support') ) add_term_thumbnails_support(self::TAXONOMY_NAME);
        global $wpdb;
        
        $wpdb->{self::TAXONOMY_SLUG_NAME . 'meta'} = $wpdb->prefix . self::TAXONOMY_SLUG_NAME . 'meta';
                
        add_action('init', array($this, 'register_custom_types') );
        add_filter('post_type_link', array($this, 'custom_permalinks'), 1, 3);
        
        register_activation_hook(__FILE__, array($this, 'activate') );
        register_deactivation_hook(__FILE__, array($this, 'deactivate') );
        
        // add custom fields to taxonomy form
        add_action( self::TAXONOMY_NAME . '_edit_form', array($this, 'taxonomy_extra_fields') );
        
        // Save the custom field to table
        add_action( 'edited_' . self::TAXONOMY_NAME, array($this, 'taxonomy_save_extra_fields'), 10, 1 );
    }
    
    // }}}
    // {{{
    
    function taxonomy_save_extra_fields( $term_id ) 
    {
        // Form field with the color value
        $color = trim($_POST['category_color']);
    
        update_metadata(self::TAXONOMY_SLUG_NAME, $term_id, 'category_color', $color);
    }
    
    // }}}
    // {{{
    
    /**
     * 
     */
    function taxonomy_extra_fields() 
    {
        $current_color = esc_attr(self::get_taxonomy_field($_GET['tag_ID'], 'category_color'));
        
        include 'category-color-field.php';
    }
    
    // }}}
    // {{{
    
    public static function get_taxonomy_field($term_id, $field, $single = true)
    {
        return get_metadata(self::TAXONOMY_SLUG_NAME, $term_id, $field, $single);
    }
    
    // }}}
    // {{{

    /* 
     * 
     */
    public function custom_permalinks($url, $post = null, $leavename = false)
    {
        // products only
        if ($post->post_type != self::POST_TYPE_NAME) {
            return $url;
        }
    
        $post_id = $post->ID;
        $taxonomy = self::TAXONOMY_NAME;
        $taxonomy_tag = '%' . $taxonomy . '%';
        
        // Check if exists the tag
        if (strpos($taxonomy_tag, $url) < 0) {
            return $url;
        }
    
        // Get the terms
        $terms = wp_get_post_terms($post_id, $taxonomy);
        
        if (is_array($terms) && sizeof($terms) > 0) {
            $category = $terms[0];
        }
    
        // replace taxonomy tag with the term slug: /products/dvd/productname
        return str_replace($taxonomy_tag, $category->slug, $url);
    }
    
    
    /* 
     * 
     *
     */
    public function register_custom_types() 
    {
        global $wp_rewrite;
    	global $wp_query;
    
    	register_post_type(self::POST_TYPE_NAME, array(
            'label'           => self::PLURAL_NAME,
            'description'     => '',
            'public'          => true,
            'show_ui'         => true,
            'show_in_menu'    => true,
            'capability_type' => 'post',
            'hierarchical'    => true,
            'rewrite'         => array('slug' => self::POST_TYPE_REWRITE),
            'query_var'       => true,
            'has_archive'     => true,
            'menu_position'   => 6,
            'supports'        => array( 'title', 'editor', 'excerpt', 'trackbacks', 'revisions', 'thumbnail', 'author' ),
            'labels'          => array(
                'name'               => self::PLURAL_NAME,
                'singular_name'      => self::SINGULAR_NAME,
                'menu_name'          => self::PLURAL_NAME,
                'add_new'            => 'Add product',
                'add_new_item'       => 'Add New product',
                'edit'               => 'Edit',
                'edit_item'          => 'Edit product',
                'new_item'           => 'New product',
                'view'               => 'View product',
                'view_item'          => 'View product',
                'search_items'       => 'Search Products',
                'not_found'          => 'No Products Found',
                'not_found_in_trash' => 'No Products Found in Trash',
                'parent'             => 'Parent product')
            )
        );
    
        register_taxonomy(self::TAXONOMY_NAME, self::POST_TYPE_NAME, array(
            'hierarchical'   => true, 
            'label'          => 'Product Categories', 
            'show_ui'        => true, 
            'query_var'      => true, 
            'rewrite'        => array('slug' => 'products'),
            'singular_label' => 'Product Category') 
        );
        
        $wp_rewrite->extra_permastructs[self::POST_TYPE_NAME][0] = '/'. self::POST_TYPE_REWRITE . '/%' . self::TAXONOMY_NAME . '%/%' . self::POST_TYPE_NAME . '%';
    }
    
    
    /**
     * 
     */
    public function activate()
    {
        self::register_custom_types();
        flush_rewrite_rules();
        
        _create_metadata_table(self::TAXONOMY_SLUG_NAME);
    }
    
    // }}}
    // {{{
    
    /**
     * 
     */
    public function deactivate()
    {
        flush_rewrite_rules();
    }
    
    public static function get_parent_categories($hide_empty = 0)
    {
        $args = array(
            'order'  => 'name',
            'parent' => 0,
            'hide_empty' => $hide_empty
        );
        
        return get_terms(self::TAXONOMY_NAME, $args );
    }

}