Category Links To

<?php
/*
Plugin Name: Category Links To
Plugin URI: http://ru.forums.wordpress.org/topic/43423
Description: Allows you to make a WordPress category link to an external URL of your choosing, instead of its WordPress URL.
Author: Sergey Biryukov
Author URI: http://profiles.wordpress.org/sergeybiryukov/
Version: 0.1
*/

class Category_Links_To {

    function __construct() {
        add_filter( 'category_add_form_fields',  array( $this, 'add_field_to_add_category_form' ), 1 );
        add_filter( 'category_edit_form_fields', array( $this, 'add_field_to_edit_category_form' ), 1 );
        add_filter( 'category_link',             array( $this, 'filter_category_link' ), 10, 2 );

        add_action( 'created_category',          array( $this, 'save_category_link' ) );
        add_action( 'edited_category',           array( $this, 'save_category_link' ) );
    }

    function get_options() {
        return get_option( 'category_links_to', array() );
    }

    function save_options( $options ) {
        update_option( 'category_links_to', $options );
    }

    function add_field_to_add_category_form() { ?>
        <div class="form-field term-link-wrap">
            <label for="tag-link">Ссылка</label>
            <input name="term-link" id="tag-link" type="text" value="" size="40" />
            <p>Здесь можно указать адрес, на который будет вести ссылка на рубрику.</p>
        </div>
        <?php
    }

    function add_field_to_edit_category_form( $term ) {
        $options = $this->get_options();

        if ( isset( $options[ $term->term_id ] ) ) {
            $term_link = $options[ $term->term_id ];
        } else {
            $term_link = '';
        }
        ?>
        <tr class="form-field term-link-wrap">
            <th scope="row"><label for="link">Ссылка</label></th>
            <td><input name="term-link" id="link" type="text" value="<?php echo esc_attr( $term_link ); ?>" size="40" />
            <p class="description">Здесь можно указать адрес, на который будет вести ссылка на рубрику.</p></td>
        </tr>
        <?php
    }

    function filter_category_link( $term_link, $term_id ) {
        $options = $this->get_options();

        if ( isset( $options[ $term_id ] ) ) {
            $term_link = esc_url( $options[ $term_id ] );
        }

        return $term_link;
    }

    function save_category_link( $term_id ) {
        $options = $this->get_options();

        if ( ! empty( $_POST['term-link'] ) ) {
            $options[ $term_id ] = esc_url_raw( $_POST['term-link'] );
        } else {
            unset( $options[ $term_id ] );
        }

        $this->save_options( $options );
    }

}

new Category_Links_To;
?>