root/tags/1.3/wp-admin/import/wp-cat2tag.php

<?php

class WP_Categories_to_Tags {
    var $categories_to_convert = array();
    var $all_categories = array();

    function header() {
        print '<div class="wrap">';
        print '<h2>' . __('Convert Categories to Tags') . '</h2>';
    }

    function footer() {
        print '</div>';
    }

    function populate_all_categories() {
        global $wpdb;

        $categories = get_categories('get=all');
        foreach ( $categories as $category ) {
            if ( !tag_exists($wpdb->escape($category->name)) )
                $this->all_categories[] = $category;    
        }
    }

    function welcome() {
        $this->populate_all_categories();

        print '<div class="narrow">';

        if (count($this->all_categories) > 0) {
            print '<p>' . __('Howdy! This converter allows you to selectively convert existing categories to tags. To get started, check the checkboxes of the categories you wish to be converted, then click the Convert button.') . '</p>';
            print '<p>' . __('Keep in mind that if you convert a category with child categories, those child categories get their parent setting removed, so they\'re in the root.') . '</p>';

            $this->categories_form();
        } else {
            print '<p>'.__('You have no categories to convert!').'</p>';
        }

        print '</div>';
    }

    function categories_form() {
        print '<form action="admin.php?import=wp-cat2tag&amp;step=2" method="post">';
        wp_nonce_field('import-cat2tag');
        print '<ul style="list-style:none">';

        $hier = _get_term_hierarchy('category');

        foreach ($this->all_categories as $category) {
            $category = sanitize_term( $category, 'category', 'display' );
        
            if ((int) $category->parent == 0) {
                print '<li><label><input type="checkbox" name="cats_to_convert[]" value="' . intval($category->term_id) . '" /> ' . $category->name . ' (' . $category->count . ')</label>';

                if (isset($hier[$category->term_id])) {
                    $this->_category_children($category, $hier);
                }

                print '</li>';
            }
        }

        print '</ul>';

        print '<p class="submit"><input type="submit" name="submit" value="' . __('Convert &raquo;') . '" /></p>';
        print '</form>';
    }

    function _category_children($parent, $hier) {
        print '<ul style="list-style:none">';

        foreach ($hier[$parent->term_id] as $child_id) {
            $child =& get_category($child_id);

            print '<li><label><input type="checkbox" name="cats_to_convert[]" value="' . intval($child->term_id) . '" /> ' . $child->name . ' (' . $child->count . ')</label>';

            if (isset($hier[$child->term_id])) {
                $this->_category_children($child, $hier);
            }

            print '</li>';
        }

        print '</ul>';
    }

    function _category_exists($cat_id) {
        global $wpdb;

        $cat_id = (int) $cat_id;

        $maybe_exists = category_exists($cat_id);

        if ( $maybe_exists ) {
            return true;
        } else {
            return false;
        }
    }

    function convert_them() {
        global $wpdb;

        if ( (!isset($_POST['cats_to_convert']) || !is_array($_POST['cats_to_convert'])) && empty($this->categories_to_convert)) {
            print '<div class="narrow">';
            print '<p>' . sprintf(__('Uh, oh. Something didn\'t work. Please <a href="%s">try again</a>.'), 'admin.php?import=wp-cat2tag') . '</p>';
            print '</div>';
            return;
        }


        if ( empty($this->categories_to_convert) )
            $this->categories_to_convert = $_POST['cats_to_convert'];
        $hier = _get_term_hierarchy('category');

        print '<ul>';

        foreach ( (array) $this->categories_to_convert as $cat_id) {
            $cat_id = (int) $cat_id;

            print '<li>' . sprintf(__('Converting category #%s ... '),  $cat_id);

            if (!$this->_category_exists($cat_id)) {
                _e('Category doesn\'t exist!');
            } else {
                $category =& get_category($cat_id);

                if ( tag_exists($wpdb->escape($category->name)) ) {
                    _e('Category is already a tag.');
                    print '</li>';
                    continue;
                }

                // If the category is the default, leave category in place and create tag.
                if ( get_option('default_category') == $category->term_id ) {
                    $id = wp_insert_term($category->name, 'post_tag', array('slug' => $category->slug));
                    $id = $id['term_taxonomy_id'];
                    $posts = get_objects_in_term($category->term_id, 'category');
                    foreach ( $posts as $post ) {
                        if ( !$wpdb->get_var("SELECT object_id FROM $wpdb->term_relationships WHERE object_id = '$post' AND term_taxonomy_id = '$id'") )                        
                            $wpdb->query("INSERT INTO $wpdb->term_relationships (object_id, term_taxonomy_id) VALUES ('$post', '$id')");
                        clean_post_cache($post);
                    }
                } else {
                    $tt_ids = $wpdb->get_col("SELECT term_taxonomy_id FROM $wpdb->term_taxonomy WHERE term_id = '{$category->term_id}' AND taxonomy = 'category'");
                    if ( $tt_ids ) {
                        $posts = $wpdb->get_col("SELECT object_id FROM $wpdb->term_relationships WHERE term_taxonomy_id IN (" . join(',', $tt_ids) . ") GROUP BY object_id");
                        foreach ( (array) $posts as $post )
                            clean_post_cache($post);
                    }

                    // Change the category to a tag.
                    $wpdb->query("UPDATE $wpdb->term_taxonomy SET taxonomy = 'post_tag' WHERE term_id = '{$category->term_id}' AND taxonomy = 'category'");

                    $terms = $wpdb->get_col("SELECT term_id FROM $wpdb->term_taxonomy WHERE parent = '{$category->term_id}' AND taxonomy = 'category'");
                    foreach ( (array) $terms as $term )
                        clean_category_cache($term);

                    // Set all parents to 0 (root-level) if their parent was the converted tag
                    $wpdb->query("UPDATE $wpdb->term_taxonomy SET parent = 0 WHERE parent = '{$category->term_id}' AND taxonomy = 'category'");
                }
                // Clean the cache
                clean_category_cache($category->term_id);

                _e('Converted successfully.');
            }

            print '</li>';
        }

        print '</ul>';
    }

    function init() {

        $step = (isset($_GET['step'])) ? (int) $_GET['step'] : 1;

        $this->header();

        if (!current_user_can('manage_categories')) {
            print '<div class="narrow">';
            print '<p>' . __('Cheatin&#8217; uh?') . '</p>';
            print '</div>';
        } else {
            if ( $step > 1 )
                check_admin_referer('import-cat2tag');

            switch ($step) {
                case 1 :
                    $this->welcome();
                break;

                case 2 :
                    $this->convert_them();
                break;
            }
        }

        $this->footer();
    }

    function WP_Categories_to_Tags() {
        // Do nothing.
    }
}

$wp_cat2tag_importer = new WP_Categories_to_Tags();

register_importer('wp-cat2tag', __('Categories to Tags Converter'), __('Convert existing categories to tags, selectively.'), array(&$wp_cat2tag_importer, 'init'));

?>