Wordpress Plugin - Remove slug from custom post type (mod)

<?php
/*
Plugin Name: Remove slug from custom post type
Plugin URI: http://www.ultimatewebtips.com/remove-slug-from-custom-post-type/
Description: Removes the slug from permalink on all custom post types
Version: 1.0.3
Author: Joakim Ling
Author URI: http://www.ultimatewebtips.com/
*/

class UWT_RemoveSlugCustomPostType{

    static $_s = null;
    private $htaccess_tag = 'REMOVE SLUG CUSTOM POST TYPE RULES';

    public function __construct() {
        $this->rewrite_rules();

        add_action('admin_menu', array(&$this, 'menu'));
        add_action('wp_insert_post', array(&$this, 'post_save'));

        add_filter('post_type_link', array(&$this, 'remove_slug'), 10, 3);
        add_filter('redirect_canonical', array(&$this, 'cancel_redirect_canonical'));
        //add_filter('posts_request', array(&$this, 'request'));

    }

    function cancel_redirect_canonical($redirect_url) {
        $suffix = get_option('uwt_permalink_customtype_suffix');
        if (empty($suffix))
            return $redirect_url;
        global $wp_post_types;
        foreach ($wp_post_types as $type=>$custom_post) {
            $hit = get_query_var($custom_post->query_var);
            if (!empty($hit))
                return false;
        }
    }

    public function menu() {
        add_options_page( 'Permalink custom post type', 'Custom post type', 'manage_options', __FILE__, array(&$this, 'menu_page'));
    }

    public function menu_page() {

        if (!current_user_can('manage_options')) {
            wp_die( __('You do not have sufficient permissions to access this page.') );
        }

        // Returns checked (for checkbox) if the provided string is found in the provided array)
        function checked_val($target_val, $target_array) {

            if ($target_array != null) {

                if (in_array( $target_val, $target_array ) ) {
                    return 'checked="checked" ';
                }

            }

        }

        // Query for getting custom post types
        $get_post_types_args = array('public'=>true, '_builtin'=>false);
        $post_types = get_post_types($get_post_types_args, 'objects');

        // Field names
        $hidden_field_name = 'uwt_submit_hidden';
        $selected_cpts_key = 'selected_cpts';
        $opt_name = 'uwt_permalink_customtype_suffix';


        // If the form has been submitted
        if(isset($_POST[$hidden_field_name]) && $_POST[$hidden_field_name] == 'Y') {

            // Loop through each custom post type
            foreach( $post_types as $post_type ) {

                // If this custom post type is selected
                if ($_POST['chk_' . $post_type->name] == 'checked') {

                    // Record it in the array
                    $selected_cpts[] = $post_type->name;

                }

            }

            update_option($selected_cpts_key, $selected_cpts);

            // Save the suffix
            $opt_val = preg_replace('/[^0-9a-z]+/i', '', $_POST[$opt_name]);
            update_option($opt_name, $opt_val);

        ?>

            <div class="updated"><p><strong><?php _e('Settings saved' ); ?></strong></p></div>

        <?php

            $this->rewrite_rules(true);
            $this->add_rules_htaccess();
        }

        else {

            // Otherwise just load existing options
            $selected_cpts = get_option($selected_cpts_key);
            $opt_val = get_option($opt_name);

        }

        ?>

<div class="wrap">

<?php screen_icon(); ?>

<h2>Permalink custom post type</h2>

<h3>Custom Post Types to remove the permalink slug from</h3>

<form name="form1" method="post" action="">

<?php

    // get the registered data about each post type with get_post_type_object
    foreach( $post_types as $post_type ) {
            echo '<p><label for="chk_' . $post_type->name . '"><input id="chk_' . $post_type->name . '" name="chk_' . $post_type->name . '" type="checkbox" value="checked" ' . checked_val( $post_type->name, $selected_cpts ) . '/> ' . $post_type->name . '</label></p>';
    }


?>

<h3>Custom Post Type Permalink Suffix</h3>


    <input type="hidden" name="<?php echo $hidden_field_name; ?>" value="Y">
    <p>Permalink custom type suffix:
        <input type="text" name="<?php echo $opt_name; ?>" value="<?php echo $opt_val; ?>" size="20">
        <br />
        <em>Use this option if you want your custom post type posts to have a suffix, e.g. ".html", leave empty if you want normal structure (http://siteurl/post_title/)</em>
    </p>

    <hr />
    <p class="submit">
        <input type="submit" name="Submit" class="button-primary" value="<?php esc_attr_e('Save Changes') ?>" />
    </p>
</form>
</div>
<?php
    }

    public function request($input) {
        global $wp_post_types;
        $array_slug[] = "wp_posts.post_type = 'post'";
        foreach ($wp_post_types as $type=>$custom_post) {
            if ($custom_post->_builtin == false)
                $array_slug[] = "wp_posts.post_type = '" . trim($type, '/') . "'";
        }
        $types = '(' . implode(' || ', $array_slug) . ')';
        $input = str_replace("wp_posts.post_type = 'post'", $types, $input);
        return $input;
    }

    static public function init() {
        if (self::$_s == null) {
            self::$_s = new self();
        }
        return self::$_s;
    }

    static public function flush_rewrite_rules() {
        $uwt_o = self::init();
        $uwt_o->rewrite_rules(true);
        $uwt_o->add_rules_htaccess();
    }

    public function post_save($post_id) {
        global $wp_post_types;
        $post_type = get_post_type($post_id);
        foreach ($wp_post_types as $type=>$custom_post) {
            if ($custom_post->_builtin == false && $type == $post_type) {
                $this->rewrite_rules(true);
                $this->add_rules_htaccess();
            }
        }
    }

    public function remove_slug($permalink, $post, $leavename) {
        global $wp_post_types;
        $suffix = get_option('uwt_permalink_customtype_suffix');
        foreach ($wp_post_types as $type=>$custom_post) {
            if ($custom_post->_builtin == false && $type == $post->post_type) {
                $custom_post->rewrite['slug'] = trim($custom_post->rewrite['slug'], '/');
                $permalink = str_replace(get_bloginfo('url') . '/' . $custom_post->rewrite['slug'] . '/', get_bloginfo('url') . "/", $permalink);
                if (!empty($suffix))
                    $permalink = substr($permalink, 0, -1) . ".{$suffix}";
            }
        }
        return $permalink;
    }

    public function rewrite_rules($flash = false) {
        global $wp_post_types, $wpdb;
        $suffix = get_option('uwt_permalink_customtype_suffix');
        foreach ($wp_post_types as $type=>$custom_post) {
            if ($custom_post->_builtin == false) {
                $querystr = "SELECT {$wpdb->posts}.post_name, {$wpdb->posts}.post_parent
                FROM {$wpdb->posts}
                WHERE {$wpdb->posts}.post_status = 'publish'
                AND {$wpdb->posts}.post_type = '{$type}'
                AND {$wpdb->posts}.post_date < NOW()";
                $posts = $wpdb->get_results($querystr, OBJECT);
                foreach ($posts as $post) {
                    if($post->post_parent > 0) {
                        $regexStr = $this->build_regex($post);
                            $regex = (!empty($suffix)) ? $regexStr . "/{$post->post_name}\\.{$suffix}\$" : $regexStr . "/{$post->post_name}\$";
                            add_rewrite_rule($regex, "index.php?{$custom_post->query_var}={$post->post_name}", 'top');
                    }
                    else {
                        $regex = (!empty($suffix)) ? "{$post->post_name}\\.{$suffix}\$" : "{$post->post_name}\$";
                            add_rewrite_rule($regex, "index.php?{$custom_post->query_var}={$post->post_name}", 'top');
                        }
                    }
                }
            }

            if ($flash == true)
            flush_rewrite_rules(false);
        } // a recursive function to build the path of the cpt's hierarchy used in the regex pattern

        private function build_regex($post) {
            $parent = get_post($post->post_parent);
        if($parent->post_parent > 0)
        $str .= $this->build_regex($parent) . '/' . $parent->post_name;
        else   $str .= $parent->post_name;
        return $str;
    }

    private function add_rules_htaccess() {
        global $wp_post_types;
        $suffix = get_option('uwt_permalink_customtype_suffix');
        $write = array();
        $htaccess_filename = ABSPATH . '/.htaccess';
        if (is_readable($htaccess_filename)) {
            $htaccess = fopen($htaccess_filename, 'r');
            $content = fread($htaccess, filesize($htaccess_filename));
            foreach ($wp_post_types as $type=>$custom_post) {
                $rewrite_rule = (!empty($suffix))
                            ? "RewriteRule ^{$custom_post->query_var}/(.+)/\$ /\$1\.{$suffix} [R=301,l]"
                            : "RewriteRule ^{$custom_post->query_var}/(.+)/\$ /\$1 [R=301,L]";
                if (strpos($content, $rewrite_rule) == false && $custom_post->_builtin == false)
                    $write[] = $rewrite_rule;
            }
            fclose($htaccess);
        }
        else {
            add_action('admin_notices', array(&$this, 'compatibility_notice'));
            return;
        }

        if (!empty($write) && is_writable($htaccess_filename)) {
            $new_rules = '# BEGIN ' . $this->htaccess_tag . PHP_EOL;
            $new_rules .= str_replace('$', '\\$', implode(PHP_EOL, $write)) . PHP_EOL;
            $new_rules .= '# END ' . $this->htaccess_tag;
            if (strpos($content, "# BEGIN {$this->htaccess_tag}") === false) {
                file_put_contents($htaccess_filename, $new_rules . PHP_EOL . PHP_EOL . $content);
            }
            else {
                $pattern = "/# BEGIN {$this->htaccess_tag}.*?# END {$this->htaccess_tag}/ims";
                $content = preg_replace($pattern, $new_rules, $content);
                file_put_contents($htaccess_filename, $content);
            }
        }
        else
            add_action('admin_notices', array(&$this, 'compatibility_notice'));
    }

    public function compatibility_notice() {
        global $wp_post_types;
        $rules = '';
        foreach ($wp_post_types as $type=>$custom_post) {
            if ($custom_post->_builtin == false) {
                $slug = str_replace('/', '', $custom_post->rewrite['slug']);
                $rules .= 'RewriteRule ^' . $slug . '/(.+)$ /$1 [R=301,L]<br />';
            }
        }

        echo '<div class="error fade" style="background-color:red;"><p><strong>Remove Slug Custom post type error!</strong><br />.htaccess is not writable, please add following lines to complete your installation: <br />'.$rules.'</p></div>';
    }
}

add_action('init', array('UWT_RemoveSlugCustomPostType', 'init'), 99);
register_activation_hook( __FILE__, array('UWT_RemoveSlugCustomPostType', 'flush_rewrite_rules') );
register_deactivation_hook( __FILE__, array('UWT_RemoveSlugCustomPostType', 'flush_rewrite_rules') );