Groups 404 Redirect to page/post with original url

Index: wp-content/plugins/groups-404-redirect/groups-404-redirect.php
IDEA additional info:
Subsystem: com.intellij.openapi.diff.impl.patch.CharsetEP
<+>UTF-8
===================================================================
--- wp-content/plugins/groups-404-redirect/groups-404-redirect.php  (date 1459415116000)
+++ wp-content/plugins/groups-404-redirect/groups-404-redirect.php  (revision )
@@ -129,6 +129,12 @@
                Groups_Options::delete_option( 'groups-404-redirect-post-id' );
            }

+           if ( !empty( $_POST['post_param'] ) ) {
+               Groups_Options::update_option( 'groups-404-redirect-post-param', $_POST['post_param'] );
+           } else {
+               Groups_Options::delete_option( 'groups-404-redirect-post-param' );
+           }
+
            Groups_Options::update_option( 'groups-404-redirect-restricted-terms', !empty( $_POST['redirect_restricted_terms'] ) );

            if ( key_exists( $_POST['status'], $http_status_codes ) ) {
@@ -143,6 +149,7 @@

        $redirect_to     = Groups_Options::get_option( 'groups-404-redirect-to', 'post' );
        $post_id         = Groups_Options::get_option( 'groups-404-redirect-post-id', '' );
+       $post_param      = Groups_Options::get_option( 'groups-404-redirect-post-param', '' );
        $redirect_status = Groups_Options::get_option( 'groups-404-redirect-status', '301' );
        $redirect_restricted_terms = Groups_Options::get_option( 'groups-404-redirect-restricted-terms', false );

@@ -188,6 +195,16 @@
        echo __( 'If the <strong>Redirect to the WordPress login</strong> option is chosen instead, visitors who are logged in but may not access a requested page, can be redirected to a specific page by setting the Page or Post ID here.', GROUPS_404_REDIRECT_PLUGIN_DOMAIN );
        echo '</p>';

+       echo '<label>';
+       echo __( 'Parameter name', GROUPS_404_REDIRECT_PLUGIN_DOMAIN );
+       echo ' ';
+       echo sprintf( '<input type="text" name="post_param" value="%s" />', $post_param );
+       echo '</label>';
+
+       echo '<p class="description">';
+       echo __( 'Indicate the parameter name which gets the original url requested when redirecting to given page or post.', GROUPS_404_REDIRECT_PLUGIN_DOMAIN );
+       echo '</p>';
+
        echo '</div>';

        echo '<br/>';
@@ -281,6 +298,7 @@
            if ( self::groups_is_active() ) {
                $redirect_to     = Groups_Options::get_option( 'groups-404-redirect-to', 'post' );
                $post_id         = Groups_Options::get_option( 'groups-404-redirect-post-id', '' );
+               $post_param      = Groups_Options::get_option( 'groups-404-redirect-post-param', '' );
                $redirect_status = intval( Groups_Options::get_option( 'groups-404-redirect-status', '301' ) );

                $current_url = ( is_ssl() ? 'https://' : 'http://' ) . $_SERVER['HTTP_HOST'] . $_SERVER['REQUEST_URI'];
@@ -328,15 +346,19 @@

                            default: // 'post'
                                if ( empty( $post_id ) ) {
-                                   wp_redirect( get_home_url(), $redirect_status );
+                                   $redirect_url = get_home_url();
                                } else {
                                    $post_id = apply_filters( 'groups_404_redirect_post_id', $post_id, $current_post_id, $current_url );
                                    if ( $post_id != $current_post_id ) {
-                                       wp_redirect( get_permalink( $post_id ), $redirect_status );
+                                       $redirect_url = get_permalink( $post_id );
                                    } else {
                                        return;
                                    }
                                }
+                               if ( !empty( $post_param ) ) {
+                                   $redirect_url .= (parse_url($redirect_url, PHP_URL_QUERY) ? '&' : '?') . $post_param . '=' . rawurlencode($current_url);
+                               }
+                               wp_redirect( $redirect_url, $redirect_status );
                                exit;

                        }