Virtual Page

class My_Virtual_Page {
    public function __construct() {
        add_action( 'init', array( $this, 'init' ) );
    }

    /**
     * Hook to add the virtual page
     */
    public function init() {
       if ( get_option( 'permalink_structure' ) ) {
            $param = trim( parse_url( $_SERVER['REQUEST_URI'], PHP_URL_PATH ), '/' );
        } else {
            parse_str( parse_url( $_SERVER['REQUEST_URI'], PHP_URL_QUERY ), $params );
            $param = ( isset( $params['page_id'] ) ? $params['page_id'] : false );
        }

        if( $param == 'my-payment-page' ) {
            //Enqueue any page specific styles and scripts here
            add_filter( 'the_posts', array( $this, 'my_virtual_payment_page' ) );
        }
    }

    /**
     * @param $posts
     * The virtual page filter
     *
     * @return array
     */
    function my_virtual_payment_page( $posts ) {
        global $wp, $wp_query;
       if(!$query->is_main_query()) {
return $posts;
}
        //Just double checking. Can be ignored.
        if ( strcasecmp( $wp->request, 'my-payment-page' ) !== 0 ) {
            return $posts;
        }

        $content = '<p>HTML Page content here!</p>';

        $post = $this->my_virtual_post_object( 'my-payment-page', __( 'Virtual payment page', 'domain' ), $content );

        // set filter results
        $posts = array( $post );

        // reset wp_query properties to simulate a found page
        $wp_query->is_page     = true;
        $wp_query->is_singular = true;
        $wp_query->is_home     = false;
        $wp_query->is_archive  = false;
        $wp_query->is_category = false;
        unset( $wp_query->query['error'] );
        $wp_query->query_vars['error'] = '';
        $wp_query->is_404              = false;

        return ( $posts );
    }

    /**
     * @param $slug
     * @param $title
     * @param $content
     *
     * Generate the post object dynamically
     *
     * @return stdClass
     */
    function my_virtual_post_object( $slug, $title, $content ) {
        $post                        = new stdClass;
        $post->ID                    = -1;
        $post->post_author           = 1;
        $post->post_date             = current_time( 'mysql' );
        $post->post_date_gmt         = current_time( 'mysql', 1 );
        $post->post_content          = $content;
        $post->post_title            = $title;
        $post->post_excerpt          = '';
        $post->post_status           = 'publish';
        $post->comment_status        = 'closed';
        $post->ping_status           = 'closed';
        $post->post_password         = '';
        $post->post_name             = $slug;
        $post->to_ping               = '';
        $post->pinged                = '';
        $post->modified              = $post->post_date;
        $post->modified_gmt          = $post->post_date_gmt;
        $post->post_content_filtered = '';
        $post->post_parent           = 0;
        $post->guid                  = get_home_url( 1, '/' . $slug );
        $post->menu_order            = 0;
        $post->post_type             = 'page';
        $post->post_mime_type        = '';
        $post->comment_count         = 0;

        return $post;
    }
}