class-wpwsl-general.php

<?php

class WPWSL_General
{

    private $file_general_tpl = '_general.php';
    private $file_edit_tpl = '_edit.php';
    private static $_instance;

    /**
     * Start up
     */
    public static function get_instance()
    {
        if (!isset(self::$_instance)) {
            self::$_instance = new self();
        }
        return self::$_instance;
    }

    private function __clone()
    {
        
    }

    private function __construct()
    {
        add_action('admin_menu', [
            $this,
            'add_plugin_page']);
    }

    /**
     * Add page
     */
    public function add_plugin_page()
    {
        // This page will be under Content manage section.
        $parent_slug = WPWSL_GENERAL_PAGE;
        $page_title = __('WeChat Subscribers', 'WPWSL');
        $menu_title = __('Custom Replies', 'WPWSL');
        $capability = 'edit_pages';
        $menu_slug = WPWSL_GENERAL_PAGE;
        add_submenu_page(
            $parent_slug, $page_title, $menu_title, $capability, $menu_slug, [
            $this,
            'create_admin_page']
        );
    }

    /**
     * Options page callback
     */
    public function create_admin_page()
    {
        if (isset($_GET['edit'])) {
            require_once( $this->file_edit_tpl);
        } else {
            require_once( $this->file_general_tpl);
        }
    }

}