Admin page metaboxes

add_action( 'admin_menu', function() {
 
    $page = add_submenu_page(
        'edit.php',
        'My Page',
        'My Page',
        'edit',
        'ccom_sample_page',
        function() {
            ?>
             <div class="wrap">
                <?php screen_icon(); ?>
                <h1>My Page</h1>
                <form name="my_form" method="post">  
                    <input type="hidden" name="action" value="some-action">
                    <?php
                    wp_nonce_field( 'some-action-nonce' );
                    wp_nonce_field( 'meta-box-order', 'meta-box-order-nonce', false );
                    wp_nonce_field( 'closedpostboxes', 'closedpostboxesnonce', false );
                    $columns = get_current_screen()->get_columns() == 1 ? 1 : 2;
                    ?>
                    <div id="poststuff">
                        <div id="post-body" class="metabox-holder columns-<?php echo $columns; ?>">
                            <div id="postbox-container-1" class="postbox-container">
                                <?php do_meta_boxes( '', 'side', null ); ?>
                            </div>
                            <div id="postbox-container-2" class="postbox-container">
                                <?php do_meta_boxes( '', 'normal', null );  ?>
                                <?php do_meta_boxes( '', 'advanced', null ); ?>
                            </div>
                        </div>
                    </div>
                </form>
            </div>
            <?php
    } );
 
	add_action( 'load-' . $page, function() {
		do_action( 'add_meta_boxes_' . $page, null );
		do_action( 'add_meta_boxes', $page, null );
		add_screen_option( 'layout_columns', [ 'max' => 2, 'default' => 2 ] );
		wp_enqueue_script( 'postbox' );
	} );
 
	add_action( 'admin_footer-' . $page, function() {
		?>
		<script type="text/javascript">
		postboxes.add_postbox_toggles( pagenow );
		</script>
		<?php
	} );

} );

add_action(
	'add_meta_boxes',
	function() {

		add_meta_box(
			'sample-box',
			'Sample Box',
			function() {

				echo 'Sample Box Contents';

			},
			'posts_page_ ccom_sample_page', 
			'normal', 'high'
		);

		add_meta_box(
			'sample-sidebar',
			'Sample Sidebar',
			function() {

				echo 'Sample Sidebar Content';

			},
			null, 'side', 'high'
		);

	}

);