Determines whether the current user can access the current admin page.

function user_can_access_admin_page() {
	global $pagenow, $menu, $submenu, $_wp_menu_nopriv, $_wp_submenu_nopriv,
		$plugin_page, $_registered_pages;

	$parent = get_admin_page_parent();

	if ( ! isset( $plugin_page ) && isset( $_wp_submenu_nopriv[ $parent ][ $pagenow ] ) ) {
		return false;
	}

	if ( isset( $plugin_page ) ) {
		if ( isset( $_wp_submenu_nopriv[ $parent ][ $plugin_page ] ) ) {
			return false;
		}

		$hookname = get_plugin_page_hookname( $plugin_page, $parent );

		if ( ! isset( $_registered_pages[ $hookname ] ) ) {
			return false;
		}
	}

	if ( empty( $parent ) ) {
		if ( isset( $_wp_menu_nopriv[ $pagenow ] ) ) {
			return false;
		}
		if ( isset( $_wp_submenu_nopriv[ $pagenow ][ $pagenow ] ) ) {
			return false;
		}
		if ( isset( $plugin_page ) && isset( $_wp_submenu_nopriv[ $pagenow ][ $plugin_page ] ) ) {
			return false;
		}
		if ( isset( $plugin_page ) && isset( $_wp_menu_nopriv[ $plugin_page ] ) ) {
			return false;
		}

		foreach ( array_keys( $_wp_submenu_nopriv ) as $key ) {
			if ( isset( $_wp_submenu_nopriv[ $key ][ $pagenow ] ) ) {
				return false;
			}
			if ( isset( $plugin_page ) && isset( $_wp_submenu_nopriv[ $key ][ $plugin_page ] ) ) {
				return false;
			}
		}

		return true;
	}

	if ( isset( $plugin_page ) && $plugin_page === $parent && isset( $_wp_menu_nopriv[ $plugin_page ] ) ) {
		return false;
	}

	if ( isset( $submenu[ $parent ] ) ) {
		foreach ( $submenu[ $parent ] as $submenu_array ) {
			if ( isset( $plugin_page ) && $submenu_array[2] === $plugin_page ) {
				return current_user_can( $submenu_array[1] );
			} elseif ( $submenu_array[2] === $pagenow ) {
				return current_user_can( $submenu_array[1] );
			}
		}
	}

	foreach ( $menu as $menu_array ) {
		if ( $menu_array[2] === $parent ) {
			return current_user_can( $menu_array[1] );
		}
	}

	return true;
}