register_post_status()

function register_post_status( $post_status, $args = array() ) {
	global $gc_post_statuses;

	if ( ! is_array( $gc_post_statuses ) ) {
		$gc_post_statuses = array();
	}

	// Args prefixed with an underscore are reserved for internal use.
	$defaults = array(
		'label'                     => false,
		'label_count'               => false,
		'exclude_from_search'       => null,
		'_builtin'                  => false,
		'public'                    => null,
		'internal'                  => null,
		'protected'                 => null,
		'private'                   => null,
		'publicly_queryable'        => null,
		'show_in_admin_status_list' => null,
		'show_in_admin_all_list'    => null,
		'date_floating'             => null,
	);
	$args     = gc_parse_args( $args, $defaults );
	$args     = (object) $args;

	$post_status = sanitize_key( $post_status );
	$args->name  = $post_status;

	// Set various defaults.
	if ( null === $args->public && null === $args->internal && null === $args->protected && null === $args->private ) {
		$args->internal = true;
	}

	if ( null === $args->public ) {
		$args->public = false;
	}

	if ( null === $args->private ) {
		$args->private = false;
	}

	if ( null === $args->protected ) {
		$args->protected = false;
	}

	if ( null === $args->internal ) {
		$args->internal = false;
	}

	if ( null === $args->publicly_queryable ) {
		$args->publicly_queryable = $args->public;
	}

	if ( null === $args->exclude_from_search ) {
		$args->exclude_from_search = $args->internal;
	}

	if ( null === $args->show_in_admin_all_list ) {
		$args->show_in_admin_all_list = ! $args->internal;
	}

	if ( null === $args->show_in_admin_status_list ) {
		$args->show_in_admin_status_list = ! $args->internal;
	}

	if ( null === $args->date_floating ) {
		$args->date_floating = false;
	}

	if ( false === $args->label ) {
		$args->label = $post_status;
	}

	if ( false === $args->label_count ) {
		// phpcs:ignore GeChiUI.GC.I18n.NonSingularStringLiteralSingle,GeChiUI.GC.I18n.NonSingularStringLiteralPlural
		$args->label_count = _n_noop( $args->label, $args->label );
	}

	$gc_post_statuses[ $post_status ] = $args;

	return $args;
}

/**
 * Add 'Unread' post status.
 */
function gcdocs_custom_post_status(){
	register_post_status( 'unread', array(
		'label'                     => _x( 'Unread', 'post' ),
		'public'                    => true,
		'exclude_from_search'       => false,
		'show_in_admin_all_list'    => true,
		'show_in_admin_status_list' => true,
		'label_count'               => _n_noop( 'Unread <span class="count">(%s)</span>', 'Unread <span class="count">(%s)</span>' ),
	) );
}
add_action( 'init', 'gcdocs_custom_post_status' );