bbp_format_buddypress_notifications( string $action, int $item_id, int $secondary_item_id, int $total_items, string $format = 'string' )

function bbp_format_buddypress_notifications( $action, $item_id, $secondary_item_id, $total_items, $format = 'string' ) {

	// New reply notifications
	if ( 'bbp_new_reply' === $action ) {
		$topic_id    = bbp_get_reply_topic_id( $item_id );
		$topic_title = bbp_get_topic_title( $topic_id );
		$topic_link  = wp_nonce_url( add_query_arg( array( 'action' => 'bbp_mark_read', 'topic_id' => $topic_id ), bbp_get_reply_url( $item_id ) ), 'bbp_mark_topic_' . $topic_id );
		$title_attr  = __( 'Discussion Replies', 'buddyboss' );

		if ( (int) $total_items > 1 ) {
			$text   = sprintf( __( 'You have %d new replies', 'buddyboss' ), (int) $total_items );
			$filter = 'bbp_multiple_new_subscription_notification';
		} else {
			if ( !empty( $secondary_item_id ) ) {
				$text = sprintf( __( 'You have %d new reply to %2$s from %3$s', 'buddyboss' ), (int) $total_items, $topic_title, bp_core_get_user_displayname( $secondary_item_id ) );
			} else {
				$text = sprintf( __( 'You have %d new reply to %s',             'buddyboss' ), (int) $total_items, $topic_title );
			}
			$filter = 'bbp_single_new_subscription_notification';
		}

		// WordPress Toolbar
		if ( 'string' === $format ) {
			$return = apply_filters( $filter, '<a href="' . esc_url( $topic_link ) . '" title="' . esc_attr( $title_attr ) . '">' . esc_html( $text ) . '</a>', (int) $total_items, $text, $topic_link );

		// Deprecated BuddyBar
		} else {
			$return = apply_filters( $filter, array(
				'text' => $text,
				'link' => $topic_link
			), $topic_link, (int) $total_items, $text, $topic_title );
		}

		/**
		 * @todo add title/description
		 *
		 * @since BuddyBoss 1.0.0
		 */
		do_action( 'bbp_format_buddypress_notifications', $action, $item_id, $secondary_item_id, $total_items );

		return $return;
	}
}