function bp_legacy_theme_mark_activity_favorite() {
	// Bail if not a POST action.
	if ( ! bp_is_post_request() ) {
		return;
	}

	if ( ! isset( $_POST['nonce'] ) ) {
		return;
	}

	// Either the 'mark' or 'unmark' nonce is accepted, for backward compatibility.
	$nonce = wp_unslash( $_POST['nonce'] );
	if ( ! wp_verify_nonce( $nonce, 'mark_favorite' ) && ! wp_verify_nonce( $nonce, 'unmark_favorite' ) ) {
		return;
	}

	$activity_id   = (int) $_POST['id'];
	$activity_item = new BP_Activity_Activity( $activity_id );
	if ( ! bp_activity_user_can_read( $activity_item, bp_loggedin_user_id() ) ) {
		return;
	}

	if ( bp_activity_add_user_favorite( $_POST['id'] ) )
		_e( 'Remove Favorite', 'buddypress' );
	else
		_e( 'Favorite', 'buddypress' );

	exit;
}