bp_get_mutual_friendships( int $user_id )

function bp_get_mutual_friendships( $user_id = 0 ) {

    if ( ! bp_loggedin_user_id() ) {
        return 0;
    }

	if ( !$user_id ) {
		$user_id = bp_displayed_user_id();
	}

	if ( !$user_id ) {
		return 0;
	}

	// get displayed user's connections
	$displayed_user_friends = friends_get_friend_user_ids( $user_id );

	// get logged in user's connections
	$logged_in_user_friends = friends_get_friend_user_ids( bp_loggedin_user_id() );

	$mutual_friends = array_intersect( $logged_in_user_friends, $displayed_user_friends );

	if ( !empty( $mutual_friends ) ) {
		$mutual_friends = implode( ',', (array) $mutual_friends );
	} else {
		$mutual_friends = 0;
	}

	/**
	 * Filters the total mutual connections for a user.
	 *
	 * @since BuddyBoss 1.0.0
	 *
	 * @param array|int $requests An array of user IDs if found, or a 0 if none are found.
	 * @param int       $user_id  ID of the queried user.
	 */
	return apply_filters( 'bp_get_mutual_friendships', $mutual_friends, $user_id );
}