BP_Friends_Friendship::get_invitable_friend_count( int $user_id, int $group_id )

	public static function get_invitable_friend_count( $user_id, $group_id ) {

		// Setup some data we'll use below.
		$is_group_admin  = groups_is_user_admin( $user_id, $group_id );
		$friend_ids      = BP_Friends_Friendship::get_friend_user_ids( $user_id );
		$invitable_count = 0;

		for ( $i = 0, $count = count( $friend_ids ); $i < $count; ++$i ) {

			// If already a member, they cannot be invited again.
			if ( groups_is_user_member( (int) $friend_ids[$i], $group_id ) ) {
				continue;
			}

			// If user already has invite, they cannot be added.
			if ( groups_check_user_has_invite( (int) $friend_ids[$i], $group_id ) ) {
				continue;
			}

			// If user is not group admin and friend is banned, they cannot be invited.
			if ( ( false === $is_group_admin ) && groups_is_user_banned( (int) $friend_ids[$i], $group_id ) ) {
				continue;
			}

			$invitable_count++;
		}

		return $invitable_count;
	}