BP_Friends_Friendship::update_bp_friends_cache( int $user_id, int|array|string $possible_friend_ids )

	public static function update_bp_friends_cache( $user_id, $possible_friend_ids ) {
		global $wpdb;
		$bp = buddypress();
		$possible_friend_ids = wp_parse_id_list( $possible_friend_ids );

		$fetch = array();
		foreach ( $possible_friend_ids as $friend_id ) {
			// Check for cached items in both friendship directions.
			if ( false === bp_core_get_incremented_cache( $user_id . ':' . $friend_id, 'bp_friends' ) 
				|| false === bp_core_get_incremented_cache( $friend_id . ':' . $user_id, 'bp_friends' ) ) {
				$fetch[] = $friend_id;
			}
		}
		if ( empty( $fetch ) ) {
			return;
		}

		$friend_ids_sql = implode( ',', array_unique( $fetch ) );
		$sql = $wpdb->prepare( "SELECT initiator_user_id, friend_user_id, is_confirmed FROM {$bp->friends->table_name} WHERE (initiator_user_id = %d AND friend_user_id IN ({$friend_ids_sql}) ) OR (initiator_user_id IN ({$friend_ids_sql}) AND friend_user_id = %d )", $user_id, $user_id );
		$friendships = $wpdb->get_results( $sql );

		// Use $handled to keep track of all of the $possible_friend_ids we've matched.
		$handled = array();
		foreach ( $friendships as $friendship ) {
			$initiator_user_id = (int) $friendship->initiator_user_id;
			$friend_user_id    = (int) $friendship->friend_user_id;
			if ( 1 === (int) $friendship->is_confirmed ) {
				$status_initiator = $status_friend = 'is_friend';
			} else {
				$status_initiator = 'pending'; 
				$status_friend    = 'awaiting_response';
			}
			bp_core_set_incremented_cache( $initiator_user_id . ':' . $friend_user_id, 'bp_friends', $status_initiator );
			bp_core_set_incremented_cache( $friend_user_id . ':' . $initiator_user_id, 'bp_friends', $status_friend );

			$handled[] = ( $initiator_user_id === $user_id ) ? $friend_user_id : $initiator_user_id;
		}

		// Set all those with no matching entry to "not friends" status.
		$not_friends = array_diff( $fetch, $handled );

		foreach ( $not_friends as $not_friend_id ) {
			bp_core_set_incremented_cache( $user_id . ':' . $not_friend_id, 'bp_friends', 'not_friends' );
			bp_core_set_incremented_cache( $not_friend_id . ':' . $user_id, 'bp_friends', 'not_friends' );
		}
	}