func (rb *ManagedRoomBinding) banAgent(ctx scope.Context, agentID proto.UserID, until time.Time) error {
	ban := &BannedAgent{
		AgentID: agentID.String(),
		Room: sql.NullString{
			String: rb.Name,
			Valid:  true,
		},
		Created: time.Now(),
		Expires: gorp.NullTime{
			Time:  until,
			Valid: !until.IsZero(),
		},
	}

	// Loop within transaction in read committed mode to simulate UPSERT.
	t, err := rb.DbMap.Begin()
	if err != nil {
		return err
	}
	for {
		// Try to insert; if this fails due to duplicate key value, try to update.
		if err := rb.DbMap.Insert(ban); err != nil {
			if !strings.HasPrefix(err.Error(), "pq: duplicate key value") {
				rollback(ctx, t)
				return err
			}
		} else {
			break
		}
		n, err := rb.DbMap.Update(ban)
		if err != nil {
			rollback(ctx, t)
			return err
		}
		if n > 0 {
			break
		}
	}

	bounceEvent := &proto.BounceEvent{Reason: "banned", AgentID: agentID}
	if err := rb.broadcast(ctx, t, proto.BounceEventType, bounceEvent); err != nil {
		rollback(ctx, t)
		return err
	}

	if err := t.Commit(); err != nil {
		return err
	}

	return nil
}

func (b *TestBackend) NotifyUser(ctx scope.Context, userID proto.UserID, packetType proto.PacketType, payload interface{}, excluding ...proto.Session) error {
	kind, id := userID.Parse()
	for _, room := range b.rooms {
		mRoom, _ := room.(*memRoom)
		for u, sessList := range mRoom.live {
			for _, sess := range sessList {
				if u == userID || (kind == "agent" && sess.AgentID() == id) {
					if !isExcluded(sess, excluding) {
						if err := sess.Send(ctx, packetType, payload); err != nil {
							return err
						}
					}
				}
			}
		}
	}
	return nil
}

func (rb *RoomBinding) banAgent(ctx scope.Context, agentID proto.UserID, until time.Time) error {
	ban := &BannedAgent{
		AgentID: agentID.String(),
		Room: sql.NullString{
			String: rb.Name,
			Valid:  true,
		},
		Created: time.Now(),
		Expires: gorp.NullTime{
			Time:  until,
			Valid: !until.IsZero(),
		},
	}

	if err := rb.DbMap.Insert(ban); err != nil {
		return err
	}

	bounceEvent := &proto.BounceEvent{Reason: "banned", AgentID: agentID.String()}
	return rb.broadcast(ctx, rb.Room, proto.BounceEventType, bounceEvent)
}

func (lm ListenerMap) NotifyUser(ctx scope.Context, userID proto.UserID, event *proto.Packet, exclude ...string) error {
	excludeSet := map[string]struct{}{}
	for _, exc := range exclude {
		excludeSet[exc] = struct{}{}
	}
	payload, err := event.Payload()
	if err != nil {
		return err
	}
	kind, id := userID.Parse()
	for sessionID, listener := range lm {
		// check that the listener is not excluded
		if _, ok := excludeSet[sessionID]; ok {
			continue
		}

		if listener.Identity().ID() == userID || (kind == "agent" && id == listener.AgentID()) {
			listener.Send(ctx, event.Type, payload)
		}
	}
	return nil
}

func (rb *ManagedRoomBinding) unbanAgent(ctx scope.Context, agentID proto.UserID) error {
	_, err := rb.DbMap.Exec(
		"DELETE FROM banned_agent WHERE agent_id = $1 AND room = $2", agentID.String(), rb.Name)
	return err
}

func (b *Backend) unbanAgent(ctx scope.Context, rb *RoomBinding, agentID proto.UserID) error {
	switch rb {
	case global:
		_, err := b.DbMap.Exec("DELETE FROM banned_agent WHERE room IS NULL AND agent_id = $1", agentID.String())
		return err
	default:
		_, err := b.DbMap.Exec("DELETE FROM banned_agent WHERE room = $1 AND agent_id = $2", rb.RoomName, agentID.String())
		return err
	}
}

func (t *PMTracker) Initiate(
	ctx scope.Context, kms security.KMS, room proto.Room, client *proto.Client, recipient proto.UserID) (
	snowflake.Snowflake, error) {

	initiatorNick, ok, err := room.ResolveNick(ctx, proto.UserID(fmt.Sprintf("account:%s", client.Account.ID())))
	if err != nil {
		return 0, err
	}
	if !ok {
		initiatorNick = fmt.Sprintf("account:%s", client.Account.ID())
	}

	recipientNick, ok, err := room.ResolveNick(ctx, recipient)
	if err != nil {
		return 0, err
	}
	if !ok {
		recipientNick = string(recipient)
	}

	pm, err := proto.InitiatePM(ctx, t.Backend, kms, client, initiatorNick, recipient, recipientNick)
	if err != nil {
		return 0, err
	}
	row := &PM{
		ID:                    pm.ID.String(),
		Initiator:             pm.Initiator.String(),
		InitiatorNick:         pm.InitiatorNick,
		Receiver:              string(pm.Receiver),
		ReceiverNick:          pm.ReceiverNick,
		ReceiverMAC:           pm.ReceiverMAC,
		IV:                    pm.IV,
		EncryptedSystemKey:    pm.EncryptedSystemKey.Ciphertext,
		EncryptedInitiatorKey: pm.EncryptedInitiatorKey.Ciphertext,
	}
	if pm.EncryptedReceiverKey != nil {
		row.EncryptedReceiverKey = pm.EncryptedReceiverKey.Ciphertext
	}

	// Look for existing PM to reuse.
	tx, err := t.DbMap.Begin()
	if err != nil {
		return 0, err
	}

	var existingRow PM
	err = tx.SelectOne(
		&existingRow,
		"SELECT id FROM pm WHERE initiator = $1 AND receiver = $2",
		client.Account.ID().String(), string(recipient))
	if err != nil && err != sql.ErrNoRows {
		rollback(ctx, tx)
		return 0, err
	}
	if err == nil {
		rollback(ctx, tx)
		var pmID snowflake.Snowflake
		if err := pmID.FromString(existingRow.ID); err != nil {
			return 0, err
		}
		return pmID, nil
	}

	kind, id := recipient.Parse()
	if kind == "account" {
		var existingRow PM
		err = tx.SelectOne(
			&existingRow,
			"SELECT id FROM pm WHERE initiator = $1 AND receiver = $2",
			id, string(client.UserID()))
		if err != nil && err != sql.ErrNoRows {
			rollback(ctx, tx)
			return 0, err
		}
		if err == nil {
			rollback(ctx, tx)
			var pmID snowflake.Snowflake
			if err := pmID.FromString(existingRow.ID); err != nil {
				return 0, err
			}
			return pmID, nil
		}
	}

	if err := tx.Insert(row); err != nil {
		rollback(ctx, tx)
		return 0, err
	}

	if err := tx.Commit(); err != nil {
		return 0, err
	}

	return pm.ID, nil
}