/*
Copyright 2015, 2016 OpenMarket Ltd
Copyright 2017 New Vector Ltd
Copyright 2019, 2020 The Matrix.org Foundation C.I.C.

Licensed under the Apache License, Version 2.0 (the "License");
you may not use this file except in compliance with the License.
You may obtain a copy of the License at

    http://www.apache.org/licenses/LICENSE-2.0

Unless required by applicable law or agreed to in writing, software
distributed under the License is distributed on an "AS IS" BASIS,
WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
See the License for the specific language governing permissions and
limitations under the License.
*/

/**
 * This is an internal module. See {@link createNewMatrixCall} for the public API.
 * @module webrtc/call
 */

import {logger} from '../logger';
import {EventEmitter} from 'events';
import * as utils from '../utils';
import MatrixEvent from '../models/event';
import {EventType} from '../@types/event';
import { RoomMember } from '../models/room-member';
import { randomString } from '../randomstring';
import { MCallReplacesEvent, MCallAnswer, MCallOfferNegotiate, CallCapabilities } from './callEventTypes';

// events: hangup, error(err), replaced(call), state(state, oldState)

/**
 * Fires whenever an error occurs when call.js encounters an issue with setting up the call.
 * <p>
 * The error given will have a code equal to either `MatrixCall.ERR_LOCAL_OFFER_FAILED` or
 * `MatrixCall.ERR_NO_USER_MEDIA`. `ERR_LOCAL_OFFER_FAILED` is emitted when the local client
 * fails to create an offer. `ERR_NO_USER_MEDIA` is emitted when the user has denied access
 * to their audio/video hardware.
 *
 * @event module:webrtc/call~MatrixCall#"error"
 * @param {Error} err The error raised by MatrixCall.
 * @example
 * matrixCall.on("error", function(err){
 *   console.error(err.code, err);
 * });
 */

interface CallOpts {
    roomId?: string,
    client?: any, // Fix when client is TSified
    forceTURN?: boolean,
    turnServers?: Array<TurnServer>,
}

interface TurnServer {
    urls: Array<string>,
    username?: string,
    password?: string,
    ttl?: number,
}

export enum CallState {
    Fledgling = 'fledgling',
    InviteSent = 'invite_sent',
    WaitLocalMedia = 'wait_local_media',
    CreateOffer = 'create_offer',
    CreateAnswer = 'create_answer',
    Connecting = 'connecting',
    Connected = 'connected',
    Ringing = 'ringing',
    Ended = 'ended',
}

export enum CallType {
    Voice = 'voice',
    Video = 'video',
}

export enum CallDirection {
    Inbound = 'inbound',
    Outbound = 'outbound',
}

export enum CallParty {
    Local = 'local',
    Remote = 'remote',
}

export enum CallEvent {
    Hangup = 'hangup',
    State = 'state',
    Error = 'error',
    Replaced = 'replaced',

    // The value of isLocalOnHold() has changed
    LocalHoldUnhold = 'local_hold_unhold',
    // The value of isRemoteOnHold() has changed
    RemoteHoldUnhold = 'remote_hold_unhold',
    // backwards compat alias for LocalHoldUnhold: remove in a major version bump
    HoldUnhold = 'hold_unhold',
}

export enum CallErrorCode {
    /** The user chose to end the call */
    UserHangup = 'user_hangup',

    /** An error code when the local client failed to create an offer. */
    LocalOfferFailed = 'local_offer_failed',
    /**
     * An error code when there is no local mic/camera to use. This may be because
     * the hardware isn't plugged in, or the user has explicitly denied access.
     */
    NoUserMedia = 'no_user_media',

    /**
     * Error code used when a call event failed to send
     * because unknown devices were present in the room
     */
    UnknownDevices = 'unknown_devices',

    /**
     * Error code usewd when we fail to send the invite
     * for some reason other than there being unknown devices
     */
    SendInvite = 'send_invite',

    /**
     * An answer could not be created
     */
    CreateAnswer = 'create_answer',

    /**
     * Error code usewd when we fail to send the answer
     * for some reason other than there being unknown devices
     */
    SendAnswer = 'send_answer',

    /**
     * The session description from the other side could not be set
     */
    SetRemoteDescription = 'set_remote_description',

    /**
     * The session description from this side could not be set
     */
    SetLocalDescription = 'set_local_description',

    /**
     * A different device answered the call
     */
    AnsweredElsewhere = 'answered_elsewhere',

    /**
     * No media connection could be established to the other party
     */
    IceFailed = 'ice_failed',

    /**
     * The invite timed out whilst waiting for an answer
     */
    InviteTimeout = 'invite_timeout',

    /**
     * The call was replaced by another call
     */
    Replaced = 'replaced',

    /**
     * Signalling for the call could not be sent (other than the initial invite)
     */
    SignallingFailed = 'signalling_timeout',
}

enum ConstraintsType {
    Audio = "audio",
    Video = "video",
}

/**
 * The version field that we set in m.call.* events
 */
const VOIP_PROTO_VERSION = 1;

/** The fallback ICE server to use for STUN or TURN protocols. */
const FALLBACK_ICE_SERVER = 'stun:turn.matrix.org';

/** The length of time a call can be ringing for. */
const CALL_TIMEOUT_MS = 60000;

/** Retrieves sources from desktopCapturer */
export function getDesktopCapturerSources(): Promise<Array<DesktopCapturerSource>> {
    const options: GetSourcesOptions = {
        thumbnailSize: {
            height: 176,
            width: 312,
        },
        types: [
            "screen",
            "window",
        ],
    };
    return window.electron.getDesktopCapturerSources(options);
}

export class CallError extends Error {
    code : string;

    constructor(code : CallErrorCode, msg: string, err: Error) {
        // Stil ldon't think there's any way to have proper nested errors
        super(msg + ": " + err);

        this.code = code;
    }
}

function genCallID(): string {
    return Date.now().toString() + randomString(16);
}

/**
 * Construct a new Matrix Call.
 * @constructor
 * @param {Object} opts Config options.
 * @param {string} opts.roomId The room ID for this call.
 * @param {Object} opts.webRtc The WebRTC globals from the browser.
 * @param {boolean} opts.forceTURN whether relay through TURN should be forced.
 * @param {Object} opts.URL The URL global.
 * @param {Array<Object>} opts.turnServers Optional. A list of TURN servers.
 * @param {MatrixClient} opts.client The Matrix Client instance to send events to.
 */
export class MatrixCall extends EventEmitter {
    roomId: string;
    type: CallType;
    callId: string;
    state: CallState;
    hangupParty: CallParty;
    hangupReason: string;
    direction: CallDirection;
    ourPartyId: string;

    private client: any; // Fix when client is TSified
    private forceTURN: boolean;
    private turnServers: Array<TurnServer>;
    private candidateSendQueue: Array<RTCIceCandidate>;
    private candidateSendTries: number;
    private sentEndOfCandidates: boolean;
    private peerConn: RTCPeerConnection;
    private localVideoElement: HTMLVideoElement;
    private remoteVideoElement: HTMLVideoElement;
    private remoteAudioElement: HTMLAudioElement;
    private screenSharingStream: MediaStream;
    private remoteStream: MediaStream;
    private localAVStream: MediaStream;
    private inviteOrAnswerSent: boolean;
    private waitForLocalAVStream: boolean;
    // XXX: I don't know why this is called 'config'.
    private config: MediaStreamConstraints;
    private successor: MatrixCall;
    private opponentMember: RoomMember;
    private opponentVersion: number;
    // The party ID of the other side: undefined if we haven't chosen a partner
    // yet, null if we have but they didn't send a party ID.
    private opponentPartyId: string;
    private opponentCaps: CallCapabilities;
    private inviteTimeout: NodeJS.Timeout; // in the browser it's 'number'

    // The logic of when & if a call is on hold is nontrivial and explained in is*OnHold
    // This flag represents whether we want the other party to be on hold
    private remoteOnHold;

    // and this one we set when we're transitioning out of the hold state because we
    // can't tell the difference between that and the other party holding us
    private unholdingRemote;

    private micMuted;
    private vidMuted;

    // the stats for the call at the point it ended. We can't get these after we
    // tear the call down, so we just grab a snapshot before we stop the call.
    // The typescript definitions have this type as 'any' :(
    private callStatsAtEnd: any[];

    // Perfect negotiation state: https://www.w3.org/TR/webrtc/#perfect-negotiation-example
    private makingOffer: boolean;
    private ignoreOffer: boolean;

    // If candidates arrive before we've picked an opponent (which, in particular,
    // will happen if the opponent sends candidates eagerly before the user answers
    // the call) we buffer them up here so we can then add the ones from the party we pick
    private remoteCandidateBuffer = new Map<string, RTCIceCandidate[]>();

    constructor(opts: CallOpts) {
        super();
        this.roomId = opts.roomId;
        this.client = opts.client;
        this.type = null;
        this.forceTURN = opts.forceTURN;
        this.ourPartyId = this.client.deviceId;
        // Array of Objects with urls, username, credential keys
        this.turnServers = opts.turnServers || [];
        if (this.turnServers.length === 0 && this.client.isFallbackICEServerAllowed()) {
            this.turnServers.push({
                urls: [FALLBACK_ICE_SERVER],
            });
        }
        for (const server of this.turnServers) {
            utils.checkObjectHasKeys(server, ["urls"]);
        }

        this.callId = genCallID();
        this.state = CallState.Fledgling;

        // A queue for candidates waiting to go out.
        // We try to amalgamate candidates into a single candidate message where
        // possible
        this.candidateSendQueue = [];
        this.candidateSendTries = 0;

        this.sentEndOfCandidates = false;
        this.inviteOrAnswerSent = false;
        this.makingOffer = false;

        this.remoteOnHold = false;
        this.unholdingRemote = false;
        this.micMuted = false;
        this.vidMuted = false;
    }

    /**
     * Place a voice call to this room.
     * @throws If you have not specified a listener for 'error' events.
     */
    async placeVoiceCall() {
        logger.debug("placeVoiceCall");
        this.checkForErrorListener();
        const constraints = getUserMediaContraints(ConstraintsType.Audio);
        this.type = CallType.Voice;
        await this.placeCallWithConstraints(constraints);
    }

    /**
     * Place a video call to this room.
     * @param {Element} remoteVideoElement a <code>&lt;video&gt;</code> DOM element
     * to render video to.
     * @param {Element} localVideoElement a <code>&lt;video&gt;</code> DOM element
     * to render the local camera preview.
     * @throws If you have not specified a listener for 'error' events.
     */
    async placeVideoCall(remoteVideoElement: HTMLVideoElement, localVideoElement: HTMLVideoElement) {
        logger.debug("placeVideoCall");
        this.checkForErrorListener();
        this.localVideoElement = localVideoElement;
        this.remoteVideoElement = remoteVideoElement;
        const constraints = getUserMediaContraints(ConstraintsType.Video);
        this.type = CallType.Video;
        await this.placeCallWithConstraints(constraints);
    }

    /**
     * Place a screen-sharing call to this room. This includes audio.
     * <b>This method is EXPERIMENTAL and subject to change without warning. It
     * only works in Google Chrome and Firefox >= 44.</b>
     * @param {Element} remoteVideoElement a <code>&lt;video&gt;</code> DOM element
     * to render video to.
     * @param {Element} localVideoElement a <code>&lt;video&gt;</code> DOM element
     * to render the local camera preview.
     * @throws If you have not specified a listener for 'error' events.
     */
    async placeScreenSharingCall(
        remoteVideoElement: HTMLVideoElement,
        localVideoElement: HTMLVideoElement,
        selectDesktopCapturerSource?: () => Promise<DesktopCapturerSource>,
    ) {
        logger.debug("placeScreenSharingCall");
        this.checkForErrorListener();
        this.localVideoElement = localVideoElement;
        this.remoteVideoElement = remoteVideoElement;

        try {
            const screenshareConstraints = await getScreenshareContraints(selectDesktopCapturerSource);
            if (!screenshareConstraints) {
                this.terminate(CallParty.Local, CallErrorCode.NoUserMedia, false);
                return;
            }

            if (window.electron?.getDesktopCapturerSources) {
                // We are using Electron
                logger.debug("Getting screen stream using getUserMedia()...");
                this.screenSharingStream = await navigator.mediaDevices.getUserMedia(screenshareConstraints);
            } else {
                // We are not using Electron
                logger.debug("Getting screen stream using getDisplayMedia()...");
                this.screenSharingStream = await navigator.mediaDevices.getDisplayMedia(screenshareConstraints);
            }

            logger.debug("Got screen stream, requesting audio stream...");
            const audioConstraints = getUserMediaContraints(ConstraintsType.Audio);
            this.placeCallWithConstraints(audioConstraints);
        } catch (err) {
            this.emit(CallEvent.Error,
                new CallError(
                    CallErrorCode.NoUserMedia,
                    "Failed to get screen-sharing stream: ", err,
                ),
            );
            this.terminate(CallParty.Local, CallErrorCode.NoUserMedia, false);
        }
        this.type = CallType.Video;
    }

    public getOpponentMember() {
        return this.opponentMember;
    }

    public opponentCanBeTransferred() {
        return Boolean(this.opponentCaps && this.opponentCaps["m.call.transferee"]);
    }

    /**
     * Retrieve the local <code>&lt;video&gt;</code> DOM element.
     * @return {Element} The dom element
     */
    public getLocalVideoElement(): HTMLVideoElement {
        return this.localVideoElement;
    }

    /**
     * Retrieve the remote <code>&lt;video&gt;</code> DOM element
     * used for playing back video capable streams.
     * @return {Element} The dom element
     */
    public getRemoteVideoElement(): HTMLVideoElement {
        return this.remoteVideoElement;
    }

    /**
     * Retrieve the remote <code>&lt;audio&gt;</code> DOM element
     * used for playing back audio only streams.
     * @return {Element} The dom element
     */
    public getRemoteAudioElement(): HTMLAudioElement {
        return this.remoteAudioElement;
    }

    /**
     * Set the local <code>&lt;video&gt;</code> DOM element. If this call is active,
     * video will be rendered to it immediately.
     * @param {Element} element The <code>&lt;video&gt;</code> DOM element.
     */
    public async setLocalVideoElement(element : HTMLVideoElement) {
        this.localVideoElement = element;

        if (element && this.localAVStream && this.type === CallType.Video) {
            element.autoplay = true;

            element.srcObject = this.localAVStream;
            element.muted = true;
            try {
                await element.play();
            } catch (e) {
                logger.info("Failed to play local video element", e);
            }
        }
    }

    /**
     * Set the remote <code>&lt;video&gt;</code> DOM element. If this call is active,
     * the first received video-capable stream will be rendered to it immediately.
     * @param {Element} element The <code>&lt;video&gt;</code> DOM element.
     */
    public setRemoteVideoElement(element : HTMLVideoElement) {
        if (element === this.remoteVideoElement) return;

        element.autoplay = true;

        // if we already have an audio element set, use that instead and mute the audio
        // on this video element.
        if (this.remoteAudioElement) element.muted = true;

        this.remoteVideoElement = element;

        if (this.remoteStream) {
            this.playRemoteVideo();
        }
    }

    /**
     * Set the remote <code>&lt;audio&gt;</code> DOM element. If this call is active,
     * the first received audio-only stream will be rendered to it immediately.
     * The audio will *not* be rendered from the remoteVideoElement.
     * @param {Element} element The <code>&lt;video&gt;</code> DOM element.
     */
    public async setRemoteAudioElement(element: HTMLAudioElement) {
        if (element === this.remoteAudioElement) return;

        this.remoteAudioElement = element;

        if (this.remoteStream) this.playRemoteAudio();
    }

    // The typescript definitions have this type as 'any' :(
    public async getCurrentCallStats(): Promise<any[]> {
        if (this.callHasEnded()) {
            return this.callStatsAtEnd;
        }

        return this.collectCallStats();
    }

    private async collectCallStats(): Promise<any[]> {
        // This happens when the call fails before it starts.
        // For example when we fail to get capture sources
        if (!this.peerConn) return;

        const statsReport = await this.peerConn.getStats();
        const stats = [];
        for (const item of statsReport) {
            stats.push(item[1]);
        }

        return stats;
    }

    /**
     * Configure this call from an invite event. Used by MatrixClient.
     * @param {MatrixEvent} event The m.call.invite event
     */
    async initWithInvite(event: MatrixEvent) {
        const invite = event.getContent();
        this.direction = CallDirection.Inbound;

        // make sure we have valid turn creds. Unless something's gone wrong, it should
        // poll and keep the credentials valid so this should be instant.
        const haveTurnCreds = await this.client._checkTurnServers();
        if (!haveTurnCreds) {
            logger.warn("Failed to get TURN credentials! Proceeding with call anyway...");
        }

        this.peerConn = this.createPeerConnection();
        // we must set the party ID before await-ing on anything: the call event
        // handler will start giving us more call events (eg. candidates) so if
        // we haven't set the party ID, we'll ignore them.
        this.chooseOpponent(event);
        try {
            await this.peerConn.setRemoteDescription(invite.offer);
            await this.addBufferedIceCandidates();
        } catch (e) {
            logger.debug("Failed to set remote description", e);
            this.terminate(CallParty.Local, CallErrorCode.SetRemoteDescription, false);
            return;
        }

        // According to previous comments in this file, firefox at some point did not
        // add streams until media started ariving on them. Testing latest firefox
        // (81 at time of writing), this is no longer a problem, so let's do it the correct way.
        if (!this.remoteStream || this.remoteStream.getTracks().length === 0) {
            logger.error("No remote stream or no tracks after setting remote description!");
            this.terminate(CallParty.Local, CallErrorCode.SetRemoteDescription, false);
            return;
        }

        this.type = this.remoteStream.getTracks().some(t => t.kind === 'video') ? CallType.Video : CallType.Voice;

        this.setState(CallState.Ringing);

        if (event.getLocalAge()) {
            setTimeout(() => {
                if (this.state == CallState.Ringing) {
                    logger.debug("Call invite has expired. Hanging up.");
                    this.hangupParty = CallParty.Remote; // effectively
                    this.setState(CallState.Ended);
                    this.stopAllMedia();
                    if (this.peerConn.signalingState != 'closed') {
                        this.peerConn.close();
                    }
                    this.emit(CallEvent.Hangup);
                }
            }, invite.lifetime - event.getLocalAge());
        }
    }

    /**
     * Configure this call from a hangup or reject event. Used by MatrixClient.
     * @param {MatrixEvent} event The m.call.hangup event
     */
    initWithHangup(event: MatrixEvent) {
        // perverse as it may seem, sometimes we want to instantiate a call with a
        // hangup message (because when getting the state of the room on load, events
        // come in reverse order and we want to remember that a call has been hung up)
        this.setState(CallState.Ended);
    }

    /**
     * Answer a call.
     */
    async answer() {
        if (this.inviteOrAnswerSent) {
            return;
        }

        logger.debug(`Answering call ${this.callId} of type ${this.type}`);

        if (!this.localAVStream && !this.waitForLocalAVStream) {
            const constraints = getUserMediaContraints(
                this.type == CallType.Video ?
                    ConstraintsType.Video:
                    ConstraintsType.Audio,
            );
            logger.log("Getting user media with constraints", constraints);
            this.setState(CallState.WaitLocalMedia);
            this.waitForLocalAVStream = true;

            try {
                const mediaStream = await navigator.mediaDevices.getUserMedia(constraints);
                this.waitForLocalAVStream = false;
                this.gotUserMediaForAnswer(mediaStream);
            } catch (e) {
                this.getUserMediaFailed(e);
                return
            }
        } else if (this.localAVStream) {
            this.gotUserMediaForAnswer(this.localAVStream);
        } else if (this.waitForLocalAVStream) {
            this.setState(CallState.WaitLocalMedia);
        }
    }

    /**
     * Replace this call with a new call, e.g. for glare resolution. Used by
     * MatrixClient.
     * @param {MatrixCall} newCall The new call.
     */
    replacedBy(newCall: MatrixCall) {
        logger.debug(this.callId + " being replaced by " + newCall.callId);
        if (this.state === CallState.WaitLocalMedia) {
            logger.debug("Telling new call to wait for local media");
            newCall.waitForLocalAVStream = true;
        } else if (this.state === CallState.CreateOffer) {
            logger.debug("Handing local stream to new call");
            newCall.gotUserMediaForAnswer(this.localAVStream);
            delete(this.localAVStream);
        } else if (this.state === CallState.InviteSent) {
            logger.debug("Handing local stream to new call");
            newCall.gotUserMediaForAnswer(this.localAVStream);
            delete(this.localAVStream);
        }
        newCall.localVideoElement = this.localVideoElement;
        newCall.remoteVideoElement = this.remoteVideoElement;
        newCall.remoteAudioElement = this.remoteAudioElement;
        this.successor = newCall;
        this.emit(CallEvent.Replaced, newCall);
        this.hangup(CallErrorCode.Replaced, true);
    }

    /**
     * Hangup a call.
     * @param {string} reason The reason why the call is being hung up.
     * @param {boolean} suppressEvent True to suppress emitting an event.
     */
    hangup(reason: CallErrorCode, suppressEvent: boolean) {
        if (this.callHasEnded()) return;

        logger.debug("Ending call " + this.callId);
        this.terminate(CallParty.Local, reason, !suppressEvent);
        // We don't want to send hangup here if we didn't even get to sending an invite
        if (this.state === CallState.WaitLocalMedia) return;
        const content = {};
        // Continue to send no reason for user hangups temporarily, until
        // clients understand the user_hangup reason (voip v1)
        if (reason !== CallErrorCode.UserHangup) content['reason'] = reason;
        this.sendVoipEvent(EventType.CallHangup, {});
    }

    /**
     * Reject a call
     * This used to be done by calling hangup, but is a separate method and protocol
     * event as of MSC2746.
     */
    reject() {
        if (this.state !== CallState.Ringing) {
            throw Error("Call must be in 'ringing' state to reject!");
        }

        if (this.opponentVersion < 1) {
            logger.info(
                `Opponent version is less than 1 (${this.opponentVersion}): sending hangup instead of reject`,
            );
            this.hangup(CallErrorCode.UserHangup, true);
            return;
        }

        logger.debug("Rejecting call: " + this.callId);
        this.terminate(CallParty.Local, CallErrorCode.UserHangup, true);
        this.sendVoipEvent(EventType.CallReject, {});
    }

    /**
     * Set whether our outbound video should be muted or not.
     * @param {boolean} muted True to mute the outbound video.
     */
    setLocalVideoMuted(muted: boolean) {
        this.vidMuted = muted;
        this.updateMuteStatus();
    }

    /**
     * Check if local video is muted.
     *
     * If there are multiple video tracks, <i>all</i> of the tracks need to be muted
     * for this to return true. This means if there are no video tracks, this will
     * return true.
     * @return {Boolean} True if the local preview video is muted, else false
     * (including if the call is not set up yet).
     */
    isLocalVideoMuted(): boolean {
        return this.vidMuted;
    }

    /**
     * Set whether the microphone should be muted or not.
     * @param {boolean} muted True to mute the mic.
     */
    setMicrophoneMuted(muted: boolean) {
        this.micMuted = muted;
        this.updateMuteStatus();
    }

    /**
     * Check if the microphone is muted.
     *
     * If there are multiple audio tracks, <i>all</i> of the tracks need to be muted
     * for this to return true. This means if there are no audio tracks, this will
     * return true.
     * @return {Boolean} True if the mic is muted, else false (including if the call
     * is not set up yet).
     */
    isMicrophoneMuted(): boolean {
        return this.micMuted;
    }

    /**
     * @returns true if we have put the party on the other side of the call on hold
     * (that is, we are signalling to them that we are not listening)
     */
    isRemoteOnHold(): boolean {
        return this.remoteOnHold;
    }

    setRemoteOnHold(onHold: boolean) {
        if (this.isRemoteOnHold() === onHold) return;
        this.remoteOnHold = onHold;
        if (!onHold) this.unholdingRemote = true;

        for (const tranceiver of this.peerConn.getTransceivers()) {
            // We set 'inactive' rather than 'sendonly' because we're not planning on
            // playing music etc. to the other side.
            tranceiver.direction = onHold ? 'inactive' : 'sendrecv';
        }
        this.updateMuteStatus();

        if (!onHold) {
            this.playRemoteAudio();
        }

        this.emit(CallEvent.RemoteHoldUnhold, this.remoteOnHold);
    }

    /**
     * Indicates whether we are 'on hold' to the remote party (ie. if true,
     * they cannot hear us). Note that this will return true when we put the
     * remote on hold too due to the way hold is implemented (since we don't
     * wish to play hold music when we put a call on hold, we use 'inactive'
     * rather than 'sendonly')
     * @returns true if the other party has put us on hold
     */
    isLocalOnHold(): boolean {
        if (this.state !== CallState.Connected) return false;
        if (this.unholdingRemote) return false;

        let callOnHold = true;

        // We consider a call to be on hold only if *all* the tracks are on hold
        // (is this the right thing to do?)
        for (const tranceiver of this.peerConn.getTransceivers()) {
            const trackOnHold = ['inactive', 'recvonly'].includes(tranceiver.currentDirection);

            if (!trackOnHold) callOnHold = false;
        }

        return callOnHold;
    }

    /**
     * Sends a DTMF digit to the other party
     * @param digit The digit (nb. string - '#' and '*' are dtmf too)
     */
    sendDtmfDigit(digit: string) {
        for (const sender of this.peerConn.getSenders()) {
            if (sender.track.kind === 'audio' && sender.dtmf) {
                sender.dtmf.insertDTMF(digit);
                return;
            }
        }

        throw new Error("Unable to find a track to send DTMF on");
    }

    private updateMuteStatus() {
        if (!this.localAVStream) {
            return;
        }

        const micShouldBeMuted = this.micMuted || this.remoteOnHold;
        setTracksEnabled(this.localAVStream.getAudioTracks(), !micShouldBeMuted);

        const vidShouldBeMuted = this.vidMuted || this.remoteOnHold;
        setTracksEnabled(this.localAVStream.getVideoTracks(), !vidShouldBeMuted);

        if (this.remoteOnHold) {
            if (this.remoteAudioElement && this.remoteAudioElement.srcObject === this.remoteStream) {
                this.remoteAudioElement.muted = true;
            } else if (this.remoteVideoElement && this.remoteVideoElement.srcObject === this.remoteStream) {
                this.remoteVideoElement.muted = true;
            }
        } else {
            this.playRemoteAudio();
        }
    }

    /**
     * Internal
     * @param {Object} stream
     */
    private gotUserMediaForInvite = async (stream: MediaStream) => {
        if (this.successor) {
            this.successor.gotUserMediaForAnswer(stream);
            return;
        }
        if (this.callHasEnded()) {
            this.stopAllMedia();
            return;
        }
        this.localAVStream = stream;
        logger.info("Got local AV stream with id " + this.localAVStream.id);

        this.setState(CallState.CreateOffer);

        logger.debug("gotUserMediaForInvite -> " + this.type);

        const videoEl = this.getLocalVideoElement();

        if (videoEl && this.type === CallType.Video) {
            videoEl.autoplay = true;
            if (this.screenSharingStream) {
                logger.debug(
                    "Setting screen sharing stream to the local video element",
                );
                videoEl.srcObject = this.screenSharingStream;
            } else {
                videoEl.srcObject = stream;
            }
            videoEl.muted = true;
            try {
                await videoEl.play();
            } catch (e) {
                logger.info("Failed to play local video element", e);
            }
        }

        // why do we enable audio (and only audio) tracks here? -- matthew
        setTracksEnabled(stream.getAudioTracks(), true);

        for (const audioTrack of stream.getAudioTracks()) {
            logger.info("Adding audio track with id " + audioTrack.id);
            this.peerConn.addTrack(audioTrack, stream);
        }
        for (const videoTrack of (this.screenSharingStream || stream).getVideoTracks()) {
            logger.info("Adding video track with id " + videoTrack.id);
            this.peerConn.addTrack(videoTrack, stream);
        }

        // Now we wait for the negotiationneeded event
    };

    private async sendAnswer() {
        const answerContent = {
            answer: {
                sdp: this.peerConn.localDescription.sdp,
                // type is now deprecated as of Matrix VoIP v1, but
                // required to still be sent for backwards compat
                type: this.peerConn.localDescription.type,
            },
        } as MCallAnswer;

        if (this.client._supportsCallTransfer) {
            answerContent.capabilities = {
                'm.call.transferee': true,
            }
        }

        // We have just taken the local description from the peerconnection which will
        // contain all the local candidates added so far, so we can discard any candidates
        // we had queued up because they'll be in the answer.
        logger.info(`Discarding ${this.candidateSendQueue.length} candidates that will be sent in answer`);
        this.candidateSendQueue = [];

        try {
            await this.sendVoipEvent(EventType.CallAnswer, answerContent);
            // If this isn't the first time we've tried to send the answer,
            // we may have candidates queued up, so send them now.
            this.inviteOrAnswerSent = true;
        } catch (error) {
            // We've failed to answer: back to the ringing state
            this.setState(CallState.Ringing);
            this.client.cancelPendingEvent(error.event);

            let code = CallErrorCode.SendAnswer;
            let message = "Failed to send answer";
            if (error.name == 'UnknownDeviceError') {
                code = CallErrorCode.UnknownDevices;
                message = "Unknown devices present in the room";
            }
            this.emit(CallEvent.Error, new CallError(code, message, error));
            throw error;
        }

        // error handler re-throws so this won't happen on error, but
        // we don't want the same error handling on the candidate queue
        this.sendCandidateQueue();
    }

    private gotUserMediaForAnswer = async (stream: MediaStream) => {
        if (this.callHasEnded()) {
            return;
        }

        const localVidEl = this.getLocalVideoElement();

        if (localVidEl && this.type === CallType.Video) {
            localVidEl.autoplay = true;
            localVidEl.srcObject = stream;

            localVidEl.muted = true;
            try {
                await localVidEl.play();
            } catch (e) {
                logger.info("Failed to play local video element", e);
            }
        }

        this.localAVStream = stream;
        logger.info("Got local AV stream with id " + this.localAVStream.id);
        setTracksEnabled(stream.getAudioTracks(), true);
        for (const track of stream.getTracks()) {
            this.peerConn.addTrack(track, stream);
        }

        this.setState(CallState.CreateAnswer);

        let myAnswer;
        try {
            myAnswer = await this.peerConn.createAnswer();
        } catch (err) {
            logger.debug("Failed to create answer: ", err);
            this.terminate(CallParty.Local, CallErrorCode.CreateAnswer, true);
            return;
        }

        try {
            await this.peerConn.setLocalDescription(myAnswer);
            this.setState(CallState.Connecting);

            // Allow a short time for initial candidates to be gathered
            await new Promise(resolve => {
                setTimeout(resolve, 200);
            });

            this.sendAnswer();
        } catch (err) {
            logger.debug("Error setting local description!", err);
            this.terminate(CallParty.Local, CallErrorCode.SetLocalDescription, true);
            return;
        }
    };

    /**
     * Internal
     * @param {Object} event
     */
    private gotLocalIceCandidate = (event: RTCPeerConnectionIceEvent) => {
        if (event.candidate) {
            logger.debug(
                "Call " + this.callId + " got local ICE " + event.candidate.sdpMid + " candidate: " +
                event.candidate.candidate,
            );

            if (this.callHasEnded()) return;

            // As with the offer, note we need to make a copy of this object, not
            // pass the original: that broke in Chrome ~m43.
            if (event.candidate.candidate !== '' || !this.sentEndOfCandidates) {
                this.queueCandidate(event.candidate);

                if (event.candidate.candidate === '') this.sentEndOfCandidates = true;
            }
        }
    };

    private onIceGatheringStateChange = (event: Event) => {
        logger.debug("ice gathering state changed to " + this.peerConn.iceGatheringState);
        if (this.peerConn.iceGatheringState === 'complete' && !this.sentEndOfCandidates) {
            // If we didn't get an empty-string candidate to signal the end of candidates,
            // create one ourselves now gathering has finished.
            // We cast because the interface lists all the properties as required but we
            // only want to send 'candidate'
            // XXX: We probably want to send either sdpMid or sdpMLineIndex, as it's not strictly
            // correct to have a candidate that lacks both of these. We'd have to figure out what
            // previous candidates had been sent with and copy them.
            const c = {
                candidate: '',
            } as RTCIceCandidate;
            this.queueCandidate(c);
            this.sentEndOfCandidates = true;
        }
    };

    async onRemoteIceCandidatesReceived(ev: MatrixEvent) {
        if (this.callHasEnded()) {
            //debuglog("Ignoring remote ICE candidate because call has ended");
            return;
        }

        const cands = ev.getContent().candidates;
        if (!cands) {
            logger.info("Ignoring candidates event with no candidates!");
            return;
        }

        const fromPartyId = ev.getContent().version === 0 ? null : ev.getContent().party_id || null;

        if (this.opponentPartyId === undefined) {
            // we haven't picked an opponent yet so save the candidates
            logger.info(`Bufferring ${cands.length} candidates until we pick an opponent`);
            const bufferedCands = this.remoteCandidateBuffer.get(fromPartyId) || [];
            bufferedCands.push(...cands);
            this.remoteCandidateBuffer.set(fromPartyId, bufferedCands);
            return;
        }

        if (!this.partyIdMatches(ev.getContent())) {
            logger.info(
                `Ignoring candidates from party ID ${ev.getContent().party_id}: ` +
                `we have chosen party ID ${this.opponentPartyId}`,
            );

            return;
        }

        await this.addIceCandidates(cands);
    }

    /**
     * Used by MatrixClient.
     * @param {Object} msg
     */
    async onAnswerReceived(event: MatrixEvent) {
        logger.debug(`Got answer for call ID ${this.callId} from party ID ${event.getContent().party_id}`);

        if (this.callHasEnded()) {
            logger.debug(`Ignoring answer because call ID ${this.callId} has ended`);
            return;
        }

        if (this.opponentPartyId !== undefined) {
            logger.info(
                `Ignoring answer from party ID ${event.getContent().party_id}: ` +
                `we already have an answer/reject from ${this.opponentPartyId}`,
            );
            return;
        }

        this.chooseOpponent(event);
        await this.addBufferedIceCandidates();

        this.setState(CallState.Connecting);

        try {
            await this.peerConn.setRemoteDescription(event.getContent().answer);
        } catch (e) {
            logger.debug("Failed to set remote description", e);
            this.terminate(CallParty.Local, CallErrorCode.SetRemoteDescription, false);
            return;
        }

        // If the answer we selected has a party_id, send a select_answer event
        // We do this after setting the remote description since otherwise we'd block
        // call setup on it
        if (this.opponentPartyId !== null) {
            try {
                await this.sendVoipEvent(EventType.CallSelectAnswer, {
                    selected_party_id: this.opponentPartyId,
                });
            } catch (err) {
                // This isn't fatal, and will just mean that if another party has raced to answer
                // the call, they won't know they got rejected, so we carry on & don't retry.
                logger.warn("Failed to send select_answer event", err);
            }
        }
    }

    async onSelectAnswerReceived(event: MatrixEvent) {
        if (this.direction !== CallDirection.Inbound) {
            logger.warn("Got select_answer for an outbound call: ignoring");
            return;
        }

        const selectedPartyId = event.getContent().selected_party_id;

        if (selectedPartyId === undefined || selectedPartyId === null) {
            logger.warn("Got nonsensical select_answer with null/undefined selected_party_id: ignoring");
            return;
        }

        if (selectedPartyId !== this.ourPartyId) {
            logger.info(`Got select_answer for party ID ${selectedPartyId}: we are party ID ${this.ourPartyId}.`);
            // The other party has picked somebody else's answer
            this.terminate(CallParty.Remote, CallErrorCode.AnsweredElsewhere, true);
        }
    }

    async onNegotiateReceived(event: MatrixEvent) {
        const description = event.getContent().description;
        if (!description || !description.sdp || !description.type) {
            logger.info("Ignoring invalid m.call.negotiate event");
            return;
        }
        // Politeness always follows the direction of the call: in a glare situation,
        // we pick either the inbound or outbound call, so one side will always be
        // inbound and one outbound
        const polite = this.direction === CallDirection.Inbound;

        // Here we follow the perfect negotiation logic from
        // https://developer.mozilla.org/en-US/docs/Web/API/WebRTC_API/Perfect_negotiation
        const offerCollision = (
            (description.type === 'offer') &&
            (this.makingOffer || this.peerConn.signalingState != 'stable')
        );

        this.ignoreOffer = !polite && offerCollision;
        if (this.ignoreOffer) {
            logger.info("Ignoring colliding negotiate event because we're impolite");
            return;
        }

        const prevLocalOnHold = this.isLocalOnHold();

        if (description.type === 'answer') {
            // whenever we get an answer back, clear the flag we set whilst trying to un-hold
            // the other party: the state of the channels now reflects reality
            this.unholdingRemote = false;
        }

        try {
            await this.peerConn.setRemoteDescription(description);

            if (description.type === 'offer') {
                // First we sent the direction of the tranciever to what we'd like it to be,
                // irresepective of whether the other side has us on hold - so just whether we
                // want the call to be on hold or not. This is necessary because in a few lines,
                // we'll adjust the direction and unless we do this too, we'll never come off hold.
                for (const tranceiver of this.peerConn.getTransceivers()) {
                    tranceiver.direction = this.isRemoteOnHold() ? 'inactive' : 'sendrecv';
                }
                const localDescription = await this.peerConn.createAnswer();
                await this.peerConn.setLocalDescription(localDescription);
                // Now we've got our answer, set the direction to the outcome of the negotiation.
                // We need to do this otherwise Firefox will notice that the direction is not the
                // currentDirection and try to negotiate itself off hold again.
                for (const tranceiver of this.peerConn.getTransceivers()) {
                    tranceiver.direction = tranceiver.currentDirection;
                }

                this.sendVoipEvent(EventType.CallNegotiate, {
                    description: this.peerConn.localDescription,
                });
            }
        } catch (err) {
            logger.warn("Failed to complete negotiation", err);
        }

        const newLocalOnHold = this.isLocalOnHold();
        if (prevLocalOnHold !== newLocalOnHold) {
            this.emit(CallEvent.LocalHoldUnhold, newLocalOnHold);
            // also this one for backwards compat
            this.emit(CallEvent.HoldUnhold, newLocalOnHold);
        }
    }

    private callHasEnded() : boolean {
        // This exists as workaround to typescript trying to be clever and erroring
        // when putting if (this.state === CallState.Ended) return; twice in the same
        // function, even though that function is async.
        return this.state === CallState.Ended;
    }

    private gotLocalOffer = async (description: RTCSessionDescriptionInit) => {
        logger.debug("Created offer: ", description);

        if (this.callHasEnded()) {
            logger.debug("Ignoring newly created offer on call ID " + this.callId +
                " because the call has ended");
            return;
        }

        try {
            await this.peerConn.setLocalDescription(description);
        } catch (err) {
            logger.debug("Error setting local description!", err);
            this.terminate(CallParty.Local, CallErrorCode.SetLocalDescription, true);
            return
        }

        if (this.peerConn.iceGatheringState === 'gathering') {
            // Allow a short time for initial candidates to be gathered
            await new Promise(resolve => {
                setTimeout(resolve, 200);
            });
        }

        if (this.callHasEnded()) return;

        const eventType = this.state === CallState.CreateOffer ? EventType.CallInvite : EventType.CallNegotiate;

        const content = {
            lifetime: CALL_TIMEOUT_MS,
        } as MCallOfferNegotiate;

        // clunky because TypeScript can't folow the types through if we use an expression as the key
        if (this.state === CallState.CreateOffer) {
            content.offer = this.peerConn.localDescription;
        } else {
            content.description = this.peerConn.localDescription;
        }

        if (this.client._supportsCallTransfer) {
            content.capabilities = {
                'm.call.transferee': true,
            }
        }

        // Get rid of any candidates waiting to be sent: they'll be included in the local
        // description we just got and will send in the offer.
        logger.info(`Discarding ${this.candidateSendQueue.length} candidates that will be sent in offer`);
        this.candidateSendQueue = [];

        try {
            await this.sendVoipEvent(eventType, content);
        } catch (error) {
            logger.error("Failed to send invite", error);
            if (error.event) this.client.cancelPendingEvent(error.event);

            let code = CallErrorCode.SignallingFailed;
            let message = "Signalling failed";
            if (this.state === CallState.CreateOffer) {
                code = CallErrorCode.SendInvite;
                message = "Failed to send invite";
            }
            if (error.name == 'UnknownDeviceError') {
                code = CallErrorCode.UnknownDevices;
                message = "Unknown devices present in the room";
            }

            this.emit(CallEvent.Error, new CallError(code, message, error));
            this.terminate(CallParty.Local, code, false);

            // no need to carry on & send the candidate queue, but we also
            // don't want to rethrow the error
            return;
        }

        this.sendCandidateQueue();
        if (this.state === CallState.CreateOffer) {
            this.inviteOrAnswerSent = true;
            this.setState(CallState.InviteSent);
            this.inviteTimeout = setTimeout(() => {
                this.inviteTimeout = null;
                if (this.state === CallState.InviteSent) {
                    this.hangup(CallErrorCode.InviteTimeout, false);
                }
            }, CALL_TIMEOUT_MS);
        }
    };

    private getLocalOfferFailed = (err: Error) => {
        logger.error("Failed to get local offer", err);

        this.emit(
            CallEvent.Error,
            new CallError(
                CallErrorCode.LocalOfferFailed,
                "Failed to get local offer!", err,
            ),
        );
        this.terminate(CallParty.Local, CallErrorCode.LocalOfferFailed, false);
    };

    private getUserMediaFailed = (err: Error) => {
        if (this.successor) {
            this.successor.getUserMediaFailed(err);
            return;
        }

        logger.warn("Failed to get user media - ending call", err);

        this.emit(
            CallEvent.Error,
            new CallError(
                CallErrorCode.NoUserMedia,
                "Couldn't start capturing media! Is your microphone set up and " +
                "does this app have permission?", err,
            ),
        );
        this.terminate(CallParty.Local, CallErrorCode.NoUserMedia, false);
    };

    onIceConnectionStateChanged = () => {
        if (this.callHasEnded()) {
            return; // because ICE can still complete as we're ending the call
        }
        logger.debug(
            "Call ID " + this.callId + ": ICE connection state changed to: " + this.peerConn.iceConnectionState,
        );
        // ideally we'd consider the call to be connected when we get media but
        // chrome doesn't implement any of the 'onstarted' events yet
        if (this.peerConn.iceConnectionState == 'connected') {
            this.setState(CallState.Connected);
        } else if (this.peerConn.iceConnectionState == 'failed') {
            this.hangup(CallErrorCode.IceFailed, false);
        }
    };

    private onSignallingStateChanged = () => {
        logger.debug(
            "call " + this.callId + ": Signalling state changed to: " +
            this.peerConn.signalingState,
        );
    };

    private onTrack = (ev: RTCTrackEvent) => {
        if (ev.streams.length === 0) {
            logger.warn(`Streamless ${ev.track.kind} found: ignoring.`);
            return;
        }
        // If we already have a stream, check this track is from the same one
        if (this.remoteStream && ev.streams[0].id !== this.remoteStream.id) {
            logger.warn(
                `Ignoring new stream ID ${ev.streams[0].id}: we already have stream ID ${this.remoteStream.id}`,
            );
            return;
        }

        if (!this.remoteStream) {
            logger.info("Got remote stream with id " + ev.streams[0].id);
        }

        // Note that we check by ID above and always set the remote stream: Chrome appears
        // to make new stream objects when tranciever directionality is changed and the 'active'
        // status of streams change
        this.remoteStream = ev.streams[0];

        logger.debug(`Track id ${ev.track.id} of kind ${ev.track.kind} added`);

        if (ev.track.kind === 'video') {
            if (this.remoteVideoElement) {
                this.playRemoteVideo();
            }
        } else {
            if (this.remoteAudioElement) this.playRemoteAudio();
        }
    };

    onNegotiationNeeded = async () => {
        logger.info("Negotation is needed!");

        if (this.state !== CallState.CreateOffer && this.opponentVersion === 0) {
            logger.info("Opponent does not support renegotiation: ignoring negotiationneeded event");
            return;
        }

        this.makingOffer = true;
        try {
            const myOffer = await this.peerConn.createOffer();
            await this.gotLocalOffer(myOffer);
        } catch (e) {
            this.getLocalOfferFailed(e);
            return;
        } finally {
            this.makingOffer = false;
        }
    };

    async playRemoteAudio() {
        if (this.remoteVideoElement) this.remoteVideoElement.muted = true;
        this.remoteAudioElement.muted = false;

        this.remoteAudioElement.srcObject = this.remoteStream;

        // if audioOutput is non-default:
        try {
            if (audioOutput) {
                // This seems quite unreliable in Chrome, although I haven't yet managed to make a jsfiddle where
                // it fails.
                // It seems reliable if you set the sink ID after setting the srcObject and then set the sink ID
                // back to the default after the call is over
                logger.info("Setting audio sink to " + audioOutput + ", was " + this.remoteAudioElement.sinkId);
                await this.remoteAudioElement.setSinkId(audioOutput);
            }
        } catch (e) {
            logger.warn("Couldn't set requested audio output device: using default", e);
        }

        try {
            await this.remoteAudioElement.play();
        } catch (e) {
            logger.error("Failed to play remote audio element", e);
        }
    }

    private async playRemoteVideo() {
        // A note on calling methods on media elements:
        // We used to have queues per media element to serialise all calls on those elements.
        // The reason given for this was that load() and play() were racing. However, we now
        // never call load() explicitly so this seems unnecessary. However, serialising every
        // operation was causing bugs where video would not resume because some play command
        // had got stuck and all media operations were queued up behind it. If necessary, we
        // should serialise the ones that need to be serialised but then be able to interrupt
        // them with another load() which will cancel the pending one, but since we don't call
        // load() explicitly, it shouldn't be a problem.
        this.remoteVideoElement.srcObject = this.remoteStream;
        logger.info("playing remote video. stream active? " + this.remoteStream.active);
        try {
            await this.remoteVideoElement.play();
        } catch (e) {
            logger.info("Failed to play remote video element", e);
        }
    }

    onHangupReceived = (msg) => {
        logger.debug("Hangup received for call ID " + this.callId);

        // party ID must match (our chosen partner hanging up the call) or be undefined (we haven't chosen
        // a partner yet but we're treating the hangup as a reject as per VoIP v0)
        if (this.partyIdMatches(msg) || this.state === CallState.Ringing) {
            // default reason is user_hangup
            this.terminate(CallParty.Remote, msg.reason || CallErrorCode.UserHangup, true);
        } else {
            logger.info(`Ignoring message from party ID ${msg.party_id}: our partner is ${this.opponentPartyId}`);
        }
    };

    onRejectReceived = (msg) => {
        logger.debug("Reject received for call ID " + this.callId);

        // No need to check party_id for reject because if we'd received either
        // an answer or reject, we wouldn't be in state InviteSent

        const shouldTerminate = (
            // reject events also end the call if it's ringing: it's another of
            // our devices rejecting the call.
            ([CallState.InviteSent, CallState.Ringing].includes(this.state)) ||
            // also if we're in the init state and it's an inbound call, since
            // this means we just haven't entered the ringing state yet
            this.state === CallState.Fledgling && this.direction === CallDirection.Inbound
        );

        if (shouldTerminate) {
            this.terminate(CallParty.Remote, CallErrorCode.UserHangup, true);
        } else {
            logger.debug(`Call is in state: ${this.state}: ignoring reject`);
        }
    };

    onAnsweredElsewhere = (msg) => {
        logger.debug("Call ID " + this.callId + " answered elsewhere");
        this.terminate(CallParty.Remote, CallErrorCode.AnsweredElsewhere, true);
    };

    setState(state: CallState) {
        const oldState = this.state;
        this.state = state;
        this.emit(CallEvent.State, state, oldState);
    }

    /**
     * Internal
     * @param {string} eventType
     * @param {Object} content
     * @return {Promise}
     */
    private sendVoipEvent(eventType: string, content: object) {
        return this.client.sendEvent(this.roomId, eventType, Object.assign({}, content, {
            version: VOIP_PROTO_VERSION,
            call_id: this.callId,
            party_id: this.ourPartyId,
        }));
    }

    queueCandidate(content: RTCIceCandidate) {
        // Sends candidates with are sent in a special way because we try to amalgamate
        // them into one message
        this.candidateSendQueue.push(content);

        // Don't send the ICE candidates yet if the call is in the ringing state: this
        // means we tried to pick (ie. started generating candidates) and then failed to
        // send the answer and went back to the ringing state. Queue up the candidates
        // to send if we sucessfully send the answer.
        // Equally don't send if we haven't yet sent the answer because we can send the
        // first batch of candidates along with the answer
        if (this.state === CallState.Ringing || !this.inviteOrAnswerSent) return;

        // MSC2746 reccomends these values (can be quite long when calling because the
        // callee will need a while to answer the call)
        const delay = this.direction === CallDirection.Inbound ? 500 : 2000;

        if (this.candidateSendTries === 0) {
            setTimeout(() => {
                this.sendCandidateQueue();
            }, delay);
        }
    }

    /*
     * Transfers this call to another user
     */
    async transfer(targetUserId: string) {
        // Fetch the target user's global profile info: their room avatar / displayname
        // could be different in whatever room we shae with them.
        const profileInfo = await this.client.getProfileInfo(targetUserId);

        const replacementId = genCallID();

        const body = {
            replacement_id: genCallID(),
            target_user: {
                id: targetUserId,
                display_name: profileInfo.display_name,
                avatar_url: profileInfo.avatar_url,
            },
            create_call: replacementId,
        } as MCallReplacesEvent;

        await this.sendVoipEvent(EventType.CallReplaces, body);

        await this.terminate(CallParty.Local, CallErrorCode.Replaced, true);
    }

    /*
     * Transfers this call to the target call, effectively 'joining' the
     * two calls (so the remote parties on each call are connected together).
     */
    async transferToCall(transferTargetCall?: MatrixCall) {
        const targetProfileInfo = await this.client.getProfileInfo(transferTargetCall.getOpponentMember().userId);
        const transfereeProfileInfo = await this.client.getProfileInfo(this.getOpponentMember().userId);

        const newCallId = genCallID();

        const bodyToTransferTarget = {
            // the replacements on each side have their own ID, and it's distinct from the
            // ID of the new call (but we can use the same function to generate it)
            replacement_id: genCallID(),
            target_user: {
                id: this.getOpponentMember().userId,
                display_name: transfereeProfileInfo.display_name,
                avatar_url: transfereeProfileInfo.avatar_url,
            },
            await_call: newCallId,
        } as MCallReplacesEvent;

        await transferTargetCall.sendVoipEvent(EventType.CallReplaces, bodyToTransferTarget);

        const bodyToTransferee = {
            replacement_id: genCallID(),
            target_user: {
                id: transferTargetCall.getOpponentMember().userId,
                display_name: targetProfileInfo.display_name,
                avatar_url: targetProfileInfo.avatar_url,
            },
            create_call: newCallId,
        } as MCallReplacesEvent;

        await this.sendVoipEvent(EventType.CallReplaces, bodyToTransferee);

        await this.terminate(CallParty.Local, CallErrorCode.Replaced, true);
        await transferTargetCall.terminate(CallParty.Local, CallErrorCode.Replaced, true);
    }

    private async terminate(hangupParty: CallParty, hangupReason: CallErrorCode, shouldEmit: boolean) {
        if (this.callHasEnded()) return;

        this.callStatsAtEnd = await this.collectCallStats();

        if (this.inviteTimeout) {
            clearTimeout(this.inviteTimeout);
            this.inviteTimeout = null;
        }

        const remoteVid = this.getRemoteVideoElement();
        const remoteAud = this.getRemoteAudioElement();
        const localVid = this.getLocalVideoElement();

        if (remoteVid) {
            remoteVid.pause();
            remoteVid.srcObject = null;
        }
        if (remoteAud) {
            remoteAud.pause();
            remoteAud.srcObject = null;
            try {
                // As per comment in playRemoteAudio, setting the sink ID back to the default
                // once the call is over makes setSinkId work reliably.
                await this.remoteAudioElement.setSinkId('')
            } catch (e) {
                logger.warn("Failed to set sink ID back to default");
            }
        }
        if (localVid) {
            localVid.pause();
            localVid.srcObject = null;
        }
        this.hangupParty = hangupParty;
        this.hangupReason = hangupReason;
        this.setState(CallState.Ended);
        this.stopAllMedia();
        if (this.peerConn && this.peerConn.signalingState !== 'closed') {
            this.peerConn.close();
        }
        if (shouldEmit) {
            this.emit(CallEvent.Hangup, this);
        }
    }

    private stopAllMedia() {
        logger.debug(`stopAllMedia (stream=${this.localAVStream})`);
        if (this.localAVStream) {
            for (const track of this.localAVStream.getTracks()) {
                track.stop();
            }
        }
        if (this.screenSharingStream) {
            for (const track of this.screenSharingStream.getTracks()) {
                track.stop();
            }
        }

        if (this.remoteStream) {
            for (const track of this.remoteStream.getTracks()) {
                track.stop();
            }
        }
    }

    private checkForErrorListener() {
        if (this.listeners("error").length === 0) {
            throw new Error(
                "You MUST attach an error listener using call.on('error', function() {})",
            );
        }
    }

    private async sendCandidateQueue() {
        if (this.candidateSendQueue.length === 0) {
            return;
        }

        const cands = this.candidateSendQueue;
        this.candidateSendQueue = [];
        ++this.candidateSendTries;
        const content = {
            candidates: cands,
        };
        logger.debug("Attempting to send " + cands.length + " candidates");
        try {
            await this.sendVoipEvent(EventType.CallCandidates, content);
        } catch (error) {
            // don't retry this event: we'll send another one later as we might
            // have more candidates by then.
            if (error.event) this.client.cancelPendingEvent(error.event);

            // put all the candidates we failed to send back in the queue
            this.candidateSendQueue.push(...cands);

            if (this.candidateSendTries > 5) {
                logger.debug(
                    "Failed to send candidates on attempt " + this.candidateSendTries +
                    ". Giving up on this call.", error,
                );

                const code = CallErrorCode.SignallingFailed;
                const message = "Signalling failed";

                this.emit(CallEvent.Error, new CallError(code, message, error));
                this.hangup(code, false);

                return;
            }

            const delayMs = 500 * Math.pow(2, this.candidateSendTries);
            ++this.candidateSendTries;
            logger.debug("Failed to send candidates. Retrying in " + delayMs + "ms", error);
            setTimeout(() => {
                this.sendCandidateQueue();
            }, delayMs);
        }
    }

    private async placeCallWithConstraints(constraints: MediaStreamConstraints) {
        logger.log("Getting user media with constraints", constraints);
        // XXX Find a better way to do this
        this.client._callEventHandler.calls.set(this.callId, this);
        this.setState(CallState.WaitLocalMedia);
        this.direction = CallDirection.Outbound;
        this.config = constraints;

        // make sure we have valid turn creds. Unless something's gone wrong, it should
        // poll and keep the credentials valid so this should be instant.
        const haveTurnCreds = await this.client._checkTurnServers();
        if (!haveTurnCreds) {
            logger.warn("Failed to get TURN credentials! Proceeding with call anyway...");
        }

        // create the peer connection now so it can be gathering candidates while we get user
        // media (assuming a candidate pool size is configured)
        this.peerConn = this.createPeerConnection();

        try {
            const mediaStream = await navigator.mediaDevices.getUserMedia(constraints);
            this.gotUserMediaForInvite(mediaStream);
        } catch (e) {
            this.getUserMediaFailed(e);
            return;
        }
    }

    private createPeerConnection(): RTCPeerConnection {
        const pc = new window.RTCPeerConnection({
            iceTransportPolicy: this.forceTURN ? 'relay' : undefined,
            iceServers: this.turnServers,
            iceCandidatePoolSize: this.client._iceCandidatePoolSize,
        });

        // 'connectionstatechange' would be better, but firefox doesn't implement that.
        pc.addEventListener('iceconnectionstatechange', this.onIceConnectionStateChanged);
        pc.addEventListener('signalingstatechange', this.onSignallingStateChanged);
        pc.addEventListener('icecandidate', this.gotLocalIceCandidate);
        pc.addEventListener('icegatheringstatechange', this.onIceGatheringStateChange);
        pc.addEventListener('track', this.onTrack);
        pc.addEventListener('negotiationneeded', this.onNegotiationNeeded);

        return pc;
    }

    private partyIdMatches(msg): boolean {
        // They must either match or both be absent (in which case opponentPartyId will be null)
        // Also we ignore party IDs on the invite/offer if the version is 0, so we must do the same
        // here and use null if the version is 0 (woe betide any opponent sending messages in the
        // same call with different versions)
        const msgPartyId = msg.version === 0 ? null : msg.party_id || null;
        return msgPartyId === this.opponentPartyId;
    }

    // Commits to an opponent for the call
    // ev: An invite or answer event
    private chooseOpponent(ev: MatrixEvent) {
        // I choo-choo-choose you
        const msg = ev.getContent();

        logger.debug(`Choosing party ID ${msg.party_id} for call ID ${this.callId}`);

        this.opponentVersion = msg.version;
        if (this.opponentVersion === 0) {
            // set to null to indicate that we've chosen an opponent, but because
            // they're v0 they have no party ID (even if they sent one, we're ignoring it)
            this.opponentPartyId = null;
        } else {
            // set to their party ID, or if they're naughty and didn't send one despite
            // not being v0, set it to null to indicate we picked an opponent with no
            // party ID
            this.opponentPartyId = msg.party_id || null;
        }
        this.opponentCaps = msg.capabilities || {};
        this.opponentMember = ev.sender;
    }

    private async addBufferedIceCandidates() {
        const bufferedCands = this.remoteCandidateBuffer.get(this.opponentPartyId);
        if (bufferedCands) {
            logger.info(`Adding ${bufferedCands.length} buffered candidates for opponent ${this.opponentPartyId}`);
            await this.addIceCandidates(bufferedCands);
        }
        this.remoteCandidateBuffer = null;
    }

    private async addIceCandidates(cands: RTCIceCandidate[]) {
        for (const cand of cands) {
            if (
                (cand.sdpMid === null || cand.sdpMid === undefined) &&
                (cand.sdpMLineIndex === null || cand.sdpMLineIndex === undefined)
            ) {
                logger.debug("Ignoring remote ICE candidate with no sdpMid or sdpMLineIndex");
                continue;
            }
            logger.debug("Call " + this.callId + " got remote ICE " + cand.sdpMid + " candidate: " + cand.candidate);
            try {
                await this.peerConn.addIceCandidate(cand);
            } catch (err) {
                if (!this.ignoreOffer) {
                    logger.info("Failed to add remote ICE candidate", err);
                }
            }
        }
    }
}

function setTracksEnabled(tracks: Array<MediaStreamTrack>, enabled: boolean) {
    for (let i = 0; i < tracks.length; i++) {
        tracks[i].enabled = enabled;
    }
}

function getUserMediaContraints(type: ConstraintsType) {
    const isWebkit = !!navigator.webkitGetUserMedia;

    switch (type) {
        case ConstraintsType.Audio: {
            return {
                audio: {
                    deviceId: audioInput ? {ideal: audioInput} : undefined,
                },
                video: false,
            };
        }
        case ConstraintsType.Video: {
            return {
                audio: {
                    deviceId: audioInput ? {ideal: audioInput} : undefined,
                }, video: {
                    deviceId: videoInput ? {ideal: videoInput} : undefined,
                    /* We want 640x360.  Chrome will give it only if we ask exactly,
                       FF refuses entirely if we ask exactly, so have to ask for ideal
                       instead
                       XXX: Is this still true?
                     */
                    width: isWebkit ? { exact: 640 } : { ideal: 640 },
                    height: isWebkit ? { exact: 360 } : { ideal: 360 },
                },
            };
        }
    }
}

async function getScreenshareContraints(selectDesktopCapturerSource?: () => Promise<DesktopCapturerSource>) {
    if (window.electron?.getDesktopCapturerSources && selectDesktopCapturerSource) {
        // We have access to getDesktopCapturerSources()
        logger.debug("Electron getDesktopCapturerSources() is available...");
        const selectedSource = await selectDesktopCapturerSource();
        if (!selectedSource) return null;
        return {
            audio: false,
            video: {
                mandatory: {
                    chromeMediaSource: "desktop",
                    chromeMediaSourceId: selectedSource.id,
                },
            },
        };
    } else {
        // We do not have access to the Electron desktop capturer,
        // therefore we can assume we are on the web
        logger.debug("Electron desktopCapturer is not available...");
        return {
            audio: false,
            video: true,
        };
    }
}

let audioOutput: string;
let audioInput: string;
let videoInput: string;
/**
 * Set an audio output device to use for MatrixCalls
 * @function
 * @param {string=} deviceId the identifier for the device
 * undefined treated as unset
 */
export function setAudioOutput(deviceId: string) { audioOutput = deviceId; }
/**
 * Set an audio input device to use for MatrixCalls
 * @function
 * @param {string=} deviceId the identifier for the device
 * undefined treated as unset
 */
export function setAudioInput(deviceId: string) { audioInput = deviceId; }
/**
 * Set a video input device to use for MatrixCalls
 * @function
 * @param {string=} deviceId the identifier for the device
 * undefined treated as unset
 */
export function setVideoInput(deviceId: string) { videoInput = deviceId; }

/**
 * Create a new Matrix call for the browser.
 * @param {MatrixClient} client The client instance to use.
 * @param {string} roomId The room the call is in.
 * @param {Object?} options DEPRECATED optional options map.
 * @param {boolean} options.forceTURN DEPRECATED whether relay through TURN should be
 * forced. This option is deprecated - use opts.forceTURN when creating the matrix client
 * since it's only possible to set this option on outbound calls.
 * @return {MatrixCall} the call or null if the browser doesn't support calling.
 */
export function createNewMatrixCall(client: any, roomId: string, options?: CallOpts) {
    // typeof prevents Node from erroring on an undefined reference
    if (typeof(window) === 'undefined' || typeof(document) === 'undefined') {
        // NB. We don't log here as apps try to create a call object as a test for
        // whether calls are supported, so we shouldn't fill the logs up.
        return null;
    }

    // Firefox throws on so little as accessing the RTCPeerConnection when operating in
    // a secure mode. There's some information at https://bugzilla.mozilla.org/show_bug.cgi?id=1542616
    // though the concern is that the browser throwing a SecurityError will brick the
    // client creation process.
    try {
        const supported = Boolean(
            window.RTCPeerConnection || window.RTCSessionDescription ||
            window.RTCIceCandidate || navigator.mediaDevices,
        );
        if (!supported) {
            logger.error("WebRTC is not supported in this browser / environment");
            return null;
        }
    } catch (e) {
        logger.error("Exception thrown when trying to access WebRTC", e);
        return null;
    }

    const optionsForceTURN = options ? options.forceTURN : false;

    const opts = {
        client: client,
        roomId: roomId,
        turnServers: client.getTurnServers(),
        // call level options
        forceTURN: client._forceTURN || optionsForceTURN,
    };
    const call = new MatrixCall(opts);

    client.reEmitter.reEmit(call, Object.values(CallEvent));

    return call;
}
