/*
Copyright 2016 OpenMarket Ltd

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.
*/

var React = require('react');
var ReactDOM = require("react-dom");
var q = require("q");

var Matrix = require("matrix-js-sdk");
var EventTimeline = Matrix.EventTimeline;

var sdk = require('../../index');
var MatrixClientPeg = require("../../MatrixClientPeg");
var dis = require("../../dispatcher");

var PAGINATE_SIZE = 20;
var INITIAL_SIZE = 20;
var TIMELINE_CAP = 250; // the most events to show in a timeline

// consider that the user remains "active" for this many milliseconds after a
// user_activity event (and thus don't make the read-marker visible on new
// events)
var CONSIDER_USER_ACTIVE_FOR_MS = 500;

var DEBUG = false;

if (DEBUG) {
    // using bind means that we get to keep useful line numbers in the console
    var debuglog = console.log.bind(console);
} else {
    var debuglog = function () {};
}

/*
 * Component which shows the event timeline in a room view.
 *
 * Also responsible for handling and sending read receipts.
 */
var TimelinePanel = React.createClass({
    displayName: 'TimelinePanel',

    propTypes: {
        // The js-sdk Room object for the room whose timeline we are
        // representing.
        room: React.PropTypes.object.isRequired,

        // true to give the component a 'display: none' style.
        hidden: React.PropTypes.bool,

        // ID of an event to highlight. If undefined, no event will be highlighted.
        // typically this will be either 'eventId' or undefined.
        highlightedEventId: React.PropTypes.string,

        // id of an event to jump to. If not given, will go to the end of the
        // live timeline.
        eventId: React.PropTypes.string,

        // where to position the event given by eventId, in pixels from the
        // bottom of the viewport. If not given, will try to put the event
        // 1/3 of the way down the viewport.
        eventPixelOffset: React.PropTypes.number,

        // callback which is called when the panel is scrolled.
        onScroll: React.PropTypes.func,

        // callback which is called when the read-up-to mark is updated.
        onReadMarkerUpdated: React.PropTypes.func,
    },

    statics: {
        // a map from room id to read marker event ID
        roomReadMarkerMap: {},

        // a map from room id to read marker event timestamp
        roomReadMarkerTsMap: {},
    },

    getInitialState: function() {
        var initialReadMarker =
            TimelinePanel.roomReadMarkerMap[this.props.room.roomId]
                       || this._getCurrentReadReceipt();

        return {
            events: [],
            timelineLoading: true, // track whether our room timeline is loading
            canBackPaginate: true,

            // start with the read-marker visible, so that we see its animated
            // disappearance when swtitching into the room.
            readMarkerVisible: true,

            readMarkerEventId: initialReadMarker,

            backPaginating: false,
            forwardPaginating: false,
        };
    },

    componentWillMount: function() {
        debuglog("TimelinePanel: mounting");

        this.last_rr_sent_event_id = undefined;
        this._resetActivityTimer();

        this.dispatcherRef = dis.register(this.onAction);
        MatrixClientPeg.get().on("Room.timeline", this.onRoomTimeline);
        MatrixClientPeg.get().on("Room.timelineReset", this.onRoomTimelineReset);
        MatrixClientPeg.get().on("Room.redaction", this.onRoomRedaction);
        MatrixClientPeg.get().on("Room.receipt", this.onRoomReceipt);

        this._initTimeline(this.props);
    },

    componentWillReceiveProps: function(newProps) {
        if (newProps.room !== this.props.room) {
            // throw new Error("changing room on a TimelinePanel is not supported");

            // regrettably, this does happen; in particular, when joining a
            // room with /join. In that case, there are two Rooms in
            // circulation - one which is created by the MatrixClient.joinRoom
            // call and used to create the RoomView, and a second which is
            // created by the sync loop once the room comes back down the /sync
            // pipe. Once the latter happens, our room is replaced with the new one.
            //
            // for now, just warn about this. But we're going to end up paginating
            // both rooms separately, and it's all bad.
            console.warn("Replacing room on a TimelinePanel - confusion may ensue");
        }

        if (newProps.eventId != this.props.eventId) {
            console.log("TimelinePanel switching to eventId " + newProps.eventId +
                        " (was " + this.props.eventId + ")");
            return this._initTimeline(newProps);
        }
    },

    componentWillUnmount: function() {
        // set a boolean to say we've been unmounted, which any pending
        // promises can use to throw away their results.
        //
        // (We could use isMounted, but facebook have deprecated that.)
        this.unmounted = true;

        dis.unregister(this.dispatcherRef);

        var client = MatrixClientPeg.get();
        if (client) {
            client.removeListener("Room.timeline", this.onRoomTimeline);
            client.removeListener("Room.timelineReset", this.onRoomTimelineReset);
            client.removeListener("Room.redaction", this.onRoomRedaction);
            client.removeListener("Room.receipt", this.onRoomReceipt);
        }
    },

    // set off a pagination request.
    onMessageListFillRequest: function(backwards) {
        var dir = backwards ? EventTimeline.BACKWARDS : EventTimeline.FORWARDS;
        if(!this._timelineWindow.canPaginate(dir)) {
            debuglog("TimelinePanel: can't paginate at this time; backwards:"+backwards);
            return q(false);
        }
        debuglog("TimelinePanel: Initiating paginate; backwards:"+backwards);
        var statekey = backwards ? 'backPaginating' : 'forwardPaginating';
        this.setState({[statekey]: true});

        return this._timelineWindow.paginate(dir, PAGINATE_SIZE).then((r) => {
            if (this.unmounted) { return; }

            debuglog("TimelinePanel: paginate complete backwards:"+backwards+"; success:"+r);
            this.setState({[statekey]: false});
            this._onTimelineUpdated(r);
            return r;
        });
    },

    onMessageListScroll: function () {
        if (this.props.onScroll) {
            this.props.onScroll();
        }

        // we hide the read marker when it first comes onto the screen, but if
        // it goes back off the top of the screen (presumably because the user
        // clicks on the 'jump to bottom' button), we need to re-enable it.
        if (this.getReadMarkerPosition() < 0) {
            this.setState({readMarkerVisible: true});
        }
    },

    onAction: function(payload) {
        switch (payload.action) {
            case 'user_activity':
                this._resetActivityTimer();

                // fall-through!

            case 'user_activity_end':
                // we could treat user_activity_end differently and not
                // send receipts for messages that have arrived between
                // the actual user activity and the time they stopped
                // being active, but let's see if this is actually
                // necessary.
                this.sendReadReceipt();
                this.updateReadMarker();
                break;
        }
    },

    _resetActivityTimer: function() {
        this.user_last_active = Date.now();
    },

    onRoomTimeline: function(ev, room, toStartOfTimeline, removed, data) {
        // ignore events for other rooms
        if (room !== this.props.room) return;

        // ignore anything but real-time updates at the end of the room:
        // updates from pagination will happen when the paginate completes.
        if (toStartOfTimeline || !data || !data.liveEvent) return;

        if (!this.refs.messagePanel) return;

        if (!this.refs.messagePanel.getScrollState().stuckAtBottom) return;

        // when a new event arrives when the user is not watching the window, but the
        // window is in its auto-scroll mode, make sure the read marker is visible.
        //
        // We consider the user to be watching the window if they performed an action
        // less than CONSIDER_USER_ACTIVE_FOR_MS ago.
        //
        // We ignore events we have sent ourselves; we don't want to see the
        // read-marker when a remote echo of an event we have just sent takes
        // more than CONSIDER_USER_ACTIVE_FOR_MS.
        //
        var myUserId = MatrixClientPeg.get().credentials.userId;
        var sender = ev.sender ? ev.sender.userId : null;
        var activity_age = Date.now() - this.user_last_active;
        if (sender != myUserId && activity_age > CONSIDER_USER_ACTIVE_FOR_MS) {
            this.setState({readMarkerVisible: true});
        }

        // tell the timeline window to try to advance itself, but not to make
        // an http request to do so.
        //
        // we deliberately avoid going via the ScrollPanel for this call - the
        // ScrollPanel might already have an active pagination promise, which
        // will fail, but would stop us passing the pagination request to the
        // timeline window. 
        //
        // see https://github.com/vector-im/vector-web/issues/1035
        this._timelineWindow.paginate(EventTimeline.FORWARDS, 1, false)
            .done(this._onTimelineUpdated);
    },

    onRoomTimelineReset: function(room) {
        if (room !== this.props.room) return;

        if (this.refs.messagePanel && this.refs.messagePanel.isAtBottom()) {
            this._loadTimeline();
        }
    },

    onRoomRedaction: function(ev, room) {
        if (this.unmounted) return;

        // ignore events for other rooms
        if (room !== this.props.room) return;

        // we could skip an update if the event isn't in our timeline,
        // but that's probably an early optimisation.
        this.forceUpdate();
    },

    onRoomReceipt: function(ev, room) {
        if (this.unmounted) return;

        // ignore events for other rooms
        if (room !== this.props.room) return;

        this.forceUpdate();
    },

    sendReadReceipt: function() {
        if (!this.refs.messagePanel) return;

        var currentReadUpToEventId = this._getCurrentReadReceipt(true);
        var currentReadUpToEventIndex = this._indexForEventId(currentReadUpToEventId);

        // We want to avoid sending out read receipts when we are looking at
        // events in the past which are before the latest RR.
        //
        // For now, let's apply a heuristic: if (a) the event corresponding to
        // the latest RR (either from the server, or sent by ourselves) doesn't
        // appear in our timeline, and (b) we could forward-paginate the event
        // timeline, then don't send any more RRs.
        //
        // This isn't watertight, as we could be looking at a section of
        // timeline which is *after* the latest RR (so we should actually send
        // RRs) - but that is a bit of a niche case. It will sort itself out when
        // the user eventually hits the live timeline.
        //
        if (currentReadUpToEventId && currentReadUpToEventIndex === null &&
                this._timelineWindow.canPaginate(EventTimeline.FORWARDS)) {
            return;
        }

        var lastReadEventIndex = this._getLastDisplayedEventIndex({
            ignoreOwn: true
        });
        if (lastReadEventIndex === null) return;

        var lastReadEvent = this.state.events[lastReadEventIndex];

        // we also remember the last read receipt we sent to avoid spamming the
        // same one at the server repeatedly
        if (lastReadEventIndex > currentReadUpToEventIndex
                && this.last_rr_sent_event_id != lastReadEvent.getId()) {
            this.last_rr_sent_event_id = lastReadEvent.getId();
            MatrixClientPeg.get().sendReadReceipt(lastReadEvent).catch(() => {
                // it failed, so allow retries next time the user is active
                this.last_rr_sent_event_id = undefined;
            });
        }
    },

    // if the read marker is on the screen, we can now assume we've caught up to the end
    // of the screen, so move the marker down to the bottom of the screen.
    updateReadMarker: function() {
        if (this.getReadMarkerPosition() !== 0) {
            return;
        }

        var currentIndex = this._indexForEventId(this.state.readMarkerEventId);

        // move the RM to *after* the message at the bottom of the screen. This
        // avoids a problem whereby we never advance the RM if there is a huge
        // message which doesn't fit on the screen.
        //
        // But ignore local echoes for this - they have a temporary event ID
        // and we'll get confused when their ID changes and we can't figure out
        // where the RM is pointing to. The read marker will be invisible for
        // now anyway, so this doesn't really matter.
        var lastDisplayedIndex = this._getLastDisplayedEventIndex({
            allowPartial: true,
            ignoreEchoes: true,
        });

        if (lastDisplayedIndex === null) {
            return;
        }

        var lastDisplayedEvent = this.state.events[lastDisplayedIndex];
        this._setReadMarker(lastDisplayedEvent.getId(),
                            lastDisplayedEvent.getTs());

        // the read-marker should become invisible, so that if the user scrolls
        // down, they don't see it.
        if(this.state.readMarkerVisible) {
            this.setState({
                readMarkerVisible: false,
            });
        }
    },

    /* jump down to the bottom of this room, where new events are arriving
     */
    jumpToLiveTimeline: function() {
        // if we can't forward-paginate the existing timeline, then there
        // is no point reloading it - just jump straight to the bottom.
        //
        // Otherwise, reload the timeline rather than trying to paginate
        // through all of space-time.
        if (this._timelineWindow.canPaginate(EventTimeline.FORWARDS)) {
            this._loadTimeline();
        } else {
            if (this.refs.messagePanel) {
                this.refs.messagePanel.scrollToBottom();
            }
        }
    },

    /* scroll to show the read-up-to marker
     */
    jumpToReadMarker: function() {
        if (!this.state.readMarkerEventId)
            return;
        if (!this.refs.messagePanel)
            return;
        this.refs.messagePanel.scrollToEvent(this.state.readMarkerEventId);
    },


    /* update the read-up-to marker to match the read receipt
     */
    forgetReadMarker: function() {
        var rmId = this._getCurrentReadReceipt();

        // see if we know the timestamp for the rr event
        var tl = this.props.room.getTimelineForEvent(rmId);
        var rmTs;
        if (tl) {
            var event = tl.getEvents().find((e) => { return e.getId() == rmId });
            if (event) {
                rmTs = event.getTs();
            }
        }

        this._setReadMarker(rmId, rmTs);
    },

    /* return true if the content is fully scrolled down and we are
     * at the end of the live timeline.
     */
    isAtEndOfLiveTimeline: function() {
        return this.refs.messagePanel
            && this.refs.messagePanel.isAtBottom()
            && this._timelineWindow
            && !this._timelineWindow.canPaginate(EventTimeline.FORWARDS);
    },


    /* get the current scroll state. See ScrollPanel.getScrollState for
     * details.
     *
     * returns null if we are not mounted.
     */
    getScrollState: function() {
        if (!this.refs.messagePanel) { return null; }
        return this.refs.messagePanel.getScrollState();
    },

    // returns one of:
    //
    //  null: there is no read marker
    //  -1: read marker is above the window
    //   0: read marker is visible
    //  +1: read marker is below the window
    getReadMarkerPosition: function() {
        if (!this.refs.messagePanel) { return null; }
        var ret = this.refs.messagePanel.getReadMarkerPosition();
        if (ret !== null) {
            return ret;
        }

        // the messagePanel doesn't know where the read marker is.
        // if we know the timestamp of the read marker, make a guess based on that.
        var rmTs = TimelinePanel.roomReadMarkerTsMap[this.props.room.roomId];
        if (rmTs && this.state.events.length > 0) {
            if (rmTs < this.state.events[0].getTs()) {
                return -1;
            } else {
                return 1;
            }
        }

        return null;
    },

    // makes the TimelinePanel update itself after it is resized (due to other
    // changes in the DOM)
    onResize: function() {
        if (!this.refs.messagePanel) { return; }
        this.refs.messagePanel.onResize();
    },

    _initTimeline: function(props) {
        var initialEvent = props.eventId;
        var pixelOffset = props.eventPixelOffset;
        return this._loadTimeline(initialEvent, pixelOffset);
    },

    /**
     * (re)-load the event timeline, and initialise the scroll state, centered
     * around the given event.
     *
     * @param {string?}  eventId the event to focus on. If undefined, will
     *    scroll to the bottom of the room.
     *
     * @param {number?} pixelOffset   offset to position the given event at
     *    (pixels from the bottom of the view). If undefined, will put the
     *    event 1/3 of the way down the view.
     *
     * returns a promise which will resolve when the load completes.
     */
    _loadTimeline: function(eventId, pixelOffset) {
        this._timelineWindow = new Matrix.TimelineWindow(
            MatrixClientPeg.get(), this.props.room,
            {windowLimit: TIMELINE_CAP});

        var prom = this._timelineWindow.load(eventId, INITIAL_SIZE);

        this.setState({
            events: [],
            timelineLoading: true,
        });

        // if we already have the event in question, TimelineWindow.load
        // returns a resolved promise.
        //
        // In this situation, we don't really want to defer the update of the
        // state to the next event loop, because it makes room-switching feel
        // quite slow. So we detect that situation and shortcut straight to
        // calling _onTimelineUpdated and updating the state.

        var onLoaded = () => {
            this._onTimelineUpdated(true);

            this.setState({timelineLoading: false}, () => {
                // initialise the scroll state of the message panel
                if (!this.refs.messagePanel) {
                    // this shouldn't happen - _onTimelineUpdated checks we're
                    // mounted, and timelineLoading is now false.
                    console.log("can't initialise scroll state because " +
                                "messagePanel didn't load");
                    return;
                }
                if (eventId) {
                    this.refs.messagePanel.scrollToEvent(eventId, pixelOffset);
                } else {
                    this.refs.messagePanel.scrollToBottom();
                }

                this.sendReadReceipt();
                this.updateReadMarker();
            });
        };

        if (prom.isPending()) {
            prom = prom.then(onLoaded);
        } else {
            onLoaded();
        }

        prom.done();
    },

    _onTimelineUpdated: function(gotResults) {
        // we might have switched rooms since the load started - just bin
        // the results if so.
        if (this.unmounted) return;

        if (gotResults) {
            this.setState({
                events: this._timelineWindow.getEvents(),
                canBackPaginate: this._timelineWindow.canPaginate(EventTimeline.BACKWARDS),
            });
        }
    },

    _indexForEventId: function(evId) {
        for (var i = 0; i < this.state.events.length; ++i) {
            if (evId == this.state.events[i].getId()) {
                return i;
            }
        }
        return null;
    },

    _getLastDisplayedEventIndex: function(opts) {
        opts = opts || {};
        var ignoreOwn = opts.ignoreOwn || false;
        var ignoreEchoes = opts.ignoreEchoes || false;
        var allowPartial = opts.allowPartial || false;

        var messagePanel = this.refs.messagePanel;
        if (messagePanel === undefined) return null;

        var wrapperRect = ReactDOM.findDOMNode(messagePanel).getBoundingClientRect();
        var myUserId = MatrixClientPeg.get().credentials.userId;

        for (var i = this.state.events.length-1; i >= 0; --i) {
            var ev = this.state.events[i];

            if (ignoreOwn && ev.sender && ev.sender.userId == myUserId) {
                continue;
            }

            // local echoes have a fake event ID
            if (ignoreEchoes && ev.status) {
                continue;
            }

            var node = messagePanel.getNodeForEventId(ev.getId());
            if (!node) continue;

            var boundingRect = node.getBoundingClientRect();
            if ((allowPartial && boundingRect.top < wrapperRect.bottom) ||
                (!allowPartial && boundingRect.bottom < wrapperRect.bottom)) {
                return i;
            }
        }
        return null;
    },

    /**
     * get the id of the event corresponding to our user's latest read-receipt.
     *
     * @param {Boolean} ignoreSynthesized If true, return only receipts that
     *                                    have been sent by the server, not
     *                                    implicit ones generated by the JS
     *                                    SDK.
     */
    _getCurrentReadReceipt: function(ignoreSynthesized) {
        var client = MatrixClientPeg.get();
        // the client can be null on logout
        if (client == null)
            return null;

        var myUserId = client.credentials.userId;
        return this.props.room.getEventReadUpTo(myUserId, ignoreSynthesized);
    },

    _setReadMarker: function(eventId, eventTs) {
        if (TimelinePanel.roomReadMarkerMap[this.props.room.roomId] == eventId) {
            // don't update the state (and cause a re-render) if there is
            // no change to the RM.
            return;
        }

        // ideally we'd sync these via the server, but for now just stash them
        // in a map.
        TimelinePanel.roomReadMarkerMap[this.props.room.roomId] = eventId;

        // in order to later figure out if the read marker is
        // above or below the visible timeline, we stash the timestamp.
        TimelinePanel.roomReadMarkerTsMap[this.props.room.roomId] = eventTs;

        // run the render cycle before calling the callback, so that
        // getReadMarkerPosition() returns the right thing.
        this.setState({
            readMarkerEventId: eventId,
        }, this.props.onReadMarkerUpdated);
    },

    render: function() {
        var MessagePanel = sdk.getComponent("structures.MessagePanel");
        var Loader = sdk.getComponent("elements.Spinner");

        // just show a spinner while the timeline loads.
        //
        // put it in a div of the right class (mx_RoomView_messagePanel) so
        // that the order in the roomview flexbox is correct, and
        // mx_RoomView_messageListWrapper to position the inner div in the
        // right place.
        //
        // Note that the click-on-search-result functionality relies on the
        // fact that the messagePanel is hidden while the timeline reloads,
        // but that the RoomHeader (complete with search term) continues to
        // exist.
        if (this.state.timelineLoading) {
            return (
                    <div className="mx_RoomView_messagePanel mx_RoomView_messageListWrapper">
                        <Loader />
                    </div>
            );
        }

        // give the messagepanel a stickybottom if we're at the end of the
        // live timeline, so that the arrival of new events triggers a
        // scroll.
        //
        // Make sure that stickyBottom is *false* if we can paginate
        // forwards, otherwise if somebody hits the bottom of the loaded
        // events when viewing historical messages, we get stuck in a loop
        // of paginating our way through the entire history of the room.
        var stickyBottom = !this._timelineWindow.canPaginate(EventTimeline.FORWARDS);

        return (
            <MessagePanel ref="messagePanel"
                    hidden={ this.props.hidden }
                    backPaginating={ this.state.backPaginating }
                    forwardPaginating={ this.state.forwardPaginating }
                    events={ this.state.events }
                    highlightedEventId={ this.props.highlightedEventId }
                    readMarkerEventId={ this.state.readMarkerEventId }
                    readMarkerVisible={ this.state.readMarkerVisible }
                    suppressFirstDateSeparator={ this.state.canBackPaginate }
                    ourUserId={ MatrixClientPeg.get().credentials.userId }
                    stickyBottom={ stickyBottom }
                    onScroll={ this.onMessageListScroll }
                    onFillRequest={ this.onMessageListFillRequest }
            />
        );
    },
});

module.exports = TimelinePanel;