/*
Copyright 2020 Bruno Windels <bruno@windels.cloud>
Copyright 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.
*/

import {AbortError} from "./error.js";
import {ObservableValue} from "../observable/ObservableValue.js";
import {createEnum} from "../utils/enum.js";

const INCREMENTAL_TIMEOUT = 30000;
const SYNC_EVENT_LIMIT = 10;

export const SyncStatus = createEnum(
    "InitialSync",
    "CatchupSync",
    "Syncing",
    "Stopped"
);

function parseRooms(roomsSection, roomCallback) {
    if (roomsSection) {
        const allMemberships = ["join", "invite", "leave"];
        for(const membership of allMemberships) {
            const membershipSection = roomsSection[membership];
            if (membershipSection) {
                return Object.entries(membershipSection).map(([roomId, roomResponse]) => {
                    return roomCallback(roomId, roomResponse, membership);
                });
            }
        }
    }
    return [];
}

function timelineIsEmpty(roomResponse) {
    try {
        const events = roomResponse?.timeline?.events;
        return Array.isArray(events) && events.length === 0;
    } catch (err) {
        return true;
    }
}

export class Sync {
    constructor({hsApi, session, storage}) {
        this._hsApi = hsApi;
        this._session = session;
        this._storage = storage;
        this._currentRequest = null;
        this._status = new ObservableValue(SyncStatus.Stopped);
        this._error = null;
    }

    get status() {
        return this._status;
    }

    /** the error that made the sync stop */
    get error() {
        return this._error;
    }

    start() {
        // not already syncing?
        if (this._status.get() !== SyncStatus.Stopped) {
            return;
        }
        let syncToken = this._session.syncToken;
        if (syncToken) {
            this._status.set(SyncStatus.CatchupSync);
        } else {
            this._status.set(SyncStatus.InitialSync);
        }
        this._syncLoop(syncToken);
    }

    async _syncLoop(syncToken) {
        // if syncToken is falsy, it will first do an initial sync ... 
        while(this._status.get() !== SyncStatus.Stopped) {
            try {
                console.log(`starting sync request with since ${syncToken} ...`);
                const timeout = syncToken ? INCREMENTAL_TIMEOUT : undefined; 
                syncToken = await this._syncRequest(syncToken, timeout);
                this._status.set(SyncStatus.Syncing);
            } catch (err) {
                if (!(err instanceof AbortError)) {
                    this._error = err;
                    this._status.set(SyncStatus.Stopped);
                }
            }
            if (!this._error) {
                try {
                    await this._session.afterSyncCompleted();
                } catch (err) {
                    console.err("error during after sync completed, continuing to sync.",  err.stack);
                    // swallowing error here apart from logging
                }
            }
        }
    }

    async _syncRequest(syncToken, timeout) {
        let {syncFilterId} = this._session;
        if (typeof syncFilterId !== "string") {
            this._currentRequest = this._hsApi.createFilter(this._session.user.id, {room: {state: {lazy_load_members: true}}});
            syncFilterId = (await this._currentRequest.response()).filter_id;
        }
        const totalRequestTimeout = timeout + (80 * 1000);  // same as riot-web, don't get stuck on wedged long requests
        this._currentRequest = this._hsApi.sync(syncToken, syncFilterId, timeout, {timeout: totalRequestTimeout});
        const response = await this._currentRequest.response();
        const isInitialSync = !syncToken;
        syncToken = response.next_batch;
        const storeNames = this._storage.storeNames;
        const syncTxn = await this._storage.readWriteTxn([
            storeNames.session,
            storeNames.roomSummary,
            storeNames.roomState,
            storeNames.roomMembers,
            storeNames.timelineEvents,
            storeNames.timelineFragments,
            storeNames.pendingEvents,
            storeNames.userIdentities,
        ]);
        const roomChanges = [];
        let sessionChanges;
        try {
            // to_device
            // presence
            if (response.rooms) {
                const promises = parseRooms(response.rooms, async (roomId, roomResponse, membership) => {
                    // ignore rooms with empty timelines during initial sync,
                    // see https://github.com/vector-im/hydrogen-web/issues/15
                    if (isInitialSync && timelineIsEmpty(roomResponse)) {
                        return;
                    }
                    let room = this._session.rooms.get(roomId);
                    if (!room) {
                        room = this._session.createRoom(roomId);
                    }
                    console.log(` * applying sync response to room ${roomId} ...`);
                    const changes = await room.writeSync(roomResponse, membership, isInitialSync, syncTxn);
                    roomChanges.push({room, changes});
                });
                await Promise.all(promises);
            }
            sessionChanges = await this._session.writeSync(response, syncFilterId, roomChanges, syncTxn);
        } catch(err) {
            console.warn("aborting syncTxn because of error");
            console.error(err);
            // avoid corrupting state by only
            // storing the sync up till the point
            // the exception occurred
            syncTxn.abort();
            throw err;
        }
        try {
            await syncTxn.complete();
            console.info("syncTxn committed!!");
        } catch (err) {
            console.error("unable to commit sync tranaction");
            throw err;
        }
        this._session.afterSync(sessionChanges);
        // emit room related events after txn has been closed
        for(let {room, changes} of roomChanges) {
            room.afterSync(changes);
        }

        return syncToken;
    }

    stop() {
        if (this._status.get() === SyncStatus.Stopped) {
            return;
        }
        this._status.set(SyncStatus.Stopped);
        if (this._currentRequest) {
            this._currentRequest.abort();
            this._currentRequest = null;
        }
    }
}