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

/**
 * Sync steps in js-pseudocode:
 * ```js
 * let preparation;
 * if (room.needsPrepareSync) {
 *     // can only read some stores
 *     preparation = await room.prepareSync(roomResponse, prepareTxn);
 *     // can do async work that is not related to storage (such as decryption)
 *     preparation = await room.afterPrepareSync(preparation);
 * }
 * // writes and calculates changes
 * const changes = await room.writeSync(roomResponse, membership, isInitialSync, preparation, syncTxn);
 * // applies and emits changes once syncTxn is committed
 * room.afterSync(changes);
 * if (room.needsAfterSyncCompleted(changes)) {
 *     // can do network requests
 *     await room.afterSyncCompleted(changes);
 * }
 * ```
 */
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) {
        let afterSyncCompletedPromise = Promise.resolve();
        // if syncToken is falsy, it will first do an initial sync ... 
        while(this._status.get() !== SyncStatus.Stopped) {
            let roomStates;
            try {
                console.log(`starting sync request with since ${syncToken} ...`);
                const timeout = syncToken ? INCREMENTAL_TIMEOUT : undefined; 
                const syncResult = await this._syncRequest(syncToken, timeout, afterSyncCompletedPromise);
                syncToken = syncResult.syncToken;
                roomStates = syncResult.roomStates;
                this._status.set(SyncStatus.Syncing);
            } catch (err) {
                if (!(err instanceof AbortError)) {
                    this._error = err;
                    this._status.set(SyncStatus.Stopped);
                }
            }
            if (!this._error) {
                afterSyncCompletedPromise = this._runAfterSyncCompleted(roomStates);
            }
        }
    }

    async _runAfterSyncCompleted(roomStates) {
        const sessionPromise = (async () => {
            try {
                await this._session.afterSyncCompleted();
            } catch (err) {
                console.error("error during session afterSyncCompleted, continuing",  err.stack);
            }
        })();

        const roomsNeedingAfterSyncCompleted = roomStates.filter(rs => {
            return rs.room.needsAfterSyncCompleted(rs.changes);
        });
        const roomsPromises = roomsNeedingAfterSyncCompleted.map(async rs => {
            try {
                await rs.room.afterSyncCompleted(rs.changes);
            } catch (err) {
                console.error(`error during room ${rs.room.id} afterSyncCompleted, continuing`,  err.stack);
            }
        });
        // run everything in parallel,
        // we don't want to delay the next sync too much
        // Also, since all promises won't reject (as they have a try/catch)
        // it's fine to use Promise.all
        await Promise.all(roomsPromises.concat(sessionPromise));
    }

    async _syncRequest(syncToken, timeout, prevAfterSyncCompletedPromise) {
        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();
        // wait here for the afterSyncCompleted step of the previous sync to complete
        // before we continue processing this sync response
        await prevAfterSyncCompletedPromise;

        const isInitialSync = !syncToken;
        syncToken = response.next_batch;
        const roomStates = this._parseRoomsResponse(response.rooms, isInitialSync);
        await this._prepareRooms(roomStates);
        let sessionChanges;
        const syncTxn = await this._openSyncTxn();
        try {
            await Promise.all(roomStates.map(async rs => {
                console.log(` * applying sync response to room ${rs.room.id} ...`);
                rs.changes = await rs.room.writeSync(
                    rs.roomResponse, rs.membership, isInitialSync, rs.preparation, syncTxn);
            }));
            sessionChanges = await this._session.writeSync(response, syncFilterId, 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 rs of roomStates) {
            rs.room.afterSync(rs.changes);
        }

        return {syncToken, roomStates};
    }

    async _openPrepareSyncTxn() {
        const storeNames = this._storage.storeNames;
        return await this._storage.readTxn([
            storeNames.inboundGroupSessions,
        ]);
    }

    async _prepareRooms(roomStates) {
        const prepareRoomStates = roomStates.filter(rs => rs.room.needsPrepareSync);
        if (prepareRoomStates.length) {
            const prepareTxn = await this._openPrepareSyncTxn();
            await Promise.all(prepareRoomStates.map(async rs => {
                rs.preparation = await rs.room.prepareSync(rs.roomResponse, prepareTxn);
            }));
            await Promise.all(prepareRoomStates.map(async rs => {
                rs.preparation = await rs.room.afterPrepareSync(rs.preparation);
            }));
        }
    }

    async _openSyncTxn() {
        const storeNames = this._storage.storeNames;
        return await this._storage.readWriteTxn([
            storeNames.session,
            storeNames.roomSummary,
            storeNames.roomState,
            storeNames.roomMembers,
            storeNames.timelineEvents,
            storeNames.timelineFragments,
            storeNames.pendingEvents,
            storeNames.userIdentities,
            storeNames.groupSessionDecryptions,
            storeNames.deviceIdentities,
            // to discard outbound session when somebody leaves a room
            // and to create room key messages when somebody leaves
            storeNames.outboundGroupSessions,
            storeNames.operations
        ]);
    }
    
    _parseRoomsResponse(roomsSection, isInitialSync) {
        const roomStates = [];
        if (roomsSection) {
            // don't do "invite", "leave" for now
            const allMemberships = ["join"];
            for(const membership of allMemberships) {
                const membershipSection = roomsSection[membership];
                if (membershipSection) {
                    for (const [roomId, roomResponse] of Object.entries(membershipSection)) {
                        // 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);
                        }
                        roomStates.push(new RoomSyncProcessState(room, roomResponse, membership));
                    }
                }
            }
        }
        return roomStates;
    }


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

class RoomSyncProcessState {
    constructor(room, roomResponse, membership) {
        this.room = room;
        this.roomResponse = roomResponse;
        this.membership = membership;
        this.preparation = null;
        this.changes = null;
    }
}