/*
Copyright 2017 New Vector 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.
*/

import EventEmitter from 'events';
import Promise from 'bluebird';

const BULK_REQUEST_DEBOUNCE_MS = 200;

// Does the server support groups? Assume yes until we receive M_UNRECOGNIZED.
// If true, flair can function and we should keep sending requests for groups and avatars.
let groupSupport = true;

const USER_GROUPS_CACHE_BUST_MS = 1800000; // 30 mins
const GROUP_PROFILES_CACHE_BUST_MS = 1800000; // 30 mins

/**
 * Stores data used by <Flair/>
 */
class FlairStore extends EventEmitter {
    constructor(matrixClient) {
        super();
        this._matrixClient = matrixClient;
        this._userGroups = {
            // $userId: ['+group1:domain', '+group2:domain', ...]
        };
        this._groupProfiles = {
            //  $groupId: {
            //      avatar_url: 'mxc://...'
            //  }
        };
        this._usersPending = {
            //  $userId: {
            //      prom: Promise
            //      resolve: () => {}
            //      reject: () => {}
            //  }
        };

        this._debounceTimeoutID = null;
    }

    groupSupport() {
        return groupSupport;
    }

    getPublicisedGroupsCached(matrixClient, userId) {
        if (this._userGroups[userId]) {
            return Promise.resolve(this._userGroups[userId]);
        }

        // Bulk lookup ongoing, return promise to resolve/reject
        if (this._usersPending[userId]) {
            return this._usersPending[userId].prom;
        }

        this._usersPending[userId] = {};
        this._usersPending[userId].prom = new Promise((resolve, reject) => {
            this._usersPending[userId].resolve = resolve;
            this._usersPending[userId].reject = reject;
        }).then((groups) => {
            this._userGroups[userId] = groups;
            setTimeout(() => {
                delete this._userGroups[userId];
            }, USER_GROUPS_CACHE_BUST_MS);
            return this._userGroups[userId];
        }).catch((err) => {
            // Indicate whether the homeserver supports groups
            if (err.errcode === 'M_UNRECOGNIZED') {
                console.warn('Cannot display flair, server does not support groups');
                groupSupport = false;
                // Return silently to avoid spamming for non-supporting servers
                return;
            }
            console.error('Could not get groups for user', this.props.userId, err);
            throw err;
        }).finally(() => {
            delete this._usersPending[userId];
        });

        // This debounce will allow consecutive requests for the public groups of users that
        // are sent in intervals of < BULK_REQUEST_DEBOUNCE_MS to be batched and only requested
        // when no more requests are received within the next BULK_REQUEST_DEBOUNCE_MS. The naive
        // implementation would do a request that only requested the groups for `userId`, leading
        // to a worst and best case of 1 user per request. This implementation's worst is still
        // 1 user per request but only if the requests are > BULK_REQUEST_DEBOUNCE_MS apart and the
        // best case is N users per request.
        //
        // This is to reduce the number of requests made whilst trading off latency when viewing
        // a Flair component.
        if (this._debounceTimeoutID) clearTimeout(this._debounceTimeoutID);
        this._debounceTimeoutID = setTimeout(() => {
            this._batchedGetPublicGroups(matrixClient);
        }, BULK_REQUEST_DEBOUNCE_MS);

        return this._usersPending[userId].prom;
    }

    async _batchedGetPublicGroups(matrixClient) {
        // Take the userIds from the keys of this._usersPending
        const usersInFlight = Object.keys(this._usersPending);
        let resp = {
            users: [],
        };
        try {
            resp = await matrixClient.getPublicisedGroups(usersInFlight);
        } catch (err) {
            // Propagate the same error to all usersInFlight
            usersInFlight.forEach((userId) => {
                this._usersPending[userId].reject(err);
            });
            return;
        }
        const updatedUserGroups = resp.users;
        usersInFlight.forEach((userId) => {
            this._usersPending[userId].resolve(updatedUserGroups[userId] || []);
        });
    }

    async getGroupProfileCached(matrixClient, groupId) {
        if (this._groupProfiles[groupId]) {
            return this._groupProfiles[groupId];
        }

        const profile = await matrixClient.getGroupProfile(groupId);
        this._groupProfiles[groupId] = {
            groupId,
            avatarUrl: profile.avatar_url,
            name: profile.name,
            shortDescription: profile.short_description,
        };
        setTimeout(() => {
            delete this._groupProfiles[groupId];
        }, GROUP_PROFILES_CACHE_BUST_MS);

        return this._groupProfiles[groupId];
    }
}

if (global.singletonFlairStore === undefined) {
    global.singletonFlairStore = new FlairStore();
}
export default global.singletonFlairStore;