// Copyright (c) 2016-present Mattermost, Inc. All Rights Reserved.
// See LICENSE.txt for license information.

import {EventEmitter} from 'events';

import electron from 'electron';
import log from 'electron-log';

const {app} = electron;

/**
 * Monitors system idle time, listens for system events and fires status updates as needed
 */
export default class UserActivityMonitor extends EventEmitter {
    isActive: boolean;
    idleTime: number;
    lastSetActive?: number;
    systemIdleTimeIntervalID: number;
    config: {
        updateFrequencyMs: number;
        inactiveThresholdMs: number;
        statusUpdateThresholdMs: number;
    };

    constructor() {
        super();

        this.isActive = true;
        this.idleTime = 0;
        this.systemIdleTimeIntervalID = -1;

        this.config = {
            updateFrequencyMs: 1 * 1000, // eslint-disable-line no-magic-numbers
            inactiveThresholdMs: 60 * 1000, // eslint-disable-line no-magic-numbers
            statusUpdateThresholdMs: 60 * 1000, // eslint-disable-line no-magic-numbers
        };
    }

    get userIsActive() {
        return this.isActive;
    }

    get userIdleTime() {
        return this.idleTime;
    }

    /**
   * Begin monitoring system events and idle time at defined frequency
   *
   * @param {Object} config - overide internal configuration defaults
   * @param {number} config.updateFrequencyMs - internal update clock frequency for monitoring idleTime
   * @param {number} config.inactiveThresholdMs - the number of milliseconds that idleTime needs to reach to internally be considered inactive
   * @param {number} config.statusUpdateThresholdMs - minimum amount of time before sending a new status update
   * @emits {error} emitted when method is called before the app is ready
   * @emits {error} emitted when this method has previously been called but not subsequently stopped
   */
    startMonitoring(config = {}) {
        if (!app.isReady()) {
            this.emit('error', new Error('UserActivityMonitor.startMonitoring can only be called after app is ready'));
            return;
        }

        if (this.systemIdleTimeIntervalID >= 0) {
            this.emit('error', new Error('User activity monitoring is already in progress'));
            return;
        }

        this.config = Object.assign({}, this.config, config);

        // TODO: Node typings don't map Timeout to number, but then clearInterval requires a number?
        this.systemIdleTimeIntervalID = setInterval(() => {
            try {
                this.updateIdleTime(electron.powerMonitor.getSystemIdleTime());
            } catch (err) {
                log.error('Error getting system idle time:', err);
            }
        }, this.config.updateFrequencyMs) as unknown as number;
    }

    /**
   * Stop monitoring system events and idle time
   */
    stopMonitoring() {
        clearInterval(this.systemIdleTimeIntervalID);
    }

    /**
   * Updates internal idle time and sets internal user activity state
   *
   * @param {integer} idleTime
   * @private
   */
    updateIdleTime(idleTime: number) {
        this.idleTime = idleTime;
        if (idleTime * 1000 > this.config.inactiveThresholdMs) { // eslint-disable-line no-magic-numbers
            this.setActivityState(false);
        } else {
            this.setActivityState(true);
        }
    }

    /**
   * Updates user active state and conditionally triggers a status update
   *
   * @param {boolean} isActive
   * @param {boolean} isSystemEvent – indicates whether the update was triggered by a system event (log in/out, screesaver on/off etc)
   * @private
   */
    setActivityState(isActive = false, isSystemEvent = false) {
        this.isActive = isActive;

        if (isSystemEvent) {
            this.sendStatusUpdate(true);
            return;
        }

        const now = Date.now();

        if (isActive && (this.lastSetActive == null || now - this.lastSetActive >= this.config.statusUpdateThresholdMs)) {
            this.sendStatusUpdate(false);
            this.lastSetActive = now;
        } else if (!isActive) {
            delete this.lastSetActive;
        }
    }

    /**
   * Sends an update with user activity status and current system idle time
   *
   * @emits {status} emitted at regular, definable intervals providing an update on user active status and idle time
   * @private
   */
    sendStatusUpdate(isSystemEvent = false) {
        this.emit('status', {
            userIsActive: this.isActive,
            idleTime: this.idleTime,
            isSystemEvent,
        });
    }
}