project-inter-server/src/notifications/schedulers/ETANotificationScheduler.ts

import { ShuttleGetterRepository } from "../../repositories/ShuttleGetterRepository";
import { TupleKey } from "../../types/TupleKey";
import { IEta } from "../../entities/entities";
import { AppleNotificationSender, NotificationAlertArguments } from "../senders/AppleNotificationSender";
import {
  NotificationLookupArguments,
  ScheduledNotification
} from "../../repositories/NotificationRepository";

type DeviceIdSecondsThresholdAssociation = { [key: string]: number };

export class ETANotificationScheduler {
  public static readonly defaultSecondsThresholdForNotificationToFire = 180;

  constructor(private shuttleRepository: ShuttleGetterRepository,
              private appleNotificationSender = new AppleNotificationSender()
  ) {
    this.etaSubscriberCallback = this.etaSubscriberCallback.bind(this);
    this.sendEtaNotificationImmediately = this.sendEtaNotificationImmediately.bind(this);
    this.etaSubscriberCallback = this.etaSubscriberCallback.bind(this);
    this.sendEtaNotificationImmediatelyIfSecondsRemainingBelowThreshold = this.sendEtaNotificationImmediatelyIfSecondsRemainingBelowThreshold.bind(this);
    this.scheduleNotification = this.scheduleNotification.bind(this);
    this.cancelNotificationIfExists = this.cancelNotificationIfExists.bind(this);
    this.isNotificationScheduled = this.isNotificationScheduled.bind(this);
    this.getSecondsThresholdForScheduledNotification = this.getSecondsThresholdForScheduledNotification.bind(this);
    this.getAllScheduledNotificationsForDevice = this.getAllScheduledNotificationsForDevice.bind(this);
  }

  /**
   * An object of device ID arrays to deliver notifications to.
   * The key should be a combination of the shuttle ID and
   * stop ID, which can be generated using `TupleKey`.
   * The value is a dictionary of the device ID to the stored seconds threshold.
   * @private
   */
  private deviceIdsToDeliverTo: { [key: string]: DeviceIdSecondsThresholdAssociation } = {}

  private async sendEtaNotificationImmediately(notificationData: ScheduledNotification): Promise<boolean> {
    const { deviceId, shuttleId, stopId } = notificationData;

    const shuttle = await this.shuttleRepository.getShuttleById(shuttleId);
    const stop = await this.shuttleRepository.getStopById(stopId);
    const eta = await this.shuttleRepository.getEtaForShuttleAndStopId(shuttleId, stopId);
    if (!shuttle) {
      console.warn(`Notification ${notificationData} fell through; no associated shuttle`);
      return false;
    }
    if (!stop) {
      console.warn(`Notification ${notificationData} fell through; no associated stop`);
      return false;
    }

    // Notification may not be sent if ETA is unavailable at the moment;
    // this is fine because it will be sent again when ETA becomes available
    if (!eta) {
      console.warn(`Notification ${notificationData} fell through; no associated ETA`);
      return false;
    }

    const notificationAlertArguments: NotificationAlertArguments = {
      title: "Shuttle is arriving",
      body: `Shuttle is approaching ${stop.name} in ${Math.ceil(eta.secondsRemaining / 60)} minutes.`,
    }
    return this.appleNotificationSender.sendNotificationImmediately(deviceId, notificationAlertArguments);
  }

  private async etaSubscriberCallback(eta: IEta) {
    const tuple = new TupleKey(eta.shuttleId, eta.stopId);
    const tupleKey = tuple.toString();
    if (this.deviceIdsToDeliverTo[tupleKey] === undefined) {
      return;
    }

    const deviceIdsToRemove = new Set<string>();
    for (let deviceId of Object.keys(this.deviceIdsToDeliverTo[tupleKey])) {
      const scheduledNotificationData: ScheduledNotification = {
        deviceId,
        secondsThreshold: this.deviceIdsToDeliverTo[tupleKey][deviceId],
        shuttleId: eta.shuttleId,
        stopId: eta.stopId,
      }

      const deliveredSuccessfully = await this.sendEtaNotificationImmediatelyIfSecondsRemainingBelowThreshold(scheduledNotificationData, eta.secondsRemaining);
      if (deliveredSuccessfully) {
        deviceIdsToRemove.add(deviceId);
      }
    }

    deviceIdsToRemove.forEach((deviceId) => {
      delete this.deviceIdsToDeliverTo[tupleKey][deviceId]
    });
  }

  private async sendEtaNotificationImmediatelyIfSecondsRemainingBelowThreshold(notificationObject: ScheduledNotification, etaSecondsRemaining: number) {
    if (etaSecondsRemaining > notificationObject.secondsThreshold) {
      return false;
    }

    return await this.sendEtaNotificationImmediately(notificationObject);
  }

  /**
   * Queue a notification to be sent.
   * @param deviceId The device ID to send the notification to.
   * @param shuttleId Shuttle ID of ETA object to check.
   * @param stopId Stop ID of ETA object to check.
   * @param secondsThreshold Value which specifies the ETA of the shuttle for when
   * the notification should fire.
   */
  public async scheduleNotification({ deviceId, shuttleId, stopId, secondsThreshold }: ScheduledNotification) {
    const tuple = new TupleKey(shuttleId, stopId);
    if (this.deviceIdsToDeliverTo[tuple.toString()] === undefined) {
      this.deviceIdsToDeliverTo[tuple.toString()] = {};
    }

    this.deviceIdsToDeliverTo[tuple.toString()][deviceId] = secondsThreshold;

    this.shuttleRepository.unsubscribeFromEtaUpdates(this.etaSubscriberCallback);
    this.shuttleRepository.subscribeToEtaUpdates(this.etaSubscriberCallback);
  }

  /**
   * Cancel a pending notification.
   * @param deviceId The device ID of the notification.
   * @param shuttleId Shuttle ID of the ETA object.
   * @param stopId Stop ID of the ETA object.
   */
  public async cancelNotificationIfExists({ deviceId, shuttleId, stopId }: NotificationLookupArguments) {
    const tupleKey = new TupleKey(shuttleId, stopId);
    if (
      this.deviceIdsToDeliverTo[tupleKey.toString()] === undefined
      || !(deviceId in this.deviceIdsToDeliverTo[tupleKey.toString()])
    ) {
      return;
    }

    delete this.deviceIdsToDeliverTo[tupleKey.toString()][deviceId];
  }

  /**
   * Check whether the notification is scheduled.
   */
  public isNotificationScheduled(lookupArguments: NotificationLookupArguments): boolean {
    return this.getSecondsThresholdForScheduledNotification(lookupArguments) != null;
  }

  public getSecondsThresholdForScheduledNotification({ deviceId, shuttleId, stopId }: NotificationLookupArguments): number | null {
    const tuple = new TupleKey(shuttleId, stopId);
    if (this.deviceIdsToDeliverTo[tuple.toString()] === undefined) {
      return null;
    }
    return this.deviceIdsToDeliverTo[tuple.toString()][deviceId];
  }

  /**
   * Return all scheduled notification for the given device ID.
   * @param deviceId
   */
  public async getAllScheduledNotificationsForDevice(deviceId: string): Promise<NotificationLookupArguments[]> {
    const scheduledNotifications: ScheduledNotification[] = [];

    for (const key of Object.keys(this.deviceIdsToDeliverTo)) {
      if (deviceId in this.deviceIdsToDeliverTo[key]) {
        const tupleKey = TupleKey.fromExistingStringKey(key);
        const shuttleId = tupleKey.tuple[0]
        const stopId = tupleKey.tuple[1];
        const secondsThreshold = this.deviceIdsToDeliverTo[key][deviceId];

        scheduledNotifications.push({
          shuttleId,
          stopId,
          deviceId,
          secondsThreshold,
        });
      }
    }

    return scheduledNotifications;
  }
}