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

import { ShuttleGetterRepository } from "../../repositories/ShuttleGetterRepository";
import { IEta } from "../../entities/ShuttleRepositoryEntities";
import { AppleNotificationSender, NotificationAlertArguments } from "../senders/AppleNotificationSender";
import {
  NotificationRepository,
  ScheduledNotification
} from "../../repositories/NotificationRepository";
import { InMemoryNotificationRepository } from "../../repositories/InMemoryNotificationRepository";

export class ETANotificationScheduler {
  public static readonly defaultSecondsThresholdForNotificationToFire = 180;

  constructor(
    private shuttleRepository: ShuttleGetterRepository,
    private notificationRepository: NotificationRepository = new InMemoryNotificationRepository(),
    private appleNotificationSender = new AppleNotificationSender(),
    private interchangeSystemId: string,
  ) {
    this.etaSubscriberCallback = this.etaSubscriberCallback.bind(this);
    this.sendEtaNotificationImmediately = this.sendEtaNotificationImmediately.bind(this);
    this.sendEtaNotificationImmediatelyIfSecondsRemainingBelowThreshold = this.sendEtaNotificationImmediatelyIfSecondsRemainingBelowThreshold.bind(this);
  }

  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.`,
      customKeys: {
        shuttleId,
        stopId,
        systemId: this.interchangeSystemId,
      },
    }
    return this.appleNotificationSender.sendNotificationImmediately(deviceId, notificationAlertArguments);
  }

  private async etaSubscriberCallback(eta: IEta) {
    const deviceIdsToRemove = new Set<string>();
    const notifications = await this.notificationRepository.getAllNotificationsForShuttleAndStopId(
      eta.shuttleId,
      eta.stopId
    )

    for (let notification of notifications) {
      const deliveredSuccessfully = await this.sendEtaNotificationImmediatelyIfSecondsRemainingBelowThreshold(notification, eta.secondsRemaining);
      if (deliveredSuccessfully) {
        deviceIdsToRemove.add(notification.deviceId);
      }
    }

    deviceIdsToRemove.forEach((deviceId) => {
      this.notificationRepository.deleteNotificationIfExists({
        shuttleId: eta.shuttleId,
        stopId: eta.stopId,
        deviceId,
      })
    });
  }

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

    return await this.sendEtaNotificationImmediately(notificationObject);
  }

  // The following is a workaround for the constructor being called twice
  public startListeningForUpdates() {
    this.shuttleRepository.subscribeToEtaUpdates(this.etaSubscriberCallback);
  }

  public stopListeningForUpdates() {
    this.shuttleRepository.subscribeToEtaUpdates(this.etaSubscriberCallback);
  }
}