import { ApplicationRef, Inject, Injectable } from "@angular/core";
import { SwUpdate } from "@angular/service-worker";
import { filter, first } from "rxjs/operators";
import { concat, interval } from "rxjs";
import { MatSnackBar } from "@angular/material/snack-bar";
import { Logging } from "../../logging/logging.service";
import { LatestChangesDialogService } from "./latest-changes-dialog.service";
import { LOCATION_TOKEN } from "../../../utils/di-tokens";
import { UnsavedChangesService } from "../../entity-details/form/unsaved-changes.service";

/**
 * Check with the server whether a new version of the app is available in order to notify the user.
 *
 * As we are using ServiceWorkers to cache the app to also work offline, explicit checking for updates is necessary.
 * The user receives a toast (hover message) if an update is available
 * and can click that to reload the app with the new version.
 */
@Injectable({ providedIn: "root" })
export class UpdateManagerService {
  private readonly UPDATE_PREFIX = "update-";

  constructor(
    private appRef: ApplicationRef,
    private updates: SwUpdate,
    private snackBar: MatSnackBar,
    private latestChangesDialogService: LatestChangesDialogService,
    private unsavedChanges: UnsavedChangesService,
    @Inject(LOCATION_TOKEN) private location: Location,
  ) {
    this.updates.unrecoverable.subscribe((err) => {
      Logging.error("App is in unrecoverable state: " + err.reason);
      this.location.reload();
    });
    const currentVersion = localStorage.getItem(
      LatestChangesDialogService.VERSION_KEY,
    );
    if (currentVersion && currentVersion.startsWith(this.UPDATE_PREFIX)) {
      localStorage.setItem(
        LatestChangesDialogService.VERSION_KEY,
        currentVersion.replace(this.UPDATE_PREFIX, ""),
      );
      this.location.reload();
    } else {
      this.latestChangesDialogService.showLatestChangesIfUpdated();
    }
  }

  /**
   * Display a notification to the user in case a new app version is detected by the ServiceWorker.
   */
  public listenToAppUpdates() {
    if (!this.updates.isEnabled) {
      return;
    }
    this.updates.versionUpdates
      .pipe(filter((e) => e.type === "VERSION_READY"))
      .subscribe(() => this.updateIfPossible());
  }

  /**
   * Schedule a regular check with the server for updates.
   */
  public regularlyCheckForUpdates() {
    if (!this.updates.isEnabled) {
      return;
    }

    // Allow the app to stabilize first, before starting polling for updates with `interval()`.
    const appIsStable$ = this.appRef.isStable.pipe(
      first((isStable) => isStable === true),
    );
    const everyHours$ = interval(60 * 60 * 1000);
    const everyHoursOnceAppIsStable$ = concat(appIsStable$, everyHours$);

    everyHoursOnceAppIsStable$.subscribe(() =>
      this.updates.checkForUpdate().catch((err) => Logging.error(err)),
    );
  }

  private updateIfPossible() {
    const currentVersion =
      localStorage.getItem(LatestChangesDialogService.VERSION_KEY) || "";
    if (currentVersion.startsWith(this.UPDATE_PREFIX)) {
      // Sometimes this is triggered multiple times for one update
      return;
    }

    if (this.unsavedChanges.pending) {
      // app cannot be safely reloaded
      localStorage.setItem(
        LatestChangesDialogService.VERSION_KEY,
        this.UPDATE_PREFIX + currentVersion,
      );
      this.snackBar
        .open(
          $localize`A new version of the app is available!`,
          $localize`:Action that a user can update the app with:Update`,
        )
        .onAction()
        .subscribe(() => {
          localStorage.setItem(
            LatestChangesDialogService.VERSION_KEY,
            currentVersion,
          );

          this.location.reload();
        });
    } else {
      this.location.reload();
    }
  }

  /**
   * Notifies user if app ends up in an unrecoverable state due to SW updates
   */
  public detectUnrecoverableState() {
    if (!this.updates.isEnabled) {
      return;
    }

    this.updates.unrecoverable.subscribe(({ reason }) => {
      Logging.warn(`SW in unrecoverable state: ${reason}`);
      this.snackBar
        .open(
          $localize`The app is in a unrecoverable state, please reload.`,
          $localize`:Action that a user can reload the app with:Reload`,
        )
        .onAction()
        .subscribe(() => this.location.reload());
    });
  }
}