fix: make gelocation work reliably

Closes #249

frontend/app/__mocks__/@capacitor/app.ts

@@ -0,0 +1,41 @@
+/*
+ * Copyright (C) 2026 StApps
+ * This program is free software: you can redistribute it and/or modify it
+ * under the terms of the GNU General Public License as published by the Free
+ * Software Foundation, version 3.
+ *
+ * This program is distributed in the hope that it will be useful, but WITHOUT
+ * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
+ * FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for
+ * more details.
+ *
+ * You should have received a copy of the GNU General Public License along with
+ * this program. If not, see <https://www.gnu.org/licenses/>.
+ */
+
+export interface URLOpenListenerEvent {
+  url: string;
+}
+
+export interface AppInfo {
+  name: string;
+  id: string;
+  build: string;
+  version: string;
+}
+
+export interface PluginListenerHandle {
+  remove: () => Promise<void>;
+}
+
+export class AppMock {
+  addListener<T>(_eventName: string, _listener: (event: T) => void): Promise<PluginListenerHandle> {
+    return Promise.resolve({remove: () => Promise.resolve()});
+  }
+
+  getInfo(): Promise<AppInfo> {
+    return Promise.resolve({name: 'StApps', id: 'de.anyschool.app', build: '1', version: '1.2.3'});
+  }
+}
+
+export const App = new AppMock();

frontend/app/android/capacitor.settings.gradle

@@ -12,28 +12,28 @@ include ':capacitor-app'
 project(':capacitor-app').projectDir = new File('../../../node_modules/.pnpm/@capacitor+app@8.0.1_@capacitor+core@8.2.0/node_modules/@capacitor/app/android')
 
 include ':capacitor-browser'
-project(':capacitor-browser').projectDir = new File('../../../node_modules/.pnpm/@capacitor+browser@8.0.2_@capacitor+core@8.2.0/node_modules/@capacitor/browser/android')
+project(':capacitor-browser').projectDir = new File('../../../node_modules/.pnpm/@capacitor+browser@8.0.4_@capacitor+core@8.2.0/node_modules/@capacitor/browser/android')
 
 include ':capacitor-clipboard'
 project(':capacitor-clipboard').projectDir = new File('../../../node_modules/.pnpm/@capacitor+clipboard@8.0.1_@capacitor+core@8.2.0/node_modules/@capacitor/clipboard/android')
 
 include ':capacitor-device'
-project(':capacitor-device').projectDir = new File('../../../node_modules/.pnpm/@capacitor+device@8.0.1_@capacitor+core@8.2.0/node_modules/@capacitor/device/android')
+project(':capacitor-device').projectDir = new File('../../../node_modules/.pnpm/@capacitor+device@8.0.3_@capacitor+core@8.2.0/node_modules/@capacitor/device/android')
 
 include ':capacitor-dialog'
 project(':capacitor-dialog').projectDir = new File('../../../node_modules/.pnpm/@capacitor+dialog@8.0.1_@capacitor+core@8.2.0/node_modules/@capacitor/dialog/android')
 
 include ':capacitor-filesystem'
-project(':capacitor-filesystem').projectDir = new File('../../../node_modules/.pnpm/@capacitor+filesystem@8.1.2_@capacitor+core@8.2.0/node_modules/@capacitor/filesystem/android')
+project(':capacitor-filesystem').projectDir = new File('../../../node_modules/.pnpm/@capacitor+filesystem@8.1.3_@capacitor+core@8.2.0/node_modules/@capacitor/filesystem/android')
 
 include ':capacitor-geolocation'
 project(':capacitor-geolocation').projectDir = new File('../../../node_modules/.pnpm/@capacitor+geolocation@8.1.0_@capacitor+core@8.2.0/node_modules/@capacitor/geolocation/android')
 
 include ':capacitor-haptics'
-project(':capacitor-haptics').projectDir = new File('../../../node_modules/.pnpm/@capacitor+haptics@8.0.1_@capacitor+core@8.2.0/node_modules/@capacitor/haptics/android')
+project(':capacitor-haptics').projectDir = new File('../../../node_modules/.pnpm/@capacitor+haptics@8.0.2_@capacitor+core@8.2.0/node_modules/@capacitor/haptics/android')
 
 include ':capacitor-keyboard'
-project(':capacitor-keyboard').projectDir = new File('../../../node_modules/.pnpm/@capacitor+keyboard@8.0.1_@capacitor+core@8.2.0/node_modules/@capacitor/keyboard/android')
+project(':capacitor-keyboard').projectDir = new File('../../../node_modules/.pnpm/@capacitor+keyboard@8.0.5_@capacitor+core@8.2.0/node_modules/@capacitor/keyboard/android')
 
 include ':capacitor-local-notifications'
 project(':capacitor-local-notifications').projectDir = new File('../../../node_modules/.pnpm/@capacitor+local-notifications@8.0.2_@capacitor+core@8.2.0/node_modules/@capacitor/local-notifications/android')
@@ -51,10 +51,10 @@ include ':capacitor-share'
 project(':capacitor-share').projectDir = new File('../../../node_modules/.pnpm/@capacitor+share@8.0.1_@capacitor+core@8.2.0/node_modules/@capacitor/share/android')
 
 include ':capacitor-splash-screen'
-project(':capacitor-splash-screen').projectDir = new File('../../../node_modules/.pnpm/@capacitor+splash-screen@8.0.1_@capacitor+core@8.2.0/node_modules/@capacitor/splash-screen/android')
+project(':capacitor-splash-screen').projectDir = new File('../../../node_modules/.pnpm/@capacitor+splash-screen@8.0.2_@capacitor+core@8.2.0/node_modules/@capacitor/splash-screen/android')
 
 include ':transistorsoft-capacitor-background-fetch'
 project(':transistorsoft-capacitor-background-fetch').projectDir = new File('../../../node_modules/.pnpm/@transistorsoft+capacitor-background-fetch@8.0.0_@capacitor+core@8.2.0/node_modules/@transistorsoft/capacitor-background-fetch/android')
 
 include ':capacitor-secure-storage-plugin'
-project(':capacitor-secure-storage-plugin').projectDir = new File('../../../node_modules/.pnpm/capacitor-secure-storage-plugin@0.12.0_@capacitor+core@8.2.0/node_modules/capacitor-secure-storage-plugin/android')
+project(':capacitor-secure-storage-plugin').projectDir = new File('../../../node_modules/.pnpm/capacitor-secure-storage-plugin@0.13.0_@capacitor+core@8.2.0/node_modules/capacitor-secure-storage-plugin/android')

frontend/app/src/app/modules/data/list/food-data-list.component.spec.ts

@@ -0,0 +1,127 @@
+/*
+ * Copyright (C) 2023 StApps
+ * This program is free software: you can redistribute it and/or modify it
+ * under the terms of the GNU General Public License as published by the Free
+ * Software Foundation, version 3.
+ *
+ * This program is distributed in the hope that it will be useful, but WITHOUT
+ * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
+ * FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for
+ * more details.
+ *
+ * You should have received a copy of the GNU General Public License along with
+ * this program. If not, see <https://www.gnu.org/licenses/>.
+ */
+import {TestBed} from '@angular/core/testing';
+import {Position} from '@capacitor/geolocation';
+import {SCSearchSort} from '@openstapps/core';
+import {BehaviorSubject, ReplaySubject} from 'rxjs';
+import {PositionService} from '../../map/position.service';
+import {ContextMenuService} from '../../menu/context/context-menu.service';
+import {FoodDataListComponent, RESORT_AFTER_METERS} from './food-data-list.component';
+
+describe('FoodDataListComponent', () => {
+  // keep well clear of the threshold: the helper below uses a flat-earth approximation,
+  // so distances right at the boundary could round either way
+  const BELOW_THRESHOLD = RESORT_AFTER_METERS * 0.6;
+  const ABOVE_THRESHOLD = RESORT_AFTER_METERS * 1.5;
+
+  let geoLocation: ReplaySubject<Position>;
+  let positionService: {
+    geoLocation: ReplaySubject<Position>;
+    requestPermission: jasmine.Spy;
+    position?: {latitude: number; longitude: number};
+  };
+  let sortQuery: BehaviorSubject<SCSearchSort[] | undefined>;
+  let sortQueryNext: jasmine.Spy;
+  let component: FoodDataListComponent;
+
+  /** A Capacitor position, `metersNorth` north of the start point (only the fields the component reads) */
+  const position = (metersNorth = 0): Position =>
+    ({
+      timestamp: 0,
+      coords: {latitude: 50.1278 + metersNorth / 111_195, longitude: 8.6674, accuracy: 20},
+    }) as Position;
+
+  const sortedBy = (p: Position): SCSearchSort[] => [
+    {
+      type: 'distance',
+      order: 'asc',
+      arguments: {field: 'geo', position: [p.coords.longitude, p.coords.latitude]},
+    },
+  ];
+
+  beforeEach(() => {
+    // the real geoLocation replays the last position to new subscribers, so does this stand-in
+    geoLocation = new ReplaySubject<Position>(1);
+    positionService = {
+      geoLocation,
+      requestPermission: jasmine.createSpy('requestPermission').and.resolveTo('granted'),
+    };
+    sortQuery = new BehaviorSubject<SCSearchSort[] | undefined>(undefined);
+    sortQueryNext = spyOn(sortQuery, 'next').and.callThrough();
+
+    TestBed.configureTestingModule({
+      providers: [
+        {provide: PositionService, useValue: positionService},
+        {provide: ContextMenuService, useValue: {sortQuery}},
+      ],
+    });
+    // only the class logic is under test, so the template is not rendered
+    component = TestBed.runInInjectionContext(() => new FoodDataListComponent());
+  });
+
+  it('should ask for location permission when the page is entered', () => {
+    component.ionViewWillEnter();
+    expect(positionService.requestPermission).toHaveBeenCalledTimes(1);
+  });
+
+  it('should not sort while the page is not in view', () => {
+    geoLocation.next(position());
+    expect(sortQueryNext).not.toHaveBeenCalled();
+  });
+
+  it('should sort by distance to the current position when the page is entered', () => {
+    geoLocation.next(position());
+    component.ionViewWillEnter();
+
+    expect(sortQueryNext).toHaveBeenCalledOnceWith(sortedBy(position()));
+    expect(positionService.position).toEqual({
+      latitude: position().coords.latitude,
+      longitude: position().coords.longitude,
+    });
+  });
+
+  it(`should not re-sort on movements below ${RESORT_AFTER_METERS} m (GPS jitter)`, () => {
+    component.ionViewWillEnter();
+    geoLocation.next(position());
+    geoLocation.next(position(RESORT_AFTER_METERS * 0.1));
+    geoLocation.next(position(BELOW_THRESHOLD));
+
+    expect(sortQueryNext).toHaveBeenCalledTimes(1);
+  });
+
+  it(`should re-sort after moving more than ${RESORT_AFTER_METERS} m`, () => {
+    component.ionViewWillEnter();
+    geoLocation.next(position());
+    geoLocation.next(position(ABOVE_THRESHOLD));
+
+    expect(sortQueryNext).toHaveBeenCalledTimes(2);
+    expect(sortQueryNext).toHaveBeenCalledWith(sortedBy(position(ABOVE_THRESHOLD)));
+  });
+
+  it('should stop sorting when the page is left and sort again with the latest position on return', () => {
+    const movedWhileAway = RESORT_AFTER_METERS * 5;
+
+    component.ionViewWillEnter();
+    geoLocation.next(position());
+    component.ionViewWillLeave();
+
+    geoLocation.next(position(movedWhileAway));
+    expect(sortQueryNext).toHaveBeenCalledTimes(1);
+
+    component.ionViewWillEnter();
+    expect(sortQueryNext).toHaveBeenCalledTimes(2);
+    expect(sortQueryNext).toHaveBeenCalledWith(sortedBy(position(movedWhileAway)));
+  });
+});

frontend/app/src/app/modules/data/list/food-data-list.component.ts

@@ -14,13 +14,18 @@
  */
 import {Component, inject} from '@angular/core';
 import {PositionService} from '../../map/position.service';
-import {Geolocation} from '@capacitor/geolocation';
-import {BehaviorSubject, catchError} from 'rxjs';
+import {BehaviorSubject, map} from 'rxjs';
 import {pauseWhen} from '../../../util/rxjs/pause-when';
+import {distinctUntilMoved} from '../../../util/rxjs/distinct-until-moved';
 import {SCSearchFilter} from '@openstapps/core';
 import {ContextMenuService} from '../../menu/context/context-menu.service';
 import {takeUntilDestroyed} from '@angular/core/rxjs-interop';
 
+/**
+ * Re-sort the list (= new search) only after the user moved this far
+ */
+export const RESORT_AFTER_METERS = 100;
+
 /**
  * Presents a list of places for eating/drinking
  */
@@ -68,43 +73,39 @@ export class FoodDataListComponent {
     type: 'boolean',
   };
 
+  private positionService = inject(PositionService);
+
   constructor() {
-    const positionService = inject(PositionService);
+    const positionService = this.positionService;
     const contextMenuService = inject(ContextMenuService);
 
-    positionService
-      .watchCurrentLocation({enableHighAccuracy: false, maximumAge: 1000})
+    // Uses the app-wide shared location watch instead of starting its own
+    positionService.geoLocation
       .pipe(
+        map(({coords}) => ({latitude: coords.latitude, longitude: coords.longitude})),
+        distinctUntilMoved(RESORT_AFTER_METERS),
         pauseWhen(this.isNotInView$),
         takeUntilDestroyed(),
-        catchError(async _error => {
-          await Geolocation.checkPermissions();
-        }),
       )
-      .subscribe({
-        next(position) {
-          if (!position) return;
-          positionService.position = position;
-          contextMenuService.sortQuery.next([
-            {
-              type: 'distance',
-              order: 'asc',
-              arguments: {
-                field: 'geo',
-                position: [position.longitude, position.latitude],
-              },
+      .subscribe(position => {
+        positionService.position = position;
+        contextMenuService.sortQuery.next([
+          {
+            type: 'distance',
+            order: 'asc',
+            arguments: {
+              field: 'geo',
+              position: [position.longitude, position.latitude],
             },
-          ]);
-        },
-        async error() {
-          positionService.position = undefined;
-          await Geolocation.checkPermissions();
-        },
+          },
+        ]);
       });
   }
 
   ionViewWillEnter() {
     this.isNotInView$.next(false);
+    // the shared watch never asks by itself; on this page, location is the point, so ask here
+    void this.positionService.requestPermission();
   }
 
   ionViewWillLeave() {

frontend/app/src/app/modules/map/controls/geolocate-control.component.ts

@@ -13,16 +13,86 @@ import {IonFabButton} from '@ionic/angular/standalone';
 import {MapService} from '@maplibre/ngx-maplibre-gl';
 import {FitBoundsOptions, GeolocateControl, GeolocateControlOptions} from 'maplibre-gl';
 import {Map as MapLibre} from 'maplibre-gl';
-import {BehaviorSubject} from 'rxjs';
+import {BehaviorSubject, Subscription} from 'rxjs';
 import {IonIconDirective} from 'src/app/util/ion-icon/ion-icon.directive';
+import {PERMISSION_GRANTED, PositionService} from '../position.service';
 
 type WatchState = InstanceType<typeof GeolocateControl>['_watchState'];
 
+type GeolocationApi = Pick<Geolocation, 'watchPosition' | 'clearWatch' | 'getCurrentPosition'>;
+
+/**
+ * A `navigator.geolocation` look-alike that serves positions from the app's PositionService.
+ * MapLibre has no option for a custom position source and always calls `navigator.geolocation`,
+ * so this lets the map share the app's single location watch instead of starting its own.
+ */
+class PositionServiceGeolocation implements GeolocationApi {
+  private nextId = 1;
+
+  private readonly watches = new Map<number, Subscription>();
+
+  constructor(private readonly positionService: PositionService) {}
+
+  watchPosition(success: PositionCallback, error?: PositionErrorCallback | null): number {
+    const id = this.nextId++;
+    const watch = new Subscription();
+    this.watches.set(id, watch);
+    void this.positionService.requestPermission().then(permission => {
+      if (watch.closed) return;
+      if (permission != PERMISSION_GRANTED) {
+        error?.({code: 1, message: 'User denied Geolocation'} as GeolocationPositionError);
+        return;
+      }
+      // Capacitor's Position has the same shape as the browser's GeolocationPosition
+      watch.add(
+        // precise: while the user tracks their location on the map, the shared watch uses GPS
+        this.positionService.preciseLocation.subscribe(position =>
+          success(position as unknown as GeolocationPosition),
+        ),
+      );
+    });
+    return id;
+  }
+
+  clearWatch(id: number): void {
+    this.watches.get(id)?.unsubscribe();
+    this.watches.delete(id);
+  }
+
+  getCurrentPosition(success: PositionCallback, error?: PositionErrorCallback | null): void {
+    const id = this.watchPosition(
+      position => {
+        this.clearWatch(id);
+        success(position);
+      },
+      positionError => {
+        this.clearWatch(id);
+        error?.(positionError);
+      },
+    );
+  }
+}
+
+/**
+ * Runs `run` while `navigator.geolocation` is replaced by `geolocation`.
+ * MapLibre only uses it synchronously inside the wrapped calls, so no other code sees the swap.
+ */
+function withGeolocation<T>(geolocation: GeolocationApi, run: () => T): T {
+  Object.defineProperty(globalThis.navigator, 'geolocation', {value: geolocation, configurable: true});
+  try {
+    return run();
+  } finally {
+    // removing the own property brings back the browser's original
+    delete (globalThis.navigator as {geolocation?: unknown}).geolocation;
+  }
+}
+
 class CustomGeolocateControl extends GeolocateControl {
   constructor(
     public _container: HTMLElement,
     watchState: BehaviorSubject<WatchState>,
     options: GeolocateControlOptions,
+    private readonly geolocation: GeolocationApi,
   ) {
     super(options);
     Object.defineProperty(this, '_watchState', {
@@ -45,7 +115,27 @@ class CustomGeolocateControl extends GeolocateControl {
     return this._container;
   }
 
-  override onRemove() {}
+  // MapLibre uses navigator.geolocation only in these three methods: point it to the PositionService
+
+  override trigger(): boolean {
+    return withGeolocation(this.geolocation, () => super.trigger());
+  }
+
+  override _clearWatch(): void {
+    withGeolocation(this.geolocation, () => super._clearWatch());
+  }
+
+  /**
+   * Run MapLibre's cleanup (stops the watch, removes the dot, resets its global watch counter),
+   * but not letting it remove the Angular-owned container
+   */
+  override onRemove() {
+    if (!this._map) return;
+    const container = this._container;
+    this._container = document.createElement('div');
+    withGeolocation(this.geolocation, () => super.onRemove());
+    this._container = container;
+  }
 }
 
 @Component({
@@ -58,6 +148,8 @@ class CustomGeolocateControl extends GeolocateControl {
 export class GeolocateControlComponent implements AfterContentInit, OnDestroy {
   private mapService = inject(MapService);
 
+  private positionService = inject(PositionService);
+
   @Input() position?: 'top-left' | 'top-right' | 'bottom-left' | 'bottom-right';
 
   @Input() positionOptions?: PositionOptions;
@@ -75,12 +167,17 @@ export class GeolocateControlComponent implements AfterContentInit, OnDestroy {
   control: CustomGeolocateControl;
 
   ngAfterContentInit() {
-    this.control = new CustomGeolocateControl(this.content.nativeElement, this.watchState, {
-      positionOptions: this.positionOptions,
-      fitBoundsOptions: this.fitBoundsOptions,
-      trackUserLocation: this.trackUserLocation,
-      showUserLocation: this.showUserLocation,
-    });
+    this.control = new CustomGeolocateControl(
+      this.content.nativeElement,
+      this.watchState,
+      {
+        positionOptions: this.positionOptions,
+        fitBoundsOptions: this.fitBoundsOptions,
+        trackUserLocation: this.trackUserLocation,
+        showUserLocation: this.showUserLocation,
+      },
+      new PositionServiceGeolocation(this.positionService),
+    );
     this.mapService.mapCreated$.subscribe(() => {
       this.mapService.addControl(this.control, this.position);
     });

frontend/app/src/app/modules/map/position.service.spec.ts

@@ -12,15 +12,25 @@
  * You should have received a copy of the GNU General Public License along with
  * this program. If not, see <https://www.gnu.org/licenses/>.
  */
-import {TestBed} from '@angular/core/testing';
+import {discardPeriodicTasks, fakeAsync, TestBed, tick} from '@angular/core/testing';
 import {MapModule} from './map.module';
 import {provideHttpClient, withInterceptorsFromDi} from '@angular/common/http';
 import {StorageModule} from '../storage/storage.module';
-import {MapPosition, PositionService} from './position.service';
+import {
+  MapPosition,
+  PERMISSION_DENIED,
+  PERMISSION_GRANTED,
+  PERMISSION_PROMPT,
+  PositionService,
+  WATCH_KEEP_ALIVE_MS,
+  WATCH_RETRY_DELAY_MS,
+} from './position.service';
 import {ConfigProvider} from '../config/config.provider';
 import {LoggerTestingModule} from 'ngx-logger/testing';
-import {firstValueFrom} from 'rxjs';
-import {Geolocation} from '@capacitor/geolocation';
+import {firstValueFrom, Subscription} from 'rxjs';
+import {Geolocation, PermissionStatus, Position} from '@capacitor/geolocation';
+import {App} from '@capacitor/app';
+import {Capacitor} from '@capacitor/core';
 
 describe('PositionService', () => {
   let positionService: PositionService;
@@ -70,4 +80,348 @@ describe('PositionService', () => {
     await new Promise(resolve => setTimeout(resolve, 100));
     expect(clearWatch).toHaveBeenCalledWith({id: 'abc'});
   });
+
+  /**  Helpers for the shared watch */
+
+  /** Some longer period of time, for "nothing happens meanwhile" checks */
+  const A_WHILE_MS = 10_000;
+
+  /** A permission status as Capacitor reports it */
+  const permission = (
+    location: PermissionStatus['location'],
+    coarseLocation: PermissionStatus['coarseLocation'] = location,
+  ): PermissionStatus => ({location, coarseLocation});
+
+  /** A position (only the fields the service reads) */
+  const position = (latitude: number): Position =>
+    ({timestamp: 0, coords: {latitude, longitude: 8.6674, accuracy: 20}}) as Position;
+
+  /** Every native watch the service started, with its options and callback */
+  let watches: Array<{
+    id: string;
+    options: PositionOptions;
+    emit: (position: Position | undefined, error?: unknown) => void;
+  }>;
+
+  /** Replaces the native watch, so tests can see how many watches exist and feed them positions */
+  const mockNativeWatch = () => {
+    watches = [];
+    spyOn(Geolocation, 'watchPosition').and.callFake((options, callback) => {
+      const id = `watch-${watches.length + 1}`;
+      watches.push({
+        id,
+        options,
+        emit: callback as (position: Position | undefined, error?: unknown) => void,
+      });
+      return Promise.resolve(id);
+    });
+    return spyOn(Geolocation, 'clearWatch').and.resolveTo();
+  };
+
+  describe('geoLocation (shared watch)', () => {
+    let clearWatch: jasmine.Spy;
+    let subscriptions: Subscription[];
+
+    beforeEach(() => {
+      clearWatch = mockNativeWatch();
+      subscriptions = [];
+    });
+
+    afterEach(() => {
+      for (const subscription of subscriptions) subscription.unsubscribe();
+    });
+
+    it('should start only one native watch for many subscribers', fakeAsync(() => {
+      spyOn(Geolocation, 'checkPermissions').and.resolveTo(permission('granted'));
+      for (let index = 0; index < 10; index++) {
+        subscriptions.push(positionService.geoLocation.subscribe());
+      }
+      tick();
+
+      expect(watches.length).toBe(1);
+      discardPeriodicTasks();
+    }));
+
+    it('should use coarse location by default', fakeAsync(() => {
+      spyOn(Geolocation, 'checkPermissions').and.resolveTo(permission('granted'));
+      subscriptions.push(positionService.geoLocation.subscribe());
+      tick();
+
+      expect(watches[0].options.enableHighAccuracy).toBeFalse();
+      discardPeriodicTasks();
+    }));
+
+    it('should give the positions of the one watch to all subscribers', fakeAsync(() => {
+      spyOn(Geolocation, 'checkPermissions').and.resolveTo(permission('granted'));
+      const first: number[] = [];
+      const second: number[] = [];
+      subscriptions.push(
+        positionService.geoLocation.subscribe(p => first.push(p.coords.latitude)),
+        positionService.geoLocation.subscribe(p => second.push(p.coords.latitude)),
+      );
+      tick();
+      watches[0].emit(position(50.1));
+
+      expect(first).toEqual([50.1]);
+      expect(second).toEqual([50.1]);
+      discardPeriodicTasks();
+    }));
+
+    it('should give new subscribers the last position right away', fakeAsync(() => {
+      spyOn(Geolocation, 'checkPermissions').and.resolveTo(permission('granted'));
+      subscriptions.push(positionService.geoLocation.subscribe());
+      tick();
+      watches[0].emit(position(50.1));
+
+      let latecomer: number | undefined;
+      subscriptions.push(positionService.geoLocation.subscribe(p => (latecomer = p.coords.latitude)));
+
+      expect(latecomer).toBe(50.1);
+      expect(watches.length).toBe(1);
+      discardPeriodicTasks();
+    }));
+
+    it('should accept approximate location (Android 12+)', fakeAsync(() => {
+      spyOn(Geolocation, 'checkPermissions').and.resolveTo(permission('prompt', 'granted'));
+      subscriptions.push(positionService.geoLocation.subscribe());
+      tick();
+
+      expect(watches.length).toBe(1);
+      discardPeriodicTasks();
+    }));
+
+    it('should not start a watch (and not ask) while permission is missing', fakeAsync(() => {
+      spyOn(Geolocation, 'checkPermissions').and.resolveTo(permission('prompt'));
+      const getCurrentPosition = spyOn(Geolocation, 'getCurrentPosition');
+      subscriptions.push(positionService.geoLocation.subscribe());
+      tick(A_WHILE_MS);
+
+      expect(watches.length).toBe(0);
+      expect(getCurrentPosition).not.toHaveBeenCalled();
+      discardPeriodicTasks();
+    }));
+
+    it('should start the watch as soon as permission is granted later (web: re-checks every 2 s)', fakeAsync(() => {
+      const checkPermissions = spyOn(Geolocation, 'checkPermissions').and.resolveTo(permission('prompt'));
+      subscriptions.push(positionService.geoLocation.subscribe());
+      tick();
+      expect(watches.length).toBe(0);
+
+      // the user clicks "Allow" in the browser prompt
+      checkPermissions.and.resolveTo(permission('granted'));
+      tick(2000);
+
+      expect(watches.length).toBe(1);
+      discardPeriodicTasks();
+    }));
+
+    it('should keep the watch alive for a while without subscribers (e.g. list re-render)', fakeAsync(() => {
+      spyOn(Geolocation, 'checkPermissions').and.resolveTo(permission('granted'));
+      positionService.geoLocation.subscribe().unsubscribe();
+      // just before the keep-alive time is over
+      tick(WATCH_KEEP_ALIVE_MS - 1000);
+      subscriptions.push(positionService.geoLocation.subscribe());
+      tick();
+
+      expect(watches.length).toBe(1);
+      expect(clearWatch).not.toHaveBeenCalled();
+      discardPeriodicTasks();
+    }));
+
+    it('should clear the native watch when the keep-alive time after the last subscriber is over', fakeAsync(() => {
+      spyOn(Geolocation, 'checkPermissions').and.resolveTo(permission('granted'));
+      const subscription = positionService.geoLocation.subscribe();
+      tick();
+      subscription.unsubscribe();
+      tick(WATCH_KEEP_ALIVE_MS);
+
+      expect(clearWatch).toHaveBeenCalledOnceWith({id: 'watch-1'});
+      discardPeriodicTasks();
+    }));
+
+    it('should retry after a delay instead of breaking the subscribers on an error', fakeAsync(() => {
+      spyOn(Geolocation, 'checkPermissions').and.resolveTo(permission('granted'));
+      let failed = false;
+      subscriptions.push(positionService.geoLocation.subscribe({error: () => (failed = true)}));
+      tick();
+
+      watches[0].emit(undefined, {code: 'OS-PLUG-GLOC-0010', message: 'timeout'});
+      tick(WATCH_RETRY_DELAY_MS);
+
+      expect(failed).toBeFalse();
+      expect(watches.length).toBe(2);
+      // the plugin removes a failed watch by itself, so it must not be cleared again
+      expect(clearWatch).not.toHaveBeenCalled();
+      discardPeriodicTasks();
+    }));
+  });
+
+  describe('preciseLocation', () => {
+    beforeEach(() => {
+      mockNativeWatch();
+      spyOn(Geolocation, 'checkPermissions').and.resolveTo(permission('granted'));
+    });
+
+    it('should switch the shared watch to GPS while subscribed, and back to coarse afterwards', fakeAsync(() => {
+      const list = positionService.geoLocation.subscribe();
+      tick();
+      expect(watches.map(watch => watch.options.enableHighAccuracy)).toEqual([false]);
+
+      const map = positionService.preciseLocation.subscribe();
+      tick();
+      expect(watches.map(watch => watch.options.enableHighAccuracy)).toEqual([false, true]);
+
+      map.unsubscribe();
+      tick();
+      expect(watches.map(watch => watch.options.enableHighAccuracy)).toEqual([false, true, false]);
+
+      list.unsubscribe();
+      tick(WATCH_KEEP_ALIVE_MS);
+      discardPeriodicTasks();
+    }));
+
+    it('should not restart the watch for a second precise subscriber', fakeAsync(() => {
+      const first = positionService.preciseLocation.subscribe();
+      tick();
+      const second = positionService.preciseLocation.subscribe();
+      tick();
+      second.unsubscribe();
+      tick();
+
+      expect(watches.length).toBe(1);
+      expect(watches[0].options.enableHighAccuracy).toBeTrue();
+
+      first.unsubscribe();
+      tick(WATCH_KEEP_ALIVE_MS);
+      discardPeriodicTasks();
+    }));
+  });
+
+  describe('requestPermission', () => {
+    let getCurrentPosition: jasmine.Spy;
+
+    beforeEach(() => {
+      getCurrentPosition = spyOn(Geolocation, 'getCurrentPosition').and.resolveTo(position(50.1));
+    });
+
+    it('should not ask again if location is already allowed (also approximate only)', async () => {
+      spyOn(Geolocation, 'checkPermissions').and.resolveTo(permission('prompt', 'granted'));
+
+      expect(await positionService.requestPermission()).toBe(PERMISSION_GRANTED);
+      expect(getCurrentPosition).not.toHaveBeenCalled();
+    });
+
+    it('should not ask again if location was denied', async () => {
+      spyOn(Geolocation, 'checkPermissions').and.resolveTo(permission('denied'));
+
+      expect(await positionService.requestPermission()).toBe(PERMISSION_DENIED);
+      expect(getCurrentPosition).not.toHaveBeenCalled();
+    });
+
+    it('should show the prompt and report "granted" if the user allows', async () => {
+      spyOn(Geolocation, 'checkPermissions').and.returnValues(
+        Promise.resolve(permission('prompt')),
+        Promise.resolve(permission('granted')),
+      );
+
+      expect(await positionService.requestPermission()).toBe(PERMISSION_GRANTED);
+      expect(getCurrentPosition).toHaveBeenCalledTimes(1);
+    });
+
+    it('should report "denied" if the user denies in the prompt', async () => {
+      getCurrentPosition.and.rejectWith({code: 1});
+      spyOn(Geolocation, 'checkPermissions').and.returnValues(
+        Promise.resolve(permission('prompt')),
+        Promise.resolve(permission('denied')),
+      );
+
+      expect(await positionService.requestPermission()).toBe(PERMISSION_DENIED);
+    });
+
+    it('should report "prompt" if the user closes the prompt without deciding', async () => {
+      getCurrentPosition.and.rejectWith({code: 1});
+      spyOn(Geolocation, 'checkPermissions').and.resolveTo(permission('prompt'));
+
+      expect(await positionService.requestPermission()).toBe(PERMISSION_PROMPT);
+    });
+
+    it('should report "granted" if location is allowed but there is no fix yet (timeout)', async () => {
+      getCurrentPosition.and.rejectWith({code: 'OS-PLUG-GLOC-0010'});
+      spyOn(Geolocation, 'checkPermissions').and.returnValues(
+        Promise.resolve(permission('prompt')),
+        Promise.resolve(permission('granted')),
+      );
+
+      expect(await positionService.requestPermission()).toBe(PERMISSION_GRANTED);
+    });
+
+    it('should judge by the position if the browser has no Permissions API', async () => {
+      spyOn(Geolocation, 'checkPermissions').and.rejectWith(new Error('Permissions API not available'));
+
+      expect(await positionService.requestPermission()).toBe(PERMISSION_GRANTED);
+
+      getCurrentPosition.and.rejectWith({code: 1});
+      expect(await positionService.requestPermission()).toBe(PERMISSION_DENIED);
+    });
+  });
+
+  describe('on devices (no permission polling)', () => {
+    let checkPermissions: jasmine.Spy;
+    let resumeApp: () => void;
+    let service: PositionService;
+
+    beforeEach(() => {
+      mockNativeWatch();
+      spyOn(Capacitor, 'isNativePlatform').and.returnValue(true);
+      spyOn(App, 'addListener').and.callFake((_event, callback) => {
+        resumeApp = callback as () => void;
+        return Promise.resolve({remove: () => Promise.resolve()});
+      });
+      spyOn(Geolocation, 'getCurrentPosition').and.resolveTo(position(50.1));
+      checkPermissions = spyOn(Geolocation, 'checkPermissions').and.resolveTo(permission('prompt'));
+      // created after the spies, because the service decides at creation whether it runs on a device
+      service = TestBed.runInInjectionContext(() => new PositionService());
+    });
+
+    it('should check the permission once instead of polling', fakeAsync(() => {
+      const subscription = service.geoLocation.subscribe();
+      tick(A_WHILE_MS);
+
+      expect(checkPermissions).toHaveBeenCalledTimes(1);
+      subscription.unsubscribe();
+      tick(WATCH_KEEP_ALIVE_MS);
+    }));
+
+    it('should start the watch right after the user allowed location in our prompt', fakeAsync(() => {
+      const subscription = service.geoLocation.subscribe();
+      tick();
+      expect(watches.length).toBe(0);
+
+      // the user allows location in the prompt shown by requestPermission()
+      (Geolocation.getCurrentPosition as jasmine.Spy).and.callFake(() => {
+        checkPermissions.and.resolveTo(permission('granted'));
+        return Promise.resolve(position(50.1));
+      });
+      void service.requestPermission();
+      tick();
+
+      expect(watches.length).toBe(1);
+      subscription.unsubscribe();
+      tick(WATCH_KEEP_ALIVE_MS);
+    }));
+
+    it('should check again when the app comes back from the system settings', fakeAsync(() => {
+      const subscription = service.geoLocation.subscribe();
+      tick();
+      expect(watches.length).toBe(0);
+
+      checkPermissions.and.resolveTo(permission('granted'));
+      resumeApp();
+      tick();
+
+      expect(watches.length).toBe(1);
+      subscription.unsubscribe();
+      tick(WATCH_KEEP_ALIVE_MS);
+    }));
+  });
 });

frontend/app/src/app/modules/map/position.service.ts

@@ -14,8 +14,113 @@
  */
 import {Injectable} from '@angular/core';
 import {Point} from 'geojson';
-import {Observable} from 'rxjs';
-import {Geolocation, Position} from '@capacitor/geolocation';
+import {
+  BehaviorSubject,
+  catchError,
+  defer,
+  distinctUntilChanged,
+  finalize,
+  first,
+  from,
+  map,
+  merge,
+  Observable,
+  of,
+  ReplaySubject,
+  retry,
+  share,
+  Subject,
+  switchMap,
+  timer,
+} from 'rxjs';
+import {Geolocation, PermissionStatus, Position} from '@capacitor/geolocation';
+import {App} from '@capacitor/app';
+import {Capacitor, PermissionState} from '@capacitor/core';
+
+export const PERMISSION_PROMPT = 'prompt' satisfies PermissionState;
+
+/**
+ * Result of requestPermission(): granted, denied, or still undecided (prompt dismissed)
+ */
+export type LocationPermission =
+  | typeof PERMISSION_GRANTED
+  | typeof PERMISSION_DENIED
+  | typeof PERMISSION_PROMPT;
+
+/**
+ * How long the shared location watch keeps running after the last subscriber left,
+ * so a short gap (e.g. a list re-render or quick page switch) doesn't restart it
+ */
+export const WATCH_KEEP_ALIVE_MS = 30_000;
+
+/**
+ * How long to wait before starting a new watch after an error (e.g. no fix indoors)
+ */
+export const WATCH_RETRY_DELAY_MS = 10_000;
+
+/**
+ * Coarse (network / Wi-Fi) location: enough for distances in lists, fast indoors, saves battery
+ */
+const COARSE_OPTIONS: PositionOptions = {enableHighAccuracy: false, maximumAge: 30_000, timeout: 30_000};
+
+/**
+ * Precise (GPS) location: for following the user on the map
+ */
+const PRECISE_OPTIONS: PositionOptions = {enableHighAccuracy: true, maximumAge: 0, timeout: 30_000};
+
+/**
+ * Permission states as defined by Capacitor (`PermissionState` is a type only, it has no runtime constants)
+ */
+export const PERMISSION_GRANTED = 'granted' satisfies PermissionState;
+export const PERMISSION_DENIED = 'denied' satisfies PermissionState;
+
+/**
+ * Location may be used. On Android, `location` is only granted for *precise* location;
+ * if the user chose "approximate", only `coarseLocation` is granted, which is enough for us
+ * (Android then just ignores enableHighAccuracy).
+ */
+function isGranted(status: PermissionStatus): boolean {
+  return status.location === PERMISSION_GRANTED || status.coarseLocation === PERMISSION_GRANTED;
+}
+
+/**
+ * The user refused both precise and approximate location
+ */
+function isDenied(status: PermissionStatus): boolean {
+  return status.location === PERMISSION_DENIED && status.coarseLocation === PERMISSION_DENIED;
+}
+
+/**
+ * Emits when the app comes back to the foreground (e.g. from the system settings)
+ */
+const appResumed$ = new Observable<void>(subscriber => {
+  const listener = App.addListener('resume', () => subscriber.next());
+  return () => void listener.then(handle => handle.remove());
+});
+
+/**
+ * Wraps a Capacitor position watch in an Observable.
+ * Passes the real error on, and only clears the watch if it is still alive
+ * (the plugin removes a watch by itself after an error).
+ */
+function nativeWatch(options: PositionOptions): Observable<Position> {
+  return new Observable<Position>(subscriber => {
+    let active = true;
+    const watcherID = Geolocation.watchPosition(options, (position, error) => {
+      if (error) {
+        active = false;
+        subscriber.error(error);
+      } else if (position) {
+        subscriber.next(position);
+      }
+    });
+    return () => {
+      const wasActive = active;
+      active = false;
+      void watcherID.then(id => (wasActive ? Geolocation.clearWatch({id}) : undefined)).catch(() => {});
+    };
+  });
+}
 
 export interface Coordinates {
   /**
@@ -39,29 +144,95 @@ export interface MapPosition extends Coordinates {
   providedIn: 'root',
 })
 export class PositionService {
-  geoLocation = new Observable<Position>(subscriber => {
-    const watcherID = Geolocation.checkPermissions().then(permissions => {
-      if (permissions.location === 'granted') {
-        return Geolocation.watchPosition({}, (position, error) => {
-          if (error) {
-            subscriber.error(position);
-          } else if (position) {
-            subscriber.next(position);
-          }
-        });
-      }
-      return;
-    });
-    return {
-      unsubscribe() {
-        watcherID.then(id => {
-          if (id) {
-            Geolocation.clearWatch({id});
-          }
-        });
-      },
-    };
-  });
+  /**
+   * How many subscribers currently need precise (GPS) location, see preciseLocation
+   */
+  private readonly preciseSubscribers$ = new BehaviorSubject(0);
+
+  /**
+   * Emits after requestPermission() showed the permission prompt
+   */
+  private readonly permissionRequested$ = new Subject<void>();
+
+  /**
+   * When to (re-)check whether location permission has been granted.
+   * Web: every 2 s, browsers don't tell us when the user clicks "Allow".
+   * Device: permission only changes via our prompt or the system settings (and coming back
+   * from there resumes the app), so no polling is needed.
+   */
+  private readonly permissionChecks$: Observable<unknown> = Capacitor.isNativePlatform()
+    ? merge(of(true), this.permissionRequested$, appResumed$)
+    : timer(0, 2000);
+
+  /**
+   * The device position, shared by everything that needs it (list distances, map, ...).
+   *
+   * - Only one native watch, however many subscribers (before: one per list item)
+   * - Waits until location permission is granted, also if that happens later (e.g. via the prompt)
+   * - New subscribers immediately get the last position
+   * - Keeps running for 30 s without subscribers, so a list re-render doesn't restart it
+   * - Retries after errors (e.g. timeouts indoors) instead of breaking all subscribers
+   * - Coarse by default; switches the same watch to GPS while someone uses preciseLocation
+   */
+  readonly geoLocation: Observable<Position> = defer(() =>
+    this.permissionChecks$.pipe(
+      switchMap(() =>
+        from(Geolocation.checkPermissions()).pipe(
+          // no Permissions API (some browsers): just start, watchPosition prompts / fails by itself
+          catchError(() =>
+            of<PermissionStatus>({location: PERMISSION_GRANTED, coarseLocation: PERMISSION_GRANTED}),
+          ),
+        ),
+      ),
+      first(isGranted),
+      // restart the one watch with other options whenever the need for precision changes
+      switchMap(() =>
+        this.preciseSubscribers$.pipe(
+          map(count => count > 0),
+          distinctUntilChanged(),
+          switchMap(precise => nativeWatch(precise ? PRECISE_OPTIONS : COARSE_OPTIONS)),
+        ),
+      ),
+      retry({delay: () => timer(WATCH_RETRY_DELAY_MS)}),
+    ),
+  ).pipe(
+    share({
+      connector: () => new ReplaySubject<Position>(1),
+      resetOnRefCountZero: () => timer(WATCH_KEEP_ALIVE_MS),
+    }),
+  );
+
+  /**
+   * Same positions as geoLocation, but while subscribed, the shared watch uses GPS.
+   * For actively following the user (map); falls back to coarse when the last one unsubscribes.
+   */
+  readonly preciseLocation: Observable<Position> = defer(() => {
+    this.preciseSubscribers$.next(this.preciseSubscribers$.value + 1);
+    return this.geoLocation;
+  }).pipe(finalize(() => this.preciseSubscribers$.next(this.preciseSubscribers$.value - 1)));
+
+  /**
+   * Shows the permission prompt if permission hasn't been decided yet
+   * @returns granted, denied, or prompt if the user closed the dialog without deciding
+   */
+  async requestPermission(): Promise<LocationPermission> {
+    const status = await Geolocation.checkPermissions().catch(() => {});
+    if (status && isGranted(status)) return PERMISSION_GRANTED;
+    if (status && isDenied(status)) return PERMISSION_DENIED;
+    // getCurrentPosition shows the prompt on web, Android and iOS
+    const located = await Geolocation.getCurrentPosition(COARSE_OPTIONS).then(
+      () => true,
+      () => false,
+    );
+    this.permissionRequested$.next();
+    const after = await Geolocation.checkPermissions().catch(() => {});
+    // no Permissions API (some browsers): judge by whether a position came back
+    if (!after) return located ? PERMISSION_GRANTED : PERMISSION_DENIED;
+    // granted also covers "allowed, but no fix yet" (timeout): the shared watch keeps trying
+    if (isGranted(after)) return PERMISSION_GRANTED;
+    if (isDenied(after)) return PERMISSION_DENIED;
+    return PERMISSION_PROMPT;
+  }
 
   /**
    * Current position
@@ -108,29 +279,17 @@ export class PositionService {
    * @param options Options which define which data should be provided (e.g., how accurate or how old)
    */
   watchCurrentLocation(options: PositionOptions = {}): Observable<MapPosition> {
-    return new Observable(subscriber => {
-      const watcherID = Geolocation.watchPosition(options, (position, error) => {
-        if (error) {
-          subscriber.error(position);
-        } else {
-          this.position = {
-            // TODO use native compass heading instead
-            // waiting for https://github.com/ionic-team/capacitor-plugins/issues/1192
-            heading: undefined,
-            latitude: position?.coords.latitude ?? 0,
-            longitude: position?.coords.longitude ?? 0, // TODO: handle null position
-          };
-
-          subscriber.next(this.position);
-        }
-      });
-      return {
-        unsubscribe() {
-          watcherID.then(id => {
-            void Geolocation.clearWatch({id});
-          });
-        },
-      };
-    });
+    return nativeWatch(options).pipe(
+      map(position => {
+        this.position = {
+          // TODO use native compass heading instead
+          // waiting for https://github.com/ionic-team/capacitor-plugins/issues/1192
+          heading: undefined,
+          latitude: position.coords.latitude,
+          longitude: position.coords.longitude,
+        };
+        return this.position;
+      }),
+    );
   }
 }

frontend/app/src/app/util/rxjs/distinct-until-moved.spec.ts

@@ -0,0 +1,82 @@
+/*
+ * Copyright (C) 2026 StApps
+ * This program is free software: you can redistribute it and/or modify it
+ * under the terms of the GNU General Public License as published by the Free
+ * Software Foundation, version 3.
+ *
+ * This program is distributed in the hope that it will be useful, but WITHOUT
+ * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
+ * FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for
+ * more details.
+ *
+ * You should have received a copy of the GNU General Public License along with
+ * this program. If not, see <https://www.gnu.org/licenses/>.
+ */
+import {LngLat, LngLatBounds} from 'maplibre-gl';
+import {of, toArray, firstValueFrom} from 'rxjs';
+import {distinctUntilMoved} from './distinct-until-moved';
+
+describe('distinctUntilMoved', () => {
+  // Frankfurt (Campus Westend), 50° N
+  const start = {latitude: 50.1278, longitude: 8.6674};
+
+  /** A box `meters` around `start` (MapLibre): its north / east edge is `meters` north / east of `start` */
+  const around = (meters: number) =>
+    LngLatBounds.fromLngLat(new LngLat(start.longitude, start.latitude), meters);
+
+  /** `start` moved `meters` north */
+  const north = (meters: number) => ({latitude: around(meters).getNorth(), longitude: start.longitude});
+
+  /** `start` moved `meters` east */
+  const east = (meters: number) => ({latitude: start.latitude, longitude: around(meters).getEast()});
+
+  /** `start` moved `northMeters` north and `eastMeters` east */
+  const moved = (northMeters: number, eastMeters: number) => ({
+    latitude: around(northMeters).getNorth(),
+    longitude: around(eastMeters).getEast(),
+  });
+
+  /** `start` moved `meters` north-east (diagonally, as the crow flies) */
+  const northEast = (meters: number) => moved(meters / Math.SQRT2, meters / Math.SQRT2);
+
+  const run = <T extends {latitude: number; longitude: number}>(positions: T[], meters = 100) =>
+    firstValueFrom(of(...positions).pipe(distinctUntilMoved<T>(meters), toArray()));
+
+  it('should always let the first position through', async () => {
+    expect(await run([start])).toEqual([start]);
+  });
+
+  it('should drop GPS jitter below the threshold', async () => {
+    expect(await run([start, north(5), north(30), north(99)])).toEqual([start]);
+  });
+
+  it('should let a position through once the threshold is reached', async () => {
+    const far = north(120);
+    expect(await run([start, north(50), far])).toEqual([start, far]);
+  });
+
+  it('should measure real meters in every direction (not degrees)', async () => {
+    // at 50° N, 100 m east is a bigger change in degrees than 100 m north
+    expect(await run([start, east(90)])).toEqual([start]);
+    expect(await run([start, east(110)])).toEqual([start, east(110)]);
+  });
+
+  it('should compare with the last position that was let through, so slow movement adds up', async () => {
+    // walk 240 m north-east in 40 m steps
+    const steps = [
+      start,
+      northEast(40),
+      northEast(80),
+      northEast(120), // 120 m from start: let through, new reference
+      northEast(160),
+      northEast(200), // 200 m from start, but only 80 m from the reference
+      northEast(240), // 120 m from the reference
+    ];
+    expect(await run(steps)).toEqual([start, northEast(120), northEast(240)]);
+  });
+
+  it('should use the given threshold', async () => {
+    expect(await run([start, north(30)], 25)).toEqual([start, north(30)]);
+    expect(await run([start, north(30)], 50)).toEqual([start]);
+  });
+});

frontend/app/src/app/util/rxjs/distinct-until-moved.ts

@@ -0,0 +1,31 @@
+/*
+ * Copyright (C) 2026 StApps
+ * This program is free software: you can redistribute it and/or modify it
+ * under the terms of the GNU General Public License as published by the Free
+ * Software Foundation, version 3.
+ *
+ * This program is distributed in the hope that it will be useful, but WITHOUT
+ * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
+ * FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for
+ * more details.
+ *
+ * You should have received a copy of the GNU General Public License along with
+ * this program. If not, see <https://www.gnu.org/licenses/>.
+ */
+import {LngLat} from 'maplibre-gl';
+import {distinctUntilChanged, MonoTypeOperatorFunction} from 'rxjs';
+
+/**
+ * Lets a position through only after the device has moved at least `meters`
+ * since the last position that was let through (ignores GPS jitter)
+ */
+export function distinctUntilMoved<T extends {latitude: number; longitude: number}>(
+  meters: number,
+): MonoTypeOperatorFunction<T> {
+  return distinctUntilChanged(
+    (previous, current) =>
+      new LngLat(previous.longitude, previous.latitude).distanceTo(
+        new LngLat(current.longitude, current.latitude),
+      ) < meters,
+  );
+}