fix: Load correct nearby location on launch (#128)

When the app was started with location permissions already granted,
nearby transit was instead loading the default camera location, rather
that the phone's current GPS location. The NearbyTransitLocationProvider
was implemented in a silly way where it was effectively immutable, and on
app startup, `currentLocation` and `viewportProvider.viewport` were both
changing and running their `onChange` at the same time, so the current
location was getting overridden by the default camera state.

iosApp/iosApp/Pages/NearbyTransit/NearbyTransitLocationProvider.swift

@@ -9,9 +9,9 @@
 import CoreLocation
 
 class NearbyTransitLocationProvider: ObservableObject {
-    let currentLocation: CLLocationCoordinate2D?
-    let cameraLocation: CLLocationCoordinate2D
-    let isFollowing: Bool
+    var currentLocation: CLLocationCoordinate2D?
+    var cameraLocation: CLLocationCoordinate2D
+    var isFollowing: Bool
 
     @Published var location: CLLocationCoordinate2D
 
@@ -20,6 +20,52 @@ class NearbyTransitLocationProvider: ObservableObject {
         self.cameraLocation = cameraLocation
         self.isFollowing = isFollowing
 
-        location = if isFollowing, currentLocation != nil { currentLocation! } else { cameraLocation }
+        location = Self.resolveLocation(currentLocation, cameraLocation, isFollowing)
+        handleFollowingCamera()
+    }
+
+    static func resolveLocation(
+        _ currentLocation: CLLocationCoordinate2D?,
+        _ cameraLocation: CLLocationCoordinate2D,
+        _ isFollowing: Bool
+    ) -> CLLocationCoordinate2D {
+        if isFollowing, currentLocation != nil { currentLocation! } else { cameraLocation }
+    }
+
+    func updateCurrentLocation(_ newLocation: CLLocationCoordinate2D?) {
+        currentLocation = newLocation
+        handleFollowingCamera()
+        updateLocation()
+    }
+
+    func updateCameraLocation(_ newLocation: CLLocationCoordinate2D) {
+        if cameraLocation.isRoughlyEqualTo(newLocation) {
+            return
+        }
+        cameraLocation = newLocation
+        updateLocation()
+    }
+
+    func updateIsFollowing(_ newFollowing: Bool, withCameraLocation newLocation: CLLocationCoordinate2D? = nil) {
+        isFollowing = newFollowing
+        if newLocation != nil {
+            cameraLocation = newLocation!
+        }
+        handleFollowingCamera()
+        updateLocation()
+    }
+
+    private func updateLocation() {
+        location = Self.resolveLocation(currentLocation, cameraLocation, isFollowing)
+    }
+
+    /*
+      Reset camera location to current location when viewport is following.
+      This prevents loading stale camera locations when the viewport stops following.
+     */
+    private func handleFollowingCamera() {
+        if isFollowing, currentLocation != nil {
+            cameraLocation = currentLocation!
+        }
     }
 }

iosApp/iosApp/Pages/NearbyTransit/NearbyTransitPageView.swift

@@ -14,7 +14,7 @@ import SwiftUI
 @_spi(Experimental) import MapboxMaps
 
 struct NearbyTransitPageView: View {
-    let currentLocation: CLLocationCoordinate2D?
+    var currentLocation: CLLocationCoordinate2D?
     @ObservedObject var globalFetcher: GlobalFetcher
     @ObservedObject var nearbyFetcher: NearbyFetcher
     @ObservedObject var scheduleFetcher: ScheduleFetcher
@@ -23,7 +23,9 @@ struct NearbyTransitPageView: View {
     @ObservedObject var alertsFetcher: AlertsFetcher
 
     @State var cancellables: [AnyCancellable]
-    @State var locationProvider: NearbyTransitLocationProvider
+    @StateObject var locationProvider: NearbyTransitLocationProvider
+
+    let inspection = Inspection<Self>()
 
     init(
         currentLocation: CLLocationCoordinate2D?,
@@ -43,16 +45,16 @@ struct NearbyTransitPageView: View {
         self.alertsFetcher = alertsFetcher
 
         cancellables = .init()
-        locationProvider = .init(
+        _locationProvider = StateObject(wrappedValue: .init(
             currentLocation: currentLocation,
             cameraLocation: viewportProvider.cameraState.center,
             isFollowing: viewportProvider.viewport.isFollowing
-        )
+        ))
     }
 
     var body: some View {
         NearbyTransitView(
-            locationProvider: locationProvider,
+            location: locationProvider.location,
             globalFetcher: globalFetcher,
             nearbyFetcher: nearbyFetcher,
             scheduleFetcher: scheduleFetcher,
@@ -64,36 +66,20 @@ struct NearbyTransitPageView: View {
                 viewportProvider.$cameraState
                     .debounce(for: .seconds(0.5), scheduler: DispatchQueue.main)
                     .sink { newCameraState in
-                        let shouldUpdateLocation = !viewportProvider.viewport.isFollowing &&
-                            !locationProvider.location.isRoughlyEqualTo(newCameraState.center)
-                        if shouldUpdateLocation {
-                            locationProvider = .init(
-                                currentLocation: currentLocation,
-                                cameraLocation: newCameraState.center,
-                                isFollowing: viewportProvider.viewport.isFollowing
-                            )
-                        }
+                        locationProvider.updateCameraLocation(newCameraState.center)
                     }
             )
         }
         .onChange(of: currentLocation) { newLocation in
-            let shouldUpdateLocation = viewportProvider.viewport.isFollowing
-                && !locationProvider.location.isRoughlyEqualTo(newLocation)
-            if shouldUpdateLocation {
-                locationProvider = .init(
-                    currentLocation: newLocation,
-                    cameraLocation: viewportProvider.cameraState.center,
-                    isFollowing: viewportProvider.viewport.isFollowing
-                )
-            }
+            locationProvider.updateCurrentLocation(newLocation)
         }
         .onChange(of: viewportProvider.viewport) { newViewport in
-            locationProvider = .init(
-                currentLocation: currentLocation,
-                cameraLocation: viewportProvider.cameraState.center,
-                isFollowing: newViewport.isFollowing
+            locationProvider.updateIsFollowing(
+                newViewport.isFollowing,
+                withCameraLocation: viewportProvider.cameraState.center
             )
         }
+        .onReceive(inspection.notice) { inspection.visit(self, $0) }
         .navigationTitle("Nearby Transit")
         .navigationBarTitleDisplayMode(.inline)
     }

iosApp/iosApp/Pages/NearbyTransit/NearbyTransitView.swift

@@ -15,7 +15,7 @@ import SwiftUI
 
 struct NearbyTransitView: View {
     @Environment(\.scenePhase) private var scenePhase
-    @ObservedObject var locationProvider: NearbyTransitLocationProvider
+    var location: CLLocationCoordinate2D
     @ObservedObject var globalFetcher: GlobalFetcher
     @ObservedObject var nearbyFetcher: NearbyFetcher
     @ObservedObject var scheduleFetcher: ScheduleFetcher
@@ -44,14 +44,14 @@ struct NearbyTransitView: View {
             }
         }
         .onAppear {
-            getNearby(location: locationProvider.location)
+            getNearby(location: location)
             joinPredictions()
             didAppear?(self)
         }
         .onChange(of: globalFetcher.response) { _ in
-            getNearby(location: locationProvider.location)
+            getNearby(location: location)
         }
-        .onChange(of: locationProvider.location) { newLocation in
+        .onChange(of: location) { newLocation in
             getNearby(location: newLocation)
         }
         .onChange(of: nearbyFetcher.nearbyByRouteAndStop) { _ in
@@ -76,7 +76,7 @@ struct NearbyTransitView: View {
         }
         .replaceWhen(nearbyFetcher.errorText) { errorText in
             IconCard(iconName: "network.slash", details: errorText)
-                .refreshable(nearbyFetcher.loading) { getNearby(location: locationProvider.location) }
+                .refreshable(nearbyFetcher.loading) { getNearby(location: location) }
         }
     }