Add cheapest-favourite price-drop alerts

FuelBoard/AlertsView.swift

@@ -12,6 +12,8 @@ struct AlertsView: View {
     @Binding var enabled: Bool
     @Binding var radius: Double   // stored in km (monitor + storage)
     @Binding var fuel: FuelType   // the fuel alerts monitor for
+    @Binding var favouriteDropEnabled: Bool
+    @Binding var favouriteDropFuel: FuelType
     /// Whether alerts mirror the Stations-tab search distance (capped at 8 mi).
     @Binding var followsSearch: Bool
     /// Whether the "cheapest nearby" Live Activity is shown on the Lock Screen
@@ -157,6 +159,19 @@ struct AlertsView: View {
                     Text("When you approach a station that is the cheapest within the radius, FuelBoard sends a notification — even with the app closed. Nearby stations selling \(fuel.displayName.lowercased()) are watched — favourites get priority — and each station alerts at most once per hour. Follow search mirrors the Stations-tab distance, capped at 8 miles for reliable geofencing. Smaller radii ping more often but later; larger radii ping rarely in town but earlier from afar.")
                 }
 
+                Section {
+                    Toggle("Cheapest-favourite price-drop alerts", isOn: $favouriteDropEnabled)
+                    Picker("Fuel", selection: $favouriteDropFuel) {
+                        ForEach(FuelType.allCases) { fuel in
+                            Text(fuel.displayName).tag(fuel)
+                        }
+                    }
+                } header: {
+                    Text("Favourite price-drop alerts")
+                } footer: {
+                    Text("Watches your cheapest saved favourite for the fuel you pick here. FuelBoard alerts when a different favourite becomes the cheapest, or when your current cheapest favourite drops by at least 1.0p. This is separate from the nearby-geofence alert, so you can monitor favourites without extra location noise.")
+                }
+
                 if enabled, let lastAlert {
                     Section("Last alert") {
                         Label(lastAlert, systemImage: "bell.badge.fill")

FuelBoard/ContentView.swift

@@ -15,6 +15,8 @@ struct ContentView: View {
     @State private var alertsEnabled: Bool = FuelStore.loadAlertsEnabled()
     @State private var alertsRadius: Double = FuelStore.loadAlertsRadius()
     @State private var alertsFuel: FuelType = FuelStore.loadAlertsFuel()
+    @State private var favouriteDropAlertsEnabled: Bool = FuelStore.loadFavouriteDropAlertsEnabled()
+    @State private var favouriteDropAlertsFuel: FuelType = FuelStore.loadFavouriteDropAlertsFuel()
     @State private var alertsFollowsSearch: Bool = FuelStore.loadAlertsFollowsSearch()
     @State private var liveActivityEnabled: Bool = FuelStore.loadLiveActivityEnabled()
     @State private var liveActivityFuel: FuelType = FuelStore.loadLiveActivityFuel()
@@ -152,59 +154,16 @@ struct ContentView: View {
     }
 
     var body: some View {
-        VStack(spacing: 0) {
-            switch dataStatus {
-            case .offlineDump(let date):
-                let title = offlineTitle(date: date)
-                statusBanner(
-                    icon: "wifi.slash",
-                    tint: .orange,
-                    title: title,
-                    subtitle: NSLocalizedString("Pull to refresh on the Stations tab", comment: ""),
-                    accessibilityLabel: date.isEmpty
-                        ? NSLocalizedString("Offline data. Pull to refresh on the Stations tab", comment: "")
-                        : String(format: NSLocalizedString("Offline data from %@. Pull to refresh on the Stations tab", comment: ""), date)
-                )
-            case .connectionProblem:
-                statusBanner(
-                    icon: "wifi.exclamationmark",
-                    tint: .red,
-                    title: NSLocalizedString("Check your internet connection", comment: ""),
-                    subtitle: NSLocalizedString("Tap to try again", comment: ""),
-                    accessibilityLabel: NSLocalizedString("Check your internet connection. Tap to try again", comment: "")
-                )
-            case .live:
-                EmptyView()
+        configuredContent
     }
-            TabView(selection: $selectedTab) {
-            stationsTab
-                .tabItem { Label("Stations", systemImage: "fuelpump.fill") }
-                .tag(0)
 
-            favouritesTab
-                .tabItem { Label("Favourites", systemImage: "star.fill") }
-                .tag(1)
-
-            AlertsView(
-                enabled: $alertsEnabled,
-                radius: $alertsRadius,
-                fuel: $alertsFuel,
-                followsSearch: $alertsFollowsSearch,
-                liveActivityEnabled: $liveActivityEnabled,
-                liveActivityFuel: $liveActivityFuel,
-                liveActivityRadiusMiles: $liveActivityRadiusMiles,
-                liveActivityFollowsSearch: $liveActivityFollowsSearch,
-                stationLimit: stationLimit,
-                distanceUnit: distanceUnit,
-                monitoredCount: monitor.monitoredStationIDs.count,
-                lastAlert: monitor.lastAlert
-            )
-            .tabItem { Label("Alerts", systemImage: "bell.fill") }
-            .tag(2)
-
-            settingsTab
-                .tag(3)
+    private var configuredContent: AnyView {
+        interactionObservedContent
     }
+
+    private var presentedContent: AnyView {
+        AnyView(
+            mainContent
                 .fullScreenCover(isPresented: $showOnboarding) {
                     OnboardingView {
                         showOnboarding = false
@@ -216,6 +175,12 @@ struct ContentView: View {
                 .sheet(item: $monitor.pendingStationMap) { request in
                     StationMapView(request: request)
                 }
+        )
+    }
+
+    private var lifecycleObservedContent: AnyView {
+        AnyView(
+            presentedContent
                 .onAppear {
             // Launch-arg hooks for the screenshot/UI-test harness (same
             // pattern as StationsView's `-showKeySheet`): `-tab <name>`
@@ -379,6 +344,12 @@ struct ContentView: View {
                 updateLiveActivity()
             }
         }
+        )
+    }
+
+    private var interactionObservedContent: AnyView {
+        AnyView(
+            lifecycleObservedContent
                 .onChange(of: selectedFuel) { _, _ in
             // No re-fetch needed — one response carries E5/E10/DIESEL prices.
             WidgetCenter.shared.reloadAllTimelines()
@@ -425,6 +396,12 @@ struct ContentView: View {
             monitor.update(stations: stations, favourites: refreshedFavourites,
                            fuel: alertsFuel, radiusKM: effectiveAlertsRadiusKM)
         }
+        .onChange(of: favouriteDropAlertsEnabled) { _, newValue in
+            FuelStore.saveFavouriteDropAlertsEnabled(newValue)
+        }
+        .onChange(of: favouriteDropAlertsFuel) { _, newValue in
+            FuelStore.saveFavouriteDropAlertsFuel(newValue)
+        }
         .onChange(of: liveActivityEnabled) { _, newValue in
             // Toggling the Live Activity on starts it with the current best
             // station; toggling off ends any running activity.
@@ -464,10 +441,63 @@ struct ContentView: View {
             // so reading storage here could push the OLD style.
             updateLiveActivity(priceDisplayStyleOverride: newValue)
         }
-        }  // VStack: status banner + TabView
+        )
+    }
+
+    private var mainContent: some View {
+        VStack(spacing: 0) {
+            statusBannerView
+            rootTabView
+        }
         .animation(.spring(response: 0.3, dampingFraction: 0.8), value: dataStatus)
     }
 
+    @ViewBuilder
+    private var statusBannerView: some View {
+        switch dataStatus {
+        case .offlineDump(let date):
+            let title = offlineTitle(date: date)
+            statusBanner(
+                icon: "wifi.slash",
+                tint: .orange,
+                title: title,
+                subtitle: NSLocalizedString("Pull to refresh on the Stations tab", comment: ""),
+                accessibilityLabel: date.isEmpty
+                    ? NSLocalizedString("Offline data. Pull to refresh on the Stations tab", comment: "")
+                    : String(format: NSLocalizedString("Offline data from %@. Pull to refresh on the Stations tab", comment: ""), date)
+            )
+        case .connectionProblem:
+            statusBanner(
+                icon: "wifi.exclamationmark",
+                tint: .red,
+                title: NSLocalizedString("Check your internet connection", comment: ""),
+                subtitle: NSLocalizedString("Tap to try again", comment: ""),
+                accessibilityLabel: NSLocalizedString("Check your internet connection. Tap to try again", comment: "")
+            )
+        case .live:
+            EmptyView()
+        }
+    }
+
+    private var rootTabView: some View {
+        TabView(selection: $selectedTab) {
+            stationsTab
+                .tabItem { Label("Stations", systemImage: "fuelpump.fill") }
+                .tag(0)
+
+            favouritesTab
+                .tabItem { Label("Favourites", systemImage: "star.fill") }
+                .tag(1)
+
+            alertsTab
+                .tabItem { Label("Alerts", systemImage: "bell.fill") }
+                .tag(2)
+
+            settingsTab
+                .tag(3)
+        }
+    }
+
     /// The banner title for the bundled-snapshot case: date when the stamp
     /// parsed, plain "Offline data" otherwise.
     private func offlineTitle(date: String) -> String {
@@ -576,6 +606,27 @@ struct ContentView: View {
         )
     }
 
+    /// The Alerts tab, extracted from `body` so the TabView expression stays
+    /// within the compiler's type-check budget.
+    private var alertsTab: some View {
+        AlertsView(
+            enabled: $alertsEnabled,
+            radius: $alertsRadius,
+            fuel: $alertsFuel,
+            favouriteDropEnabled: $favouriteDropAlertsEnabled,
+            favouriteDropFuel: $favouriteDropAlertsFuel,
+            followsSearch: $alertsFollowsSearch,
+            liveActivityEnabled: $liveActivityEnabled,
+            liveActivityFuel: $liveActivityFuel,
+            liveActivityRadiusMiles: $liveActivityRadiusMiles,
+            liveActivityFollowsSearch: $liveActivityFollowsSearch,
+            stationLimit: stationLimit,
+            distanceUnit: distanceUnit,
+            monitoredCount: monitor.monitoredStationIDs.count,
+            lastAlert: monitor.lastAlert
+        )
+    }
+
     /// The Settings tab, extracted from `body` so the TabView expression stays
     /// within the compiler's type-check budget.
     private var settingsTab: some View {
@@ -635,6 +686,7 @@ struct ContentView: View {
         isLoading = true
         defer { isLoading = false }
         do {
+            let previousFavouriteSnapshots = FuelStore.loadFavouriteAlertSnapshots()
             let fetched = try await FuelPriceProvider.active.fetchStations(
                 near: location?.lat, lng: location?.lng,
                 fuel: selectedFuel,
@@ -654,6 +706,12 @@ struct ContentView: View {
             // channel shared on SideStore free), so stale star-time snapshots
             // would otherwise show old prices.
             FuelStore.saveFavourites(refreshedFavourites)
+            monitor.evaluateFavouritePriceDropAlert(
+                favourites: refreshedFavourites,
+                previousSnapshots: previousFavouriteSnapshots,
+                monitoredFuel: favouriteDropAlertsFuel,
+                enabled: favouriteDropAlertsEnabled
+            )
             WidgetCenter.shared.reloadAllTimelines()
             statusMessage = "Loaded \(fetched.count) stations · \(Date().formatted(date: .omitted, time: .shortened))"
             // Live data restored — any status banner no longer applies.

FuelBoard/ProximityMonitor.swift

@@ -79,6 +79,7 @@ struct TieChoice {
 /// entering the winner's circle — not at the forecourt.
 @MainActor
 final class ProximityMonitor: NSObject, ObservableObject, @preconcurrency CLLocationManagerDelegate, UNUserNotificationCenterDelegate {
+    private static let favouriteDropThresholdPence: Double = 1.0
     @Published var monitoredStationIDs: [String] = []
     @Published var lastAlert: String?
     @Published private(set) var lastTestResult: String?
@@ -218,6 +219,46 @@ final class ProximityMonitor: NSObject, ObservableObject, @preconcurrency CLLoca
 
     var isEnabled: Bool { enabled }
 
+    /// Compares the latest refreshed favourites against the persisted cheapest-
+    /// favourite baseline for one fuel and schedules a notification when the
+    /// winner changes or the current winner drops by a meaningful amount.
+    func evaluateFavouritePriceDropAlert(
+        favourites: [FavouriteEntry],
+        previousSnapshots: [FuelType: FavouriteAlertSnapshot],
+        monitoredFuel: FuelType,
+        enabled: Bool
+    ) {
+        var snapshots = previousSnapshots
+        guard let current = FuelStore.cheapestFavourite(in: favourites, fuel: monitoredFuel),
+              let currentPrice = current.station.prices[monitoredFuel] else {
+            snapshots.removeValue(forKey: monitoredFuel)
+            FuelStore.saveFavouriteAlertSnapshots(snapshots)
+            return
+        }
+
+        let currentSnapshot = FavouriteAlertSnapshot(
+            fuel: monitoredFuel,
+            stationID: current.station.id,
+            stationName: current.station.name,
+            price: currentPrice
+        )
+
+        defer {
+            snapshots[monitoredFuel] = currentSnapshot
+            FuelStore.saveFavouriteAlertSnapshots(snapshots)
+        }
+
+        guard enabled else { return }
+        guard let previous = previousSnapshots[monitoredFuel] else { return }
+
+        let winnerChanged = previous.stationID != currentSnapshot.stationID
+        let priceDropped = previous.stationID == currentSnapshot.stationID
+            && currentSnapshot.price <= previous.price - Self.favouriteDropThresholdPence
+
+        guard winnerChanged || priceDropped else { return }
+        fireFavouriteDropAlert(current: current, previous: previous, price: currentPrice, winnerChanged: winnerChanged)
+    }
+
     /// Records a stage in the live alert trace, newest first, capped at 8.
     private func logAlert(_ kind: AlertLogEntry.Kind, _ text: String) {
         alertLog.insert(AlertLogEntry(date: Date(), kind: kind, text: text), at: 0)
@@ -452,6 +493,31 @@ final class ProximityMonitor: NSObject, ObservableObject, @preconcurrency CLLoca
         lastAlert = "\(brand) · \(String(format: "%.1fp", price)) · \(distanceText) away"
     }
 
+    private func fireFavouriteDropAlert(
+        current: FavouriteEntry,
+        previous: FavouriteAlertSnapshot,
+        price: Double,
+        winnerChanged: Bool
+    ) {
+        let content = UNMutableNotificationContent()
+        content.sound = .default
+        let fuel = current.fuel
+        let previousPriceText = String(format: "%.1fp", previous.price)
+        let currentPriceText = String(format: "%.1fp", price)
+
+        if winnerChanged {
+            content.title = "New cheapest \(fuel.displayName.lowercased()) favourite"
+            content.body = "\(current.station.name) is now your cheapest favourite at \(currentPriceText), ahead of \(previous.stationName)."
+        } else {
+            content.title = "Cheapest favourite just dropped"
+            content.body = "\(current.station.name) fell from \(previousPriceText) to \(currentPriceText) for \(fuel.displayName.lowercased())."
+        }
+
+        addAlertRequest(content: content, station: current.station)
+        logAlert(.fired, "favourite alert scheduled — \(current.station.name) · \(currentPriceText)")
+        lastAlert = "Favourite · \(current.station.name) · \(currentPriceText)"
+    }
+
     /// Adds a notification whose tap opens directions to `station`. The
     /// station's coordinates ride in `userInfo` so the tap handler can route
     /// to Apple Maps (or an in-app fallback), and a map snapshot with a pin is

Shared/FuelStore.swift

@@ -31,6 +31,16 @@ struct FavouriteEntry: Identifiable, Codable, Equatable {
     var id: String { "\(fuel.rawValue)|\(station.id)" }
 }
 
+/// Persisted baseline for the per-fuel cheapest-favourite price-drop alert.
+/// Stored separately from the favourites list so refresh-time comparison can
+/// survive app relaunches without immediately alerting on first fetch.
+struct FavouriteAlertSnapshot: Codable, Equatable {
+    let fuel: FuelType
+    let stationID: String
+    let stationName: String
+    let price: Double
+}
+
 enum SortMode: String, Codable, CaseIterable, Identifiable {
     case cheapest
     case closest
@@ -318,6 +328,9 @@ struct FuelStore {
     static let alertsRadiusKey = "fuelboard.alertsRadius"   // Double km
     static let alertsFuelKey = "fuelboard.alertsFuel"       // FuelType raw value
     static let alertsFollowSearchKey = "fuelboard.alertsFollowSearch"  // Bool — alerts mirror the Stations-tab distance
+    static let favouriteDropAlertsEnabledKey = "fuelboard.favouriteDropAlertsEnabled" // Bool
+    static let favouriteDropAlertsFuelKey = "fuelboard.favouriteDropAlertsFuel" // FuelType raw value
+    static let favouriteAlertSnapshotsKey = "fuelboard.favouriteAlertSnapshots" // [fuel: FavouriteAlertSnapshot] JSON
     static let liveActivityFollowSearchKey = "fuelboard.liveActivityFollowSearch" // Bool — Live Activity mirrors the Stations-tab distance
     static let debugModeKey = "fuelboard.debugMode"         // Bool — hidden dev flag
     static let relayFallbackKey = "fuelboard.relayFallback" // Bool — dev-only relay fallback
@@ -627,6 +640,24 @@ struct FuelStore {
         }
     }
 
+    /// The cheapest favourite for one fuel, preserving the user's stored order
+    /// on price ties. Used by the favourite price-drop alert so a tie does not
+    /// flap between equally-priced favourites.
+    static func cheapestFavourite(in favourites: [FavouriteEntry], fuel: FuelType) -> FavouriteEntry? {
+        var best: FavouriteEntry?
+        for entry in favourites where entry.fuel == fuel {
+            guard let price = entry.station.prices[fuel] else { continue }
+            guard let current = best, let currentPrice = current.station.prices[fuel] else {
+                best = entry
+                continue
+            }
+            if price < currentPrice {
+                best = entry
+            }
+        }
+        return best
+    }
+
     /// Reorders ONE fuel's favourites within the global array (drag-and-drop in
     /// the Favourites tab). The moved fuel's block stays at its original
     /// position in the array; other fuels keep their relative order. The array
@@ -710,6 +741,48 @@ struct FuelStore {
         saveString(enabled ? "1" : "0", service: alertsFollowSearchKey)
     }
 
+    // MARK: Favourite price-drop alerts
+
+    static func loadFavouriteDropAlertsEnabled() -> Bool {
+        loadString(service: favouriteDropAlertsEnabledKey) == "1"
+    }
+
+    static func saveFavouriteDropAlertsEnabled(_ enabled: Bool) {
+        saveString(enabled ? "1" : "0", service: favouriteDropAlertsEnabledKey)
+    }
+
+    static func loadFavouriteDropAlertsFuel() -> FuelType {
+        if let raw = loadString(service: favouriteDropAlertsFuelKey), let fuel = FuelType(rawValue: raw) {
+            return fuel
+        }
+        return .e10
+    }
+
+    static func saveFavouriteDropAlertsFuel(_ fuel: FuelType) {
+        saveString(fuel.rawValue, service: favouriteDropAlertsFuelKey)
+    }
+
+    static func loadFavouriteAlertSnapshots() -> [FuelType: FavouriteAlertSnapshot] {
+        if let data = keychainData(service: favouriteAlertSnapshotsKey),
+           let stored = try? JSONDecoder().decode([String: FavouriteAlertSnapshot].self, from: data) {
+            var result: [FuelType: FavouriteAlertSnapshot] = [:]
+            for (key, value) in stored {
+                if let fuel = FuelType(rawValue: key) {
+                    result[fuel] = value
+                }
+            }
+            return result
+        }
+        return [:]
+    }
+
+    static func saveFavouriteAlertSnapshots(_ snapshots: [FuelType: FavouriteAlertSnapshot]) {
+        let keyed = Dictionary(uniqueKeysWithValues: snapshots.map { ($0.key.rawValue, $0.value) })
+        if let data = try? JSONEncoder().encode(keyed) {
+            writeKeychain(data: data, service: favouriteAlertSnapshotsKey)
+        }
+    }
+
     // MARK: Live Activity
 
     static func loadLiveActivityEnabled() -> Bool {