Clarify Best Value route confidence

FuelBoard/ContentView.swift

@@ -244,38 +244,43 @@ struct ContentView: View {
         guard fuelSavingsSettings.isConfigured else { return { _ in nil } }
         guard let location else { return { _ in .unavailable("Location unavailable") } }
         let baselineJourney = baseline.flatMap { savingsJourneyMiles(for: $0, location: location) }
+        let baselineID = baseline?.id
+        let settings = fuelSavingsSettings
+        let amount = sessionFuelSavingsAmount
+        let fuel = selectedFuel
+        var journeys: [String: FuelSavingsJourney] = [:]
+        for station in stations {
+            if journeys[station.id] == nil,
+               let journey = savingsJourneyMiles(for: station, location: location) {
+                journeys[station.id] = journey
+            }
+        }
         return { station in
             FuelSavingsEstimator.availability(
                 station: station,
-                fuel: selectedFuel,
+                fuel: fuel,
                 baseline: baseline,
-                settings: fuelSavingsSettings,
-                amount: sessionFuelSavingsAmount,
-                journey: savingsJourneyMiles(for: station, location: location),
-                baselineJourney: baselineJourney
+                settings: settings,
+                amount: amount,
+                journey: journeys[station.id],
+                baselineJourney: baselineID.flatMap { journeys[$0] } ?? baselineJourney
             )
         }
     }
 
-    /// The nearest station that sells the selected fuel — the Worth-the-Drive
-    /// comparison baseline.
-    ///
-    /// Single O(n) pass on purpose: `min(by:)` re-evaluates its closure twice
-    /// per comparison, and each evaluation reads the road-distance cache. With
-    /// the full UK list that is thousands of redundant lookups per render, all
-    /// on the main thread during scene creation (see `loadRoadDistances`).
+    /// The nearest station that sells the selected fuel — the Best Value
+    /// comparison baseline. It is chosen with the SAME journey values used by
+    /// the savings calculation, so a cached road route can change the baseline
+    /// and keep the "more driving than closest" labels synchronized with the
+    /// cost calculation. When no road route is cached, the journey falls back to
+    /// straight-line out-and-back, and the result is marked as an estimate.
     private var nearestSavingsBaseline: FuelStation? {
         guard let location else { return nil }
-        var bestStation: FuelStation?
-        var bestMiles = Double.infinity
-        for station in stations where station.prices[selectedFuel] != nil {
-            let miles = savingsFallbackMiles(for: station, location: location)
-            if miles < bestMiles {
-                bestMiles = miles
-                bestStation = station
-            }
-        }
-        return bestStation
+        return FuelSavingsEstimator.baselineStation(
+            stations,
+            fuel: selectedFuel,
+            journeyMiles: { [self] station in savingsJourneyMiles(for: station, location: location) }
+        )
     }
 
     /// The sort the UI and the list actually use.
@@ -296,11 +301,19 @@ struct ContentView: View {
     /// that every station the app lists can carry a saving.
     private func savingsJourneyMiles(for station: FuelStation, location: Coordinate) -> FuelSavingsJourney? {
         if let roadMeters = FuelStore.roadJourneyMeters(for: station, userLat: location.lat, userLng: location.lng) {
-            return FuelSavingsJourney(miles: roadMeters / FuelSavingsCalculator.metresPerMile, basis: .roadRoute)
+            let confidence: JourneyConfidence = FuelStore.hasMeasuredReturnRoadDistance(
+                for: station, userLat: location.lat, userLng: location.lng
+            ) ? .confirmed : .estimated
+            return FuelSavingsJourney(
+                miles: roadMeters / FuelSavingsCalculator.metresPerMile,
+                basis: .roadRoute,
+                confidence: confidence
+            )
         }
         return FuelSavingsJourney(
             miles: savingsFallbackMiles(for: station, location: location),
-            basis: .straightLine
+            basis: .straightLine,
+            confidence: .estimated
         )
     }
 
@@ -335,6 +348,57 @@ struct ContentView: View {
     }
 
     #if DEBUG
+    private func journeyDiagnostics(for station: FuelStation, baseline: FuelStation?) -> FuelSavingsJourneyDiagnostics? {
+        guard let location else { return nil }
+        let stationDistance = FuelStore.roadDistanceDiagnostics(for: station, userLat: location.lat, userLng: location.lng)
+        let baselineDiagnostics = baseline.map { FuelStore.roadDistanceDiagnostics(for: $0, userLat: location.lat, userLng: location.lng) }
+        let journey = savingsJourneyMiles(for: station, location: location)
+        let baselineJourney = baseline.flatMap { savingsJourneyMiles(for: $0, location: location) }
+        let availability = FuelSavingsEstimator.availability(
+            station: station,
+            fuel: selectedFuel,
+            baseline: baseline,
+            settings: fuelSavingsSettings,
+            amount: sessionFuelSavingsAmount,
+            journey: journey,
+            baselineJourney: baselineJourney
+        )
+        let result = availability?.result
+
+        func miles(_ value: Double?) -> String {
+            value.map { String(format: "%.3f mi", $0) } ?? "—"
+        }
+        func meters(_ value: Double?) -> String {
+            value.map { String(format: "%.0f m", $0) } ?? "—"
+        }
+        func source(_ basis: FuelSavingsDistanceBasis) -> String {
+            basis == .roadRoute ? "road route" : "straight-line estimate"
+        }
+        let price = station.prices[selectedFuel].map { String(format: "%.1fp/L", $0) } ?? "—"
+        let baselinePrice = baseline?.prices[selectedFuel].map { String(format: "%.1fp/L", $0) } ?? "—"
+        let rows: [(String, String)] = [
+            ("Station", "\(station.name) (\(station.id))"),
+            ("Displayed distance", "\(distanceUnit.format(stationDistance.displayDistanceKM)) · \(source(stationDistance.displaySource))"),
+            ("Outward road", meters(stationDistance.outwardMeters)),
+            ("Return road", stationDistance.hasMeasuredReturn ? meters(stationDistance.returnMeters) : "inferred or unavailable"),
+            ("Total journey", meters(stationDistance.totalJourneyMeters)),
+            ("Cache", stationDistance.hasValidCacheEntry ? "valid" : "missing/invalid"),
+            ("Baseline", baseline.map { "\($0.name) (\($0.id))" } ?? "—"),
+            ("Baseline distance", baselineDiagnostics.map { "\(distanceUnit.format($0.displayDistanceKM)) · \(source($0.displaySource))" } ?? "—"),
+            ("Baseline total", meters(baselineDiagnostics?.totalJourneyMeters)),
+            ("Station journey", miles(journey?.miles)),
+            ("Baseline journey", miles(baselineJourney?.miles)),
+            ("Additional journey", miles(result?.extraDistanceMiles)),
+            ("Confidence", result?.journeyConfidence.rawValue ?? "estimated"),
+            ("Fuel price", price),
+            ("Baseline price", baselinePrice),
+            ("Gross saving", result.map { FuelSavingsFormat.money($0.grossSavingGBP) } ?? "—"),
+            ("Travel cost", result.map { FuelSavingsFormat.money($0.extraDrivingCostGBP) } ?? "—"),
+            ("Net saving", result.map { FuelSavingsFormat.money($0.netSavingGBP) } ?? "—")
+        ]
+        return FuelSavingsJourneyDiagnostics(rows: rows)
+    }
+
     /// Last FB-DRIVE line printed, so the ranking (which runs on every render)
     /// only reports when the result actually changes.
     private static var lastDriveLogLine: String?
@@ -443,6 +507,7 @@ struct ContentView: View {
                         fuelSavings: savingsLookup(baseline: nearestSavingsBaseline)(station),
                         fuelSavingsAmount: sessionFuelSavingsAmount,
                         savingsBaselineStationName: nearestSavingsBaseline?.name,
+                        journeyDiagnostics: journeyDiagnostics(for: station, baseline: nearestSavingsBaseline),
                         isFavourite: favouriteIDs.contains(station.id),
                         onToggleFavourite: { toggleFavourite(station, fuel: selectedFuel) }
                     )
@@ -1033,6 +1098,7 @@ struct ContentView: View {
             fuelSavingsAmount: $sessionFuelSavingsAmount,
             savingsForStation: savingsLookup(baseline: baselineStation),
             savingsBaselineStationName: baselineStation?.name,
+            journeyDiagnosticsForStation: { station in journeyDiagnostics(for: station, baseline: baselineStation) },
             onToggleFavourite: toggleFavourite,
             onRefresh: { await refresh(force: true) }
         )
@@ -1053,6 +1119,7 @@ struct ContentView: View {
             fuelSavingsAmount: $sessionFuelSavingsAmount,
             savingsForStation: savingsLookup(baseline: baselineStation),
             savingsBaselineStationName: baselineStation?.name,
+            journeyDiagnosticsForStation: { station in journeyDiagnostics(for: station, baseline: baselineStation) },
             onToggleFavourite: toggleFavourite,
             onReorder: reorderFavourites,
             onHistoryUnavailable: { if dataStatus == .live { dataStatus = .connectionProblem } },

FuelBoard/FavouritesView.swift

@@ -25,6 +25,7 @@ struct FavouritesView: View {
     /// the same baseline and definition the Stations list uses.
     var savingsForStation: (FuelStation) -> FuelSavingsAvailability? = { _ in nil }
     var savingsBaselineStationName: String?
+    var journeyDiagnosticsForStation: (FuelStation) -> FuelSavingsJourneyDiagnostics? = { _ in nil }
     var onToggleFavourite: (FuelStation, FuelType) -> Void = { _, _ in }
     /// Persists a reordered favourites array (after drag-and-drop).
     var onReorder: ([FavouriteEntry]) -> Void = { _ in }
@@ -84,6 +85,7 @@ struct FavouritesView: View {
          fuelSavingsAmount: Binding<FuelSavingsFillAmount>,
          savingsForStation: @escaping (FuelStation) -> FuelSavingsAvailability? = { _ in nil },
          savingsBaselineStationName: String? = nil,
+         journeyDiagnosticsForStation: @escaping (FuelStation) -> FuelSavingsJourneyDiagnostics? = { _ in nil },
          onToggleFavourite: @escaping (FuelStation, FuelType) -> Void = { _, _ in },
          onReorder: @escaping ([FavouriteEntry]) -> Void = { _ in },
          onHistoryUnavailable: (() -> Void)? = nil,
@@ -98,6 +100,7 @@ struct FavouritesView: View {
         _fuelSavingsAmount = fuelSavingsAmount
         self.savingsForStation = savingsForStation
         self.savingsBaselineStationName = savingsBaselineStationName
+        self.journeyDiagnosticsForStation = journeyDiagnosticsForStation
         self.onToggleFavourite = onToggleFavourite
         self.onReorder = onReorder
         self.onHistoryUnavailable = onHistoryUnavailable
@@ -219,6 +222,7 @@ struct FavouritesView: View {
                     fuelSavings: savingsForStation(station),
                     fuelSavingsAmount: fuelSavingsAmount,
                     savingsBaselineStationName: savingsBaselineStationName,
+                    journeyDiagnostics: journeyDiagnosticsForStation(station),
                     // Every station listed here IS a favourite for the tab's
                     // fuel, so the star starts filled; tapping it unstars.
                     isFavourite: true,

FuelBoard/FuelSavingsViews.swift

@@ -92,9 +92,11 @@ struct FuelSavingsSummaryView: View {
                 // it to one line, so rows stay even.
                 VStack(alignment: .leading, spacing: 2) {
                     capsule(for: result, compact: true)
+                        .accessibilityLabel(accessibilityHeadline(for: result))
                     if let extraTravel = FuelSavingsFormat.extraTravelLabel(
                         extraDistanceMiles: result.extraDistanceMiles,
-                        unit: distanceUnit
+                        unit: distanceUnit,
+                        confidence: result.journeyConfidence
                     ) {
                         Text(extraTravel)
                             .font(.caption2)
@@ -114,9 +116,11 @@ struct FuelSavingsSummaryView: View {
                 // matched neither the listing nor each other.
                 VStack(alignment: .leading, spacing: 10) {
                     capsule(for: result, compact: false)
+                        .accessibilityLabel(accessibilityHeadline(for: result))
                     if let extraTravel = FuelSavingsFormat.extraTravelLabel(
                         extraDistanceMiles: result.extraDistanceMiles,
-                        unit: distanceUnit
+                        unit: distanceUnit,
+                        confidence: result.journeyConfidence
                     ) {
                         Text(extraTravel)
                             .font(.subheadline)
@@ -130,8 +134,8 @@ struct FuelSavingsSummaryView: View {
                         Text("Compared with \(baselineStationName ?? "your nearest station") for \(amountText).").font(.caption).foregroundStyle(.secondary)
                         LabeledContent("Fuel-price saving", value: FuelSavingsFormat.money(result.grossSavingGBP))
                         LabeledContent("Extra driving cost", value: FuelSavingsFormat.money(result.extraDrivingCostGBP))
-                        if result.distanceBasis.isEstimate {
-                            Text("Estimated from straight-line distance — refined once the route is measured.")
+                        if result.journeyConfidence.isEstimated {
+                            Text("Estimated from straight-line or incomplete route data — refined once both routes are measured.")
                                 .font(.caption2)
                                 .foregroundStyle(.secondary)
                         }
@@ -157,6 +161,13 @@ struct FuelSavingsSummaryView: View {
         }
     }
 
+    private func accessibilityHeadline(for result: FuelSavingsResult) -> String {
+        let headline = result.headline()
+        return result.journeyConfidence.isEstimated && result.status != .baseline
+            ? "Approximate: \(headline.replacingOccurrences(of: "~", with: ""))"
+            : headline
+    }
+
     /// The colour-coded verdict capsule — ONE implementation for the listing rows
     /// and the detail sheet, so the verdict reads identically in both; the sheet
     /// just gets the larger font and padding.

FuelBoard/StationDetailView.swift

@@ -2,6 +2,12 @@ import SwiftUI
 import MapKit
 import UIKit
 
+/// DEBUG-only explanation of the Best Value numbers for one station. It carries
+/// no precise user coordinates and is never persisted.
+struct FuelSavingsJourneyDiagnostics {
+    let rows: [(label: String, value: String)]
+}
+
 /// Detail sheet for a tapped station (when Settings → Tap station = More info).
 /// Shows a small map preview, the address, distance from the current location,
 /// and a Directions button that opens Apple Maps — the same destination a direct
@@ -14,6 +20,7 @@ struct StationDetailView: View {
     var fuelSavings: FuelSavingsAvailability? = nil
     var fuelSavingsAmount: FuelSavingsFillAmount = FuelSavingsSettings.defaultPreferredAmount
     var savingsBaselineStationName: String? = nil
+    var journeyDiagnostics: FuelSavingsJourneyDiagnostics? = nil
     /// Whether this station is starred for the fuel currently being viewed, and
     /// the toggle that flips it. Passed from the list that opened the sheet, so
     /// the star here and the star on the row are the same fuel-scoped
@@ -86,6 +93,18 @@ struct StationDetailView: View {
                     }
                 }
 
+#if DEBUG
+                if let journeyDiagnostics {
+                    Section("Best Value Diagnostics") {
+                        ForEach(journeyDiagnostics.rows, id: \.label) { row in
+                            LabeledContent(row.label, value: row.value)
+                                .font(.caption)
+                                .monospacedDigit()
+                        }
+                    }
+                }
+#endif
+
                 Section {
                     Button {
                         if let url = station.mapsDirectionsURL {

FuelBoard/StationsView.swift

@@ -20,6 +20,7 @@ struct StationsView: View {
     @Binding var fuelSavingsAmount: FuelSavingsFillAmount
     var savingsForStation: (FuelStation) -> FuelSavingsAvailability? = { _ in nil }
     var savingsBaselineStationName: String?
+    var journeyDiagnosticsForStation: (FuelStation) -> FuelSavingsJourneyDiagnostics? = { _ in nil }
     var onToggleFavourite: (FuelStation, FuelType) -> Void = { _, _ in }
     var onRefresh: () async -> Void = {}
 
@@ -317,6 +318,7 @@ struct StationsView: View {
                     fuelSavings: savingsForStation(station),
                     fuelSavingsAmount: fuelSavingsAmount,
                     savingsBaselineStationName: savingsBaselineStationName,
+                    journeyDiagnostics: journeyDiagnosticsForStation(station),
                     isFavourite: favouriteIDs.contains(station.id),
                     onToggleFavourite: { onToggleFavourite(station, selectedFuel) }
                 )