anim: consistent bold crossfade in fuel-type picker

FuelBoard/StationsView.swift

@@ -342,20 +342,26 @@ struct FuelTypeSegmentedPicker: View {
     var fuels: [FuelType] = FuelType.allCases
     var onSelect: (FuelType) -> Void = { _ in }
 
+    @Namespace private var selectionSlider
+
     var body: some View {
         HStack(spacing: 3) {
             ForEach(fuels) { fuel in
                 let isSelected = fuel == selection
                 Button {
+                    withAnimation(.spring(response: 0.42, dampingFraction: 0.78)) {
                         selection = fuel
+                    }
                     onSelect(fuel)
                 } label: {
                     HStack(spacing: 5) {
                         Image(systemName: "fuelpump.fill")
                             .font(.caption2)
                             .foregroundStyle(fuel.tintColor)
+                            .scaleEffect(isSelected ? 1.08 : 0.94)
                         Text(fuel.shortName)
                             .font(.subheadline.weight(isSelected ? .semibold : .regular))
+                            .contentTransition(.opacity)
                     }
                     .foregroundStyle(isSelected ? Color.primary : Color.secondary)
                     .frame(maxWidth: .infinity)
@@ -364,14 +370,29 @@ struct FuelTypeSegmentedPicker: View {
                         if isSelected {
                             Capsule()
                                 .fill(Color(UIColor.systemBackground))
-                                .shadow(color: .black.opacity(0.08), radius: 1, y: 0.5)
+                                .overlay {
+                                    Capsule()
+                                        .stroke(fuel.tintColor.opacity(0.28), lineWidth: 1)
+                                }
+                                .shadow(color: fuel.tintColor.opacity(0.16), radius: 6, y: 2)
+                                .matchedGeometryEffect(id: "fuelSelectionSlider", in: selectionSlider)
                         }
                     }
+                    .scaleEffect(isSelected ? 1.02 : 0.98)
+                    .contentShape(Capsule())
                 }
                 .buttonStyle(.plain)
             }
         }
         .padding(3)
         .background(Capsule().fill(Color(.secondarySystemBackground)))
+        .animation(.spring(response: 0.42, dampingFraction: 0.78), value: selection)
     }
 }
+
+#Preview("Fuel Picker") {
+    @Previewable @State var selectedFuel: FuelType = .e10
+    FuelTypeSegmentedPicker(selection: $selectedFuel)
+        .padding()
+        .background(Color(.systemGroupedBackground))
+}