Seat a unit's crew in the car that has the cab

A driver in cab 1 goes into the first car of a unit and one in cab 2 into the
last - the ET42-A has only cab 1, the ET42-B only cab 2. The crew is the
unit's: the card, the details and replacing a vehicle all set it there,
rather than in whichever car happened to be selected.

StarterNG.Tests/ConsistCrewTests.cs

@@ -123,6 +123,39 @@ public class ConsistCrewTests
         Assert.Equal(eDriverType.Headdriver, loco.Cars[0].DriverType);
     }
 
+    [Fact]
+    public void A_unit_staffed_at_the_head_has_its_driver_in_cab_1_of_the_first_car()
+    {
+        var unit = Unit("ep07-001", "ep07-002");
+
+        _consist.Staff(unit, 0);
+
+        Assert.Equal(eDriverType.Headdriver, unit.Cars[0].DriverType);
+        Assert.Equal(eDriverType.Nobody, unit.Cars[1].DriverType);
+    }
+
+    [Fact]
+    public void A_driver_in_cab_2_moves_into_the_last_car_of_a_unit()
+    {
+        var loco = Add("ep07-001", 0);
+        loco.Cars[0].DriverType = eDriverType.Reardriver;
+        loco.Driver = eDriverType.Reardriver;
+        var unit = Unit("ep07-001", "ep07-002");
+
+        _consist.Replace(0, unit);
+
+        Assert.Equal(eDriverType.Nobody, unit.Cars[0].DriverType);
+        Assert.Equal(eDriverType.Reardriver, unit.Cars[1].DriverType);
+        Assert.Equal(eDriverType.Reardriver, unit.Driver);
+    }
+
+    private ConsistItem Unit(params string[] skins) =>
+        new()
+        {
+            Cars = skins.Select(skin => _consist.MakeDynamic(_catalog.TextureForSkin(skin)!, null)).ToList(),
+            Grouped = true
+        };
+
     private ConsistItem Add(string skin, int at)
     {
         var item = Item(skin);

StarterNG/Domain/Consist.cs

@@ -274,16 +274,36 @@ public sealed class Consist : IReadOnlyList<ConsistItem>
     }
 
     // The crew lives on the cars - they are what is shown and exported - and the
-    // card only mirrors it.
+    // card only mirrors it. A unit has one crew, in the car that has the cab.
     private static void Crew(ConsistItem item, eDriverType crew)
     {
         if (item.Cars.Count == 0)
             return;
 
-        item.Cars[0].DriverType = crew;
+        foreach (var car in item.Cars)
+            car.DriverType = eDriverType.Nobody;
+        CrewCar(item, crew).DriverType = crew;
         item.Driver = crew;
     }
 
+    /// <summary>
+    /// Where a unit's crew sits: cab 1 is at the front of its first car and cab 2
+    /// at the back of its last - the ET42-A has only cab 1, the ET42-B only cab 2.
+    /// The unit's own order, so turning it round takes the cabs along.
+    /// </summary>
+    public static Dynamic CrewCar(ConsistItem item, eDriverType crew) =>
+        crew == eDriverType.Reardriver ? item.Cars[^1] : item.Cars[0];
+
+    /// <summary>Puts the crew into the unit, in the car its cab is in.</summary>
+    public void SetCrew(ConsistItem item, eDriverType crew)
+    {
+        Crew(item, crew);
+        if (ReferenceEquals(Selected, item))
+            SyncStartingVehicle();
+        Raise();
+        AppServices.Current.State.NotifyChanged();
+    }
+
     private bool IsPowered(ConsistItem item) =>
         item.Cars.Count > 0 && _db.TextureFor(item.Cars[0].DataFolder, item.Cars[0].SkinFile, item.Cars[0].MmdFile) is { } texture &&
         VehicleInfo.IsPoweredCategory(VehicleInfo.CategoryOf(texture));
@@ -400,22 +420,14 @@ public sealed class Consist : IReadOnlyList<ConsistItem>
             _items.Reverse(first, last - first + 1);
     }
 
-    public void CycleDriver(ConsistItem item)
-    {
-        var car = ActiveCar(item);
-        car.DriverType = car.DriverType switch
+    public void CycleDriver(ConsistItem item) =>
+        SetCrew(item, item.Driver switch
         {
             eDriverType.Nobody => eDriverType.Headdriver,
             eDriverType.Headdriver => eDriverType.Reardriver,
             eDriverType.Reardriver => eDriverType.Passenger,
             _ => eDriverType.Nobody
-        };
-        item.Driver = UnitDriver(item.Cars);
-        if (ReferenceEquals(Selected, item))
-            SyncStartingVehicle();
-        Raise();
-        AppServices.Current.State.NotifyChanged();
-    }
+        });
 
     public void Split(ConsistItem item)
     {

StarterNG/Views/Depot/VehicleCards.cs

@@ -612,9 +612,7 @@ public sealed class VehicleCards
 
     private void PaintDriverButton(Button btn, ConsistItem item)
     {
-        var type = ReferenceEquals(item, _consist.Selected) && item.Cars.Count > 1
-            ? _consist.ActiveCar(item).DriverType
-            : item.Driver;
+        var type = item.Driver;
 
         (string glyph, string color) = type switch
         {

StarterNG/Views/Depot/VehicleDetails.cs

@@ -262,17 +262,16 @@ public sealed class VehicleDetails
     }
 
     /// <summary>
-    /// The vehicle's own settings. Every write path is unchanged: crew and wagon number
-    /// go through the unit's active car, the coolant flag to its first car only.
+    /// The vehicle's own settings: the crew is the unit's and sits where its cab is,
+    /// the wagon number goes through the unit's active car, the coolant flag to its
+    /// first car only.
     /// </summary>
     private Control BuildVehicleSection(ConsistItem item)
     {
         var driver = new ComboBox { FontSize = 12, MinWidth = 0 };
         foreach (string key in new[] { "DriverHead", "DriverRear", "DriverPassenger", "DriverNobody" })
             driver.Items.Add(new ComboBoxItem { Content = App.Loc[key] });
-        var crewCar = _consist.ActiveCar(item);
-
-        driver.SelectedIndex = crewCar.DriverType switch
+        driver.SelectedIndex = item.Driver switch
         {
             eDriverType.Headdriver => 0,
             eDriverType.Reardriver => 1,
@@ -288,14 +287,9 @@ public sealed class VehicleDetails
                 2 => eDriverType.Passenger,
                 _ => eDriverType.Nobody
             };
-            if (picked == crewCar.DriverType) return;
+            if (picked == item.Driver) return;
 
-            crewCar.DriverType = picked;
-            item.Driver = Consist.UnitDriver(item.Cars);
-            if (ReferenceEquals(_consist.Selected, item))
-                _consist.SyncStartingVehicle();
-            _redraw();
-            AppServices.Current.State.NotifyChanged();
+            _consist.SetCrew(item, picked);
         };
         driver.MinWidth = 0;
         driver.HorizontalAlignment = HorizontalAlignment.Stretch;