Keep the crew when a vehicle is swapped in the depot

The crew was copied to the card but not to the new cars, which are what is
shown and exported, so a swapped locomotive came out unstaffed. Swapping now
moves the crew over and otherwise staffs the vehicle as adding would.

StarterNG.Tests/ConsistCrewTests.cs

@@ -0,0 +1,107 @@
+using StarterNG.Classes;
+using StarterNG.Domain;
+using StarterNG.Domain.Vehicles;
+using StarterNG.Tests.Fakes;
+
+namespace StarterNG.Tests;
+
+public class ConsistCrewTests
+{
+    private readonly Consist _consist;
+    private readonly VehicleCatalog _catalog;
+
+    public ConsistCrewTests()
+    {
+        var installation = new TestInstallation(new InMemoryFileSystem()
+            .WithFile(TestInstallation.At("dynamic", "pkp", "ep07", "textures.txt"),
+                      "!=e\nep07-001.mat=ep07,EP07\nep07-002.mat=ep07,EP07")
+            .WithFile(TestInstallation.At("dynamic", "pkp", "b111", "textures.txt"),
+                      "!=b\nb111-01.mat=b111,B111"));
+        installation.Vehicles.Load(installation.Library.Vehicles);
+
+        _catalog = installation.Library.Vehicles;
+        _consist = new Consist(_catalog, new VehicleInfo(_catalog));
+    }
+
+    [Fact]
+    public void A_locomotive_added_at_the_head_gets_a_driver_in_cab_a()
+    {
+        var loco = Add("ep07-001", 0);
+
+        Assert.Equal(eDriverType.Headdriver, loco.Cars[0].DriverType);
+    }
+
+    [Fact]
+    public void Replacing_the_locomotive_keeps_the_driver_on_the_new_one()
+    {
+        Add("ep07-001", 0);
+        Add("b111-01", 1);
+
+        var replacement = Replace(0, "ep07-002");
+
+        Assert.Equal(eDriverType.Headdriver, replacement.Cars[0].DriverType);
+        Assert.Equal(eDriverType.Headdriver, replacement.Driver);
+    }
+
+    [Fact]
+    public void An_unstaffed_locomotive_replaced_at_the_head_is_staffed_in_cab_a()
+    {
+        var loco = Add("ep07-001", 0);
+        loco.Cars[0].DriverType = eDriverType.Nobody;
+        loco.Driver = eDriverType.Nobody;
+
+        var replacement = Replace(0, "ep07-002");
+
+        Assert.Equal(eDriverType.Headdriver, replacement.Cars[0].DriverType);
+    }
+
+    [Fact]
+    public void A_driver_in_cab_b_stays_in_cab_b()
+    {
+        var loco = Add("ep07-001", 0);
+        loco.Cars[0].DriverType = eDriverType.Reardriver;
+        loco.Driver = eDriverType.Reardriver;
+
+        var replacement = Replace(0, "ep07-002");
+
+        Assert.Equal(eDriverType.Reardriver, replacement.Cars[0].DriverType);
+    }
+
+    [Fact]
+    public void A_wagon_put_in_place_of_the_locomotive_gets_no_driver()
+    {
+        Add("ep07-001", 0);
+
+        var wagon = Replace(0, "b111-01");
+
+        Assert.Equal(eDriverType.Nobody, wagon.Cars[0].DriverType);
+    }
+
+    [Fact]
+    public void A_second_locomotive_behind_a_staffed_one_stays_unstaffed()
+    {
+        Add("ep07-001", 0);
+
+        var second = Add("ep07-002", 1);
+
+        Assert.Equal(eDriverType.Nobody, second.Cars[0].DriverType);
+    }
+
+    private ConsistItem Add(string skin, int at)
+    {
+        var item = Item(skin);
+        _consist.Staff(item, at);
+        _consist.Insert(at, item);
+        return item;
+    }
+
+    private ConsistItem Replace(int at, string skin)
+    {
+        var item = Item(skin);
+        _consist.Replace(at, item);
+        return item;
+    }
+
+    private ConsistItem Item(string skin) =>
+        new() { Cars = new List<Dynamic> { _consist.MakeDynamic(_catalog.TextureForSkin(skin)!, null) } };
+}

StarterNG/Domain/Consist.cs

@@ -236,6 +236,57 @@ public sealed class Consist : IReadOnlyList<ConsistItem>
     public void Insert(int at, ConsistItem item) =>
         _items.Insert(Math.Clamp(at, 0, _items.Count), item);
 
+    /// <summary>
+    /// Crew for a vehicle joining at position: a driver in cab A when it is powered
+    /// and either leads or the consist has no driver yet, nobody otherwise.
+    /// </summary>
+    public void Staff(ConsistItem item, int position)
+    {
+        item.Driver = eDriverType.Nobody;
+        foreach (var car in item.Cars)
+            car.DriverType = eDriverType.Nobody;
+
+        if (!IsPowered(item))
+            return;
+
+        bool staffed = _items.Any(other => !ReferenceEquals(other, item) &&
+                                           other.Driver is eDriverType.Headdriver or eDriverType.Reardriver);
+        if (position == 0 || !staffed)
+            Crew(item, eDriverType.Headdriver);
+    }
+
+    /// <summary>
+    /// Puts item in place of the vehicle at index. Its crew moves over where the
+    /// replacement can take it - a driver only into something powered - and the
+    /// rest is staffed as a newly added vehicle would be.
+    /// </summary>
+    public void Replace(int index, ConsistItem item)
+    {
+        var replaced = _items[index];
+        _items[index] = item;
+        Staff(item, index);
+
+        var crew = replaced.Driver;
+        if (crew == eDriverType.Passenger ||
+            (crew is eDriverType.Headdriver or eDriverType.Reardriver && IsPowered(item)))
+            Crew(item, crew);
+    }
+
+    // The crew lives on the cars - they are what is shown and exported - and the
+    // card only mirrors it.
+    private static void Crew(ConsistItem item, eDriverType crew)
+    {
+        if (item.Cars.Count == 0)
+            return;
+
+        item.Cars[0].DriverType = crew;
+        item.Driver = crew;
+    }
+
+    private bool IsPowered(ConsistItem item) =>
+        item.Cars.Count > 0 && _db.TextureForSkin(item.Cars[0].SkinFile) is { } texture &&
+        VehicleInfo.IsPoweredCategory(VehicleInfo.CategoryOf(texture));
+
     public void MoveLeft(ConsistItem item)
     {
         int i = _items.IndexOf(item);

StarterNG/Views/Depot.axaml.cs

@@ -573,10 +573,9 @@ public partial class Depot : UserControl
         {
             Cars = unit.Select(NewVehicle).ToList(),
             Grouped = unit.Count > 1,
-            Driver = _consist.Selected.Driver,
             Flipped = _consist.Selected.Flipped
         };
-        _consist[i] = item;
+        _consist.Replace(i, item);
         _consist.Selected = item;
         _consist.AutoConnectAll();
         RebuildConsist();
@@ -607,36 +606,13 @@ public partial class Depot : UserControl
         };
 
         at = Math.Clamp(at, 0, _consist.Count);
-        MatchOccupancy(item, at);
+        _consist.Staff(item, at);
         _consist.Insert(at, item);
         _consist.Selected = item;
         _consist.AutoConnectAll();
         RebuildConsist();
     }
 
-    private void MatchOccupancy(ConsistItem item, int position)
-    {
-        item.Driver = eDriverType.Nobody;
-        var lead = item.Cars.FirstOrDefault();
-        if (lead is null) return;
-
-        foreach (var car in item.Cars)
-            car.DriverType = eDriverType.Nobody;
-
-        var tex = _db.TextureForSkin(lead.SkinFile);
-        string? cat = tex != null ? VehicleInfo.CategoryOf(tex) : null;
-        if (!VehicleInfo.IsPoweredCategory(cat))
-            return;
-
-        bool staffed = _consist.Any(i =>
-            i.Driver is eDriverType.Headdriver or eDriverType.Reardriver);
-        if (position == 0 || !staffed)
-        {
-            item.Driver = eDriverType.Headdriver;
-            lead.DriverType = eDriverType.Headdriver;
-        }
-    }
-
     private async void TextureBaseButton_OnClick(object? sender, Avalonia.Interactivity.RoutedEventArgs e)
     {
         if (TopLevel.GetTopLevel(this) is not Window owner) return;