Turn multi-car units as a whole when orientation is randomised or a unit swapped

Randomising flipped only the card's flag, so a multi-car unit was exported
with its cars in reverse order but each still facing forward - coupled back
to front. A swap copied the flag without turning the new cars. Both now turn
flag, cars and order together, as Flip does, and a locked unit as one.

StarterNG.Tests/ConsistCrewTests.cs

@@ -20,7 +20,7 @@ public class ConsistCrewTests
         installation.Vehicles.Load(installation.Library.Vehicles);
 
         _catalog = installation.Library.Vehicles;
-        _consist = new Consist(_catalog, new VehicleInfo(_catalog));
+        _consist = new Consist(_catalog, new VehicleInfo(_catalog, installation.Physics));
     }
 
     [Fact]

StarterNG.Tests/ConsistOrientationTests.cs

@@ -0,0 +1,82 @@
+using StarterNG.Classes;
+using StarterNG.Domain;
+using StarterNG.Domain.Vehicles;
+using StarterNG.Tests.Fakes;
+
+namespace StarterNG.Tests;
+
+public class ConsistOrientationTests
+{
+    private readonly VehicleCatalog _catalog;
+    private readonly TestInstallation _installation;
+
+    public ConsistOrientationTests()
+    {
+        var installation = new TestInstallation(new InMemoryFileSystem()
+            .WithFile(TestInstallation.At("dynamic", "pkp", "et40", "textures.txt"),
+                      "!=e\n^2\net40-10-a.mat=et40a,ET40-A\net40-10-b.mat=et40b,ET40-B\n" +
+                      "et40-16-a.mat=et40a,ET40-A\net40-16-b.mat=et40b,ET40-B"));
+        installation.Vehicles.Load(installation.Library.Vehicles);
+        _catalog = installation.Library.Vehicles;
+        _installation = installation;
+    }
+
+    [Fact]
+    public void Randomly_turned_unit_comes_out_like_a_flipped_one()
+    {
+        var flipped = NewConsist(out var unit);
+        flipped.Flip(unit);
+
+        var randomized = NewConsist(out _);
+        randomized.RandomizeOrientation(new AlwaysTurn());
+
+        Assert.Equal(Describe(flipped), Describe(randomized));
+    }
+
+    [Fact]
+    public void A_turned_unit_has_its_cars_reversed_and_each_one_turned()
+    {
+        var consist = NewConsist(out _);
+
+        consist.RandomizeOrientation(new AlwaysTurn());
+
+        // B leads, A trails, and both face backwards - not A-B reordered but facing forward.
+        Assert.Equal(new[] { "et40-10-b -1", "et40-10-a -1" }, Describe(consist));
+    }
+
+    [Fact]
+    public void A_unit_put_in_place_of_a_turned_one_faces_the_same_way()
+    {
+        var consist = NewConsist(out var unit);
+        consist.Flip(unit);
+
+        consist.Replace(0, Unit(consist, "et40-16-a"));
+
+        Assert.Equal(new[] { "et40-16-b -1", "et40-16-a -1" }, Describe(consist));
+    }
+
+    private Consist NewConsist(out ConsistItem unit)
+    {
+        var consist = new Consist(_catalog, new VehicleInfo(_catalog, _installation.Physics));
+        unit = Unit(consist, "et40-10-a");
+        consist.Insert(0, unit);
+        return consist;
+    }
+
+    private ConsistItem Unit(Consist consist, string lead) => new()
+    {
+        Cars = _catalog.ResolveSet(_catalog.TextureForSkin(lead)!)!
+                       .Select(texture => consist.MakeDynamic(texture, null))
+                       .ToList(),
+        Grouped = true
+    };
+
+    // The export order, each car with the way it faces.
+    private static string[] Describe(Consist consist) =>
+        consist.Flatten().Select(car => $"{car.SkinFile} {(car.Offset < 0 ? -1 : 1)}").ToArray();
+
+    private sealed class AlwaysTurn : Random
+    {
+        public override int Next(int maxValue) => 0;
+    }
+}

StarterNG/Domain/Consist.cs

@@ -256,9 +256,9 @@ public sealed class Consist : IReadOnlyList<ConsistItem>
     }
 
     /// <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.
+    /// Puts item in place of the vehicle at index, facing the same way. 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)
     {
@@ -266,6 +266,10 @@ public sealed class Consist : IReadOnlyList<ConsistItem>
         _items[index] = item;
         Staff(item, index);
 
+        // Facing the way the replaced vehicle did - cars and all, as Flip would.
+        if (item.Flipped != replaced.Flipped)
+            Turn(index, index);
+
         var crew = replaced.Driver;
         if (crew == eDriverType.Passenger ||
             (crew is eDriverType.Headdriver or eDriverType.Reardriver && IsPowered(item)))
@@ -339,6 +343,16 @@ public sealed class Consist : IReadOnlyList<ConsistItem>
         int index = _items.IndexOf(item);
         if (index < 0) return;
 
+        var (first, last) = UnitAround(index);
+        Turn(first, last);
+
+        AutoConnectAll();
+        Raise();
+    }
+
+    /// <summary>The cards locked together with the one at index, as the range they span.</summary>
+    private (int First, int Last) UnitAround(int index)
+    {
         int first = index;
         while (first > 0 && HoldsTail(_items[first - 1]))
             first--;
@@ -347,6 +361,17 @@ public sealed class Consist : IReadOnlyList<ConsistItem>
         while (last + 1 < _items.Count && HoldsTail(_items[last]))
             last++;
 
+        return (first, last);
+    }
+
+    /// <summary>
+    /// Turns the cards first..last end for end - the flag on each card, the cars it
+    /// holds and the order of the cards. All three or nothing: the export writes the
+    /// cars in card order and each car with its own orientation, so a flag turned
+    /// alone couples a multi-car unit back to front.
+    /// </summary>
+    private void Turn(int first, int last)
+    {
         for (int k = first; k <= last; k++)
         {
             var card = _items[k];
@@ -357,9 +382,6 @@ public sealed class Consist : IReadOnlyList<ConsistItem>
 
         if (last > first)
             _items.Reverse(first, last - first + 1);
-
-        AutoConnectAll();
-        Raise();
     }
 
     public void CycleDriver(ConsistItem item)
@@ -492,9 +514,15 @@ public sealed class Consist : IReadOnlyList<ConsistItem>
         if (start < 0) start = 0;
         if (start >= _items.Count) return;
 
-        for (int i = start; i < _items.Count; i++)
+        // Unit by unit, as Flip turns them: half a locked unit turned on its own
+        // would be coupled back to front.
+        for (int i = start; i < _items.Count;)
+        {
+            var (first, last) = UnitAround(i);
             if (rng.Next(2) == 0)
-                _items[i].Flipped = !_items[i].Flipped;
+                Turn(first, last);
+            i = last + 1;
+        }
 
         AutoConnectAll();
         Raise();

StarterNG/Domain/VehicleInfo.cs

@@ -1,14 +1,19 @@
 using StarterNG.Classes;
 using StarterNG.Domain.Vehicles;
-using StarterNG.Application;
+using StarterNG.Application.Abstractions;
 
 namespace StarterNG.Domain;
 
 public sealed class VehicleInfo
 {
     private readonly VehicleCatalog _db;
+    private readonly IPhysicsRepository _physics;
 
-    public VehicleInfo(VehicleCatalog db) => _db = db;
+    public VehicleInfo(VehicleCatalog db, IPhysicsRepository physics)
+    {
+        _db = db;
+        _physics = physics;
+    }
 
     public static string ClassOf(VehicleTexture t) => t.ResolvedClass;
 
@@ -23,14 +28,14 @@ public sealed class VehicleInfo
         TextureFor(car) is { } t ? CategoryOf(t) : null;
 
     public VehiclePhysics? PhysicsFor(VehicleTexture texture) =>
-        AppServices.Current.Physics.For(texture.Directory, texture.Model)
-        ?? AppServices.Current.Physics.For(texture.Directory, texture.Skinfile);
+        _physics.For(texture.Directory, texture.Model)
+        ?? _physics.For(texture.Directory, texture.Skinfile);
 
     public VehiclePhysics? PhysicsFor(Dynamic car)
     {
         string? dbModel = TextureFor(car)?.Model;
-        return AppServices.Current.Physics.For(car.DataFolder, dbModel)
-            ?? AppServices.Current.Physics.For(car.DataFolder, car.MmdFile)
-            ?? AppServices.Current.Physics.For(car.DataFolder, car.SkinFile);
+        return _physics.For(car.DataFolder, dbModel)
+            ?? _physics.For(car.DataFolder, car.MmdFile)
+            ?? _physics.For(car.DataFolder, car.SkinFile);
     }
 }

StarterNG/Views/Depot.axaml.cs

@@ -56,7 +56,7 @@ public partial class Depot : UserControl
 
     public Depot()
     {
-        _info = new VehicleInfo(_db);
+        _info = new VehicleInfo(_db, AppServices.Current.Physics);
         _consist = new Consist(_db, _info);
         _cargo = new Cargo(_info, _rng);
         _consist.Changed += RebuildConsist;
@@ -572,8 +572,7 @@ public partial class Depot : UserControl
         var item = new ConsistItem
         {
             Cars = unit.Select(NewVehicle).ToList(),
-            Grouped = unit.Count > 1,
-            Flipped = _consist.Selected.Flipped
+            Grouped = unit.Count > 1
         };
         _consist.Replace(i, item);
         _consist.Selected = item;