Add branch-aware junction flow

tests/ReactorMaintenance.Simulation.Tests/SimulationEngineTests.cs

@@ -1,4 +1,4 @@
-namespace ReactorMaintenance.Simulation.Tests;
+namespace ReactorMaintenance.Simulation.Tests;
 
 public sealed class SimulationEngineTests
 {
@@ -86,6 +86,57 @@ public sealed class SimulationEngineTests
         Assert.NotEqual(ELevelState.Lost, next.Global.LevelState);
     }
 
+    [Fact]
+    public void TJunctionRatioSplitsFlowAcrossInferredOutgoingBranches()
+    {
+        var level = BuildTJunctionLevel(ETJunctionMode.TwoTwo);
+
+        var next = m_Engine.AdvanceTurn(level);
+
+        Assert.True(next.GetUnderground(new(2, 2), ECarrierType.Fuel).Amount > 0);
+        Assert.Equal(next.GetUnderground(new(2, 2), ECarrierType.Fuel).Amount, next.GetUnderground(new(3, 3), ECarrierType.Fuel).Amount);
+        Assert.True(next.GetUnderground(new(2, 2), ECarrierType.Fuel).Amount < next.GetUnderground(new(2, 3), ECarrierType.Fuel).Amount);
+    }
+
+    [Fact]
+    public void TJunctionZeroWeightBranchReceivesNoIntentionalOutflow()
+    {
+        var level = BuildTJunctionLevel(ETJunctionMode.ZeroFour);
+
+        var next = m_Engine.AdvanceTurn(level);
+
+        Assert.Equal(0, next.GetUnderground(new(2, 2), ECarrierType.Fuel).Amount);
+        Assert.True(next.GetUnderground(new(3, 3), ECarrierType.Fuel).Amount > 0);
+    }
+
+    [Fact]
+    public void ValidatorRejectsAmbiguousJunctionSourceBranches()
+    {
+        var level = BuildTJunctionLevel(ETJunctionMode.TwoTwo);
+        level = level.SetProp(new(3, 3), new() { Type = EPropType.Flow, Carrier = ECarrierType.Fuel });
+
+        var report = new LevelValidator().Validate(level);
+
+        Assert.False(report.IsValid);
+        Assert.Contains(report.Errors, error => error.Message.Contains("Ambiguous junction flow", StringComparison.Ordinal));
+    }
+
+    [Fact]
+    public void NonJunctionCellsAcceptBestFlowFromMultipleSourcePaths()
+    {
+        var level = LevelState.Create("Best path", 7, 7);
+        level = AddHorizontalUnderground(level, ECarrierType.Fuel, 1, 5, 3);
+        level = level.SetProp(new(1, 3), new() { Type = EPropType.Flow, Carrier = ECarrierType.Fuel });
+        level = level.SetProp(new(5, 3), new() { Type = EPropType.Flow, Carrier = ECarrierType.Fuel });
+        level = level.SetProp(new(3, 3), new() { Type = EPropType.Consumer, Carrier = ECarrierType.Fuel });
+
+        var report = new LevelValidator().Validate(level);
+        var next = m_Engine.AdvanceTurn(level);
+
+        Assert.True(report.IsValid);
+        Assert.Equal(EConsumerServiceState.Producing, next.GetProp(new(3, 3)).ServiceState);
+    }
+
     [Fact]
     public void RobotLosesOnUnsafeElementHazard()
     {
@@ -199,5 +250,24 @@ public sealed class SimulationEngineTests
         return level;
     }
 
+    private static LevelState BuildTJunctionLevel(ETJunctionMode mode)
+    {
+        var level = LevelState.Create("T junction", 6, 6);
+        level = level.SetUnderground(new(1, 3), ECarrierType.Fuel, new() { State = EUndergroundState.Intact });
+        level = level.SetUnderground(new(2, 3), ECarrierType.Fuel, new() { State = EUndergroundState.Intact });
+        level = level.SetUnderground(new(2, 2), ECarrierType.Fuel, new() { State = EUndergroundState.Intact });
+        level = level.SetUnderground(new(3, 3), ECarrierType.Fuel, new() { State = EUndergroundState.Intact });
+        level = level.SetProp(new(1, 3), new() { Type = EPropType.Flow, Carrier = ECarrierType.Fuel });
+        return level.SetProp(new(2, 3), new() { Type = EPropType.TJunction, Carrier = ECarrierType.Fuel, TJunctionMode = mode });
+    }
+
+    private static LevelState AddHorizontalUnderground(LevelState level, ECarrierType carrier, int startX, int endX, int y)
+    {
+        for (var x = startX; x <= endX; x++)
+            level = level.SetUnderground(new(x, y), carrier, new() { State = EUndergroundState.Intact });
+
+        return level;
+    }
+
     private readonly SimulationEngine m_Engine = new();
-}
+}