Add branch-aware junction flow

src/ReactorMaintenance.Simulation/JunctionFlow.cs

@@ -0,0 +1,59 @@
+namespace ReactorMaintenance.Simulation;
+
+public sealed record JunctionFlow
+{
+    public GridPosition Position { get; init; } = new(0, 0);
+    public PropState Prop { get; init; } = new();
+    public ECarrierType Carrier { get; init; }
+    public IReadOnlyList<GridPosition> Branches { get; init; } = Array.Empty<GridPosition>();
+    public GridPosition? IncomingBranch { get; init; }
+    public IReadOnlyList<GridPosition> OutgoingBranches { get; init; } = Array.Empty<GridPosition>();
+    public IReadOnlyList<string> Errors { get; init; } = Array.Empty<string>();
+    public bool IsValid => Errors.Count == 0;
+
+    public float WeightFor(GridPosition outgoingBranch)
+    {
+        var index = IndexOfOutgoingBranch(outgoingBranch);
+        if (index < 0)
+            return 0;
+
+        var weights = Prop.Type == EPropType.TJunction
+            ? TJunctionWeights(Prop.TJunctionMode)
+            : CrossJunctionWeights(Prop.CrossJunctionMode);
+        return index < weights.Length ? weights[index] : 0;
+    }
+
+    private int IndexOfOutgoingBranch(GridPosition outgoingBranch)
+    {
+        for (var i = 0; i < OutgoingBranches.Count; i++)
+        {
+            if (OutgoingBranches[i] == outgoingBranch)
+                return i;
+        }
+
+        return -1;
+    }
+
+    private static float[] TJunctionWeights(ETJunctionMode mode)
+    {
+        return mode switch {
+            ETJunctionMode.ZeroFour => [0, 1],
+            ETJunctionMode.OneThree => [0.25f, 0.75f],
+            ETJunctionMode.TwoTwo => [0.5f, 0.5f],
+            ETJunctionMode.ThreeOne => [0.75f, 0.25f],
+            ETJunctionMode.FourZero => [1, 0],
+            _ => throw new ArgumentOutOfRangeException(nameof(mode), mode, "Unsupported T-junction mode.")
+        };
+    }
+
+    private static float[] CrossJunctionWeights(ECrossJunctionMode mode)
+    {
+        return mode switch {
+            ECrossJunctionMode.ZeroThreeThree => [0, 0.5f, 0.5f],
+            ECrossJunctionMode.ThreeZeroThree => [0.5f, 0, 0.5f],
+            ECrossJunctionMode.ThreeThreeZero => [0.5f, 0.5f, 0],
+            ECrossJunctionMode.TwoTwoTwo => [1f / 3f, 1f / 3f, 1f / 3f],
+            _ => throw new ArgumentOutOfRangeException(nameof(mode), mode, "Unsupported cross-junction mode.")
+        };
+    }
+}