Refactor simulation effects and forecast hazards

src/ReactorMaintenance.Simulation/CellIntegrityEffect.cs

@@ -0,0 +1,33 @@
+namespace ReactorMaintenance.Simulation;
+
+public sealed class CellIntegrityEffect : ISimulationEffect
+{
+    public CellState Apply(CellState cell)
+    {
+        var integrity = cell.Integrity;
+        var hazards = cell.Hazards;
+
+        if (cell is { HasPipe: true, Pressure: > 7 })
+            integrity -= cell.Pressure - 7;
+
+        if (hazards.Heat >= 10 || hazards.Fire)
+        {
+            integrity -= cell.HasPipe ? 1 : 0;
+            hazards = hazards with { Stability = hazards.Stability - 1 };
+        }
+
+        cell = cell with {
+            Integrity = Rules.Clamp(integrity),
+            Hazards = hazards.Clamp()
+        };
+
+        if (integrity > 0 || !cell.HasPipe)
+            return cell;
+
+        return cell with {
+            LeakRate = Math.Max(cell.LeakRate, 3),
+            Flow = 0,
+            PipeOpen = false
+        };
+    }
+}

src/ReactorMaintenance.Simulation/FireAndElectricalHazardEffect.cs

@@ -0,0 +1,28 @@
+namespace ReactorMaintenance.Simulation;
+
+public sealed class FireAndElectricalHazardEffect : ISimulationEffect
+{
+    public CellState Apply(CellState cell)
+    {
+        var hazards = cell.Hazards;
+        if (hazards.CoolantPooling >= 3 && cell.Powered)
+            hazards = hazards with { ElectricalCharge = hazards.ElectricalCharge + 2 };
+
+        var hasFuel = hazards.FuelVapor >= 4 || hazards.LiquidFuel >= 6;
+        var hasIgnition = hazards.Heat >= 8 || hazards.ElectricalCharge >= 4 || cell is { Kind: ECellKind.Generator, Powered: true };
+        if ((hasFuel && hasIgnition) || hazards.Fire)
+        {
+            hazards = hazards with {
+                Fire = hasFuel || hazards.Fire,
+                Heat = hazards.Heat + 2,
+                Smoke = hazards.Smoke + 2,
+                LiquidFuel = Math.Max(0, hazards.LiquidFuel - 1),
+                FuelVapor = Math.Max(0, hazards.FuelVapor - 1)
+            };
+        }
+        else if (hazards.Smoke > 0)
+            hazards = hazards with { Smoke = hazards.Smoke - 1 };
+
+        return cell with { Hazards = hazards.Clamp() };
+    }
+}

src/ReactorMaintenance.Simulation/Hazard.cs

@@ -0,0 +1,6 @@
+namespace ReactorMaintenance.Simulation;
+
+public abstract class Hazard
+{
+    public abstract IEnumerable<Forecast> Predict(LevelState level, int turns);
+}

src/ReactorMaintenance.Simulation/IAreaSimulationEffect.cs

@@ -0,0 +1,6 @@
+namespace ReactorMaintenance.Simulation;
+
+public interface IAreaSimulationEffect
+{
+    CellState[] Apply(LevelState level, CellState[] cells);
+}

src/ReactorMaintenance.Simulation/ISimulationEffect.cs

@@ -0,0 +1,6 @@
+namespace ReactorMaintenance.Simulation;
+
+public interface ISimulationEffect
+{
+    CellState Apply(CellState cell);
+}

src/ReactorMaintenance.Simulation/IgnitionHazard.cs

@@ -0,0 +1,18 @@
+namespace ReactorMaintenance.Simulation;
+
+public sealed class IgnitionHazard : Hazard
+{
+    public override IEnumerable<Forecast> Predict(LevelState level, int turns)
+    {
+        for (var y = 0; y < level.Height; y++)
+        {
+            for (var x = 0; x < level.Width; x++)
+            {
+                var position = new GridPosition(x, y);
+                var cell = level.GetCell(position);
+                if (cell.Hazards.Fire)
+                    yield return new(EFailureKind.Ignition, position, turns, turns == 1 ? $"FUEL IGNITION PREDICTED AT {x},{y} NEXT TURN" : $"FUEL IGNITION PREDICTED AT {x},{y} IN {turns} TURNS");
+            }
+        }
+    }
+}

src/ReactorMaintenance.Simulation/MachineEffect.cs

@@ -0,0 +1,16 @@
+namespace ReactorMaintenance.Simulation;
+
+public sealed class MachineEffect : ISimulationEffect
+{
+    public CellState Apply(CellState cell)
+    {
+        var hazards = cell.Kind switch {
+            ECellKind.Generator when cell.Powered => cell.Hazards with { Heat = cell.Hazards.Heat + 1 },
+            ECellKind.CoolingPump when cell.Powered => cell.Hazards with { Heat = cell.Hazards.Heat - 2 },
+            ECellKind.Reactor => cell.Hazards with { Heat = cell.Hazards.Heat + 1 },
+            _ => cell.Hazards
+        };
+
+        return cell with { Hazards = hazards.Clamp() };
+    }
+}

src/ReactorMaintenance.Simulation/MeltdownHazard.cs

@@ -0,0 +1,10 @@
+namespace ReactorMaintenance.Simulation;
+
+public sealed class MeltdownHazard : Hazard
+{
+    public override IEnumerable<Forecast> Predict(LevelState level, int turns)
+    {
+        if (level.Global is { Lost: true, Status: "CORE MELTDOWN" })
+            yield return new(EFailureKind.Meltdown, null, turns, "CORE MELTDOWN APPROACHING");
+    }
+}

src/ReactorMaintenance.Simulation/PipeBurstHazard.cs

@@ -0,0 +1,18 @@
+namespace ReactorMaintenance.Simulation;
+
+public sealed class PipeBurstHazard : Hazard
+{
+    public override IEnumerable<Forecast> Predict(LevelState level, int turns)
+    {
+        for (var y = 0; y < level.Height; y++)
+        {
+            for (var x = 0; x < level.Width; x++)
+            {
+                var position = new GridPosition(x, y);
+                var cell = level.GetCell(position);
+                if (cell is { HasPipe: true, PipeOpen: false, Flow: 0, LeakRate: >= 3 })
+                    yield return new(EFailureKind.PipeBurst, position, turns, $"PIPE BURST PREDICTED AT {x},{y} IN {turns} TURNS");
+            }
+        }
+    }
+}

src/ReactorMaintenance.Simulation/PipeLeakEffect.cs

@@ -0,0 +1,26 @@
+namespace ReactorMaintenance.Simulation;
+
+public sealed class PipeLeakEffect : ISimulationEffect
+{
+    public CellState Apply(CellState cell)
+    {
+        if (!cell.HasPipe || cell.LeakRate <= 0)
+            return cell;
+
+        var hazards = cell.Pipe switch {
+            EPipeMedium.Fuel => cell.Hazards with {
+                LiquidFuel = cell.Hazards.LiquidFuel + cell.LeakRate,
+                FuelVapor = cell.Hazards.FuelVapor + (cell.Pressure >= 7 ? cell.LeakRate : Math.Max(0, cell.Hazards.Heat - 3) / 3)
+            },
+            EPipeMedium.Coolant => cell.Hazards with {
+                CoolantPooling = cell.Hazards.CoolantPooling + cell.LeakRate,
+                Heat = cell.Hazards.Heat - Math.Max(1, cell.LeakRate / 2),
+                Smoke = cell.Hazards.Smoke + (cell.Hazards.Heat >= 7 ? 2 : 0)
+            },
+            EPipeMedium.Pressure => cell.Hazards with { Smoke = cell.Hazards.Smoke + (cell.Pressure >= 8 ? 1 : 0) },
+            _ => cell.Hazards
+        };
+
+        return cell with { Hazards = hazards.Clamp() };
+    }
+}

src/ReactorMaintenance.Simulation/SimulationEngine.cs

@@ -2,93 +2,51 @@
 
 public sealed class SimulationEngine
 {
+    private const int c_MaxForecastStepCount = 12;
+
+    public SimulationEngine()
+        : this(
+            [new PipeLeakEffect(), new MachineEffect(), new FireAndElectricalHazardEffect(), new CellIntegrityEffect()],
+            [new SmokeSpreadEffect()],
+            [new PipeBurstHazard(), new IgnitionHazard(), new MeltdownHazard(), new StabilityCollapseHazard()])
+    {
+    }
+
+    public SimulationEngine(IEnumerable<ISimulationEffect> effects, IEnumerable<IAreaSimulationEffect> areaEffects, IEnumerable<Hazard> hazards)
+    {
+        m_Effects = effects.ToArray();
+        m_AreaEffects = areaEffects.ToArray();
+        m_Hazards = hazards.ToArray();
+    }
+
     public LevelState AdvanceTurn(LevelState level)
     {
-        var cells = level.Cells.ToArray();
-
-        for (var y = 0; y < level.Height; y++)
-        {
-            for (var x = 0; x < level.Width; x++)
-            {
-                var position = new GridPosition(x, y);
-                var index = level.Index(position);
-                var cell = cells[index];
-
-                if (!cell.IsWalkable)
-                    continue;
-
-                var hazards = ApplyPipeLeaks(cell);
-                hazards = ApplyMachineEffects(cell, hazards);
-                hazards = ApplyFireAndElectricalHazards(cell, hazards);
-                hazards = hazards.Clamp();
-
-                var integrity = cell.Integrity;
-                if (cell is { HasPipe: true, Pressure: > 7 })
-                    integrity -= cell.Pressure - 7;
-
-                if (hazards.Heat >= 10 || hazards.Fire)
-                {
-                    integrity -= cell.HasPipe ? 1 : 0;
-                    hazards = hazards with { Stability = hazards.Stability - 1 };
-                }
-
-                if (integrity <= 0 && cell.HasPipe)
-                {
-                    cell = cell with {
-                        LeakRate = Math.Max(cell.LeakRate, 3),
-                        Flow = 0,
-                        PipeOpen = false
-                    };
-                }
-
-                cells[index] = cell with {
-                    Integrity = Rules.Clamp(integrity),
-                    Hazards = hazards.Clamp()
-                };
-            }
-        }
-
-        cells = SpreadSmoke(level, cells);
-
-        var global = UpdateGlobal(level, cells);
-        var next = level with {
-            Cells = cells,
-            Global = global with { Turn = level.Global.Turn + 1 }
-        };
-
-        return next with { Forecasts = Forecast(next) };
+        return AdvanceTurn(level, true);
     }
 
     public IReadOnlyList<Forecast> Forecast(LevelState level)
     {
         var forecasts = new List<Forecast>();
+        var seen = new HashSet<ForecastKey>();
+        var forecastLevel = level with { Cells = level.Cells.ToArray(), Forecasts = Array.Empty<Forecast>() };
 
-        for (var y = 0; y < level.Height; y++)
-        for (var x = 0; x < level.Width; x++)
+        if (forecastLevel.Global.Lost)
+            AddHazardForecasts(forecasts, seen, forecastLevel, 0);
+
+        AddReactorReadyForecast(forecasts, seen, forecastLevel, 0);
+        if (IsReactorReady(forecastLevel) || forecastLevel.Global.Lost || forecastLevel.Global.ReactorActivated)
+            return forecasts.OrderBy(f => f.Turns).ThenBy(f => f.Message).ToArray();
+
+        for (var step = 1; step <= c_MaxForecastStepCount; step++)
         {
-            var position = new GridPosition(x, y);
-            var cell = level.GetCell(position);
+            forecastLevel = AdvanceTurn(forecastLevel, false);
+            AddHazardForecasts(forecasts, seen, forecastLevel, step);
+            AddReactorReadyForecast(forecasts, seen, forecastLevel, step);
 
-            if (cell is { HasPipe: true, Pressure: > 7, Integrity: > 0 })
-            {
-                var damagePerTurn = Math.Max(1, cell.Pressure - 7);
-                var turns = (int)Math.Ceiling(cell.Integrity / (double)damagePerTurn);
-                if (turns <= 4)
-                    forecasts.Add(new(EFailureKind.PipeBurst, position, turns, $"PIPE BURST PREDICTED AT {x},{y} IN {turns} TURNS"));
+            if (forecastLevel.Global.Lost || IsReactorReady(forecastLevel) || forecastLevel.Global.ReactorActivated)
+                break;
         }
 
-            var fuelLeakNearIgnition = cell is { Pipe: EPipeMedium.Fuel, LeakRate: > 0 } && (cell.Pressure >= 7 || cell.Kind == ECellKind.Generator);
-            var ignitionRisk = (cell.Hazards.FuelVapor >= 4 || cell.Hazards.LiquidFuel >= 6 || fuelLeakNearIgnition) && (cell.Hazards.Heat >= 8 || cell.Hazards.ElectricalCharge >= 4 || cell.Kind == ECellKind.Generator);
-            if (ignitionRisk && !cell.Hazards.Fire)
-                forecasts.Add(new(EFailureKind.Ignition, position, 1, $"FUEL IGNITION PREDICTED AT {x},{y} NEXT TURN"));
-        }
-
-        if (level.Global.CoreHeat >= 8)
-            forecasts.Add(new(EFailureKind.Meltdown, null, Math.Max(1, 11 - level.Global.CoreHeat), "CORE MELTDOWN APPROACHING"));
-
-        if (IsReactorReady(level))
-            forecasts.Add(new(EFailureKind.ReactorReady, null, 0, "REACTOR READY"));
-
         return forecasts.OrderBy(f => f.Turns).ThenBy(f => f.Message).ToArray();
     }
 
@@ -105,84 +63,59 @@ public sealed class SimulationEngine
         };
     }
 
-    private static HazardState ApplyPipeLeaks(CellState cell)
+    private LevelState AdvanceTurn(LevelState level, bool updateForecasts)
     {
-        var hazards = cell.Hazards;
-        if (!cell.HasPipe || cell.LeakRate <= 0)
-            return hazards;
+        var cells = level.Cells.ToArray();
 
-        return cell.Pipe switch {
-            EPipeMedium.Fuel => hazards with {
-                LiquidFuel = hazards.LiquidFuel + cell.LeakRate,
-                FuelVapor = hazards.FuelVapor + (cell.Pressure >= 7 ? cell.LeakRate : Math.Max(0, hazards.Heat - 3) / 3)
-            },
-            EPipeMedium.Coolant => hazards with {
-                CoolantPooling = hazards.CoolantPooling + cell.LeakRate,
-                Heat = hazards.Heat - Math.Max(1, cell.LeakRate / 2),
-                Smoke = hazards.Smoke + (hazards.Heat >= 7 ? 2 : 0)
-            },
-            EPipeMedium.Pressure => hazards with { Smoke = hazards.Smoke + (cell.Pressure >= 8 ? 1 : 0) },
-            _ => hazards
-        };
-    }
-
-    private static HazardState ApplyMachineEffects(CellState cell, HazardState hazards)
-    {
-        return cell.Kind switch {
-            ECellKind.Generator when cell.Powered => hazards with { Heat = hazards.Heat + 1 },
-            ECellKind.CoolingPump when cell.Powered => hazards with { Heat = hazards.Heat - 2 },
-            ECellKind.Reactor => hazards with { Heat = hazards.Heat + 1 },
-            _ => hazards
-        };
-    }
-
-    private static HazardState ApplyFireAndElectricalHazards(CellState cell, HazardState hazards)
-    {
-        if (hazards.CoolantPooling >= 3 && cell.Powered)
-            hazards = hazards with { ElectricalCharge = hazards.ElectricalCharge + 2 };
-
-        var hasFuel = hazards.FuelVapor >= 4 || hazards.LiquidFuel >= 6;
-        var hasIgnition = hazards.Heat >= 8 || hazards.ElectricalCharge >= 4 || cell is { Kind: ECellKind.Generator, Powered: true };
-        if ((hasFuel && hasIgnition) || hazards.Fire)
-        {
-            hazards = hazards with {
-                Fire = hasFuel || hazards.Fire,
-                Heat = hazards.Heat + 2,
-                Smoke = hazards.Smoke + 2,
-                LiquidFuel = Math.Max(0, hazards.LiquidFuel - 1),
-                FuelVapor = Math.Max(0, hazards.FuelVapor - 1)
-            };
-        }
-        else if (hazards.Smoke > 0)
-            hazards = hazards with { Smoke = hazards.Smoke - 1 };
-
-        return hazards;
-    }
-
-    private static CellState[] SpreadSmoke(LevelState level, CellState[] cells)
-    {
-        var next = cells.ToArray();
         for (var y = 0; y < level.Height; y++)
         {
             for (var x = 0; x < level.Width; x++)
             {
                 var position = new GridPosition(x, y);
-                var cell = cells[level.Index(position)];
-                if (cell.Hazards.Smoke < 6)
+                var index = level.Index(position);
+                var cell = cells[index];
+
+                if (!cell.IsWalkable)
                     continue;
 
-                foreach (var neighbor in position.Neighbors().Where(level.InBounds))
+                foreach (var effect in m_Effects)
+                    cell = effect.Apply(cell);
+
+                cells[index] = cell with { Hazards = cell.Hazards.Clamp() };
+            }
+        }
+
+        foreach (var areaEffect in m_AreaEffects)
+            cells = areaEffect.Apply(level, cells);
+
+        var global = UpdateGlobal(level, cells);
+        var next = level with {
+            Cells = cells,
+            Global = global with { Turn = level.Global.Turn + 1 }
+        };
+
+        return updateForecasts ? next with { Forecasts = Forecast(next) } : next;
+    }
+
+    private void AddHazardForecasts(List<Forecast> forecasts, HashSet<ForecastKey> seen, LevelState level, int turns)
     {
-                    var neighborCell = next[level.Index(neighbor)];
-                    if (!neighborCell.IsWalkable || neighborCell.DoorLocked)
-                        continue;
-
-                    next[level.Index(neighbor)] = neighborCell with { Hazards = neighborCell.Hazards with { Smoke = Rules.Clamp(neighborCell.Hazards.Smoke + 1) } };
-                }
+        foreach (var hazard in m_Hazards)
+        {
+            foreach (var forecast in hazard.Predict(level, turns))
+                AddForecast(forecasts, seen, forecast);
         }
     }
 
-        return next;
+    private static void AddReactorReadyForecast(List<Forecast> forecasts, HashSet<ForecastKey> seen, LevelState level, int turns)
+    {
+        if (IsReactorReady(level))
+            AddForecast(forecasts, seen, new(EFailureKind.ReactorReady, null, turns, "REACTOR READY"));
+    }
+
+    private static void AddForecast(List<Forecast> forecasts, HashSet<ForecastKey> seen, Forecast forecast)
+    {
+        if (seen.Add(new(forecast.Kind, forecast.Position)))
+            forecasts.Add(forecast);
     }
 
     private static GlobalState UpdateGlobal(LevelState level, CellState[] cells)
@@ -214,4 +147,10 @@ public sealed class SimulationEngine
         var reactorStable = level.Global.CoreHeat < 8;
         return hasReactor && hasStablePower && hasCooling && reactorStable && !level.Global.Lost;
     }
+
+    private readonly IReadOnlyList<ISimulationEffect> m_Effects;
+    private readonly IReadOnlyList<IAreaSimulationEffect> m_AreaEffects;
+    private readonly IReadOnlyList<Hazard> m_Hazards;
+
+    private sealed record ForecastKey(EFailureKind Kind, GridPosition? Position);
 }

src/ReactorMaintenance.Simulation/SmokeSpreadEffect.cs

@@ -0,0 +1,35 @@
+namespace ReactorMaintenance.Simulation;
+
+public sealed class SmokeSpreadEffect : IAreaSimulationEffect
+{
+    public CellState[] Apply(LevelState level, CellState[] cells)
+    {
+        var next = cells.ToArray();
+        for (var y = 0; y < level.Height; y++)
+        {
+            for (var x = 0; x < level.Width; x++)
+            {
+                var position = new GridPosition(x, y);
+                var cell = cells[level.Index(position)];
+                if (cell.Hazards.Smoke < 6)
+                    continue;
+
+                SpreadToNeighbors(level, next, position);
+            }
+        }
+
+        return next;
+    }
+
+    private static void SpreadToNeighbors(LevelState level, CellState[] next, GridPosition position)
+    {
+        foreach (var neighbor in position.Neighbors().Where(level.InBounds))
+        {
+            var neighborCell = next[level.Index(neighbor)];
+            if (!neighborCell.IsWalkable || neighborCell.DoorLocked)
+                continue;
+
+            next[level.Index(neighbor)] = neighborCell with { Hazards = neighborCell.Hazards with { Smoke = Rules.Clamp(neighborCell.Hazards.Smoke + 1) } };
+        }
+    }
+}

src/ReactorMaintenance.Simulation/StabilityCollapseHazard.cs

@@ -0,0 +1,10 @@
+namespace ReactorMaintenance.Simulation;
+
+public sealed class StabilityCollapseHazard : Hazard
+{
+    public override IEnumerable<Forecast> Predict(LevelState level, int turns)
+    {
+        if (level.Global is { Lost: true, Status: "FACILITY STABILITY COLLAPSE" })
+            yield return new(EFailureKind.StabilityCollapse, null, turns, "FACILITY STABILITY COLLAPSE APPROACHING");
+    }
+}

tests/ReactorMaintenance.Simulation.Tests/SimulationEngineTests.cs

@@ -17,7 +17,7 @@ public sealed class SimulationEngineTests
 
         var forecasts = m_Engine.Forecast(level);
 
-        Assert.Contains(forecasts, forecast => forecast.Kind == EFailureKind.Ignition && forecast.Position == new GridPosition(2, 2));
+        Assert.Contains(forecasts, forecast => forecast.Kind == EFailureKind.Ignition && forecast.Position == new GridPosition(2, 2) && forecast.Turns == 1);
     }
 
     [Fact]
@@ -35,6 +35,22 @@ public sealed class SimulationEngineTests
         Assert.True(next.GetCell(new(3, 3)).Hazards.ElectricalCharge >= 2);
     }
 
+    [Fact]
+    public void ActiveFireSpreadsSmokeToOpenNeighbors()
+    {
+        var level = LevelState.Create("Smoke", 6, 6)
+                              .SetCell(new(2, 2), new() {
+                                  Hazards = new() {
+                                      Fire = true,
+                                      Smoke = 6
+                                  }
+                              });
+
+        var next = m_Engine.AdvanceTurn(level);
+
+        Assert.True(next.GetCell(new(2, 3)).Hazards.Smoke > 0);
+    }
+
     [Fact]
     public void OverpressurePredictsPipeBurst()
     {
@@ -50,6 +66,64 @@ public sealed class SimulationEngineTests
         Assert.Contains(forecasts, forecast => forecast.Kind == EFailureKind.PipeBurst && forecast.Turns == 2);
     }
 
+    [Fact]
+    public void ForecastCapsFutureSimulationWhenNoTerminalConditionOccurs()
+    {
+        var engine = new SimulationEngine([], [], [new StepCountingHazard()]);
+        var level = LevelState.Create("Stable", 6, 6);
+
+        var forecasts = engine.Forecast(level);
+
+        Assert.Equal(12, forecasts.Count);
+        Assert.Equal(12, forecasts.Max(forecast => forecast.Turns));
+    }
+
+    [Fact]
+    public void ForecastPredictsMeltdownFromFutureSimulation()
+    {
+        var level = LevelState.Create("Meltdown", 6, 6)
+                              .SetCell(new(2, 2), new() {
+                                  Kind = ECellKind.Reactor,
+                                  Hazards = new() { Heat = 9 }
+                              });
+
+        var forecasts = m_Engine.Forecast(level);
+
+        Assert.Contains(forecasts, forecast => forecast.Kind == EFailureKind.Meltdown && forecast.Turns == 1);
+    }
+
+    [Fact]
+    public void ForecastReportsAlreadyLostLevelAtCurrentTurn()
+    {
+        var level = LevelState.Create("Lost", 6, 6) with {
+            Global = new() {
+                CoreHeat = 10,
+                Lost = true,
+                Status = "CORE MELTDOWN"
+            }
+        };
+
+        var forecasts = m_Engine.Forecast(level);
+
+        Assert.Contains(forecasts, forecast => forecast.Kind == EFailureKind.Meltdown && forecast.Turns == 0);
+    }
+
+    [Fact]
+    public void ForecastPredictsStabilityCollapseFromFutureSimulation()
+    {
+        var level = LevelState.Create("Collapse", 6, 6)
+                              .SetCell(new(2, 2), new() {
+                                  Kind = ECellKind.Generator,
+                                  Hazards = new() { Stability = 3 }
+                              }) with {
+            Global = new() { FacilityStability = 1 }
+        };
+
+        var forecasts = m_Engine.Forecast(level);
+
+        Assert.Contains(forecasts, forecast => forecast.Kind == EFailureKind.StabilityCollapse && forecast.Turns == 1);
+    }
+
     [Fact]
     public void StableReactorWithPowerAndCoolingCanActivate()
     {
@@ -92,4 +166,12 @@ public sealed class SimulationEngineTests
     }
 
     private readonly SimulationEngine m_Engine = new();
+
+    private sealed class StepCountingHazard : Hazard
+    {
+        public override IEnumerable<Forecast> Predict(LevelState level, int turns)
+        {
+            yield return new(EFailureKind.PipeBurst, new(turns, 0), turns, $"STEP {turns}");
+        }
+    }
 }