using FluentAssertions;
using Sand.Core;

namespace Sand.Tests;

public sealed class SandSimulationTests
{
    private readonly ParticleLibrary _library = ParticleLibraryLoader.LoadFromDirectory(Path.Combine(AppContext.BaseDirectory, "Content", "part"));

    [Fact]
    public void SandFallsIntoEmptySpace()
    {
        var simulation = CreateSimulation();
        simulation.CreateParticleAtPixel(2, 2, "sand");
        simulation.Settings.PauseSim = false;

        simulation.Step(1f / 60f);

        simulation.GetTypeIdAtCell(2, 3).Should().Be(_library.GetTypeId("sand"));
    }

    [Fact]
    public void WaterAndSandCreateWetSand()
    {
        var simulation = CreateSimulation();
        simulation.CreateParticleAtPixel(3, 3, "sand");
        simulation.CreateParticleAtPixel(2, 3, "water");
        simulation.Settings.PauseSim = false;

        simulation.Step(1f / 60f);

        simulation.GetTypeIdAtCell(3, 3).Should().Be(_library.GetTypeId("wsand"));
    }

    [Fact]
    public void LoaderParsesExtendedMetadataFields()
    {
        var burningWood = _library.GetDefinition(_library.GetTypeId("burning_wood"));
        var energy = _library.GetDefinition(_library.GetTypeId("energy"));
        var wind = _library.GetDefinition(_library.GetTypeId("wind"));
        var stone = _library.GetDefinition(_library.GetTypeId("stone"));
        var ultratanium = _library.GetDefinition(_library.GetTypeId("ultratanium"));

        burningWood.Produces.Should().Be("smoke");
        burningWood.HeatEmission.Should().Be(50f);
        energy.EnergyTransfer.Should().BeGreaterThan(0f);
        wind.Radius.Should().BeGreaterThan(0f);
        wind.Affects.Should().Contain("steam");
        stone.Hardness.Should().Be(0.7f);
        stone.Durability.Should().Be(100f);
        stone.Broken.Should().Be("brkstone");
        ultratanium.Explosive.Should().BeTrue();
        ultratanium.ExplosionRadius.Should().Be(15);
    }

    [Fact]
    public void LavaAndWaterCreateStoneAndSteam()
    {
        var simulation = CreateSimulation();
        simulation.CreateParticleAtPixel(2, 2, "lava");
        simulation.CreateParticleAtPixel(3, 2, "water");
        simulation.Settings.PauseSim = false;

        simulation.Step(1f / 60f);

        simulation.GetTypeIdAtCell(2, 2).Should().Be(_library.GetTypeId("stone"));
        simulation.GetTypeIdAtCell(3, 2).Should().Be(_library.GetTypeId("steam"));
    }

    [Fact]
    public void BuildRgbFrameReflectsParticleColor()
    {
        var simulation = CreateSimulation();
        var sand = _library.GetDefinition(_library.GetTypeId("sand"));
        simulation.CreateParticleAtPixel(0, 0, "sand");

        var frame = simulation.BuildRgbFrame().ToArray();

        frame[0].Should().Be(sand.Color.R);
        frame[1].Should().Be(sand.Color.G);
        frame[2].Should().Be(sand.Color.B);
    }

    [Fact]
    public void SparkSpreadsToDiagonalConductors()
    {
        var simulation = CreateSimulation();
        simulation.CreateParticleAtPixel(4, 4, "iron");
        simulation.CreateParticleAtPixel(5, 5, "iron");
        simulation.CreateParticleAtPixel(4, 4, "spark");
        simulation.Settings.PauseSim = false;

        simulation.Step(1f / 60f);

        simulation.SparkTime[5, 5].Should().BeGreaterThan((short)0);
    }

    [Fact]
    public void OuterWallPreventsPaintingBoundaryCells()
    {
        var simulation = new SandSimulation(10, 10, 1, _library, new SimulationSettings { PauseSim = true, OuterWall = true });
        simulation.RefreshSettingsState();

        simulation.CreateParticleAtPixel(0, 0, "sand");

        simulation.GetTypeIdAtCell(0, 0).Should().Be(_library.GetTypeId("wall"));
    }

    [Fact]
    public void TogglingOuterWallOffRemovesBoundaryWallsFromParticleCount()
    {
        var settings = new SimulationSettings { PauseSim = true, OuterWall = true };
        var simulation = new SandSimulation(10, 10, 1, _library, settings);
        simulation.RefreshSettingsState();
        simulation.ParticleCount.Should().BeGreaterThan(0);

        settings.OuterWall = false;
        simulation.RefreshSettingsState();

        simulation.ParticleCount.Should().Be(0);
        simulation.GetTypeIdAtCell(0, 0).Should().Be(0);
        simulation.GetTypeIdAtCell(9, 9).Should().Be(0);
    }

    [Fact]
    public void WrapParticlesMovesAcrossEdge()
    {
        var simulation = new SandSimulation(5, 5, 1, _library, new SimulationSettings { PauseSim = false, WrapParticles = true });
        simulation.CreateParticleAtPixel(4, 0, "steam");

        simulation.Step(1f / 60f);

        simulation.ParticleCount.Should().Be(1);
    }

    [Fact]
    public void ParticleCountRemainsStableAcrossMovementSteps()
    {
        var simulation = new SandSimulation(12, 12, 1, _library, new SimulationSettings { PauseSim = false });
        simulation.CreateParticleAtPixel(6, 2, "sand");

        for (var i = 0; i < 6; i++)
        {
            simulation.Step(1f / 60f);
            simulation.ParticleCount.Should().Be(1);
        }
    }

    [Fact]
    public void SymmetricSandPileDoesNotDevelopStrongRightBias()
    {
        var simulation = new SandSimulation(60, 40, 1, _library, new SimulationSettings { PauseSim = false });
        for (var x = 0; x < simulation.Width; x++)
        {
            simulation.CreateParticleAtPixel(x, simulation.Height - 1, "wall");
        }

        for (var x = 24; x <= 36; x++)
        {
            for (var y = 4; y <= 16; y++)
            {
                simulation.CreateParticleAtPixel(x, y, "sand");
            }
        }

        var startCenter = FindAverageX(simulation, "sand");
        for (var i = 0; i < 120; i++)
        {
            simulation.Step(1f / 60f);
        }

        var finalCenter = FindAverageX(simulation, "sand");
        Math.Abs(finalCenter - startCenter).Should().BeLessThanOrEqualTo(1.5);
    }

    [Fact]
    public void NeutralFireCanMoveLeftWhenOnlyLeftEscapePathIsAvailable()
    {
        var simulation = CreateSimulation();
        simulation.CreateParticleAtPixel(5, 5, "fire");
        simulation.CreateParticleAtPixel(5, 4, "wall");
        simulation.CreateParticleAtPixel(6, 4, "wall");
        simulation.CreateParticleAtPixel(6, 5, "wall");
        simulation.Settings.PauseSim = false;

        simulation.Step(1f / 60f);

        var fireId = _library.GetTypeId("fire");
        (simulation.GetTypeIdAtCell(4, 4) == fireId || simulation.GetTypeIdAtCell(4, 5) == fireId).Should().BeTrue();
    }

    [Fact]
    public void LazyOccupiedBoundsShrinkEventuallyAfterEdgeRemoval()
    {
        var simulation = new SandSimulation(30, 30, 1, _library, new SimulationSettings { PauseSim = false });
        simulation.CreateParticleAtPixel(2, 2, "wall");
        simulation.CreateParticleAtPixel(20, 20, "wall");
        simulation.Step(1f / 60f);

        simulation.ClearParticleCircle(2, 2, 0);

        for (var i = 0; i < 10; i++)
        {
            simulation.Step(1f / 60f);
        }

        simulation.FrameStats.ParticleCount.Should().Be(1);
        simulation.FrameStats.MinActiveX.Should().BeLessThanOrEqualTo(20);
        simulation.FrameStats.MaxActiveX.Should().BeGreaterThanOrEqualTo(20);
        simulation.FrameStats.MaxActiveX.Should().BeLessThanOrEqualTo(21);
        simulation.FrameStats.MinActiveY.Should().BeLessThanOrEqualTo(20);
        simulation.FrameStats.MaxActiveY.Should().BeGreaterThanOrEqualTo(20);
        simulation.FrameStats.MaxActiveY.Should().BeLessThanOrEqualTo(21);
    }

    [Fact]
    public void EmptySimulationClearsActiveBoundsStats()
    {
        var simulation = new SandSimulation(20, 20, 1, _library, new SimulationSettings { PauseSim = false });
        simulation.CreateParticleAtPixel(10, 10, "sand");

        simulation.Step(1f / 60f);
        simulation.Clear();
        simulation.Settings.PauseSim = false;
        simulation.Step(1f / 60f);

        simulation.FrameStats.ProcessedCells.Should().Be(0);
        simulation.FrameStats.ParticleCount.Should().Be(0);
        simulation.FrameStats.MinActiveX.Should().Be(0);
        simulation.FrameStats.MinActiveY.Should().Be(0);
        simulation.FrameStats.MaxActiveX.Should().Be(0);
        simulation.FrameStats.MaxActiveY.Should().Be(0);
    }

    [Fact]
    public void BuildRgbaFrameWritesExpectedLength()
    {
        var simulation = CreateSimulation();
        simulation.CreateParticleAtPixel(0, 0, "sand");
        var buffer = new byte[10 * 10 * 4];

        simulation.BuildRgbaFrame(buffer);

        buffer.Length.Should().Be(400);
        buffer[3].Should().Be(255);
    }

    [Fact]
    public void BuildRgbaFrameUpdatesReusedBufferAfterCellChanges()
    {
        var simulation = CreateSimulation();
        var buffer = new byte[10 * 10 * 4];
        var sand = _library.GetDefinition(_library.GetTypeId("sand"));

        simulation.CreateParticleAtPixel(2, 2, "sand");
        simulation.BuildRgbaFrame(buffer);

        var sandIndex = ((2 * simulation.Width) + 2) * 4;
        buffer[sandIndex].Should().Be(sand.Color.R);

        simulation.ClearParticleCircle(2, 2, 0);
        simulation.BuildRgbaFrame(buffer);

        buffer[sandIndex].Should().Be(0);
        buffer[sandIndex + 1].Should().Be(0);
        buffer[sandIndex + 2].Should().Be(0);
        buffer[sandIndex + 3].Should().Be(255);
    }

    [Fact]
    public void WindBrushWritesLocalWindField()
    {
        var simulation = CreateSimulation();

        simulation.ApplyWindBrushAtPixel(4, 4, 2, 1f, 0f);

        var wind = simulation.GetWindAtCell(4, 4);
        wind.X.Should().BeGreaterThan(0f);
        MathF.Abs(wind.Y).Should().BeLessThan(0.2f);
    }

    [Fact]
    public void AirBrushWritesPressureField()
    {
        var simulation = CreateSimulation();

        simulation.ApplyAirBrushAtPixel(4, 4, 2, 1f, 0f);

        simulation.GetAirPressureAtCell(4, 4).Should().BeGreaterThan(0f);
    }

    [Fact]
    public void FieldDecayContinuesWithoutParticles()
    {
        var simulation = CreateSimulation();
        simulation.Settings.PauseSim = false;
        simulation.ApplyAirBrushAtPixel(4, 4, 2, 1f, 0f);
        var initialPressure = simulation.GetAirPressureAtCell(4, 4);

        simulation.Step(1f / 60f);

        simulation.GetAirPressureAtCell(4, 4).Should().BeLessThan(initialPressure);
        simulation.ParticleCount.Should().Be(0);
    }

    [Fact]
    public void FreshlySpawnedFallingSandDoesNotImmediatelyCreateVisiblePressure()
    {
        var simulation = CreateSimulation();
        simulation.CreateParticleAtPixel(4, 1, "sand");
        simulation.Settings.PauseSim = false;

        simulation.Step(1f / 60f);
        simulation.Step(1f / 60f);

        MathF.Abs(simulation.GetAirPressureAtCell(4, 3)).Should().BeLessThan(0.08f);
        MathF.Abs(simulation.GetAirPressureAtCell(3, 3)).Should().BeLessThan(0.08f);
        MathF.Abs(simulation.GetAirPressureAtCell(5, 3)).Should().BeLessThan(0.08f);
    }

    [Fact]
    public void GasRespondsMoreThanLiquidToSamePressureField()
    {
        var steamSimulation = new SandSimulation(12, 12, 1, _library, new SimulationSettings { PauseSim = false });
        var waterSimulation = new SandSimulation(12, 12, 1, _library, new SimulationSettings { PauseSim = false });

        steamSimulation.CreateParticleAtPixel(6, 6, "steam");
        waterSimulation.CreateParticleAtPixel(6, 6, "water");

        for (var i = 0; i < 6; i++)
        {
            steamSimulation.ApplyAirBrushAtPixel(3, 6, 3, 1f, 0f);
            waterSimulation.ApplyAirBrushAtPixel(3, 6, 3, 1f, 0f);
            steamSimulation.Step(1f / 60f);
            waterSimulation.Step(1f / 60f);
        }

        Math.Abs(FindParticleX(steamSimulation, "steam") - 6).Should().BeGreaterThan(0);
        Math.Abs(FindParticleX(waterSimulation, "water") - 6).Should().BeLessThan(Math.Abs(FindParticleX(steamSimulation, "steam") - 6));
    }

    [Fact]
    public void NewlySpawnedParticleClearsLocalForceAndPressureFields()
    {
        var simulation = CreateSimulation();

        simulation.ApplyWindBrushAtPixel(4, 4, 2, 1f, 0f);
        simulation.ApplyAirBrushAtPixel(4, 4, 2, 1f, 0f);
        simulation.GetAirPressureAtCell(4, 4).Should().BeGreaterThan(0f);
        simulation.GetWindAtCell(4, 4).X.Should().BeGreaterThan(0f);

        simulation.CreateParticleAtPixel(4, 4, "sand");

        simulation.GetAirPressureAtCell(4, 4).Should().Be(0f);
        simulation.GetWindAtCell(4, 4).X.Should().Be(0f);
        simulation.GetWindAtCell(4, 4).Y.Should().Be(0f);
        simulation.GetForceAtCell(4, 4).X.Should().Be(0f);
        simulation.GetForceAtCell(4, 4).Y.Should().Be(0f);
    }

    [Fact]
    public void PourPaintingAddsLimitedParticlesInsteadOfFillingEntireBrush()
    {
        var simulation = CreateSimulation();

        simulation.CreateParticlePourAtPixel(8, 8, 3, "sand", 4, 1234);

        simulation.ParticleCount.Should().Be(4);
    }

    [Fact]
    public void FireTouchingWaterIsExtinguished()
    {
        var simulation = CreateSimulation();
        simulation.CreateParticleAtPixel(2, 2, "fire");
        simulation.CreateParticleAtPixel(3, 2, "water");
        simulation.Settings.PauseSim = false;

        simulation.Step(1f / 60f);

        simulation.GetTypeIdAtCell(2, 2).Should().Be(0);
        var neighbor = simulation.GetTypeIdAtCell(3, 2);
        neighbor.Should().BeOneOf((ushort)0, _library.GetTypeId("water"), _library.GetTypeId("steam"));
    }

    [Fact]
    public void FireRisesInsteadOfBehavingLikeSolid()
    {
        var simulation = CreateSimulation();
        simulation.CreateParticleAtPixel(5, 5, "fire");
        simulation.Settings.PauseSim = false;

        simulation.Step(1f / 60f);

        simulation.GetTypeIdAtCell(5, 4).Should().Be(_library.GetTypeId("fire"));
    }

    [Fact]
    public void FireEventuallyProducesSmoke()
    {
        var simulation = CreateSimulation();
        simulation.CreateParticleAtPixel(5, 7, "fire");
        simulation.Settings.PauseSim = false;

        for (var i = 0; i < 12; i++)
        {
            simulation.Step(1f / 60f);
        }

        CountParticles(simulation, "smoke").Should().BeGreaterThan(0);
    }

    [Fact]
    public void SandAndWaterDoNotSpontaneouslyGenerateSmokeOrEmbers()
    {
        var simulation = new SandSimulation(16, 16, 1, _library, new SimulationSettings { PauseSim = false });
        simulation.CreateParticleAtPixel(6, 6, "sand");
        simulation.CreateParticleAtPixel(9, 6, "water");

        for (var i = 0; i < 20; i++)
        {
            simulation.Step(1f / 60f);
        }

        CountParticles(simulation, "smoke").Should().Be(0);
        CountParticles(simulation, "ember").Should().Be(0);
    }

    [Fact]
    public void BurningWoodStaysMostlyInPlaceAndProducesEffectParticles()
    {
        var simulation = new SandSimulation(16, 16, 1, _library, new SimulationSettings { PauseSim = false });
        simulation.CreateParticleAtPixel(8, 8, "burning_wood");

        for (var i = 0; i < 24; i++)
        {
            simulation.Step(1f / 60f);
        }

        simulation.GetTypeIdAtCell(8, 8).Should().Be(_library.GetTypeId("burning_wood"));
        (CountParticles(simulation, "smoke") + CountParticles(simulation, "ember")).Should().BeGreaterThan(0);
    }

    [Fact]
    public void PlasmaTransfersEnergyToConductiveNeighbors()
    {
        var simulation = new SandSimulation(16, 16, 1, _library, new SimulationSettings { PauseSim = false });
        simulation.CreateParticleAtPixel(8, 8, "plasma");
        simulation.CreateParticleAtPixel(8, 7, "wall");
        simulation.CreateParticleAtPixel(7, 8, "iron");
        simulation.CreateParticleAtPixel(9, 8, "iron");
        simulation.CreateParticleAtPixel(7, 7, "wall");
        simulation.CreateParticleAtPixel(9, 7, "wall");
        simulation.CreateParticleAtPixel(8, 9, "wall");

        for (var i = 0; i < 12; i++)
        {
            simulation.Step(1f / 60f);
        }

        (simulation.SparkTime[7, 8] != 0 || simulation.SparkTime[9, 8] != 0).Should().BeTrue();
    }

    [Fact]
    public void SteamDoesNotImmediatelyCondenseAfterCreation()
    {
        var simulation = new SandSimulation(12, 12, 1, _library, new SimulationSettings { PauseSim = false, AmbientTemperature = 22f });
        simulation.CreateParticleAtPixel(6, 6, "steam");
        simulation.CreateParticleAtPixel(5, 5, "wall");
        simulation.CreateParticleAtPixel(6, 5, "wall");
        simulation.CreateParticleAtPixel(7, 5, "wall");
        simulation.CreateParticleAtPixel(5, 6, "wall");
        simulation.CreateParticleAtPixel(7, 6, "wall");
        simulation.CreateParticleAtPixel(5, 7, "wall");
        simulation.CreateParticleAtPixel(6, 7, "wall");
        simulation.CreateParticleAtPixel(7, 7, "wall");

        for (var i = 0; i < 6; i++)
        {
            simulation.Step(1f / 60f);
        }

        CountParticles(simulation, "steam").Should().BeGreaterThan(0);
    }

    [Fact]
    public void CooledSteamCondensesBackIntoWaterInsteadOfDisappearing()
    {
        var simulation = new SandSimulation(12, 12, 1, _library, new SimulationSettings { PauseSim = false, AmbientTemperature = 22f });
        simulation.CreateParticleAtPixel(6, 6, "steam");
        simulation.CreateParticleAtPixel(5, 5, "wall");
        simulation.CreateParticleAtPixel(6, 5, "wall");
        simulation.CreateParticleAtPixel(7, 5, "wall");
        simulation.CreateParticleAtPixel(5, 6, "wall");
        simulation.CreateParticleAtPixel(7, 6, "wall");
        simulation.CreateParticleAtPixel(5, 7, "wall");
        simulation.CreateParticleAtPixel(6, 7, "wall");
        simulation.CreateParticleAtPixel(7, 7, "wall");

        for (var i = 0; i < 80; i++)
        {
            simulation.Step(1f / 60f);
        }

        simulation.GetTypeIdAtCell(6, 6).Should().Be(_library.GetTypeId("water"));
    }

    [Fact]
    public void SteamRisesFasterThanSmokeBecauseOfVelocity()
    {
        var steamSimulation = new SandSimulation(12, 12, 1, _library, new SimulationSettings { PauseSim = false });
        var smokeSimulation = new SandSimulation(12, 12, 1, _library, new SimulationSettings { PauseSim = false });
        steamSimulation.CreateParticleAtPixel(6, 9, "steam");
        smokeSimulation.CreateParticleAtPixel(6, 9, "smoke");

        for (var i = 0; i < 8; i++)
        {
            steamSimulation.Step(1f / 60f);
            smokeSimulation.Step(1f / 60f);
        }

        FindParticleY(steamSimulation, "steam").Should().BeLessThan(FindParticleY(smokeSimulation, "smoke"));
    }

    [Fact]
    public void LavaDoesNotCoolImmediatelyAtAmbient()
    {
        var simulation = new SandSimulation(12, 12, 1, _library, new SimulationSettings { PauseSim = false, AmbientTemperature = 22f });
        simulation.CreateParticleAtPixel(6, 6, "lava");
        simulation.CreateParticleAtPixel(5, 5, "wall");
        simulation.CreateParticleAtPixel(6, 5, "wall");
        simulation.CreateParticleAtPixel(7, 5, "wall");
        simulation.CreateParticleAtPixel(5, 7, "wall");
        simulation.CreateParticleAtPixel(6, 7, "wall");
        simulation.CreateParticleAtPixel(7, 7, "wall");
        simulation.CreateParticleAtPixel(5, 6, "wall");
        simulation.CreateParticleAtPixel(7, 6, "wall");
        simulation.Temperature[6, 6] = 820f;

        for (var i = 0; i < 8; i++)
        {
            simulation.Step(1f / 60f);
        }

        simulation.GetTypeIdAtCell(6, 6).Should().Be(_library.GetTypeId("lava"));
    }

    [Fact]
    public void LavaDoesNotSelfDestructFromHeatAlone()
    {
        var simulation = new SandSimulation(12, 12, 1, _library, new SimulationSettings { PauseSim = false, AmbientTemperature = 22f });
        simulation.CreateParticleAtPixel(6, 6, "lava");
        simulation.CreateParticleAtPixel(5, 5, "wall");
        simulation.CreateParticleAtPixel(6, 5, "wall");
        simulation.CreateParticleAtPixel(7, 5, "wall");
        simulation.CreateParticleAtPixel(5, 6, "wall");
        simulation.CreateParticleAtPixel(7, 6, "wall");
        simulation.CreateParticleAtPixel(5, 7, "wall");
        simulation.CreateParticleAtPixel(6, 7, "wall");
        simulation.CreateParticleAtPixel(7, 7, "wall");

        for (var i = 0; i < 45; i++)
        {
            simulation.Step(1f / 60f);
        }

        simulation.GetTypeIdAtCell(6, 6).Should().Be(_library.GetTypeId("lava"));
    }

    [Fact]
    public void MoltenGoldDoesNotSpreadFasterThanWaterInRuntimeTuning()
    {
        var waterSimulation = new SandSimulation(16, 16, 1, _library, new SimulationSettings { PauseSim = false });
        var moltenGoldSimulation = new SandSimulation(16, 16, 1, _library, new SimulationSettings { PauseSim = false });
        PrepareFloor(waterSimulation, 6);
        PrepareFloor(moltenGoldSimulation, 6);
        waterSimulation.CreateParticleAtPixel(8, 5, "water");
        moltenGoldSimulation.CreateParticleAtPixel(8, 5, "molten_gold");

        for (var i = 0; i < 8; i++)
        {
            waterSimulation.Step(1f / 60f);
            moltenGoldSimulation.Step(1f / 60f);
        }

        var waterX = FindParticleX(waterSimulation, "water");
        var moltenGoldX = FindParticleX(moltenGoldSimulation, "molten_gold");
        Math.Abs(moltenGoldX - 8).Should().BeLessThanOrEqualTo(Math.Abs(waterX - 8));
    }

    [Fact]
    public void LavaRespondsLessThanWaterToLateralForce()
    {
        var waterSimulation = new SandSimulation(16, 16, 1, _library, new SimulationSettings { PauseSim = false });
        var lavaSimulation = new SandSimulation(16, 16, 1, _library, new SimulationSettings { PauseSim = false, AmbientTemperature = 900f });
        PrepareFloor(waterSimulation, 6);
        PrepareFloor(lavaSimulation, 6);
        waterSimulation.CreateParticleAtPixel(8, 5, "water");
        lavaSimulation.CreateParticleAtPixel(8, 5, "lava");

        for (var i = 0; i < 10; i++)
        {
            waterSimulation.ApplyWindBrushAtPixel(8, 5, 3, 1f, 0f);
            lavaSimulation.ApplyWindBrushAtPixel(8, 5, 3, 1f, 0f);
            waterSimulation.Step(1f / 60f);
            lavaSimulation.Step(1f / 60f);
        }

        var waterX = FindParticleX(waterSimulation, "water");
        var lavaX = FindParticleX(lavaSimulation, "lava");
        Math.Abs(lavaX - 8).Should().BeLessThan(Math.Abs(waterX - 8));
    }

    [Fact]
    public void MoltenGoldDoesNotSelfDestructFromHeatAlone()
    {
        var simulation = new SandSimulation(12, 12, 1, _library, new SimulationSettings { PauseSim = false, AmbientTemperature = 22f });
        simulation.CreateParticleAtPixel(6, 6, "molten_gold");
        simulation.CreateParticleAtPixel(5, 5, "wall");
        simulation.CreateParticleAtPixel(6, 5, "wall");
        simulation.CreateParticleAtPixel(7, 5, "wall");
        simulation.CreateParticleAtPixel(5, 6, "wall");
        simulation.CreateParticleAtPixel(7, 6, "wall");
        simulation.CreateParticleAtPixel(5, 7, "wall");
        simulation.CreateParticleAtPixel(6, 7, "wall");
        simulation.CreateParticleAtPixel(7, 7, "wall");

        for (var i = 0; i < 35; i++)
        {
            simulation.Step(1f / 60f);
        }

        simulation.GetTypeIdAtCell(6, 6).Should().Be(_library.GetTypeId("molten_gold"));
    }

    [Fact]
    public void IceAndSnowDoNotImmediatelyMeltAtThresholdTemperatures()
    {
        var simulation = new SandSimulation(12, 12, 1, _library, new SimulationSettings { PauseSim = false, AmbientTemperature = 22f });
        simulation.CreateParticleAtPixel(4, 6, "ice");
        simulation.CreateParticleAtPixel(8, 6, "snow");
        simulation.CreateParticleAtPixel(3, 6, "wall");
        simulation.CreateParticleAtPixel(5, 6, "wall");
        simulation.CreateParticleAtPixel(3, 7, "wall");
        simulation.CreateParticleAtPixel(4, 7, "wall");
        simulation.CreateParticleAtPixel(5, 7, "wall");
        simulation.CreateParticleAtPixel(7, 6, "wall");
        simulation.CreateParticleAtPixel(9, 6, "wall");
        simulation.CreateParticleAtPixel(7, 7, "wall");
        simulation.CreateParticleAtPixel(8, 7, "wall");
        simulation.CreateParticleAtPixel(9, 7, "wall");
        simulation.Temperature[4, 6] = 8f;
        simulation.Temperature[8, 6] = 10f;

        for (var i = 0; i < 6; i++)
        {
            simulation.Step(1f / 60f);
        }

        simulation.GetTypeIdAtCell(4, 6).Should().Be(_library.GetTypeId("ice"));
        simulation.GetTypeIdAtCell(8, 6).Should().Be(_library.GetTypeId("snow"));
    }

    [Fact]
    public void ExplosiveParticleDetonatesUnderSustainedPressure()
    {
        var simulation = new SandSimulation(32, 32, 1, _library, new SimulationSettings { PauseSim = false });
        simulation.CreateParticleAtPixel(16, 16, "ultratanium");

        for (var i = 0; i < 8; i++)
        {
            simulation.ApplyAirBrushAtPixel(16, 16, 6, 1f, 0f);
            simulation.Step(1f / 60f);
        }

        simulation.GetTypeIdAtCell(16, 16).Should().Be(0);
        (CountParticles(simulation, "smoke") + CountParticles(simulation, "fire")).Should().BeGreaterThanOrEqualTo(0);
    }

    [Fact]
    public void AdjacentExplosivesDoNotRecursivelyOverflowWhenDetonated()
    {
        var simulation = new SandSimulation(32, 32, 1, _library, new SimulationSettings { PauseSim = false });
        for (var x = 12; x <= 18; x++)
        {
            for (var y = 12; y <= 18; y++)
            {
                simulation.CreateParticleAtPixel(x, y, "ultratanium");
            }
        }

        for (var i = 0; i < 10; i++)
        {
            simulation.ApplyAirBrushAtPixel(15, 15, 8, 1f, 0f);
            simulation.Step(1f / 60f);
        }

        simulation.ParticleCount.Should().BeGreaterThanOrEqualTo(0);
    }

    [Fact]
    public void SustainedPressureBreaksStoneIntoBrokenStone()
    {
        var simulation = new SandSimulation(20, 20, 1, _library, new SimulationSettings { PauseSim = false });
        var brokenStone = _library.GetTypeId("brkstone");
        simulation.CreateParticleAtPixel(10, 10, "stone");
        simulation.CreateParticleAtPixel(9, 9, "wall");
        simulation.CreateParticleAtPixel(10, 9, "wall");
        simulation.CreateParticleAtPixel(11, 9, "wall");
        simulation.CreateParticleAtPixel(9, 10, "wall");
        simulation.CreateParticleAtPixel(11, 10, "wall");
        simulation.CreateParticleAtPixel(9, 11, "wall");
        simulation.CreateParticleAtPixel(10, 11, "wall");
        simulation.CreateParticleAtPixel(11, 11, "wall");

        var broke = false;
        for (var i = 0; i < 28; i++)
        {
            simulation.ApplyAirBrushAtPixel(10, 10, 6, 1f, 0f);
            simulation.Step(1f / 60f);
            if (simulation.GetTypeIdAtCell(10, 10) == brokenStone)
            {
                broke = true;
                break;
            }
        }

        broke.Should().BeTrue();
    }

    [Fact]
    public void WindBiasPushesGasSidewaysWhenUpwardPathIsBlocked()
    {
        var simulation = CreateSimulation();
        simulation.CreateParticleAtPixel(4, 4, "steam");
        simulation.CreateParticleAtPixel(4, 3, "wall");
        simulation.CreateParticleAtPixel(3, 3, "wall");
        simulation.CreateParticleAtPixel(5, 3, "wall");
        simulation.ApplyWindBrushAtPixel(4, 4, 2, 1f, 0f);
        simulation.ApplyWindBrushAtPixel(4, 4, 2, 1f, 0f);
        simulation.ApplyWindBrushAtPixel(4, 4, 2, 1f, 0f);
        simulation.Settings.PauseSim = false;

        simulation.Step(1f / 60f);

        simulation.GetTypeIdAtCell(5, 4).Should().Be(_library.GetTypeId("steam"));
    }

    [Fact]
    public void WindToolDoesNotPushWaterWhenMetadataExcludesIt()
    {
        var simulation = CreateSimulation();
        simulation.CreateParticleAtPixel(4, 4, "water");
        simulation.ApplyWindBrushAtPixel(4, 4, 3, 1f, 0f);
        simulation.ApplyWindBrushAtPixel(4, 4, 3, 1f, 0f);
        simulation.ApplyWindBrushAtPixel(4, 4, 3, 1f, 0f);

        var wind = simulation.GetWindAtCell(4, 4);
        MathF.Abs(wind.X).Should().BeLessThan(0.01f);
        MathF.Abs(wind.Y).Should().BeLessThan(0.01f);
    }

    [Fact]
    public void GravityWellPullsGasSidewaysWhenUpwardPathIsBlocked()
    {
        var simulation = CreateSimulation();
        simulation.CreateParticleAtPixel(5, 4, "steam");
        simulation.CreateParticleAtPixel(5, 3, "wall");
        simulation.CreateParticleAtPixel(4, 3, "wall");
        simulation.CreateParticleAtPixel(6, 3, "wall");
        simulation.ApplyGravityBrushAtPixel(3, 4, 3, 6f);
        simulation.ApplyGravityBrushAtPixel(3, 4, 3, 6f);
        simulation.Settings.PauseSim = false;

        simulation.Step(1f / 60f);

        simulation.GetTypeIdAtCell(4, 4).Should().Be(_library.GetTypeId("steam"));
    }

    [Fact]
    public void RepulsorPushesLiquidSidewaysWhenUpwardPathIsBlocked()
    {
        var simulation = CreateSimulation();
        simulation.CreateParticleAtPixel(4, 4, "water");
        simulation.CreateParticleAtPixel(4, 5, "wall");
        simulation.CreateParticleAtPixel(3, 5, "wall");
        simulation.CreateParticleAtPixel(5, 5, "wall");
        simulation.ApplyRepulsorBrushAtPixel(3, 4, 3, 6f);
        simulation.ApplyRepulsorBrushAtPixel(3, 4, 3, 6f);
        simulation.Settings.PauseSim = false;

        simulation.Step(1f / 60f);

        simulation.GetTypeIdAtCell(5, 4).Should().Be(_library.GetTypeId("water"));
    }

    [Fact]
    public void SolidDoesNotDiagonalSwapIntoLiquid()
    {
        var simulation = CreateSimulation();
        simulation.CreateParticleAtPixel(4, 4, "sand");
        simulation.CreateParticleAtPixel(4, 5, "wall");
        simulation.CreateParticleAtPixel(3, 5, "wall");
        simulation.CreateParticleAtPixel(5, 5, "water");
        simulation.CreateParticleAtPixel(5, 6, "wall");
        simulation.CreateParticleAtPixel(4, 6, "wall");
        simulation.CreateParticleAtPixel(6, 6, "wall");
        simulation.CreateParticleAtPixel(6, 5, "wall");
        simulation.Settings.PauseSim = false;

        simulation.Step(1f / 60f);

        simulation.GetTypeIdAtCell(4, 4).Should().Be(_library.GetTypeId("sand"));
        simulation.GetTypeIdAtCell(5, 5).Should().Be(_library.GetTypeId("water"));
    }

    [Fact]
    public void MoltenLiquidCanSinkThroughLighterLiquidBelow()
    {
        var simulation = CreateSimulation();
        simulation.CreateParticleAtPixel(3, 3, "molten_gold");
        simulation.CreateParticleAtPixel(3, 4, "water");
        simulation.CreateParticleAtPixel(2, 3, "wall");
        simulation.CreateParticleAtPixel(4, 3, "wall");
        simulation.CreateParticleAtPixel(2, 4, "wall");
        simulation.CreateParticleAtPixel(4, 4, "wall");
        simulation.CreateParticleAtPixel(3, 5, "wall");
        simulation.CreateParticleAtPixel(2, 5, "wall");
        simulation.CreateParticleAtPixel(4, 5, "wall");
        simulation.Temperature[3, 3] = 2000f;
        simulation.Settings.PauseSim = false;

        simulation.Step(1f / 60f);

        simulation.GetTypeIdAtCell(3, 4).Should().Be(_library.GetTypeId("molten_gold"));
        simulation.GetTypeIdAtCell(3, 3).Should().Be(_library.GetTypeId("water"));
    }

    private int CountParticles(SandSimulation simulation, string particleId)
    {
        var typeId = _library.GetTypeId(particleId);
        var count = 0;
        for (var y = 0; y < simulation.Height; y++)
        {
            for (var x = 0; x < simulation.Width; x++)
            {
                if (simulation.GetTypeIdAtCell(x, y) == typeId)
                {
                    count++;
                }
            }
        }

        return count;
    }

    private int FindParticleX(SandSimulation simulation, string particleId)
    {
        var typeId = _library.GetTypeId(particleId);
        for (var y = 0; y < simulation.Height; y++)
        {
            for (var x = 0; x < simulation.Width; x++)
            {
                if (simulation.GetTypeIdAtCell(x, y) == typeId)
                {
                    return x;
                }
            }
        }

        return -1;
    }

    private int FindParticleY(SandSimulation simulation, string particleId)
    {
        var typeId = _library.GetTypeId(particleId);
        for (var y = 0; y < simulation.Height; y++)
        {
            for (var x = 0; x < simulation.Width; x++)
            {
                if (simulation.GetTypeIdAtCell(x, y) == typeId)
                {
                    return y;
                }
            }
        }

        return int.MaxValue;
    }

    private double FindAverageX(SandSimulation simulation, string particleId)
    {
        var typeId = _library.GetTypeId(particleId);
        double total = 0;
        var count = 0;
        for (var y = 0; y < simulation.Height; y++)
        {
            for (var x = 0; x < simulation.Width; x++)
            {
                if (simulation.GetTypeIdAtCell(x, y) == typeId)
                {
                    total += x;
                    count++;
                }
            }
        }

        return count == 0 ? -1 : total / count;
    }

    private void PrepareFloor(SandSimulation simulation, int y)
    {
        for (var x = 0; x < simulation.Width; x++)
        {
            simulation.CreateParticleAtPixel(x, y, "wall");
        }
    }

    private SandSimulation CreateSimulation() => new(10, 10, 1, _library, new SimulationSettings { PauseSim = true });
}