h-school/tests/HSchool.Simulation.Tests/GameWorldTests.cs

using HSchool.Protocol;

namespace HSchool.Simulation.Tests;

public class GameWorldTests
{
    private static SimulationOptions Options() => new()
    {
        TickRate = 20,
        WorldWidth = 1000f,
        WorldHeight = 1000f,
        PlayerSpeed = 200f,
        PlayerRadius = 10f,
    };

    private static EntitySnapshot Entity(GameWorld world, uint networkId)
    {
        var buffer = new List<EntitySnapshot>();
        world.CaptureSnapshot(buffer);
        return buffer.Single(entity => entity.Id == networkId);
    }

    [Fact]
    public void Tick_AdvancesTheTickCounter()
    {
        using var world = new GameWorld(Options());

        world.Tick();
        world.Tick();

        Assert.Equal(2u, world.CurrentTick);
    }

    [Fact]
    public void SpawnPlayer_AddsAPlayerEntityToSnapshots()
    {
        using var world = new GameWorld(Options());

        var networkId = world.SpawnPlayer(playerId: 1);

        Assert.Equal(1, world.PlayerCount);
        Assert.Equal(EntityKind.Player, Entity(world, networkId).Kind);
    }

    [Fact]
    public void SpawnPlayer_Twice_Throws()
    {
        using var world = new GameWorld(Options());
        world.SpawnPlayer(playerId: 1);

        Assert.Throws<InvalidOperationException>(() => world.SpawnPlayer(playerId: 1));
    }

    [Fact]
    public void Input_MovesThePlayerAtExactlySpeedTimesDelta()
    {
        var options = Options();
        using var world = new GameWorld(options);
        var networkId = world.SpawnPlayer(playerId: 1);
        var startX = Entity(world, networkId).X;

        world.ApplyInput(playerId: 1, InputButtons.Right, sequence: 1);
        world.Tick();

        var expected = startX + (options.PlayerSpeed * options.FixedDeltaTime);
        Assert.Equal(expected, Entity(world, networkId).X, tolerance: 0.001f);
    }

    [Fact]
    public void DiagonalInput_IsNotFasterThanCardinal()
    {
        var options = Options();
        using var world = new GameWorld(options);

        var straight = world.SpawnPlayer(playerId: 1);
        var diagonal = world.SpawnPlayer(playerId: 2);

        world.ApplyInput(playerId: 1, InputButtons.Right, sequence: 1);
        world.ApplyInput(playerId: 2, InputButtons.Right | InputButtons.Down, sequence: 1);
        world.Tick();

        var straightBefore = Entity(world, straight);
        var diagonalBefore = Entity(world, diagonal);
        world.Tick();

        var straightStep = Distance(straightBefore, Entity(world, straight));
        var diagonalStep = Distance(diagonalBefore, Entity(world, diagonal));

        Assert.Equal(straightStep, diagonalStep, tolerance: 0.01f);
    }

    [Fact]
    public void Player_StopsAtTheWorldBounds()
    {
        var options = Options();
        using var world = new GameWorld(options);
        var networkId = world.SpawnPlayer(playerId: 1);

        world.ApplyInput(playerId: 1, InputButtons.Left, sequence: 1);
        for (var i = 0; i < 200; i++)
        {
            world.Tick();
        }

        Assert.Equal(options.PlayerRadius, Entity(world, networkId).X, tolerance: 0.001f);
    }

    [Fact]
    public void StaleInput_IsIgnored()
    {
        using var world = new GameWorld(Options());
        var networkId = world.SpawnPlayer(playerId: 1);
        var startX = Entity(world, networkId).X;

        world.ApplyInput(playerId: 1, InputButtons.None, sequence: 10);
        world.ApplyInput(playerId: 1, InputButtons.Right, sequence: 2);
        world.Tick();

        Assert.Equal(startX, Entity(world, networkId).X, tolerance: 0.001f);
    }

    [Fact]
    public void InputForAnUnknownPlayer_IsIgnored()
    {
        using var world = new GameWorld(Options());

        world.ApplyInput(playerId: 999, InputButtons.Right, sequence: 1);
        world.Tick();

        Assert.Equal(0, world.PlayerCount);
    }

    [Fact]
    public void DespawnPlayer_RemovesItFromSnapshots()
    {
        using var world = new GameWorld(Options());
        var networkId = world.SpawnPlayer(playerId: 1);

        world.DespawnPlayer(playerId: 1);

        var buffer = new List<EntitySnapshot>();
        world.CaptureSnapshot(buffer);

        Assert.Equal(0, world.PlayerCount);
        Assert.DoesNotContain(buffer, entity => entity.Id == networkId);
        Assert.Null(world.GetNetworkId(playerId: 1));
    }

    [Fact]
    public void DespawnPlayer_Twice_IsHarmless()
    {
        using var world = new GameWorld(Options());
        world.SpawnPlayer(playerId: 1);

        world.DespawnPlayer(playerId: 1);
        world.DespawnPlayer(playerId: 1);

        Assert.Equal(0, world.PlayerCount);
    }

    [Fact]
    public void NetworkIds_AreNotRecycledAfterDespawn()
    {
        using var world = new GameWorld(Options());
        var first = world.SpawnPlayer(playerId: 1);
        world.DespawnPlayer(playerId: 1);

        var second = world.SpawnPlayer(playerId: 1);

        Assert.NotEqual(first, second);
    }

    [Fact]
    public void EmptyWorld_StillContainsTheStaticObstacles()
    {
        using var world = new GameWorld(Options());

        var buffer = new List<EntitySnapshot>();
        world.CaptureSnapshot(buffer);

        Assert.NotEmpty(buffer);
        Assert.All(buffer, entity => Assert.Equal(EntityKind.Obstacle, entity.Kind));
    }

    [Fact]
    public void Simulation_IsDeterministicForTheSameInputs()
    {
        var first = Run();
        var second = Run();

        Assert.Equal(first, second);

        static (float X, float Y) Run()
        {
            using var world = new GameWorld(Options());
            var networkId = world.SpawnPlayer(playerId: 3);

            for (var i = 0; i < 25; i++)
            {
                world.ApplyInput(playerId: 3, i % 2 == 0 ? InputButtons.Right : InputButtons.Down, (uint)i + 1);
                world.Tick();
            }

            var entity = Entity(world, networkId);
            return (entity.X, entity.Y);
        }
    }

    [Fact]
    public void UsingADisposedWorld_Throws()
    {
        var world = new GameWorld(Options());
        world.Dispose();

        Assert.Throws<ObjectDisposedException>(world.Tick);
    }

    private static float Distance(EntitySnapshot from, EntitySnapshot to)
    {
        var dx = to.X - from.X;
        var dy = to.Y - from.Y;
        return MathF.Sqrt((dx * dx) + (dy * dy));
    }
}