acdream/tests/AcDream.Core.Tests/Physics/SupportProbeClassifierTests.cs

using System.Numerics;
using AcDream.Core.Physics;
using Xunit;

namespace AcDream.Core.Tests.Physics;

/// <summary>
/// #337 (2026-08-06 — TEMPORARY, delete with the <c>[support]</c> probe).
///
/// <para>
/// The <c>[support]</c> line's whole value is its <c>support=</c> verdict:
/// terrain, an object surface, or nothing. If that classifier is wrong, a
/// capture does not merely fail to answer — it answers CONFIDENTLY WRONG, and
/// this campaign has already spent two diagnoses on confident wrong answers.
/// These cover the decision boundaries directly, so the live capture can be
/// read at face value.
/// </para>
/// </summary>
public sealed class SupportProbeClassifierTests
{
    private const float FlatNormalZ = 1f;

    [Fact]
    public void NoContactPlane_IsUnsupported()
    {
        Assert.Equal(
            "none",
            PhysicsDiagnostics.ClassifySupport(
                contactPlaneValid: false,
                terrainSampled: true,
                contactPlaneZAtXY: 100f,
                contactPlaneNormalZ: FlatNormalZ,
                terrainZ: 100f,
                terrainNormalZ: FlatNormalZ));
    }

    [Fact]
    public void PlaneAtTerrainHeightAndTilt_IsTerrain()
    {
        Assert.Equal(
            "terrain",
            PhysicsDiagnostics.ClassifySupport(
                contactPlaneValid: true,
                terrainSampled: true,
                contactPlaneZAtXY: 41.25f,
                contactPlaneNormalZ: 0.94f,
                terrainZ: 41.26f,
                terrainNormalZ: 0.94f));
    }

    [Fact]
    public void PlaneWellAboveTerrain_IsObject()
    {
        // The rock-plateau shape: the body rests six metres above the ground.
        Assert.Equal(
            "object",
            PhysicsDiagnostics.ClassifySupport(
                contactPlaneValid: true,
                terrainSampled: true,
                contactPlaneZAtXY: 47.5f,
                contactPlaneNormalZ: FlatNormalZ,
                terrainZ: 41.5f,
                terrainNormalZ: 0.9f));
    }

    [Fact]
    public void SameHeightDifferentTilt_IsReportedSeparately()
    {
        // A collision surface lying flat against sloped ground. This must NOT
        // collapse into either answer: it is precisely the ambiguous case, and
        // guessing between them is what the probe exists to avoid.
        Assert.Equal(
            "coplanar-tilt-mismatch",
            PhysicsDiagnostics.ClassifySupport(
                contactPlaneValid: true,
                terrainSampled: true,
                contactPlaneZAtXY: 41.5f,
                contactPlaneNormalZ: 1.0f,
                terrainZ: 41.5f,
                terrainNormalZ: 0.72f));
    }

    [Fact]
    public void NoTerrainUnderTheBody_SaysSoRatherThanGuessing()
    {
        Assert.Equal(
            "no-terrain",
            PhysicsDiagnostics.ClassifySupport(
                contactPlaneValid: true,
                terrainSampled: false,
                contactPlaneZAtXY: 12f,
                contactPlaneNormalZ: FlatNormalZ,
                terrainZ: float.NaN,
                terrainNormalZ: float.NaN));
    }

    [Fact]
    public void PlaneHeightIsEvaluatedAtTheBodysOwnXy()
    {
        // A 45-degree ramp through the origin: height must track X, or a body
        // standing on a slope would read as displaced from its own support.
        var slope = new Plane(Vector3.Normalize(new Vector3(-1f, 0f, 1f)), 0f);

        Assert.True(PhysicsDiagnostics.TryPlaneZAt(slope, 0f, 0f, out float atOrigin));
        Assert.Equal(0f, atOrigin, 3);

        Assert.True(PhysicsDiagnostics.TryPlaneZAt(slope, 10f, 0f, out float atTen));
        Assert.Equal(10f, atTen, 3);
    }

    [Fact]
    public void VerticalPlaneHasNoHeight()
    {
        // A wall is never a floor. Reporting a height for one would read as a
        // wildly displaced surface and manufacture a false positive.
        var wall = new Plane(new Vector3(1f, 0f, 0f), -5f);

        Assert.False(PhysicsDiagnostics.TryPlaneZAt(wall, 0f, 0f, out _));
    }
}