using System;
using AcDream.App.Rendering;
using Xunit;

namespace AcDream.App.Tests.Rendering;

/// <summary>
/// #129 — doors/doorways leak through terrain and houses from over a landblock
/// away. The punch's mark pass (#117, AD-18) biased the aperture fan toward
/// the viewer by a CONSTANT 0.0005 NDC. NDC depth is non-linear: a constant
/// NDC bias b spans ≈ b·d²·(f−n)/(f·n) meters of eye depth at eye distance d
/// — 0.125 m at 5 m but ~190 m at a landblock (znear 0.1), so distant
/// occluders in front of an aperture passed the mark and were far-Z punched:
/// the door-shaped leak. The fix caps the bias's eye-space span
/// (PortalDepthMaskRenderer.MarkBiasNdc): identical to the validated constant
/// below the ~10 m crossover, never more than the cap beyond it.
/// </summary>
public class Issue129PunchBiasTests
{
    private const float Near = PortalDepthMaskRenderer.CameraNearPlaneMeters; // 0.1 (retail znear)
    private const float Far = 5000f;

    /// <summary>Eye-depth span (meters) covered by an NDC depth bias b at eye
    /// distance d: ndc(d) = f(d−n)/((f−n)d) ⇒ d(ndc) inverse ⇒
    /// span = b·d²·(f−n)/(f·n) (exact for small b via the derivative).</summary>
    private static float EyeSpanMeters(float biasNdc, float d) =>
        biasNdc * d * d * (Far - Near) / (Far * Near);

    [Fact]
    public void OldConstantBias_SpansMetersAtALandblock_TheLeak()
    {
        // The refuted form (documentation of WHY the constant was wrong):
        // 0.0005 NDC at ~one landblock spans far more eye depth than any
        // occluder separation — everything in front got punched.
        Assert.True(EyeSpanMeters(0.0005f, 192f) > 100f);
        // ...while at close range it was a sane sliver:
        Assert.InRange(EyeSpanMeters(0.0005f, 5f), 0.05f, 0.30f);
    }

    [Fact]
    public void CappedBias_MatchesValidatedConstant_AtCloseRange()
    {
        // Below the crossover the T5-validated constant must win unchanged —
        // this preserves the #108 grass coverage bit-for-bit.
        foreach (float d in new[] { 0.5f, 1f, 3f, 5f, 8f, 9.9f })
            Assert.Equal(0.0005f, PortalDepthMaskRenderer.MarkBiasNdc(d), 6);
    }

    [Fact]
    public void CappedBias_EyeSpanNeverExceedsCap_AtAnyDistance()
    {
        for (float d = 1f; d <= 400f; d += 1f)
        {
            float span = EyeSpanMeters(PortalDepthMaskRenderer.MarkBiasNdc(d), d);
            Assert.True(span <= PortalDepthMaskRenderer.PunchMarkBiasEyeCapMeters * 1.02f,
                FormattableString.Invariant($"bias spans {span:F2} m of eye depth at d={d} m"));
        }
    }

    [Fact]
    public void CappedBias_At200m_CannotReachOccluders()
    {
        // The reported #129 distance: occluder separations are tens of
        // meters; the punch reach must stay under the 0.5 m cap.
        float span = EyeSpanMeters(PortalDepthMaskRenderer.MarkBiasNdc(200f), 200f);
        Assert.True(span <= 0.51f, FormattableString.Invariant($"span {span:F3} m at 200 m"));
    }
}