using AcDream.Core.Physics;
using Xunit;

namespace AcDream.Core.Tests.Physics;

/// <summary>
/// Unit tests for the <c>obstruction_ethereal</c> mechanism ported verbatim
/// from retail in Task 3 of the collision-inclusion phase.
///
/// <para>
/// Retail oracle: <c>CPhysicsObj::FindObjCollisions @ 0x0050f050</c>
/// (<c>acclient_2013_pseudo_c.txt:276782</c>):
/// <list type="bullet">
///   <item>pc:276782 — Gate 1: instant-skip requires BOTH ETHEREAL_PS (0x4) AND
///     IGNORE_COLLISIONS_PS (0x10). ETHEREAL alone does NOT instant-skip.</item>
///   <item>pc:276806 — ETHEREAL-alone sets <c>sphere_path.obstruction_ethereal = 1</c>
///     and continues to the shape dispatch.</item>
///   <item>pc:276989 — After the per-object shape test, retail clears
///     <c>obstruction_ethereal = 0</c>.</item>
/// </list>
/// </para>
///
/// <para>
/// Consume site: <c>BSPTREE::find_collisions @ 0x0053a496</c>
/// (<c>acclient_2013_pseudo_c.txt:323742</c>): Path 1 fires when
/// <c>insert_type == PLACEMENT_INSERT || obstruction_ethereal != 0</c>,
/// routing to <c>sphere_intersects_solid</c> (passable-ethereal) instead
/// of the blocking paths.
/// </para>
///
/// <para>
/// Retail divergence register: row AD-7 retired in this commit — the
/// ETHEREAL-alone shim is replaced by the faithful port.
/// </para>
/// </summary>
public class ObstructionEtherealTests
{
    private const uint ETHEREAL_PS          = 0x4u;
    private const uint IGNORE_COLLISIONS_PS = 0x10u;

    // ── Gate-1 tests: ShouldSkip dual-bit contract ─────────────────────────

    [Fact]
    public void ShouldSkip_BothBits_InstantSkip()
    {
        // ETHEREAL | IGNORE_COLLISIONS together → instant-skip (Gate 1 fires).
        // Retail pc:276782: `if ((state & 4) AND (state & 0x10)) return 1`.
        Assert.True(CollisionExemption.ShouldSkip(
            targetState: ETHEREAL_PS | IGNORE_COLLISIONS_PS,
            targetFlags: EntityCollisionFlags.None,
            moverState:  ObjectInfoState.IsPlayer));
    }

    [Fact]
    public void ShouldSkip_EtherealAlone_NotInstantSkip()
    {
        // ETHEREAL alone (0x4) must NOT instant-skip — retail takes the
        // obstruction_ethereal branch instead. The old AD-7 shim is retired.
        // Retail pc:276782: only the COMBINED gate returns early; ETHEREAL-alone
        // falls through to set obstruction_ethereal and run the shape test.
        Assert.False(CollisionExemption.ShouldSkip(
            targetState: ETHEREAL_PS,
            targetFlags: EntityCollisionFlags.None,
            moverState:  ObjectInfoState.IsPlayer));
    }

    [Fact]
    public void ShouldSkip_IgnoreCollisionsAlone_NotSkipped()
    {
        // IGNORE_COLLISIONS alone (0x10) without ETHEREAL → not instant-skipped;
        // falls through to shape dispatch (no obstruction_ethereal set either).
        Assert.False(CollisionExemption.ShouldSkip(
            targetState: IGNORE_COLLISIONS_PS,
            targetFlags: EntityCollisionFlags.None,
            moverState:  ObjectInfoState.IsPlayer));
    }

    // ── SpherePath.ObstructionEthereal field ───────────────────────────────

    [Fact]
    public void SpherePath_HasObstructionEtherealField()
    {
        // Compile-time check that the field was added to SpherePath.
        var sp = new SpherePath();
        Assert.False(sp.ObstructionEthereal);   // default is false
        sp.ObstructionEthereal = true;
        Assert.True(sp.ObstructionEthereal);
    }

    // ── BSPQuery Path-1 gate: ObstructionEthereal routes through
    //    sphere_intersects_solid (not the blocking slide path) ──────────────
    //
    // A full transition-level harness for the BSP path requires a real
    // BSP tree fixture and is deferred to the DoorCollisionApparatusTests
    // integration tests. Here we verify the GATE condition in isolation
    // via the FindEnvCollisions D5 clear and the SpherePath property
    // round-trip. The DoorCollisionApparatusTests and CellarUpTrajectory-
    // ReplayTests are the regression guards for the consume-site change.
}