using AcDream.Core.Physics;
using Xunit;

namespace AcDream.Core.Tests.Physics;

/// <summary>
/// A6.P7 (2026-05-25) — retail-binary dispatch rule. Retail's
/// <c>CPhysicsObj::FindObjCollisions</c> at
/// <c>docs/research/named-retail/acclient_2013_pseudo_c.txt:276861</c>
/// dispatches BINARILY between "BSP-only" and "cyl + sphere" based on
/// the <c>HAS_PHYSICS_BSP_PS</c> flag (bit 16, hex 0x10000) in
/// <c>PhysicsState</c>. The flag is defined in
/// <c>docs/research/named-retail/acclient.h:2833</c> and mirrored in
/// ACE at <c>references/ACE/Source/ACE.Entity/Enum/PhysicsState.cs:24</c>
/// as <c>HasPhysicsBSP = 0x00010000</c>.
///
/// <para>
/// For non-PvP, non-missile movers (M1.5 scope — walking-vs-static), an
/// entity with HAS_PHYSICS_BSP_PS in its state tests its BSP exclusively
/// — the foot cyl is NEVER tested. The closed cottage door (state
/// <c>0x10008</c> = <c>STATIC | REPORT_COLLISIONS | HAS_PHYSICS_BSP</c>)
/// hits this branch.
/// </para>
///
/// <para>
/// Pre-A6.P7: our dispatcher iterates every <c>ShadowEntry</c>
/// independently and tests both the cyl AND the BSP for a door. The
/// cyl's radial normal contaminates the slide direction at NE/SE
/// approach headings (see
/// <c>docs/research/2026-05-25-a6-door-cyl-retail-dispatch-investigation.md</c>).
/// </para>
///
/// <para>
/// Post-A6.P7: the dispatcher consults
/// <see cref="Transition.BspOnlyDispatch(uint)"/> on each cyl/sphere
/// entry and skips it when the entity has BSP, matching retail.
/// </para>
/// </summary>
public class A6P7DispatchRulesTests
{
    /// <summary>
    /// Retail bit constant <c>HAS_PHYSICS_BSP_PS = 0x10000</c>
    /// (acclient.h:2833) and ACE's <c>HasPhysicsBSP = 0x00010000</c>
    /// (PhysicsState.cs:24) must match the value we expose on
    /// <see cref="PhysicsStateFlags"/>.
    /// </summary>
    [Fact]
    public void PhysicsStateFlags_HasPhysicsBsp_Is_Bit_16()
    {
        Assert.Equal(0x00010000u, (uint)PhysicsStateFlags.HasPhysicsBsp);
    }

    /// <summary>
    /// The dispatch predicate maps directly from retail's branch at
    /// acclient_2013_pseudo_c.txt:276861:
    /// <code>
    /// ((state &amp; 0x10000) == 0 || ebp_1 != 0 || eax_12 != 0)
    ///   → cyl + sphere path
    /// else
    ///   → BSP-only path
    /// </code>
    /// For M1.5 scope <c>ebp_1</c> (PvP-target-player) and <c>eax_12</c>
    /// (missile_ignore) are treated as false. The predicate reduces to:
    /// "BSP-only iff <c>HAS_PHYSICS_BSP_PS</c> is set".
    /// </summary>
    [Theory]
    [InlineData(0x00010008u, true)]   // closed cottage door — STATIC | REPORT | HAS_BSP
    [InlineData(0x00010000u, true)]   // bare HAS_BSP
    [InlineData(0x00110000u, true)]   // HAS_BSP | CLOAKED
    [InlineData(0x00000008u, false)]  // creature — REPORT_COLLISIONS only
    [InlineData(0x00000000u, false)]  // empty state
    [InlineData(0x0000FFFFu, false)]  // every bit BELOW 0x10000 set
    public void BspOnlyDispatch_RespectsHasPhysicsBspFlag(
        uint entityState, bool expected)
    {
        Assert.Equal(expected, Transition.BspOnlyDispatch(entityState));
    }
}