using AcDream.Core.Physics;
using Xunit;

namespace AcDream.Core.Tests.Physics;

/// <summary>
/// Unit tests for <see cref="EntityCollisionFlags"/> — Commit A of the
/// 2026-04-29 live-entity collision port. Verifies retail-faithful
/// conversion from PWD bitfield bits to the boolean collision-decision
/// flags that <c>FindObjCollisions</c> consumes for the PvP exemption.
///
/// <para>Bit positions confirmed against:</para>
/// <list type="bullet">
///   <item><c>docs/research/named-retail/acclient_2013_pseudo_c.txt:406898-406918</c>
///         (<c>ACCWeenieObject::IsPKLite/IsPK/IsImpenetrable</c>) — the
///         retail client itself reads bits 25 / 5 / 21 of <c>pwd._bitfield</c>.</item>
///   <item><c>docs/research/named-retail/acclient.h:6431-6463</c>
///         (<c>PublicWeenieDesc::BitfieldIndex</c>) — names the bits:
///         <c>BF_PLAYER=0x8</c>, <c>BF_PLAYER_KILLER=0x20</c>,
///         <c>BF_FREE_PKSTATUS=0x200000</c>, <c>BF_PKLITE_PKSTATUS=0x2000000</c>.</item>
///   <item><c>docs/research/named-retail/acclient_2013_pseudo_c.txt:441868-441890</c>
///         (<c>PublicWeenieDesc::SetPlayerKillerStatus</c>) — confirms
///         the writer maps PKStatusEnum values onto these exact bits.</item>
/// </list>
/// </summary>
public class EntityCollisionFlagsTests
{
    [Fact]
    public void FromPwdBitfield_AllZeros_NoFlags()
    {
        Assert.Equal(EntityCollisionFlags.None, EntityCollisionFlagsExt.FromPwdBitfield(0u));
    }

    [Fact]
    public void FromPwdBitfield_PlayerBit_SetsIsPlayer()
    {
        // BF_PLAYER = 0x8 (bit 3)
        var flags = EntityCollisionFlagsExt.FromPwdBitfield(0x8u);
        Assert.True(flags.HasFlag(EntityCollisionFlags.IsPlayer));
        Assert.False(flags.HasFlag(EntityCollisionFlags.IsPK));
    }

    [Fact]
    public void FromPwdBitfield_PlayerKillerBit_SetsIsPK()
    {
        // BF_PLAYER_KILLER = 0x20 (bit 5)
        var flags = EntityCollisionFlagsExt.FromPwdBitfield(0x20u);
        Assert.True(flags.HasFlag(EntityCollisionFlags.IsPK));
        Assert.False(flags.HasFlag(EntityCollisionFlags.IsPKLite));
    }

    [Fact]
    public void FromPwdBitfield_PkLiteBit_SetsIsPKLite()
    {
        // BF_PKLITE_PKSTATUS = 0x2000000 (bit 25)
        var flags = EntityCollisionFlagsExt.FromPwdBitfield(0x2000000u);
        Assert.True(flags.HasFlag(EntityCollisionFlags.IsPKLite));
        Assert.False(flags.HasFlag(EntityCollisionFlags.IsPK));
    }

    [Fact]
    public void FromPwdBitfield_FreePkStatusBit_SetsIsImpenetrable()
    {
        // BF_FREE_PKSTATUS = 0x200000 (bit 21)
        var flags = EntityCollisionFlagsExt.FromPwdBitfield(0x200000u);
        Assert.True(flags.HasFlag(EntityCollisionFlags.IsImpenetrable));
    }

    [Fact]
    public void FromPwdBitfield_PlayerAndPK_SetsBoth()
    {
        // A PK player: BF_PLAYER (0x8) | BF_PLAYER_KILLER (0x20) = 0x28
        var flags = EntityCollisionFlagsExt.FromPwdBitfield(0x28u);
        Assert.True(flags.HasFlag(EntityCollisionFlags.IsPlayer));
        Assert.True(flags.HasFlag(EntityCollisionFlags.IsPK));
        Assert.False(flags.HasFlag(EntityCollisionFlags.IsPKLite));
        Assert.False(flags.HasFlag(EntityCollisionFlags.IsImpenetrable));
    }

    [Fact]
    public void FromPwdBitfield_UnrelatedBits_Ignored()
    {
        // Set BF_OPENABLE (0x1), BF_INSCRIBABLE (0x2), BF_STUCK (0x4) — none
        // map to collision flags. A creature spawn might have BF_ATTACKABLE
        // (0x10) set; that's ItemType-derived IsCreature, not a PvP flag.
        var flags = EntityCollisionFlagsExt.FromPwdBitfield(0x1u | 0x2u | 0x4u | 0x10u);
        Assert.Equal(EntityCollisionFlags.None, flags);
    }
}