namespace AcDream.Core.Physics;

/// <summary>
/// Per-entity flags driving the retail-faithful PvP / Player /
/// Impenetrable exemption logic in <c>FindObjCollisions</c>. Decoded
/// from <c>PublicWeenieDesc._bitfield</c> at <c>CreateObject</c> time.
///
/// <para>
/// Bit positions (verified against
/// <c>docs/research/named-retail/acclient_2013_pseudo_c.txt:406898-406918</c>
/// where <c>ACCWeenieObject::IsPK/IsPKLite/IsImpenetrable</c> read directly
/// from <c>this-&gt;pwd._bitfield</c>):
/// </para>
/// <list type="bullet">
///   <item><c>BF_PLAYER          = 0x8</c>        (bit 3)  → <see cref="IsPlayer"/></item>
///   <item><c>BF_PLAYER_KILLER   = 0x20</c>       (bit 5)  → <see cref="IsPK"/></item>
///   <item><c>BF_FREE_PKSTATUS   = 0x200000</c>   (bit 21) → <see cref="IsImpenetrable"/></item>
///   <item><c>BF_PKLITE_PKSTATUS = 0x2000000</c>  (bit 25) → <see cref="IsPKLite"/></item>
/// </list>
///
/// <para>
/// <see cref="IsCreature"/> is NOT a PWD bit — retail derives it from
/// <c>PublicWeenieDesc._type</c> matching <c>ITEM_TYPE_CREATURE</c>
/// (acclient.h ITEM_TYPE enum). Set at registration time by callers that
/// already know the item type.
/// </para>
/// </summary>
[Flags]
public enum EntityCollisionFlags : byte
{
    None           = 0x00,
    /// <summary>Set when <c>BF_PLAYER (0x8)</c> is set in <c>pwd._bitfield</c>.</summary>
    IsPlayer       = 0x01,
    /// <summary>Derived from <c>ItemType.Creature</c> on the spawn payload.</summary>
    IsCreature     = 0x02,
    /// <summary>Set when <c>BF_PLAYER_KILLER (0x20)</c> is set.</summary>
    IsPK           = 0x04,
    /// <summary>Set when <c>BF_PKLITE_PKSTATUS (0x2000000)</c> is set.</summary>
    IsPKLite       = 0x08,
    /// <summary>Set when <c>BF_FREE_PKSTATUS (0x200000)</c> is set (a.k.a. "Free" PK status — cannot be PKed).</summary>
    IsImpenetrable = 0x10,
}

/// <summary>Helpers to convert raw retail bitfields into <see cref="EntityCollisionFlags"/>.</summary>
public static class EntityCollisionFlagsExt
{
    /// <summary>
    /// Decode the player/PK/PKLite/Impenetrable bits from a
    /// <c>PublicWeenieDesc._bitfield</c> value (the WeenieHeader trailer
    /// field acdream's parser surfaces as <c>ObjectDescriptionFlags</c>).
    ///
    /// <para>Bit positions per
    /// <c>docs/research/named-retail/acclient.h:6431-6463</c>
    /// (<c>PublicWeenieDesc::BitfieldIndex</c>) and
    /// <c>acclient_2013_pseudo_c.txt:441868-441890</c>
    /// (<c>PublicWeenieDesc::SetPlayerKillerStatus</c>).</para>
    /// </summary>
    public static EntityCollisionFlags FromPwdBitfield(uint bitfield)
    {
        var flags = EntityCollisionFlags.None;
        if ((bitfield & 0x8u)        != 0) flags |= EntityCollisionFlags.IsPlayer;
        if ((bitfield & 0x20u)       != 0) flags |= EntityCollisionFlags.IsPK;
        if ((bitfield & 0x200000u)   != 0) flags |= EntityCollisionFlags.IsImpenetrable;
        if ((bitfield & 0x2000000u)  != 0) flags |= EntityCollisionFlags.IsPKLite;
        return flags;
    }
}