using System.Buffers.Binary;

namespace AcDream.Core.Net.Messages;

/// <summary>
/// Inbound retail <c>ParentEvent</c> (<c>0xF749</c>): attach a child physics
/// object (weapon, shield, ammunition) to a named holding location on a
/// parent creature and apply the child's placement frame.
///
/// Wire oracle: <c>CM_Physics::DispatchSB_ParentEvent @ 0x006ACAF0</c>.
/// Runtime oracle: <c>SmartBox::HandleParentEvent @ 0x004535D0</c> and
/// <c>SmartBox::DoParentEvent @ 0x00452290</c>.
/// </summary>
public static class ParentEvent
{
    public const uint Opcode = 0xF749u;

    public readonly record struct Parsed(
        uint ParentGuid,
        uint ChildGuid,
        uint ParentLocation,
        uint PlacementId,
        ushort ParentInstanceSequence,
        ushort ChildPositionSequence);

    public static Parsed? TryParse(ReadOnlySpan<byte> body)
    {
        if (body.Length < 24)
            return null;

        if (BinaryPrimitives.ReadUInt32LittleEndian(body) != Opcode)
            return null;

        return new Parsed(
            BinaryPrimitives.ReadUInt32LittleEndian(body.Slice(4, 4)),
            BinaryPrimitives.ReadUInt32LittleEndian(body.Slice(8, 4)),
            BinaryPrimitives.ReadUInt32LittleEndian(body.Slice(12, 4)),
            BinaryPrimitives.ReadUInt32LittleEndian(body.Slice(16, 4)),
            BinaryPrimitives.ReadUInt16LittleEndian(body.Slice(20, 2)),
            BinaryPrimitives.ReadUInt16LittleEndian(body.Slice(22, 2)));
    }
}