using System;
using System.Buffers.Binary;

namespace AcDream.Core.Net.Messages;

/// <summary>
/// Inbound <c>SetStackSize (0x0197)</c> — a top-level GameMessage (UIQueue group),
/// NOT a GameEvent. The server updates a stack's count + value after a merge / split.
/// Client consumer: ACCWeenieObject::ServerSaysSetStackSize.
///
/// <para>Wire layout (ACE <c>GameMessageSetStackSize.cs</c>, size hint 17):</para>
/// <code>
///   u32 opcode = 0x0197
///   u8  sequence    // ByteSequence (UpdatePropertyInt) — not honored
///   u32 guid
///   i32 stackSize
///   i32 value
/// </code>
/// </summary>
public static class SetStackSize
{
    public const uint Opcode = 0x0197u;

    public readonly record struct Parsed(uint Guid, int StackSize, int Value);

    /// <summary>Parse a raw 0x0197 body. Returns null on opcode mismatch / truncation.</summary>
    public static Parsed? TryParse(ReadOnlySpan<byte> body)
    {
        if (body.Length < 17) return null;          // 4 + 1 + 4 + 4 + 4
        if (BinaryPrimitives.ReadUInt32LittleEndian(body) != Opcode) return null;
        int pos = 4;
        pos += 1;                                   // sequence byte (not honored)
        uint guid = BinaryPrimitives.ReadUInt32LittleEndian(body[pos..]); pos += 4;
        int stack = BinaryPrimitives.ReadInt32LittleEndian(body[pos..]); pos += 4;
        int value = BinaryPrimitives.ReadInt32LittleEndian(body[pos..]);
        return new Parsed(guid, stack, value);
    }
}