using System;
using System.Buffers.Binary;

namespace AcDream.Core.Net.Messages;

/// <summary>
/// Inbound <c>PublicUpdatePropertyInt (0x02CE)</c> — the server updates one
/// <c>PropertyInt</c> on a visible object (carries the object guid). Standalone
/// GameMessage, dispatched like <see cref="PrivateUpdateVital"/> / CreateObject.
///
/// <para>
/// The companion <c>PrivateUpdatePropertyInt (0x02CD)</c> targets the player's OWN
/// object (no guid) and is not parsed here — it has no item-icon impact.
/// </para>
///
/// <para>Wire layout (ACE <c>GameMessagePublicUpdatePropertyInt</c>, size hint 17):</para>
/// <code>
///   u32 opcode = 0x02CE
///   u8  sequence    // single byte (ByteSequence.NextBytes) — see PrivateUpdateVital
///   u32 guid
///   u32 property    // PropertyInt enum; UiEffects = 18
///   i32 value
/// </code>
/// The sequence is parsed-past but not honored (latest-wins; divergence DR-4).
/// </summary>
public static class PublicUpdatePropertyInt
{
    public const uint Opcode = 0x02CEu;

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

    /// <summary>Parse a raw 0x02CE 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;
        uint prop = BinaryPrimitives.ReadUInt32LittleEndian(body[pos..]); pos += 4;
        int value = BinaryPrimitives.ReadInt32LittleEndian(body[pos..]);
        return new Parsed(guid, prop, value);
    }
}