using System.Buffers.Binary;

namespace AcDream.Core.Net.Messages;

/// <summary>
/// Inbound retail <c>PrivateUpdatePropertyInt64 (0x02CF)</c>: one signed
/// 64-bit quality update for the local player. Total Experience (quality 1)
/// and Available Experience (quality 2) use this message.
/// </summary>
/// <remarks>
/// Retail: <c>CM_Qualities::DispatchUI_PrivateUpdateInt64 @ 0x006AEAD0</c>
/// reads the sequence byte at +4, property at +5, and value at +9, then calls
/// <c>ClientObjMaintSystem::Handle_Qualities__PrivateUpdateInt64 @ 0x00559000</c>.
/// ACE <c>GameMessagePrivateUpdatePropertyInt64</c> and holtburger's
/// <c>PrivateUpdatePropertyInt64Data</c> confirm the same field order.
/// </remarks>
public static class PrivateUpdatePropertyInt64
{
    public const uint Opcode = 0x02CFu;
    public const int BodySize = 17; // opcode(4) + sequence(1) + property(4) + value(8)

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

    /// <summary>Parse a complete 0x02CF body, or return null on mismatch/truncation.</summary>
    public static Parsed? TryParse(ReadOnlySpan<byte> body)
    {
        if (body.Length < BodySize) return null;
        if (BinaryPrimitives.ReadUInt32LittleEndian(body) != Opcode) return null;

        const int propertyOffset = 5; // opcode + one-byte quality sequence
        uint property = BinaryPrimitives.ReadUInt32LittleEndian(body[propertyOffset..]);
        long value = BinaryPrimitives.ReadInt64LittleEndian(body[(propertyOffset + 4)..]);
        return new Parsed(property, value);
    }
}