HellionChat/HellionChat/Util/ExtraPayload.cs

namespace HellionChat.Util;

public class ColorPayload
{
    private const byte StartByte = 2;

    public bool Enabled;
    public uint Color;
    public uint UnshiftedColor;

    public static ColorPayload? From(byte[] data)
    {
        using var stream = new MemoryStream(data);
        if (stream.ReadByte() != StartByte || stream.ReadByte() != 0x13)
            return null;

        stream.ReadByte(); // skip the length byte;

        var typeByte = stream.ReadByte();
        var payload = new ColorPayload();
        switch (typeByte)
        {
            case 0xEC:
                payload.Enabled = false;
                return payload;
            case 0xE9:
                var param = stream.ReadByte();
                if (param == -1)
                    throw new ArgumentException(
                        "Encountered premature end of input (unexpected EOF).",
                        nameof(stream)
                    );
                var globalValue = (uint)GlobalParametersCache.GetValue(param - 2);
                payload.Enabled = true;
                payload.UnshiftedColor = globalValue;
                payload.Color = ColourUtil.ArgbToRgba(globalValue);

                return payload;
            case >= 0xF0 and <= 0xFE:
                // From: https://github.com/NotAdam/Lumina/blob/master/src/Lumina/Text/Expressions/IntegerExpression.cs#L119-L128
                uint ShiftAndThrowIfZero(int v, int shift)
                {
                    return v switch
                    {
                        // ReSharper disable once LocalizableElement
                        -1 => throw new ArgumentException(
                            "Encountered premature end of input (unexpected EOF).",
                            nameof(v)
                        ),
                        // ReSharper disable once LocalizableElement
                        0 => throw new ArgumentException(
                            "Encountered premature end of input (unexpected null character).",
                            nameof(v)
                        ),
                        _ => (uint)v << shift,
                    };
                }

                typeByte += 1;
                var argbValue = 0u;
                if ((typeByte & 8) != 0)
                    argbValue |= ShiftAndThrowIfZero(stream.ReadByte(), 24);
                else
                    argbValue |= 0xff000000u;

                if ((typeByte & 4) != 0)
                    argbValue |= ShiftAndThrowIfZero(stream.ReadByte(), 16);
                if ((typeByte & 2) != 0)
                    argbValue |= ShiftAndThrowIfZero(stream.ReadByte(), 8);
                if ((typeByte & 1) != 0)
                    argbValue |= ShiftAndThrowIfZero(stream.ReadByte(), 0);

                payload.Enabled = true;
                payload.Color = ColourUtil.ArgbToRgba(argbValue);

                return payload;
            default:
                return null;
        }
    }
}