NdsDsiIntegrityOptions.cs

namespace NdsForge;

public sealed class NdsDsiIntegrityOptions
{
    private readonly byte[]? _hmacKey;
    private readonly INdsDsiSignatureProvider? _signatureProvider;

    public static NdsDsiIntegrityOptions Unauthenticated { get; } = new(null, NdsDsiSignatureMode.Cleared, null);

    public static NdsDsiIntegrityOptions NdstoolHomebrew { get; } = new(
        [
            0x21, 0x06, 0xC0, 0xDE, 0xBA, 0x98, 0xCE, 0x3F, 0xA6, 0x92, 0xE3, 0x9D, 0x46, 0xF2, 0xED, 0x01,
            0x76, 0xE3, 0xCC, 0x08, 0x56, 0x23, 0x63, 0xFA, 0xCA, 0xD4, 0xEC, 0xDF, 0x9A, 0x62, 0x78, 0x34,
            0x8F, 0x6D, 0x63, 0x3C, 0xFE, 0x22, 0xCA, 0x92, 0x20, 0x88, 0x97, 0x23, 0xD2, 0xCF, 0xAE, 0xC2,
            0x32, 0x67, 0x8D, 0xFE, 0xCA, 0x83, 0x64, 0x98, 0xAC, 0xFD, 0x3E, 0x37, 0x87, 0x46, 0x58, 0x24,
        ],
        NdsDsiSignatureMode.NoGbaDevelopmentMarker,
        null);

    private NdsDsiIntegrityOptions(
        byte[]? hmacKey,
        NdsDsiSignatureMode signatureMode,
        INdsDsiSignatureProvider? signatureProvider)
    {
        _hmacKey = hmacKey;
        SignatureMode = signatureMode;
        _signatureProvider = signatureProvider;
    }

    public static NdsDsiIntegrityOptions CreateHmacSha1(
        ReadOnlySpan<byte> key,
        NdsDsiSignatureMode signatureMode = NdsDsiSignatureMode.Cleared)
    {
        if (key.IsEmpty)
        {
            throw new ArgumentException("A DSi HMAC-SHA1 key cannot be empty.", nameof(key));
        }
 
        if (signatureMode == NdsDsiSignatureMode.RsaSha1)
        {
            throw new ArgumentException("RSA signature mode requires CreateSignedHmacSha1 and a signing provider.", nameof(signatureMode));
        }
 
        return new(key.ToArray(), signatureMode, null);
    }

    public static NdsDsiIntegrityOptions CreateSignedHmacSha1(
        ReadOnlySpan<byte> hmacKey,
        INdsDsiSignatureProvider signatureProvider)
    {
        if (hmacKey.IsEmpty)
        {
            throw new ArgumentException("A DSi HMAC-SHA1 key cannot be empty.", nameof(hmacKey));
        }
 
        ArgumentNullException.ThrowIfNull(signatureProvider);
        return new(hmacKey.ToArray(), NdsDsiSignatureMode.RsaSha1, signatureProvider);
    }

    public bool ComputesHmacSha1 => _hmacKey is not null;

    public NdsDsiSignatureMode SignatureMode { get; }

    internal ReadOnlyMemory<byte> HmacKey => _hmacKey;

    internal INdsDsiSignatureProvider? SignatureProvider => _signatureProvider;
}