using System.Security.Cryptography;
using Org.BouncyCastle.Crypto.Parameters;

namespace VoiceCat.Crypto;

public sealed class ServerIdentity : IDisposable
{
    private readonly byte[] seed;
    private readonly byte[] publicKey;
    private bool disposed;

    private ServerIdentity(byte[] seed)
    {
        this.seed = seed;
        publicKey = new Ed25519PrivateKeyParameters(seed, 0).GeneratePublicKey().GetEncoded();
    }

    public byte[] PublicKey => (byte[])publicKey.Clone();
    public string Fingerprint => Convert.ToHexString(SHA256.HashData(publicKey));

    public static ServerIdentity Generate() => new(RandomNumberGenerator.GetBytes(32));

    public static ServerIdentity Load(string path)
    {
        byte[] data = File.ReadAllBytes(path);
        try
        {
            if (data.Length != 96) throw new InvalidDataException("Server identity must contain 96 bytes.");
            var identity = new ServerIdentity(data.AsSpan(32, 32).ToArray());
            if (!CryptographicOperations.FixedTimeEquals(identity.publicKey, data.AsSpan(0, 32)) ||
                !CryptographicOperations.FixedTimeEquals(identity.publicKey, data.AsSpan(64, 32)))
            {
                identity.Dispose();
                throw new InvalidDataException("Server identity public key does not match its seed.");
            }
            return identity;
        }
        finally { CryptographicOperations.ZeroMemory(data); }
    }

    public void Save(string path)
    {
        ObjectDisposedException.ThrowIf(disposed, this);
        byte[] data = new byte[96];
        publicKey.CopyTo(data, 0);
        seed.CopyTo(data, 32);
        publicKey.CopyTo(data, 64);
        try { PrivateFiles.Write(path, data); }
        finally { CryptographicOperations.ZeroMemory(data); }
    }

    public void Dispose()
    {
        if (disposed) return;
        disposed = true;
        CryptographicOperations.ZeroMemory(seed);
    }
}