using System;
using System.IO;
using System.Security.Cryptography;

using FrostFS.Refs;
using FrostFS.SDK.Cryptography;
using FrostFS.SDK.Proto.Interfaces;
using FrostFS.Session;

using Google.Protobuf;

using Org.BouncyCastle.Asn1.Sec;
using Org.BouncyCastle.Crypto.Digests;
using Org.BouncyCastle.Crypto.Parameters;
using Org.BouncyCastle.Crypto.Signers;
using Org.BouncyCastle.Math;
using Org.BouncyCastle.Utilities;
using Signature = FrostFS.Refs.Signature;

namespace FrostFS.SDK.Client;

public static class RequestSigner
{
    internal const int RFC6979SignatureSize = 64;

    internal static ByteString SignRFC6979(this ECDsa key, byte[] data)
    {
        if (key is null)
        {
            throw new ArgumentNullException(nameof(key));
        }

        var digest = new Sha256Digest();
        var secp256R1 = SecNamedCurves.GetByName("secp256r1");
        var ecParameters = new ECDomainParameters(secp256R1.Curve, secp256R1.G, secp256R1.N);
        var privateKey = new ECPrivateKeyParameters(new BigInteger(1, key.PrivateKey()), ecParameters);
        var signer = new ECDsaSigner(new HMacDsaKCalculator(digest));
        var hash = new byte[digest.GetDigestSize()];

        digest.BlockUpdate(data, 0, data.Length);
        digest.DoFinal(hash, 0);
        signer.Init(true, privateKey);

        var rs = signer.GenerateSignature(hash);

        Span<byte> signature = stackalloc byte[RFC6979SignatureSize];

        var rbytes = rs[0].ToByteArrayUnsigned();
        var sbytes = rs[1].ToByteArrayUnsigned();
        var index = RFC6979SignatureSize / 2 - rbytes.Length;

        rbytes.AsSpan().CopyTo(signature.Slice(index));
        index = RFC6979SignatureSize - sbytes.Length;
        sbytes.AsSpan().CopyTo(signature.Slice(index));

        return ByteString.CopyFrom(signature);
    }

    internal static SignatureRFC6979 SignRFC6979(this ECDsa key, IMessage message)
    {
        return new SignatureRFC6979
        {
            Key = ByteString.CopyFrom(key.PublicKey()),
            Sign = key.SignRFC6979(message.ToByteArray()),
        };
    }

    internal static SignatureRFC6979 SignRFC6979(this ECDsa key, ByteString data)
    {
        return new SignatureRFC6979
        {
            Key = ByteString.CopyFrom(key.PublicKey()),
            Sign = key.SignRFC6979(data.ToByteArray()),
        };
    }

    public static ByteString SignData(this ECDsa key, ReadOnlyMemory<byte> data)
    {
        if (key is null)
        {
            throw new ArgumentNullException(nameof(key));
        }

        Span<byte> result = stackalloc byte[65];
        result[0] = 0x04;

        key.SignHash(data.Sha512()).AsSpan().CopyTo(result.Slice(1));

        return ByteString.CopyFrom(result);
    }
    
    public static ByteString SignDataByHash(this ECDsa key, byte[] hash)
    {
        if (key is null)
        {
            throw new ArgumentNullException(nameof(key));
        }

        Span<byte> result = stackalloc byte[65];
        result[0] = 0x04;

        key.SignHash(hash).AsSpan().CopyTo(result.Slice(1));

        return ByteString.CopyFrom(result);
    }

    internal static Signature SignMessagePart(this ClientKey key, IMessage? data)
    {
        if (data is null)
        {
            return new Signature
            {
                Key = key.PublicKeyProto,
                Sign = key.ECDsaKey.SignData(ReadOnlyMemory<byte>.Empty),
            };
        }

        var size = data.CalculateSize();

        if (size == 0)
        {
            return new Signature
            {
                Key = key.PublicKeyProto,
                Sign = key.ECDsaKey.SignData(ReadOnlyMemory<byte>.Empty),
            };
        }
       
        using HashStream stream = new();
        data.WriteTo(stream);

        var sig = new Signature
        {
            Key = key.PublicKeyProto,
            Sign = key.ECDsaKey.SignDataByHash(stream.Hash())
        };

        return sig;
    }

    internal static void Sign(this IVerifiableMessage message, ClientKey key)
    {
        var meta = message.GetMetaHeader();
        IVerificationHeader verify = message switch
        {
            IRequest => new RequestVerificationHeader(),
            IResponse => new ResponseVerificationHeader(),
            _ => throw new InvalidOperationException("Unsupported message type")
        };

        var verifyOrigin = message.GetVerificationHeader();

        if (verifyOrigin is null)
            verify.BodySignature = key.SignMessagePart(message.GetBody());
        else
            verify.SetOrigin(verifyOrigin);

        verify.MetaSignature = key.SignMessagePart(meta);
        verify.OriginSignature = key.SignMessagePart(verifyOrigin);

        message.SetVerificationHeader(verify);
    }
}