using System.Security.Cryptography;
using System.Text;
using System.Text.Json.Serialization;

var builder = WebApplication.CreateBuilder(args);
var app = builder.Build();

// Static key material for simulations (not for production use).
using var ecdsa = ECDsa.Create(ECCurve.NamedCurves.nistP256);
var ecdsaPublic = ecdsa.ExportSubjectPublicKeyInfo();

byte[] Sign(string message, string algorithm)
{
    var data = Encoding.UTF8.GetBytes(message);
    var lower = algorithm.Trim().ToLowerInvariant();
    var upper = algorithm.Trim().ToUpperInvariant();

    if (lower is "pq.dilithium3" or "pq.falcon512" or "pq.sim" || upper is "DILITHIUM3" or "FALCON512")
    {
        return HMACSHA256.HashData(Encoding.UTF8.GetBytes("pq-sim-key"), data);
    }

    if (lower is "ru.magma.sim" or "ru.kuznyechik.sim" || upper is "GOST12-256" or "GOST12-512")
    {
        return HMACSHA256.HashData(Encoding.UTF8.GetBytes("gost-sim-key"), data);
    }

    if (lower is "sm.sim" or "sm2.sim" || upper is "SM2")
    {
        return HMACSHA256.HashData(Encoding.UTF8.GetBytes("sm-sim-key"), data);
    }

    return ecdsa.SignData(data, HashAlgorithmName.SHA256);
}

bool Verify(string message, string algorithm, byte[] signature)
{
    var data = Encoding.UTF8.GetBytes(message);
    var lower = algorithm.Trim().ToLowerInvariant();
    var upper = algorithm.Trim().ToUpperInvariant();

    if (lower is "pq.dilithium3" or "pq.falcon512" or "pq.sim" || upper is "DILITHIUM3" or "FALCON512")
    {
        return CryptographicOperations.FixedTimeEquals(HMACSHA256.HashData(Encoding.UTF8.GetBytes("pq-sim-key"), data), signature);
    }

    if (lower is "ru.magma.sim" or "ru.kuznyechik.sim" || upper is "GOST12-256" or "GOST12-512")
    {
        return CryptographicOperations.FixedTimeEquals(HMACSHA256.HashData(Encoding.UTF8.GetBytes("gost-sim-key"), data), signature);
    }

    if (lower is "sm.sim" or "sm2.sim" || upper is "SM2")
    {
        return CryptographicOperations.FixedTimeEquals(HMACSHA256.HashData(Encoding.UTF8.GetBytes("sm-sim-key"), data), signature);
    }

    return ecdsa.VerifyData(data, signature, HashAlgorithmName.SHA256);
}

app.MapPost("/sign", (SignRequest request) =>
{
    if (string.IsNullOrWhiteSpace(request.Algorithm) || string.IsNullOrWhiteSpace(request.Message))
    {
        return Results.BadRequest("Algorithm and message are required.");
    }

    var sig = Sign(request.Message, request.Algorithm);
    return Results.Json(new SignResponse(Convert.ToBase64String(sig), request.Algorithm));
});

app.MapPost("/verify", (VerifyRequest request) =>
{
    if (string.IsNullOrWhiteSpace(request.Algorithm) || string.IsNullOrWhiteSpace(request.Message) || string.IsNullOrWhiteSpace(request.SignatureBase64))
    {
        return Results.BadRequest("Algorithm, message, and signature are required.");
    }

    var sig = Convert.FromBase64String(request.SignatureBase64);
    var ok = Verify(request.Message, request.Algorithm, sig);
    return Results.Json(new VerifyResponse(ok, request.Algorithm));
});

app.MapGet("/keys", () =>
{
    return Results.Json(new KeysResponse(
        Convert.ToBase64String(ecdsaPublic),
        "nistp256",
        new[]
        {
            "pq.sim",
            "DILITHIUM3",
            "FALCON512",
            "ru.magma.sim",
            "ru.kuznyechik.sim",
            "GOST12-256",
            "GOST12-512",
            "sm.sim",
            "SM2",
            "fips.sim",
            "eidas.sim",
            "kcmvp.sim",
            "world.sim"
        }));
});

app.Run();

public record SignRequest(
    [property: JsonPropertyName("message")] string Message,
    [property: JsonPropertyName("algorithm")] string Algorithm);

public record SignResponse(
    [property: JsonPropertyName("signature_b64")] string SignatureBase64,
    [property: JsonPropertyName("algorithm")] string Algorithm);

public record VerifyRequest(
    [property: JsonPropertyName("message")] string Message,
    [property: JsonPropertyName("signature_b64")] string SignatureBase64,
    [property: JsonPropertyName("algorithm")] string Algorithm);

public record VerifyResponse(
    [property: JsonPropertyName("ok")] bool Ok,
    [property: JsonPropertyName("algorithm")] string Algorithm);

public record KeysResponse(
    [property: JsonPropertyName("public_key_b64")] string PublicKeyBase64,
    [property: JsonPropertyName("curve")] string Curve,
    [property: JsonPropertyName("simulated_providers")] IEnumerable<string> Providers);