namespace StellaOps.Cryptography.Profiles.Ecdsa;

using System.Security.Cryptography;
using StellaOps.Cryptography;
using StellaOps.Cryptography.Models;

/// <summary>
/// ECDSA P-256 signer using .NET cryptography (FIPS 186-4 compliant).
/// </summary>
public sealed class EcdsaP256Signer : IContentSigner
{
    private readonly ECDsa _ecdsa;
    private readonly string _keyId;
    private readonly TimeProvider _timeProvider;
    private bool _disposed;

    public string KeyId => _keyId;
    public SignatureProfile Profile => SignatureProfile.EcdsaP256;
    public string Algorithm => "ES256";

    public EcdsaP256Signer(string keyId, ECDsa ecdsa, TimeProvider? timeProvider = null)
    {
        _keyId = keyId ?? throw new ArgumentNullException(nameof(keyId));
        _ecdsa = ecdsa ?? throw new ArgumentNullException(nameof(ecdsa));
        _timeProvider = timeProvider ?? TimeProvider.System;

        if (_ecdsa.KeySize != 256)
            throw new ArgumentException("ECDSA key must be P-256 (256 bits)", nameof(ecdsa));
    }

    public static EcdsaP256Signer Generate(string keyId, TimeProvider? timeProvider = null)
    {
        var ecdsa = ECDsa.Create(ECCurve.NamedCurves.nistP256);
        return new EcdsaP256Signer(keyId, ecdsa, timeProvider);
    }

    public Task<SignatureResult> SignAsync(ReadOnlyMemory<byte> payload, CancellationToken ct = default)
    {
        ObjectDisposedException.ThrowIf(_disposed, this);
        ct.ThrowIfCancellationRequested();

        var signature = _ecdsa.SignData(payload.Span, HashAlgorithmName.SHA256);

        return Task.FromResult(new SignatureResult
        {
            KeyId = _keyId,
            Profile = Profile,
            Algorithm = Algorithm,
            Signature = signature,
            SignedAt = _timeProvider.GetUtcNow()
        });
    }

    public byte[]? GetPublicKey()
    {
        ObjectDisposedException.ThrowIf(_disposed, this);
        return _ecdsa.ExportSubjectPublicKeyInfo();
    }

    public void Dispose()
    {
        if (_disposed) return;
        _ecdsa?.Dispose();
        _disposed = true;
    }
}