using DigitalData.Core.Abstractions.Security;
using Microsoft.Extensions.Options;
using System.Security.Cryptography;

namespace DigitalData.Core.Security
{
    public class RSAFactory<TRSAFactoryParams> : IRSAFactory<TRSAFactoryParams> where TRSAFactoryParams : RSAFactoryParams
    {
        private static readonly Lazy<RSAFactory<RSAFactoryParams>> LazyInstance = new(() => new(Options.Create<RSAFactoryParams>(new())));

        public static RSAFactory<RSAFactoryParams> Static => LazyInstance.Value;

        protected readonly TRSAFactoryParams _params;
        
        public RSAFactory(IOptions<TRSAFactoryParams> options) => _params = options.Value;

        public string CreateRSAPrivateKeyPem(int? keySizeInBits = null)
            => RSA.Create(keySizeInBits ?? _params.KeySizeInBits).ExportRSAPrivateKeyPem();

        public string CreateEncryptedPrivateKeyPem(
            int? keySizeInBits = null,
            string? password = null,
            PbeEncryptionAlgorithm? pbeEncryptionAlgorithm = null,
            HashAlgorithmName? hashAlgorithmName = null,
            int? iterationCount = null)
        {
            password ??= _params.PbePassword;

            var pbeParameters = (pbeEncryptionAlgorithm is null && hashAlgorithmName is null && iterationCount is null)
                ? new PbeParameters(
                    pbeEncryptionAlgorithm ?? _params.PbeEncryptionAlgorithm,
                    hashAlgorithmName ?? _params.PbeHashAlgorithmName,
                    iterationCount ?? _params.PbeIterationCount)
                : _params.PbeParameters;
            
            var encryptedPrivateKey = RSA.Create(keySizeInBits ?? _params.KeySizeInBits).ExportEncryptedPkcs8PrivateKey(password.AsSpan(), pbeParameters);

            var pemChars = PemEncoding.Write(_params.EncryptedPrivateKeyPemLabel, encryptedPrivateKey);

            return new string(pemChars);
        }

        public async Task<IRSADecryptor> ReadRSADecryptorAsync(string path, Version? version = null, CancellationToken cancellationToken = default)
        {
            var pem = await File.ReadAllTextAsync(path, cancellationToken);

            (string Value, Version Version)? versionedPassword = null;

            if(version is not null)
            {
                if (version != Secrets.Version)
                    throw new InvalidOperationException($"The provided version {version} does not match the expected version {Secrets.Version}.");

                versionedPassword = (Secrets.PBE_PASSWORD, Secrets.Version);
            }

            return new RSADecryptor()
            {
                Pem = pem,
                VersionedPassword = versionedPassword
            };
        }
    }
}