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using System;
using System.Security.Cryptography;
using System.Threading.Tasks;
using Moq;
using NUnit.Framework;
using Opc.Ua.Identity;
using Opc.Ua.Security.Certificates;
using Opc.Ua.Tests;

namespace Opc.Ua.Server.Tests
{
    [TestFixture]
    [Category("Session")]
    [Category("Identity")]
    public sealed class SessionAuthenticationErrorRegressionTests
    {
        /// <summary>
        /// Verifies padding, plaintext length and policy errors are indistinguishable at ActivateSession.
        /// </summary>
        [TestCase("padding")]
        [TestCase("length")]
        [TestCase("algorithm")]
        public Task SessionDecryptFailuresReturnIdentityTokenInvalidAsync(string failure)
        {
            return AssertActivationRejectionAsync(
                new ServerIdentityRegistry(),
                StatusCodes.BadIdentityTokenInvalid,
                "Could not decrypt identity token.",
                failure);
        }

        /// <summary>
        /// Verifies an RSAEncryptedSecret whose KeyData fails RSA unpadding and one whose KeyData
        /// unpads but does not hold the expected keys produce the same error, with no inner result
        /// a client asking for inner diagnostics could use to tell them apart (OPC 10000-4 7.40.2.1).
        /// </summary>
        [TestCase(SecurityPolicies.Basic128Rsa15)]
        [TestCase(SecurityPolicies.Basic256Sha256)]
        [TestCase(SecurityPolicies.Aes256_Sha256_RsaPss)]
        public async Task RsaEncryptedSecretKeyDataFailuresAreIndistinguishableAsync(string policyUri)
        {
            ServiceResultException badPadding = await ActivateWithRsaEncryptedSecretAsync(
                policyUri, wellFormedPadding: false).ConfigureAwait(false);
            ServiceResultException badLayout = await ActivateWithRsaEncryptedSecretAsync(
                policyUri, wellFormedPadding: true).ConfigureAwait(false);

            foreach (ServiceResultException error in new[] { badPadding, badLayout })
            {
                Assert.That(error.StatusCode, Is.EqualTo(StatusCodes.BadIdentityTokenInvalid));
                Assert.That(error.InnerResult, Is.Null);
            }
            Assert.That(badLayout.Result.LocalizedText, Is.EqualTo(badPadding.Result.LocalizedText));
            Assert.That(badLayout.AdditionalInfo, Is.EqualTo(badPadding.AdditionalInfo));
        }

        [TestCaseSource(nameof(s_rejectionCodes))]
        public Task AuthenticatorRejectionPreservesStatusAndMessageAsync(StatusCode statusCode)
        {
            var error = new ServiceResult(statusCode, new LocalizedText("Authenticator rejection must survive."));
            var registry = new ServerIdentityRegistry(new UserNamePasswordAuthenticator(
                (_, _) => throw new ServiceResultException(error)));
            return AssertActivationRejectionAsync(registry, statusCode, error.LocalizedText.Text!);
        }

        [Test]
        public Task UnhandledNonAnonymousTokenStillFailsClosedAsync()
        {
            return AssertActivationRejectionAsync(
                new ServerIdentityRegistry(), StatusCodes.BadIdentityTokenRejected, null!);
        }

        private static async Task AssertActivationRejectionAsync(
            ServerIdentityRegistry registry,
            StatusCode expectedStatus,
            string expectedMessage,
            string? decryptionFailure = null)
        {
            ServiceResultException error = await ActivateAsync(
                registry,
                decryptionFailure == null ? SecurityPolicies.None : SecurityPolicies.Basic128Rsa15,
                (certificate, _) =>
                {
                    var token = new UserNameIdentityToken
                    {
                        PolicyId = "username",
                        UserName = "test-user",
                        Password = ByteString.From([1])
                    };
                    if (decryptionFailure != null)
                    {
                        using RSA rsa = certificate.GetRSAPublicKey()!;
                        token.Password = decryptionFailure == "padding"
                            ? ByteString.From(new byte[rsa!.KeySize / 8])
                            : ByteString.From(rsa!.Encrypt(
                                [0xFF, 0xFF, 0xFF, 0x7F], RSAEncryptionPadding.Pkcs1));
                        token.EncryptionAlgorithm = decryptionFailure == "algorithm"
                            ? SecurityAlgorithms.RsaOaep
                            : SecurityAlgorithms.Rsa15;
                    }
                    return token;
                }).ConfigureAwait(false);

            Assert.That(error.StatusCode, Is.EqualTo(expectedStatus));
            if (expectedMessage != null)
            {
                Assert.That(error.Result.LocalizedText.Text, Is.EqualTo(expectedMessage));
            }
            if (decryptionFailure != null)
            {
                Assert.That(error.InnerResult, Is.Null);
            }
        }

        /// <summary>
        /// Activates with a UserName token whose password is an RSAEncryptedSecret carrying a
        /// KeyData block that either fails RSA unpadding or unpads to a KeyData of the wrong layout.
        /// </summary>
        private static Task<ServiceResultException> ActivateWithRsaEncryptedSecretAsync(
            string policyUri,
            bool wellFormedPadding)
        {
            return ActivateAsync(
                new ServerIdentityRegistry(),
                policyUri,
                (certificate, serverNonce) =>
                {
                    IServiceMessageContext messageContext =
                        ServiceMessageContext.CreateEmpty(NUnitTelemetryContext.Create());
                    using var encryptor = EncryptedSecret.CreateForRsa(messageContext, policyUri, certificate);
                    byte[] encoded = encryptor.EncryptRsa([1, 2, 3, 4], serverNonce.ToArray());

                    // locate the KeyData behind the fixed RSAEncryptedSecret header.
                    using var decoder = new BinaryDecoder(encoded, messageContext);
                    decoder.ReadNodeId(null);
                    decoder.ReadByte(null);
                    decoder.ReadUInt32(null);
                    decoder.ReadString(null);
                    decoder.ReadByteString(null);
                    decoder.ReadDateTime(null);
                    int keyDataLength = decoder.ReadUInt16(null);
                    int keyDataStart = decoder.Position;

                    using RSA rsa = certificate.GetRSAPublicKey()!;
                    byte[] keyData = wellFormedPadding
                        ? rsa!.Encrypt(
                            [0x03, 0x00, 0x00, 0x00, 0x01, 0x02, 0x03],
                            policyUri switch
                            {
                                SecurityPolicies.Basic128Rsa15 => RSAEncryptionPadding.Pkcs1,
                                SecurityPolicies.Aes256_Sha256_RsaPss => RSAEncryptionPadding.OaepSHA256,
                                _ => RSAEncryptionPadding.OaepSHA1
                            })
                        : new byte[rsa!.KeySize / 8];
                    Assert.That(keyData, Has.Length.EqualTo(keyDataLength));
                    Buffer.BlockCopy(keyData, 0, encoded, keyDataStart, keyDataLength);

                    return new UserNameIdentityToken
                    {
                        PolicyId = "username",
                        UserName = "test-user",
                        Password = ByteString.From(encoded)
                    };
                });
        }

        private static async Task<ServiceResultException> ActivateAsync(
            ServerIdentityRegistry registry,
            string tokenSecurityPolicyUri,
            Func<Certificate, ByteString, UserIdentityToken> createToken)
        {
            ITelemetryContext telemetry = NUnitTelemetryContext.Create();
            var server = new Mock<IServerInternal>();
            server.Setup(value => value.Telemetry).Returns(telemetry);
            server.Setup(value => value.NamespaceUris).Returns(new NamespaceTable());
            server.Setup(value => value.MessageContext).Returns(ServiceMessageContext.CreateEmpty(telemetry));
            server.Setup(value => value.IdentityRegistry).Returns(registry);
            server.Setup(value => value.DiagnosticsNodeManager).Returns(Mock.Of<IDiagnosticsNodeManager>());
            server.Setup(value => value.DefaultSystemContext).Returns(new ServerSystemContext(server.Object));
            var configuration = new ApplicationConfiguration
            {
                ServerConfiguration = new ServerConfiguration
                {
                    MinSessionTimeout = 1000,
                    MaxSessionTimeout = 60000,
                    MaxSessionCount = 10
                }
            };
            using Certificate certificate = CertificateBuilder.Create("CN=Authentication Error Regression")
                .SetRSAKeySize(2048).CreateForRSA();
            using var manager = new SessionManager(server.Object, configuration);
            server.Setup(value => value.SessionManager).Returns(manager);
            var endpoint = new EndpointDescription
            {
                EndpointUrl = "opc.tcp://localhost/authentication-error",
                SecurityPolicyUri = SecurityPolicies.None,
                SecurityMode = MessageSecurityMode.None,
                UserIdentityTokens =
                [
                    new UserTokenPolicy
                    {
                        PolicyId = "username",
                        TokenType = UserTokenType.UserName,
                        SecurityPolicyUri = tokenSecurityPolicyUri
                    }
                ]
            };
            using var context = new OperationContext(
                new RequestHeader(),
                new SecureChannelContext("authentication-error", endpoint, RequestEncoding.Binary),
                RequestType.ActivateSession,
                RequestLifetime.None);
            CreateSessionResult created = await manager.CreateSessionAsync(
                context, certificate, "authentication-error", default, new ApplicationDescription(),
                endpoint.EndpointUrl, null, [], 60000, 64 * 1024, default).ConfigureAwait(false);
            try
            {
                UserIdentityToken token = createToken(certificate, created.ServerNonce);
                ServiceResultException error = Assert.ThrowsAsync<ServiceResultException>(async () =>
                    await manager.ActivateSessionAsync(
                        context, created.AuthenticationToken, new SignatureData(), new ExtensionObject(token),
                        new SignatureData(), [], default).ConfigureAwait(false));

                Assert.That(created.Session.Activated, Is.False);
                return error;
            }
            finally
            {
                await manager.CloseSessionAsync(created.SessionId).ConfigureAwait(false);
            }
        }

        private static readonly StatusCode[] s_rejectionCodes =
        [
            StatusCodes.BadIdentityTokenInvalid,
            StatusCodes.BadUserAccessDenied,
            StatusCodes.BadIdentityTokenRejected,
            StatusCodes.BadCertificateUntrusted
        ];
    }
}