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using System;
using System.Security.Cryptography;
using System.Security.Cryptography.X509Certificates;

namespace Opc.Ua.Core.Security.Tests
{
    /// <summary>
    /// Test certificate helpers used by Security conformance tests. Mints
    /// self-signed user certs, CA roots, intermediate-issued chains, and CRLs
    /// with controllable validity / key-usage / subject so the tests can drive
    /// the server-side CertificateValidator down each rejection / acceptance
    /// path.
    /// </summary>
    /// <remarks>
    /// Uses System.Security.Cryptography directly so the helpers stay
    /// dependency-free and safe to call from any conformance test fixture.
    /// </remarks>
    internal static class TestCertificates
    {
        /// <summary>
        /// Creates a self-signed RSA-2048 user certificate.
        /// </summary>
        public static X509Certificate2 CreateSelfSignedUserCert(
            string cn = "CN=TestUser, O=OPC Foundation",
            DateTimeOffset? notBefore = null,
            DateTimeOffset? notAfter = null,
            X509KeyUsageFlags keyUsage =
                X509KeyUsageFlags.DigitalSignature |
                X509KeyUsageFlags.NonRepudiation |
                X509KeyUsageFlags.DataEncipherment |
                X509KeyUsageFlags.KeyEncipherment,
            int keySize = 2048)
        {
            using var rsa = RSA.Create(keySize);
            var certReq = new CertificateRequest(
                cn, rsa, HashAlgorithmName.SHA256, RSASignaturePadding.Pkcs1);
            certReq.CertificateExtensions.Add(
                new X509BasicConstraintsExtension(false, false, 0, false));
            certReq.CertificateExtensions.Add(
                new X509KeyUsageExtension(keyUsage, false));

            DateTimeOffset nb = notBefore ?? DateTimeOffset.UtcNow.AddMinutes(-5);
            DateTimeOffset na = notAfter ?? DateTimeOffset.UtcNow.AddYears(1);

            X509Certificate2 cert = certReq.CreateSelfSigned(nb, na);
            return ReimportWithExportablePrivateKey(cert);
        }

        /// <summary>
        /// Creates a self-signed RSA CA root certificate.
        /// </summary>
        public static X509Certificate2 CreateRootCa(
            string cn = "CN=TestRootCA, O=OPC Foundation",
            DateTimeOffset? notBefore = null,
            DateTimeOffset? notAfter = null,
            int keySize = 2048)
        {
            using var rsa = RSA.Create(keySize);
            var certReq = new CertificateRequest(
                cn, rsa, HashAlgorithmName.SHA256, RSASignaturePadding.Pkcs1);
            certReq.CertificateExtensions.Add(
                new X509BasicConstraintsExtension(true, true, 2, true));
            certReq.CertificateExtensions.Add(
                new X509KeyUsageExtension(
                    X509KeyUsageFlags.KeyCertSign | X509KeyUsageFlags.CrlSign,
                    true));
            certReq.CertificateExtensions.Add(
                new X509SubjectKeyIdentifierExtension(certReq.PublicKey, false));

            DateTimeOffset nb = notBefore ?? DateTimeOffset.UtcNow.AddMinutes(-5);
            DateTimeOffset na = notAfter ?? DateTimeOffset.UtcNow.AddYears(10);

            X509Certificate2 cert = certReq.CreateSelfSigned(nb, na);
            return ReimportWithExportablePrivateKey(cert);
        }

        /// <summary>
        /// Creates an intermediate CA certificate signed by <paramref name="rootCa"/>.
        /// </summary>
        public static X509Certificate2 CreateIntermediateCa(
            X509Certificate2 rootCa,
            string cn = "CN=TestIntermediateCA, O=OPC Foundation",
            DateTimeOffset? notBefore = null,
            DateTimeOffset? notAfter = null,
            int keySize = 2048)
        {
            using var rsa = RSA.Create(keySize);
            var certReq = new CertificateRequest(
                cn, rsa, HashAlgorithmName.SHA256, RSASignaturePadding.Pkcs1);
            certReq.CertificateExtensions.Add(
                new X509BasicConstraintsExtension(true, true, 1, true));
            certReq.CertificateExtensions.Add(
                new X509KeyUsageExtension(
                    X509KeyUsageFlags.KeyCertSign | X509KeyUsageFlags.CrlSign,
                    true));
            certReq.CertificateExtensions.Add(
                new X509SubjectKeyIdentifierExtension(certReq.PublicKey, false));

            DateTimeOffset nb = notBefore ?? DateTimeOffset.UtcNow.AddMinutes(-5);
            DateTimeOffset na = notAfter ?? DateTimeOffset.UtcNow.AddYears(5);

            byte[] serial = new byte[16];
            using (var rng = RandomNumberGenerator.Create())
            {
                rng.GetBytes(serial);
            }

            X509Certificate2 issued = certReq.Create(rootCa, nb, na, serial);
            X509Certificate2 withKey = issued.CopyWithPrivateKey(rsa);
            issued.Dispose();
            return ReimportWithExportablePrivateKey(withKey);
        }

        /// <summary>
        /// Creates a user certificate signed by the given <paramref name="issuerCa"/>.
        /// </summary>
        public static X509Certificate2 CreateUserCertSignedBy(
            X509Certificate2 issuerCa,
            string cn = "CN=TestUserChained, O=OPC Foundation",
            DateTimeOffset? notBefore = null,
            DateTimeOffset? notAfter = null,
            X509KeyUsageFlags keyUsage =
                X509KeyUsageFlags.DigitalSignature |
                X509KeyUsageFlags.NonRepudiation |
                X509KeyUsageFlags.DataEncipherment |
                X509KeyUsageFlags.KeyEncipherment,
            int keySize = 2048)
        {
            using var rsa = RSA.Create(keySize);
            var certReq = new CertificateRequest(
                cn, rsa, HashAlgorithmName.SHA256, RSASignaturePadding.Pkcs1);
            certReq.CertificateExtensions.Add(
                new X509BasicConstraintsExtension(false, false, 0, false));
            certReq.CertificateExtensions.Add(
                new X509KeyUsageExtension(keyUsage, false));

            DateTimeOffset nb = notBefore ?? DateTimeOffset.UtcNow.AddMinutes(-5);
            DateTimeOffset na = notAfter ?? DateTimeOffset.UtcNow.AddYears(1);

            byte[] serial = new byte[16];
            using (var rng = RandomNumberGenerator.Create())
            {
                rng.GetBytes(serial);
            }

            X509Certificate2 issued = certReq.Create(issuerCa, nb, na, serial);
            X509Certificate2 withKey = issued.CopyWithPrivateKey(rsa);
            issued.Dispose();
            return ReimportWithExportablePrivateKey(withKey);
        }

        private static X509Certificate2 ReimportWithExportablePrivateKey(X509Certificate2 cert)
        {
            // Reimporting via PKCS#12 ensures the private key is fully accessible
            // and detaches the cert from any per-thread CSP that might lock it.
            byte[] pfx = cert.Export(X509ContentType.Pfx, "test");
            cert.Dispose();
            return X509CertificateLoader.LoadPkcs12(pfx, "test",
                X509KeyStorageFlags.Exportable);
        }
    }
}