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 *
 * OPC Foundation MIT License 1.00
 *
 * Permission is hereby granted, free of charge, to any person
 * obtaining a copy of this software and associated documentation
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 *
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 * OTHER DEALINGS IN THE SOFTWARE.
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 * The complete license agreement can be found here:
 * http://opcfoundation.org/License/MIT/1.00/
 * ======================================================================*/

using System;
using System.Threading;
using System.Threading.Tasks;
using Opc.Ua.Security.Certificates;

namespace Opc.Ua.Client
{
    /// <summary>
    /// Session factory that creates raw <see cref="Session"/> instances
    /// without automatic reconnection or failover.
    /// </summary>
    /// <remarks>
    /// Use <see cref="ManagedSessionFactory"/> instead to get
    /// <see cref="ManagedSession"/> instances that handle reconnection
    /// and failover automatically.
    /// </remarks>
    public class DefaultSessionFactory : ISessionFactory
    {
        /// <summary>
        /// The default instance of the factory.
        /// </summary>
        // Telemetry is required by the modern ctor; this obsolete singleton forwards null!
        // to preserve the pre-nullable static-instance pattern.
        [Obsolete("Use new DefaultSessionFactory(ITelemetryContext) instead.")]
        public static readonly DefaultSessionFactory Instance = new(null!);

        /// <inheritdoc/>
        public ITelemetryContext Telemetry { get; init; }

        /// <inheritdoc/>
        public DiagnosticsMasks ReturnDiagnostics { get; set; }

        /// <summary>
        /// Optional subscription engine factory to use when constructing
        /// a <see cref="Session"/>. When <c>null</c>, the session uses
        /// the classic engine (<see cref="ClassicSubscriptionEngineFactory"/>).
        /// New <see cref="ManagedSession"/> code paths default to the V2
        /// engine (<see cref="DefaultSubscriptionEngineFactory"/>) via
        /// the <c>ManagedSessionBuilder</c>.
        /// </summary>
        public ISubscriptionEngineFactory? SubscriptionEngineFactory { get; init; }

        /// <summary>
        /// Optional <see cref="TimeProvider"/> forwarded to every
        /// <see cref="Session"/> created by this factory. When
        /// <see langword="null"/>, the session uses
        /// <see cref="TimeProvider.System"/>.
        /// </summary>
        public TimeProvider? TimeProvider { get; init; }

        /// <summary>
        /// Obsolete default constructor
        /// </summary>
        [Obsolete("Use DefaultSessionFactory(ITelemetryContext) instead.")]
        public DefaultSessionFactory()
            // Telemetry is required by the modern ctor; this obsolete bridge forwards null!
            // to preserve the parameterless instantiation pattern.
            : this(null!)
        {
        }

        /// <summary>
        /// Creates a new instance of the <see cref="DefaultSessionFactory"/>.
        /// </summary>
        public DefaultSessionFactory(ITelemetryContext telemetry)
        {
            Telemetry = telemetry;
        }

        /// <inheritdoc/>
        public virtual Task<ISession> CreateAsync(
            ApplicationConfiguration configuration,
            ConfiguredEndpoint endpoint,
            bool updateBeforeConnect,
            string sessionName,
            uint sessionTimeout,
            IUserIdentity? identity,
            ArrayOf<string> preferredLocales,
            CancellationToken ct = default)
        {
            return CreateAsync(
                configuration,
                endpoint,
                updateBeforeConnect,
                false,
                sessionName,
                sessionTimeout,
                identity,
                preferredLocales,
                ct);
        }

        /// <inheritdoc/>
        public virtual Task<ISession> CreateAsync(
            ApplicationConfiguration configuration,
            ConfiguredEndpoint endpoint,
            bool updateBeforeConnect,
            bool checkDomain,
            string sessionName,
            uint sessionTimeout,
            IUserIdentity? identity,
            ArrayOf<string> preferredLocales,
            CancellationToken ct = default)
        {
            return CreateAsync(
                configuration,
                null,
                endpoint,
                updateBeforeConnect,
                checkDomain,
                sessionName,
                sessionTimeout,
                identity,
                preferredLocales,
                ReturnDiagnostics,
                ct);
        }

        /// <inheritdoc/>
        public virtual Task<ISession> CreateAsync(
            ApplicationConfiguration configuration,
            ITransportWaitingConnection connection,
            ConfiguredEndpoint endpoint,
            bool updateBeforeConnect,
            bool checkDomain,
            string sessionName,
            uint sessionTimeout,
            IUserIdentity? identity,
            ArrayOf<string> preferredLocales,
            CancellationToken ct = default)
        {
            return CreateAsync(
                configuration,
                connection,
                endpoint,
                updateBeforeConnect,
                checkDomain,
                sessionName,
                sessionTimeout,
                identity,
                preferredLocales,
                ReturnDiagnostics,
                ct);
        }

        /// <inheritdoc/>
        public virtual async Task<ISession> CreateAsync(
            ApplicationConfiguration configuration,
            ReverseConnectManager reverseConnectManager,
            ConfiguredEndpoint endpoint,
            bool updateBeforeConnect,
            bool checkDomain,
            string sessionName,
            uint sessionTimeout,
            IUserIdentity? userIdentity,
            ArrayOf<string> preferredLocales,
            CancellationToken ct = default)
        {
            if (reverseConnectManager == null)
            {
                return await CreateAsync(
                    configuration,
                    endpoint,
                    updateBeforeConnect,
                    checkDomain,
                    sessionName,
                    sessionTimeout,
                    userIdentity,
                    preferredLocales,
                    ct).ConfigureAwait(false);
            }

            ITransportWaitingConnection? connection;
            do
            {
                // Reverse-connect endpoints always carry an EndpointUrl and SecurityPolicyUri
                // populated when the configured endpoint was loaded; the bangs reflect that.
                connection = await reverseConnectManager
                    .WaitForConnectionAsync(
                        endpoint.EndpointUrl!,
                        endpoint.ReverseConnect?.ServerUri,
                        ct)
                    .ConfigureAwait(false);

                if (updateBeforeConnect)
                {
                    await endpoint.UpdateFromServerAsync(
                        endpoint.EndpointUrl!,
                        connection,
                        endpoint.Description.SecurityMode,
                        endpoint.Description.SecurityPolicyUri!,
                        Telemetry,
                        ct).ConfigureAwait(false);
                    updateBeforeConnect = false;
                    connection = null;
                }
            } while (connection == null);

            return await CreateAsync(
                configuration,
                connection,
                endpoint,
                false,
                checkDomain,
                sessionName,
                sessionTimeout,
                userIdentity,
                preferredLocales,
                ct).ConfigureAwait(false);
        }

        /// <inheritdoc/>
        public virtual async Task<ITransportChannel> CreateChannelAsync(
            ApplicationConfiguration configuration,
            ITransportWaitingConnection? connection,
            ConfiguredEndpoint endpoint,
            bool updateBeforeConnect,
            bool checkDomain,
            CancellationToken ct = default)
        {
            endpoint.UpdateBeforeConnect = updateBeforeConnect;

            EndpointDescription endpointDescription = endpoint.Description;

            // create the endpoint configuration (use the application configuration to provide default values).
            EndpointConfiguration? endpointConfiguration = endpoint.Configuration;

            if (endpointConfiguration == null)
            {
                endpoint.Configuration = endpointConfiguration = EndpointConfiguration.Create(
                    configuration);
            }

            // create message context.
            ServiceMessageContext messageContext = configuration.CreateMessageContext();

            // update endpoint description using the discovery endpoint.
            if (endpoint.UpdateBeforeConnect && connection == null)
            {
                await endpoint.UpdateFromServerAsync(messageContext.Telemetry, ct).ConfigureAwait(false);
                endpointDescription = endpoint.Description;
                // UpdateFromServerAsync re-reads Configuration from the discovery response;
                // it is set whenever the description was updated successfully.
                endpointConfiguration = endpoint.Configuration!;
            }

            // checks the domains in the certificate.
            if (checkDomain && endpoint.Description.ServerCertificate.Length > 0)
            {
                using var certificate = Certificate.FromRawData(endpoint.Description.ServerCertificate);
                ICertificateValidatorEx? validator = configuration.CertificateManager;
                validator?.ValidateDomains(certificate, endpoint);
            }

            Certificate? clientCertificate = null;
            CertificateCollection? clientCertificateChain = null;
            try
            {
                if (endpointDescription.SecurityPolicyUri is not null and not SecurityPolicies.None)
                {
                    clientCertificate = await Session.LoadInstanceCertificateAsync(
                        configuration,
                        endpointDescription.SecurityPolicyUri,
                        messageContext.Telemetry,
                        ct).ConfigureAwait(false);
                    clientCertificateChain = await Session.LoadCertificateChainAsync(
                        configuration,
                        clientCertificate,
                        ct).ConfigureAwait(false);
                }

                // initialize the channel which will be created with the server.
                ITransportChannel channel;
                if (connection != null)
                {
                    channel = await UaChannelBase.CreateUaBinaryChannelAsync(
                        configuration,
                        connection,
                        endpointDescription,
                        endpointConfiguration,
                        clientCertificate,
                        clientCertificateChain,
                        messageContext,
                        ct).ConfigureAwait(false);
                }
                else
                {
                    channel = await UaChannelBase.CreateUaBinaryChannelAsync(
                        configuration,
                        endpointDescription,
                        endpointConfiguration,
                        clientCertificate,
                        clientCertificateChain,
                        messageContext,
                        ct).ConfigureAwait(false);
                }

                // Ownership of the cert and chain has been transferred to the
                // channel's TransportChannelSettings; the channel disposes
                // them when it is disposed, so we must not dispose here.
                clientCertificate = null;
                clientCertificateChain = null;
                return channel;
            }
            finally
            {
                clientCertificateChain?.Dispose();
                clientCertificate?.Dispose();
            }
        }

        /// <inheritdoc/>
        public virtual async Task<ISession> RecreateAsync(
            ISession sessionTemplate,
            CancellationToken ct = default)
        {
            if (sessionTemplate is not Session template)
            {
                throw new ArgumentException(
                    "The ISession provided is not of a supported type.",

                    nameof(sessionTemplate));
            }

            template.ReturnDiagnostics = ReturnDiagnostics;
            return await template.RecreateAsync(ct).ConfigureAwait(false);
        }

        /// <inheritdoc/>
        public virtual async Task<ISession> RecreateAsync(
            ISession sessionTemplate,
            ITransportWaitingConnection connection,
            CancellationToken ct = default)
        {
            if (sessionTemplate is not Session template)
            {
                throw new ArgumentException(
                    "The ISession provided is not of a supported type.",

                    nameof(sessionTemplate));
            }

            template.ReturnDiagnostics = ReturnDiagnostics;
            return await template.RecreateAsync(connection, ct).ConfigureAwait(false);
        }

        /// <inheritdoc/>
        public virtual async Task<ISession> RecreateAsync(
            ISession sessionTemplate,
            ITransportChannel transportChannel,
            CancellationToken ct = default)
        {
            if (sessionTemplate is not Session template)
            {
                throw new ArgumentException(
                    "The ISession provided is not of a supported type.",

                    nameof(sessionTemplate));
            }
            template.ReturnDiagnostics = ReturnDiagnostics;
            return await template.RecreateAsync(transportChannel, ct)
                .ConfigureAwait(false);
        }

        /// <inheritdoc/>
        public virtual ISession Create(
            ITransportChannel channel,
            ApplicationConfiguration configuration,
            ConfiguredEndpoint endpoint,
            Certificate? clientCertificate = null,
            CertificateCollection? clientCertificateChain = null,
            ArrayOf<EndpointDescription> availableEndpoints = default,
            ArrayOf<string> discoveryProfileUris = default)
        {
            return new Session(
                channel,
                configuration,
                endpoint,
                clientCertificate,
                clientCertificateChain,
                availableEndpoints,
                discoveryProfileUris,
                SubscriptionEngineFactory,
                TimeProvider)
            {
                ReturnDiagnostics = ReturnDiagnostics
            };
        }

        /// <summary>
        /// Creates a new communication session with a server using a reverse connection.
        /// </summary>
        /// <param name="configuration">The configuration for the client application.</param>
        /// <param name="connection">The client endpoint for the reverse connect.</param>
        /// <param name="endpoint">The endpoint for the server.</param>
        /// <param name="updateBeforeConnect">If set to <c>true</c> the discovery endpoint is used to
        /// update the endpoint description before connecting.</param>
        /// <param name="checkDomain">If set to <c>true</c> then the domain in the certificate must match
        /// the endpoint used.</param>
        /// <param name="sessionName">The name to assign to the session.</param>
        /// <param name="sessionTimeout">The timeout period for the session.</param>
        /// <param name="identity">The user identity to associate with the session.</param>
        /// <param name="preferredLocales">The preferred locales.</param>
        /// <param name="returnDiagnostics">The return diagnostics to use on this session</param>
        /// <param name="ct">The cancellation token.</param>
        /// <returns>The new session object.</returns>
        private async Task<ISession> CreateAsync(
            ApplicationConfiguration configuration,
            ITransportWaitingConnection? connection,
            ConfiguredEndpoint endpoint,
            bool updateBeforeConnect,
            bool checkDomain,
            string sessionName,
            uint sessionTimeout,
            IUserIdentity? identity,
            ArrayOf<string> preferredLocales,
            DiagnosticsMasks returnDiagnostics,
            CancellationToken ct = default)
        {
            // initialize the channel which will be created with the server.
            ITransportChannel channel = await CreateChannelAsync(
                    configuration,
                    connection,
                    endpoint,
                    updateBeforeConnect,
                    checkDomain,
                    ct)
                .ConfigureAwait(false);

            // create the session object.
            ISession session = Create(channel, configuration, endpoint, null);
            session.ReturnDiagnostics = returnDiagnostics;

            // create the session.
            UserIdentity? tempIdentity = identity == null ? new UserIdentity() : null;
            try
            {
                await session
                    .OpenAsync(
                        sessionName,
                        sessionTimeout,
                        // tempIdentity is set when identity is null (line above), so the
                        // coalesce always yields a non-null IUserIdentity at runtime.
                        identity ?? tempIdentity!,
                        preferredLocales,
                        checkDomain,
                        ct)
                    .ConfigureAwait(false);
                tempIdentity = null; // ownership transferred to session
            }
            catch (Exception)
            {
                session.Dispose();
                throw;
            }

            return session;
        }
    }
}