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using System;
using System.Collections.Generic;
using System.Threading;
using System.Threading.Tasks;
using Microsoft.Extensions.Logging;
using Opc.Ua.Security;

namespace Opc.Ua.Client
{
    /// <summary>
    /// Defines numerous re-useable utility functions for clients.
    /// </summary>
    public static partial class CoreClientUtils
    {
        /// <summary>
        /// The default discover operation timeout.
        /// </summary>
        public static readonly int DefaultDiscoverTimeout = 15000;

        /// <summary>
        /// Discovers the servers on the local machine.
        /// </summary>
        /// <param name="configuration">The configuration.</param>
        /// <param name="telemetry">The telemetry context to use to create obvservability instruments</param>
        /// <param name="ct">Cancellation token to cancel operation with</param>
        /// <returns>A list of server urls.</returns>
        public static ValueTask<IList<string>> DiscoverServersAsync(
            ApplicationConfiguration configuration,
            ITelemetryContext telemetry,
            CancellationToken ct = default)
        {
            return DiscoverServersAsync(configuration, DefaultDiscoverTimeout, telemetry, ct);
        }

        /// <summary>
        /// Discovers the servers on the local machine.
        /// </summary>
        /// <param name="configuration">The configuration.</param>
        /// <param name="discoverTimeout">Operation timeout in milliseconds.</param>
        /// <param name="telemetry">The telemetry context to use to create obvservability instruments</param>
        /// <param name="ct">Cancellation token to cancel operation with</param>
        /// <returns>A list of server urls.</returns>
        public static async ValueTask<IList<string>> DiscoverServersAsync(
            ApplicationConfiguration configuration,
            int discoverTimeout,
            ITelemetryContext telemetry,
            CancellationToken ct = default)
        {
            var serverUrls = new List<string>();

            // set a short timeout because this is happening in the drop down event.
            var endpointConfiguration = EndpointConfiguration.Create(configuration);
            endpointConfiguration.OperationTimeout = discoverTimeout;

            // Connect to the local discovery server and find the available servers.
            using DiscoveryClient client = await DiscoveryClient.CreateAsync(
                    new Uri(Utils.Format(Utils.DiscoveryUrls[0], "localhost")),
                    endpointConfiguration,
                    telemetry,
                    ct: ct).ConfigureAwait(false);

            ArrayOf<ApplicationDescription> servers =
                await client.FindServersAsync(default, ct).ConfigureAwait(false);

            // populate the drop down list with the discovery URLs for the available servers.
            for (int ii = 0; ii < servers.Count; ii++)
            {
                if (servers[ii].ApplicationType == ApplicationType.DiscoveryServer)
                {
                    continue;
                }

                for (int jj = 0; jj < servers[ii].DiscoveryUrls.Count; jj++)
                {
                    string discoveryUrl = servers[ii].DiscoveryUrls[jj];

                    // Many servers will use the '/discovery' suffix for the discovery endpoint.
                    // The URL without this prefix should be the base URL for the server.
                    if (discoveryUrl.EndsWith(
                        ConfiguredEndpoint.DiscoverySuffix, StringComparison.OrdinalIgnoreCase))
                    {
                        discoveryUrl =
                            discoveryUrl[..^ConfiguredEndpoint.DiscoverySuffix.Length];
                    }

                    // ensure duplicates do not get added.
                    if (!serverUrls.Exists(serverUrl =>
                            serverUrl.Equals(discoveryUrl, StringComparison.OrdinalIgnoreCase)))
                    {
                        serverUrls.Add(discoveryUrl);
                    }
                }
            }

            return serverUrls;
        }

        /// <summary>
        /// Finds the endpoint that best matches the current settings.
        /// </summary>
        public static ValueTask<EndpointDescription?> SelectEndpointAsync(
            ApplicationConfiguration application,
            ITransportWaitingConnection connection,
            bool useSecurity,
            ITelemetryContext telemetry,
            CancellationToken ct = default)
        {
            return SelectEndpointAsync(
                application,
                connection,
                useSecurity,
                DefaultDiscoverTimeout,
                telemetry,
                ct);
        }

        /// <summary>
        /// Finds the endpoint that best matches the current settings.
        /// </summary>
        /// <exception cref="ServiceResultException"></exception>
        public static async ValueTask<EndpointDescription?> SelectEndpointAsync(
            ApplicationConfiguration application,
            ITransportWaitingConnection connection,
            bool useSecurity,
            int discoverTimeout,
            ITelemetryContext telemetry,
            CancellationToken ct = default)
        {
            var endpointConfiguration = EndpointConfiguration.Create(application);
            endpointConfiguration.OperationTimeout = discoverTimeout > 0
                ? discoverTimeout
                : DefaultDiscoverTimeout;

            using DiscoveryClient client = await DiscoveryClient.CreateAsync(
                application,
                connection,
                endpointConfiguration,
                ct: ct).ConfigureAwait(false);
            var url = new Uri(client.Endpoint?.EndpointUrl ??
                throw ServiceResultException.Unexpected("Endpoint missing"));
            ArrayOf<EndpointDescription> endpoints =
                await client.GetEndpointsAsync(default, ct).ConfigureAwait(false);
            return SelectEndpoint(
                application,
                url,
                endpoints,
                useSecurity,
                telemetry);
        }

        /// <summary>
        /// Finds the endpoint that best matches the current settings.
        /// </summary>
        /// <param name="application">The application configuration.</param>
        /// <param name="discoveryUrl">The discovery URL.</param>
        /// <param name="useSecurity">if set to <c>true</c> select an endpoint
        /// that uses security.</param>
        /// <param name="telemetry">The telemetry context to use to create obvservability instruments</param>
        /// <param name="ct">Cancellation token to cancel operation with</param>
        /// <returns>The best available endpoint.</returns>
        public static ValueTask<EndpointDescription?> SelectEndpointAsync(
            ApplicationConfiguration application,
            string discoveryUrl,
            bool useSecurity,
            ITelemetryContext telemetry,
            CancellationToken ct = default)
        {
            return SelectEndpointAsync(
                application,
                discoveryUrl,
                useSecurity,
                DefaultDiscoverTimeout,
                telemetry,
                ct);
        }

        /// <summary>
        /// Finds the endpoint that best matches the current settings.
        /// </summary>
        /// <param name="application">The application configuration.</param>
        /// <param name="discoveryUrl">The discovery URL.</param>
        /// <param name="useSecurity">if set to <c>true</c> select an endpoint that uses security.</param>
        /// <param name="discoverTimeout">The timeout for the discover operation.</param>
        /// <param name="telemetry">The telemetry context to use to create obvservability instruments</param>
        /// <param name="ct">Cancellation token to cancel operation with</param>
        /// <returns>The best available endpoint.</returns>
        /// <exception cref="ServiceResultException"></exception>
        public static async ValueTask<EndpointDescription?> SelectEndpointAsync(
            ApplicationConfiguration application,
            string discoveryUrl,
            bool useSecurity,
            int discoverTimeout,
            ITelemetryContext telemetry,
            CancellationToken ct = default)
        {
            Uri uri = GetDiscoveryUrl(discoveryUrl);
            var endpointConfiguration = EndpointConfiguration.Create(application);
            endpointConfiguration.OperationTimeout = discoverTimeout;

            using DiscoveryClient client = await DiscoveryClient.CreateAsync(
                application,
                uri,
                endpointConfiguration,
                ct: ct).ConfigureAwait(false);

            // Connect to the server's discovery endpoint and find the available configuration.
            var url = new Uri(client.Endpoint?.EndpointUrl ??
                throw ServiceResultException.Unexpected("Endpoint missing"));
            ArrayOf<EndpointDescription> endpoints =
                await client.GetEndpointsAsync(default, ct).ConfigureAwait(false);
            EndpointDescription? selectedEndpoint = SelectEndpoint(
                application,
                url,
                endpoints,
                useSecurity,
                telemetry);

            if (selectedEndpoint != null)
            {
                Uri? endpointUrl = Utils.ParseUri(selectedEndpoint.EndpointUrl);
                if (endpointUrl != null && endpointUrl.Scheme == uri.Scheme)
                {
                    var builder = new UriBuilder(endpointUrl)
                    {
                        Host = uri.IdnHost,
                        Port = uri.Port
                    };
                    selectedEndpoint.EndpointUrl = builder.ToString();
                }
            }
            return selectedEndpoint;
        }

        /// <summary>
        /// Select the best supported endpoint from the
        /// EndpointDescriptions, with or without security.
        /// </summary>
        public static EndpointDescription? SelectEndpoint(
            ApplicationConfiguration configuration,
            Uri url,
            ArrayOf<EndpointDescription> endpoints,
            bool useSecurity,
            ITelemetryContext telemetry)
        {
            EndpointDescription? selectedEndpoint = null;

            // select the best endpoint to use based on the selected URL and the UseSecurity checkbox.
            for (int ii = 0; ii < endpoints.Count; ii++)
            {
                EndpointDescription endpoint = endpoints[ii];

                // check for a match on the URL scheme.
                if (endpoint.EndpointUrl != null &&
                    endpoint.EndpointUrl.StartsWith(url.Scheme, StringComparison.Ordinal))
                {
                    // check if security was requested.
                    if (useSecurity)
                    {
                        if (endpoint.SecurityMode == MessageSecurityMode.None)
                        {
                            continue;
                        }

                        if (configuration != null)
                        {
                            // skip unsupported security policies
                            if (!configuration.SecurityConfiguration.SupportedSecurityPolicies
                                    .Contains(p => p == endpoint.SecurityPolicyUri))
                            {
                                continue;
                            }
                        }
                        else
                        {
                            // skip unsupported security policies, for backward compatibility only
                            // may contain policies for which no certificate is available
                            // SecurityPolicyUri is annotated nullable on EndpointDescription but is
                            // populated for any endpoint advertising security; downstream API takes
                            // a non-nullable string parameter.
                            if (SecurityPolicies.GetDisplayName(endpoint.SecurityPolicyUri!) == null)
                            {
                                continue;
                            }
                        }
                    }
                    else if (endpoint.SecurityMode != MessageSecurityMode.None)
                    {
                        continue;
                    }

                    // pick the first available endpoint by default.
                    selectedEndpoint ??= endpoint;

                    ILogger logger = telemetry.CreateLogger<DiscoveryClient>();

                    //Select endpoint if it has a higher calculated security level, than the previously selected one
                    // SecurityPolicyUri is populated for any endpoint reaching this code path
                    // (security mode != None); CalculateSecurityLevel takes a non-nullable string.
                    if (SecuredApplication.CalculateSecurityLevel(
                            endpoint.SecurityMode,
                            endpoint.SecurityPolicyUri!,
                            logger) >
                        SecuredApplication.CalculateSecurityLevel(
                            selectedEndpoint.SecurityMode,
                            selectedEndpoint.SecurityPolicyUri!,
                            logger))
                    {
                        selectedEndpoint = endpoint;
                    }
                }
            }

            // pick the first available endpoint by default.
            if (selectedEndpoint == null && endpoints.Count > 0)
            {
                selectedEndpoint = endpoints.Find(e =>
                    e.EndpointUrl?.StartsWith(url.Scheme, StringComparison.Ordinal) == true);
            }

            // return the selected endpoint.
            return selectedEndpoint;
        }

        /// <summary>
        /// Convert the discoveryUrl to a Uri and modify endpoint as per connection scheme if required.
        /// </summary>
        public static Uri GetDiscoveryUrl(string discoveryUrl)
        {
            // needs to add the '/discovery' back onto non-UA TCP URLs.
            if (Utils.IsUriHttpRelatedScheme(discoveryUrl) &&
                !discoveryUrl.EndsWith(
                    ConfiguredEndpoint.DiscoverySuffix,
                    StringComparison.OrdinalIgnoreCase))
            {
                discoveryUrl += ConfiguredEndpoint.DiscoverySuffix;
            }

            // parse the selected URL.
            return new Uri(discoveryUrl);
        }
    }
}