/* ========================================================================
 * Copyright (c) 2005-2025 The OPC Foundation, Inc. All rights reserved.
 *
 * 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
 * files (the "Software"), to deal in the Software without
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 * copies of the Software, and to permit persons to whom the
 * Software is furnished to do so, subject to the following
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 *
 * The above copyright notice and this permission notice shall be
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 * OTHER DEALINGS IN THE SOFTWARE.
 *
 * The complete license agreement can be found here:
 * http://opcfoundation.org/License/MIT/1.00/
 * ======================================================================*/

using System;
using System.Collections.Concurrent;
using System.Collections.Generic;
using System.Globalization;
using System.Linq;
using System.Threading;
using System.Threading.Tasks;
using NUnit.Framework;
using Opc.Ua.Client;
using Opc.Ua.Client.TestFramework;
using ISession = Opc.Ua.Client.ISession;
using Subscription = Opc.Ua.Client.Subscription;

#pragma warning disable CS0618 // tests exercise the obsolete classic API

namespace Opc.Ua.Sessions.Tests
{
    /// <summary>
    /// Long-running connection stability test.
    /// </summary>
    [TestFixture]
    [SetCulture("en-us")]
    [SetUICulture("en-us")]
    [Category("Client")]
    public class ConnectionStabilityTest : ClientTestFramework
    {
        /// <summary>
        /// 5 minutes for CI
        /// </summary>
        private const int kSecurityTokenLifetimeCIMs = 5 * 60 * 1000;

        /// <summary>
        /// 10 seconds for local testing
        /// </summary>
        private const int kSecurityTokenLifetimeLocalMs = 10 * 1000;

        /// <summary>
        /// Report status every 60 seconds
        /// </summary>
        private const int kStatusReportIntervalSeconds = 60;

        /// <summary>
        /// Accept 95% of expected notifications (5% tolerance)
        /// </summary>
        private const double kNotificationToleranceRatio = 0.95;

        public ConnectionStabilityTest()
            : base(Utils.UriSchemeOpcTcp)
        {
            SupportsExternalServerUrl = true;
        }

        [Test]
        [Explicit]
        [Category("ConnectionStability")]
        public async Task ShortHaulStabilityTestAsync()
        {
            try
            {
                SecurityTokenLifetime = kSecurityTokenLifetimeLocalMs;
                await OneTimeSetUpAsync().ConfigureAwait(false);

                // 2 minutes for local testing
                await RunStabilityTestAsync(2).ConfigureAwait(false);
            }
            finally
            {
                await OneTimeTearDownAsync().ConfigureAwait(false);
            }
        }

        [Test]
        [Explicit]
        [Category("ConnectionStability")]
        public async Task LongHaulStabilityTestAsync()
        {
            try
            {
                SecurityTokenLifetime = kSecurityTokenLifetimeCIMs;
                await OneTimeSetUpAsync().ConfigureAwait(false);

                // Configurable duration for CI testing
                string envValue = Environment.GetEnvironmentVariable("TEST_DURATION_MINUTES")!;
                if (string.IsNullOrEmpty(envValue) ||
                    !int.TryParse(envValue, out int minutes) ||
                    minutes <= 0)
                {
                    minutes = 90; // Default to 90 minutes for CI
                }
                await RunStabilityTestAsync(minutes).ConfigureAwait(false);
            }
            finally
            {
                await OneTimeTearDownAsync().ConfigureAwait(false);
            }
        }

        /// <summary>
        /// Long-running test that verifies connection stability over a configurable duration.
        /// Tests that:
        /// - Connection remains stable over extended period
        /// - Subscriptions deliver all expected values (no message loss)
        /// - Security token renewals happen correctly
        /// </summary>
        private async Task RunStabilityTestAsync(int testDurationMinutes)
        {
            // Get test duration from environment variable or use default
            int testDurationSeconds = testDurationMinutes * 60;
            int tokenLifetimeMs = SecurityTokenLifetime;

            TestContext.Out.WriteLine(
                $"Starting connection stability test for {testDurationMinutes} minutes ({testDurationSeconds} seconds)");
            TestContext.Out.WriteLine(
                $"Security token lifetime: {tokenLifetimeMs / 1000} seconds ({tokenLifetimeMs / 60000.0:F1} minutes)");

            const int publishingInterval = 1000; // 1 second
            const int writerInterval = 2000;     // 2 seconds
            const int samplingInterval = 500;    // 500 ms

            var valueChanges = new ConcurrentDictionary<NodeId, int>();
            var clientHandles = new ConcurrentDictionary<uint, NodeId>();
            var errors = new ConcurrentBag<string>();

            ISession? session = null;
            Subscription? subscription = null;

            try
            {
                // Get nodes for subscription
                IDictionary<NodeId, Type> nodeIds = GetTestSetStaticMassNumeric(Session.NamespaceUris);
                if (nodeIds.Count == 0)
                {
                    Assert.Ignore("No nodes for simulation found, ignoring test.");
                }

                TestContext.Out.WriteLine($"Subscribing to {nodeIds.Count} nodes.");

                // Create session
                session = await ClientFixture.ConnectAsync(
                    ServerUrl,
                    SecurityPolicies.Basic256Sha256).ConfigureAwait(false);
                Assert.That(session, Is.Not.Null, "Failed to create session");

                // Create subscription
                subscription = new Subscription(session.DefaultSubscription)
                {
                    PublishingInterval = publishingInterval,
                    PublishingEnabled = true,
                    KeepAliveCount = 10,
                    LifetimeCount = 100,
                    MaxNotificationsPerPublish = 1000,
                    Priority = 100
                };

                // Add monitored items
                foreach (NodeId nodeId in nodeIds.Keys)
                {
                    var item = new MonitoredItem(subscription.DefaultItem)
                    {
                        StartNodeId = nodeId,
                        AttributeId = Attributes.Value,
                        MonitoringMode = MonitoringMode.Reporting,
                        SamplingInterval = samplingInterval,
                        QueueSize = 10,
                        DiscardOldest = true
                    };

                    valueChanges.TryAdd(nodeId, 0);
                    clientHandles.TryAdd(item.ClientHandle, nodeId);
                    subscription.AddItem(item);
                }

                // Set up notification callback
                subscription.FastDataChangeCallback = (sub, item, value) =>
                {
                    try
                    {
                        foreach (MonitoredItemNotification notification in item.MonitoredItems)
                        {
                            if (!StatusCode.IsGood(notification.Value.StatusCode))
                            {
                                string error = $"Bad status code received: {notification.Value.StatusCode} for client handle {notification.ClientHandle}";
                                errors.Add(error);
                                TestContext.Out.WriteLine($"ERROR: {error}");
                            }
                            else if (clientHandles.TryGetValue(notification.ClientHandle, out NodeId nodeId))
                            {
                                valueChanges.AddOrUpdate(nodeId, 1, (key, count) => count + 1);
                            }
                        }
                    }
                    catch (Exception ex)
                    {
                        string error = $"Exception in data change callback: {ex.Message}";
                        errors.Add(error);
                        TestContext.Out.WriteLine($"ERROR: {error}");
                    }
                };

                // Create subscription on server
                session.AddSubscription(subscription);
                await subscription.CreateAsync().ConfigureAwait(false);

                TestContext.Out.WriteLine($"Subscription created with {subscription.MonitoredItemCount} monitored items");

                // Wait for the subscription to deliver initial values for all nodes before
                // starting writes. This prevents the first few writes from being missed when
                // the CI machine is under load and the subscription is still starting up.
                TestContext.Out.WriteLine("Waiting for subscription to deliver initial values...");
                DateTime settleDeadline = DateTime.UtcNow.AddSeconds(15);
                while (valueChanges.Values.Sum() < nodeIds.Count && DateTime.UtcNow < settleDeadline)
                {
                    await Task.Delay(200).ConfigureAwait(false);
                }

                int settledCount = valueChanges.Values.Sum();
                TestContext.Out.WriteLine($"Subscription settled: {settledCount}/{nodeIds.Count} initial notifications received");

                // Reset counters so the measurement period starts from when the subscription
                // is confirmed active (initial-value notifications don't count as write-triggered).
                foreach (NodeId nodeId in nodeIds.Keys)
                {
                    valueChanges[nodeId] = 0;
                }

                // Create writer session
                ISession writerSession = await ClientFixture.ConnectAsync(
                    ServerUrl,
                    SecurityPolicies.Basic256Sha256).ConfigureAwait(false);
                Assert.That(writerSession, Is.Not.Null, "Failed to create writer session");

                // Writer task - continuously write values
                int writeCount = 0;
                using var writerCts = new CancellationTokenSource();
                var writerTask = Task.Run(async () =>
                {
                    while (!writerCts.IsCancellationRequested)
                    {
                        writeCount++;
                        var nodesToWrite = new List<WriteValue>();

                        foreach (KeyValuePair<NodeId, Type> node in nodeIds)
                        {
                            nodesToWrite.Add(new WriteValue
                            {
                                NodeId = node.Key,
                                AttributeId = Attributes.Value,
                                Value = new DataValue(
                                    new Variant(
                                        Convert.ChangeType(writeCount, node.Value, CultureInfo.InvariantCulture)
                                    )
                                )
                            });
                        }

                        try
                        {
                            await writerSession.WriteAsync(null, nodesToWrite, writerCts.Token).ConfigureAwait(false);
                        }
                        catch (ServiceResultException sre)
                            when (sre.StatusCode == StatusCodes.BadRequestInterrupted)
                        {
                            // BadRequestInterrupted is expected when a write is in-flight during a
                            // secure channel renewal. The channel renewal briefly interrupts the old
                            // channel before the new one activates, so this is not a test failure.
                            TestContext.Out.WriteLine(
                                $"INFO: Write interrupted during channel renewal (expected): {sre.Message}");
                        }
                        catch (Exception ex)
                        {
                            string error = $"Writer session error: {ex.Message}";
                            errors.Add(error);
                            TestContext.Out.WriteLine($"ERROR: {error}");
                        }

                        try
                        {
                            await Task.Delay(writerInterval, writerCts.Token).ConfigureAwait(false);
                        }
                        catch (OperationCanceledException)
                        {
                            break;
                        }
                    }

                    TestContext.Out.WriteLine($"Writer task completed. Total writes: {writeCount}");
                }, writerCts.Token);

                // Status reporting task
                using var statusReportingCts = new CancellationTokenSource();
                var statusTask = Task.Run(async () =>
                {
                    int reportCount = 0;

                    while (!statusReportingCts.IsCancellationRequested)
                    {
                        try
                        {
                            await Task.Delay(
                                TimeSpan.FromSeconds(kStatusReportIntervalSeconds),
                                statusReportingCts.Token).ConfigureAwait(false);
                        }
                        catch (OperationCanceledException)
                        {
                            break;
                        }

                        reportCount++;
                        int totalNotifications = valueChanges.Values.Sum();
                        int elapsedMinutes = reportCount * kStatusReportIntervalSeconds / 60;

                        TestContext.Out.WriteLine(
                            $"[Status Report {reportCount}] Elapsed: {elapsedMinutes} minutes, " +
                            $"Total notifications: {totalNotifications}, Write count: {writeCount}, Errors: {errors.Count}");

#if DEBUG
                        // Report per-node statistics
                        if (reportCount % 5 == 0) // Every 5 minutes
                        {
                            TestContext.Out.WriteLine("Per-node notification counts:");
                            foreach (KeyValuePair<NodeId, int> kvp in valueChanges.OrderBy(x => x.Key.ToString()))
                            {
                                TestContext.Out.WriteLine($"  {kvp.Key}: {kvp.Value} notifications");
                            }
                        }
#endif
                    }
                }, statusReportingCts.Token);

                // Run test for the specified duration
                TestContext.Out.WriteLine($"Test running... will complete at {DateTime.UtcNow.AddSeconds(testDurationSeconds):yyyy-MM-dd HH:mm:ss} UTC");
                await Task.Delay(TimeSpan.FromSeconds(testDurationSeconds)).ConfigureAwait(false);

                // Stop tasks
                TestContext.Out.WriteLine("Test duration elapsed. Stopping writer and status tasks...");
                await writerCts.CancelAsync().ConfigureAwait(false);
                await statusReportingCts.CancelAsync().ConfigureAwait(false);

                try
                {
                    await writerTask.ConfigureAwait(false);
                }
                catch (OperationCanceledException)
                {
                    /* expected */
                }

                try
                {
                    await statusTask.ConfigureAwait(false);
                }
                catch (OperationCanceledException)
                {
                    /* expected */
                }

                // Wait for final notifications to be processed
                TestContext.Out.WriteLine("Waiting for final notifications to be processed...");
                await Task.Delay(publishingInterval * 5).ConfigureAwait(false);

                // Verification
                TestContext.Out.WriteLine("=== Final Results ===");
                TestContext.Out.WriteLine($"Test duration: {testDurationMinutes} minutes");
                TestContext.Out.WriteLine($"Security token lifetime: {tokenLifetimeMs / 1000} seconds ({tokenLifetimeMs / 60000.0:F1} minutes)");
                TestContext.Out.WriteLine($"Expected token renewals: ~{testDurationMinutes * 60000 / tokenLifetimeMs} times");
                TestContext.Out.WriteLine($"Total write operations: {writeCount}");
                TestContext.Out.WriteLine($"Total errors: {errors.Count}");

                // Calculate expected and received notifications
                int totalNotifications = valueChanges.Values.Sum();
                int expectedMinNotifications = (writeCount - 1) * nodeIds.Count; // Allow for some timing variance

                TestContext.Out.WriteLine($"Total notifications received: {totalNotifications}");
                TestContext.Out.WriteLine($"Expected minimum notifications: {expectedMinNotifications}");

                // Per-node verification
                TestContext.Out.WriteLine("Per-node results:");
                bool allNodesReceivedData = true;
                foreach (NodeId nodeId in nodeIds.Keys)
                {
                    if (valueChanges.TryGetValue(nodeId, out int changes))
                    {
#if DEBUG
                        TestContext.Out.WriteLine($"  {nodeId}: {changes} notifications");
#endif
                        double expected = Math.Max(0, writeCount - 1) * kNotificationToleranceRatio;
                        if (changes < expected)
                        {
                            allNodesReceivedData = false;
                            TestContext.Out.WriteLine(
                                $"    WARNING: Expected at least {expected:F0} but got {changes} on {nodeId}");
                        }
                    }
                    else
                    {
                        allNodesReceivedData = false;
                        TestContext.Out.WriteLine($"  {nodeId}: 0 notifications (ERROR)");
                    }
                }

                // List all errors
                if (!errors.IsEmpty)
                {
                    TestContext.Out.WriteLine($"Errors encountered ({errors.Count}):");
                    foreach (string error in errors.Take(20)) // Show first 20 errors
                    {
                        TestContext.Out.WriteLine($"  - {error}");
                    }
                    if (errors.Count > 20)
                    {
                        TestContext.Out.WriteLine($"  ... and {errors.Count - 20} more errors");
                    }
                }

                // Cleanup writer session
                try
                {
                    await writerSession.CloseAsync().ConfigureAwait(false);
                    writerSession.Dispose();
                }
                catch (Exception ex)
                {
                    TestContext.Out.WriteLine($"Failed to close writer session: {ex.Message}");
                }

                // Assertions
                Assert.That(allNodesReceivedData, Is.True, "Not all nodes received expected data");
                Assert.That(errors, Is.Empty, $"Test encountered {errors.Count} errors");
                Assert.That(
                    totalNotifications,
                    Is.GreaterThanOrEqualTo(expectedMinNotifications),
                    "Total notifications received is less than expected minimum");

                TestContext.Out.WriteLine("Connection stability test PASSED");
            }
            finally
            {
                // Cleanup
                if (subscription != null)
                {
                    try
                    {
                        await subscription.DeleteAsync(true).ConfigureAwait(false);
                    }
                    catch (Exception ex)
                    {
                        TestContext.Out.WriteLine($"Failed to delete subscription: {ex.Message}");
                    }

                    subscription.Dispose();
                }

                if (session != null)
                {
                    try
                    {
                        await session.CloseAsync().ConfigureAwait(false);
                        session.Dispose();
                    }
                    catch (Exception ex)
                    {
                        TestContext.Out.WriteLine($"Failed to close session: {ex.Message}");
                    }
                }
            }
        }
    }
}