using System;
using System.Threading.Tasks;
using Shouldly;
using Xunit;
using ZB.MOM.WW.LmxOpcUa.Host.Configuration;
using ZB.MOM.WW.LmxOpcUa.Host.Domain;
using ZB.MOM.WW.LmxOpcUa.Host.Metrics;
using ZB.MOM.WW.LmxOpcUa.Host.MxAccess;
using ZB.MOM.WW.LmxOpcUa.Tests.Helpers;

namespace ZB.MOM.WW.LmxOpcUa.Tests.MxAccess
{
    /// <summary>
    /// Verifies the background connectivity monitor used to reconnect the MXAccess bridge after faults or stale probes.
    /// </summary>
    public class MxAccessClientMonitorTests : IDisposable
    {
        private readonly StaComThread _staThread;
        private readonly FakeMxProxy _proxy;
        private readonly PerformanceMetrics _metrics;

        /// <summary>
        /// Initializes the monitor test fixture with a shared STA thread, fake proxy, and metrics collector.
        /// </summary>
        public MxAccessClientMonitorTests()
        {
            _staThread = new StaComThread();
            _staThread.Start();
            _proxy = new FakeMxProxy();
            _metrics = new PerformanceMetrics();
        }

        /// <summary>
        /// Disposes the monitor test fixture resources.
        /// </summary>
        public void Dispose()
        {
            _staThread.Dispose();
            _metrics.Dispose();
        }

        /// <summary>
        /// Confirms that the monitor reconnects the client after an observed disconnect.
        /// </summary>
        [Fact]
        public async Task Monitor_ReconnectsOnDisconnect()
        {
            var config = new MxAccessConfiguration
            {
                MonitorIntervalSeconds = 1,
                AutoReconnect = true
            };
            var client = new MxAccessClient(_staThread, _proxy, config, _metrics);

            await client.ConnectAsync();
            await client.DisconnectAsync();

            client.StartMonitor();

            // Wait for monitor to detect disconnect and reconnect
            await Task.Delay(2500);

            client.StopMonitor();
            client.State.ShouldBe(ConnectionState.Connected);
            client.ReconnectCount.ShouldBeGreaterThan(0);
            client.Dispose();
        }

        /// <summary>
        /// Confirms that the monitor can be started and stopped without throwing.
        /// </summary>
        [Fact]
        public async Task Monitor_StopsOnCancel()
        {
            var config = new MxAccessConfiguration { MonitorIntervalSeconds = 1 };
            var client = new MxAccessClient(_staThread, _proxy, config, _metrics);

            await client.ConnectAsync();
            client.StartMonitor();
            client.StopMonitor();

            // Should not throw
            await Task.Delay(200);
            client.Dispose();
        }

        /// <summary>
        /// Confirms that a stale probe tag triggers a reconnect when monitoring is enabled.
        /// </summary>
        [Fact]
        public async Task Monitor_ProbeStale_ForcesReconnect()
        {
            var config = new MxAccessConfiguration
            {
                ProbeTag = "TestProbe",
                ProbeStaleThresholdSeconds = 2,
                MonitorIntervalSeconds = 1,
                AutoReconnect = true
            };
            var client = new MxAccessClient(_staThread, _proxy, config, _metrics);

            await client.ConnectAsync();
            client.StartMonitor();

            // Wait long enough for probe to go stale (threshold=2s, monitor interval=1s)
            // No data changes simulated → probe becomes stale → reconnect triggered
            await Task.Delay(4000);

            client.StopMonitor();
            client.ReconnectCount.ShouldBeGreaterThan(0);
            client.Dispose();
        }

        /// <summary>
        /// Confirms that fresh probe updates prevent unnecessary reconnects.
        /// </summary>
        [Fact]
        public async Task Monitor_ProbeDataChange_PreventsStaleReconnect()
        {
            var config = new MxAccessConfiguration
            {
                ProbeTag = "TestProbe",
                ProbeStaleThresholdSeconds = 2,
                MonitorIntervalSeconds = 1,
                AutoReconnect = true
            };
            var client = new MxAccessClient(_staThread, _proxy, config, _metrics);

            await client.ConnectAsync();
            client.StartMonitor();

            // Continuously simulate probe data changes to keep it fresh
            for (int i = 0; i < 8; i++)
            {
                await Task.Delay(500);
                _proxy.SimulateDataChangeByAddress("TestProbe", i, 192);
            }

            client.StopMonitor();
            // Probe was kept fresh → no reconnect should have happened
            client.ReconnectCount.ShouldBe(0);
            client.State.ShouldBe(ConnectionState.Connected);
            client.Dispose();
        }

        /// <summary>
        /// Confirms that enabling the monitor without a probe tag does not trigger false reconnects.
        /// </summary>
        [Fact]
        public async Task Monitor_NoProbeConfigured_NoFalseReconnect()
        {
            var config = new MxAccessConfiguration
            {
                ProbeTag = null, // No probe
                MonitorIntervalSeconds = 1,
                AutoReconnect = true
            };
            var client = new MxAccessClient(_staThread, _proxy, config, _metrics);

            await client.ConnectAsync();
            client.StartMonitor();

            // Wait several monitor cycles — should stay connected with no reconnects
            await Task.Delay(3000);

            client.StopMonitor();
            client.State.ShouldBe(ConnectionState.Connected);
            client.ReconnectCount.ShouldBe(0);
            client.Dispose();
        }
    }
}