using System;
using System.Threading.Tasks;
using Shouldly;
using Xunit;
using ZB.MOM.WW.OtOpcUa.Tests.Helpers;

namespace ZB.MOM.WW.OtOpcUa.Tests.OpcUa
{
    /// <summary>
    ///     Verifies that subscription and unsubscription failures in the MXAccess client
    ///     are handled gracefully by the node manager instead of silently lost.
    /// </summary>
    public class LmxNodeManagerSubscriptionFaultTests
    {
        /// <summary>
        ///     Confirms that a faulted SubscribeAsync is caught and logged rather than silently discarded.
        /// </summary>
        [Fact]
        public async Task SubscribeTag_WhenClientFaults_DoesNotThrowAndDoesNotHang()
        {
            var mxClient = new FakeMxAccessClient
            {
                SubscribeException = new InvalidOperationException("COM connection lost")
            };
            var fixture = OpcUaServerFixture.WithFakeMxAccessClient(mxClient);
            await fixture.InitializeAsync();
            try
            {
                var nodeManager = fixture.Service.NodeManagerInstance!;

                // SubscribeTag should catch the fault — not throw and not hang
                Should.NotThrow(() => nodeManager.SubscribeTag("TestMachine_001.MachineID"));
            }
            finally
            {
                await fixture.DisposeAsync();
            }
        }

        /// <summary>
        ///     Confirms that a faulted UnsubscribeAsync is caught and logged rather than silently discarded.
        /// </summary>
        [Fact]
        public async Task UnsubscribeTag_WhenClientFaults_DoesNotThrowAndDoesNotHang()
        {
            var mxClient = new FakeMxAccessClient();
            var fixture = OpcUaServerFixture.WithFakeMxAccessClient(mxClient);
            await fixture.InitializeAsync();
            try
            {
                var nodeManager = fixture.Service.NodeManagerInstance!;

                // Subscribe first (succeeds)
                nodeManager.SubscribeTag("TestMachine_001.MachineID");
                mxClient.ActiveSubscriptionCount.ShouldBe(1);

                // Now inject fault for unsubscribe
                mxClient.UnsubscribeException = new InvalidOperationException("COM connection lost");

                // UnsubscribeTag should catch the fault — not throw and not hang
                Should.NotThrow(() => nodeManager.UnsubscribeTag("TestMachine_001.MachineID"));
            }
            finally
            {
                await fixture.DisposeAsync();
            }
        }

        /// <summary>
        ///     Confirms that subscription failure does not corrupt the ref-count bookkeeping,
        ///     allowing a retry to succeed after the fault clears.
        /// </summary>
        [Fact]
        public async Task SubscribeTag_AfterFaultClears_CanSubscribeAgain()
        {
            var mxClient = new FakeMxAccessClient
            {
                SubscribeException = new InvalidOperationException("transient fault")
            };
            var fixture = OpcUaServerFixture.WithFakeMxAccessClient(mxClient);
            await fixture.InitializeAsync();
            try
            {
                var nodeManager = fixture.Service.NodeManagerInstance!;

                // First subscribe faults (caught)
                nodeManager.SubscribeTag("TestMachine_001.MachineID");
                mxClient.ActiveSubscriptionCount.ShouldBe(0); // subscribe failed

                // Clear the fault
                mxClient.SubscribeException = null;

                // Unsubscribe to reset ref count, then subscribe again
                nodeManager.UnsubscribeTag("TestMachine_001.MachineID");
                nodeManager.SubscribeTag("TestMachine_001.MachineID");
                mxClient.ActiveSubscriptionCount.ShouldBe(1);
            }
            finally
            {
                await fixture.DisposeAsync();
            }
        }
    }
}