using System;
using System.Collections.Generic;
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 MXAccess client connection lifecycle behavior, including transitions, registration, and reconnect handling.
    /// </summary>
    public class MxAccessClientConnectionTests : IDisposable
    {
        private readonly StaComThread _staThread;
        private readonly FakeMxProxy _proxy;
        private readonly PerformanceMetrics _metrics;
        private readonly MxAccessClient _client;
        private readonly List<(ConnectionState Previous, ConnectionState Current)> _stateChanges = new();

        /// <summary>
        /// Initializes the connection test fixture with a fake runtime proxy and state-change recorder.
        /// </summary>
        public MxAccessClientConnectionTests()
        {
            _staThread = new StaComThread();
            _staThread.Start();
            _proxy = new FakeMxProxy();
            _metrics = new PerformanceMetrics();
            var config = new MxAccessConfiguration();
            _client = new MxAccessClient(_staThread, _proxy, config, _metrics);
            _client.ConnectionStateChanged += (_, e) => _stateChanges.Add((e.PreviousState, e.CurrentState));
        }

        /// <summary>
        /// Disposes the connection test fixture and its supporting resources.
        /// </summary>
        public void Dispose()
        {
            _client.Dispose();
            _staThread.Dispose();
            _metrics.Dispose();
        }

        /// <summary>
        /// Confirms that a newly created MXAccess client starts in the disconnected state.
        /// </summary>
        [Fact]
        public void InitialState_IsDisconnected()
        {
            _client.State.ShouldBe(ConnectionState.Disconnected);
        }

        /// <summary>
        /// Confirms that connecting drives the expected disconnected-to-connecting-to-connected transitions.
        /// </summary>
        [Fact]
        public async Task Connect_TransitionsToConnected()
        {
            await _client.ConnectAsync();

            _client.State.ShouldBe(ConnectionState.Connected);
            _stateChanges.ShouldContain(s => s.Previous == ConnectionState.Disconnected && s.Current == ConnectionState.Connecting);
            _stateChanges.ShouldContain(s => s.Previous == ConnectionState.Connecting && s.Current == ConnectionState.Connected);
        }

        /// <summary>
        /// Confirms that a successful connect registers exactly once with the runtime proxy.
        /// </summary>
        [Fact]
        public async Task Connect_RegistersCalled()
        {
            await _client.ConnectAsync();
            _proxy.RegisterCallCount.ShouldBe(1);
        }

        /// <summary>
        /// Confirms that disconnecting drives the expected shutdown transitions back to disconnected.
        /// </summary>
        [Fact]
        public async Task Disconnect_TransitionsToDisconnected()
        {
            await _client.ConnectAsync();
            await _client.DisconnectAsync();

            _client.State.ShouldBe(ConnectionState.Disconnected);
            _stateChanges.ShouldContain(s => s.Current == ConnectionState.Disconnecting);
            _stateChanges.ShouldContain(s => s.Current == ConnectionState.Disconnected);
        }

        /// <summary>
        /// Confirms that disconnecting unregisters the runtime proxy session.
        /// </summary>
        [Fact]
        public async Task Disconnect_UnregistersCalled()
        {
            await _client.ConnectAsync();
            await _client.DisconnectAsync();
            _proxy.UnregisterCallCount.ShouldBe(1);
        }

        /// <summary>
        /// Confirms that registration failures move the client into the error state.
        /// </summary>
        [Fact]
        public async Task ConnectFails_TransitionsToError()
        {
            _proxy.ShouldFailRegister = true;

            await Should.ThrowAsync<InvalidOperationException>(_client.ConnectAsync());
            _client.State.ShouldBe(ConnectionState.Error);
        }

        /// <summary>
        /// Confirms that repeated connect calls do not perform duplicate runtime registrations.
        /// </summary>
        [Fact]
        public async Task DoubleConnect_NoOp()
        {
            await _client.ConnectAsync();
            await _client.ConnectAsync(); // Should be no-op
            _proxy.RegisterCallCount.ShouldBe(1);
        }

        /// <summary>
        /// Confirms that reconnect increments the reconnect counter and restores the connected state.
        /// </summary>
        [Fact]
        public async Task Reconnect_IncrementsCount()
        {
            await _client.ConnectAsync();
            _client.ReconnectCount.ShouldBe(0);

            await _client.ReconnectAsync();
            _client.ReconnectCount.ShouldBe(1);
            _client.State.ShouldBe(ConnectionState.Connected);
        }
    }
}