ScadaBridge/lmxproxy/src/ZB.MOM.WW.LmxProxy.Host/MxAccess/MxAccessClient.Connection.cs

using System;
using System.Runtime.InteropServices;
using System.Threading;
using System.Threading.Tasks;
using ArchestrA.MxAccess;
using Serilog;
using ZB.MOM.WW.LmxProxy.Host.Domain;

namespace ZB.MOM.WW.LmxProxy.Host.MxAccess
{
    public sealed partial class MxAccessClient
    {
        /// <summary>
        ///     Connects to MxAccess on the STA thread.
        /// </summary>
        public async Task ConnectAsync(CancellationToken ct = default)
        {
            if (_disposed) throw new ObjectDisposedException(nameof(MxAccessClient));
            if (IsConnected) return;

            SetState(ConnectionState.Connecting);

            try
            {
                await _staThread.DispatchAsync(() =>
                {
                    // Create COM object
                    _lmxProxy = new LMXProxyServer();

                    // Wire event handlers
                    _lmxProxy.OnDataChange += OnDataChange;
                    _lmxProxy.OnWriteComplete += OnWriteComplete;

                    // Register with MxAccess
                    _connectionHandle = _lmxProxy.Register("ZB.MOM.WW.LmxProxy.Host");
                });

                lock (_lock)
                {
                    _connectedSince = DateTime.UtcNow;
                }

                SetState(ConnectionState.Connected);
                Log.Information("Connected to MxAccess (handle={Handle})", _connectionHandle);

                // Recreate any stored subscriptions from a previous connection
                await RecreateStoredSubscriptionsAsync();
            }
            catch (Exception ex)
            {
                Log.Error(ex, "Failed to connect to MxAccess");
                await CleanupComObjectsAsync();
                SetState(ConnectionState.Error, ex.Message);
                throw;
            }
        }

        /// <summary>
        ///     Disconnects from MxAccess on the STA thread.
        /// </summary>
        public async Task DisconnectAsync(CancellationToken ct = default)
        {
            if (!IsConnected) return;

            SetState(ConnectionState.Disconnecting);

            try
            {
                await _staThread.DispatchAsync(() =>
                {
                    if (_lmxProxy != null && _connectionHandle > 0)
                    {
                        try
                        {
                            // Remove event handlers first
                            _lmxProxy.OnDataChange -= OnDataChange;
                            _lmxProxy.OnWriteComplete -= OnWriteComplete;

                            // Unregister
                            _lmxProxy.Unregister(_connectionHandle);
                        }
                        catch (Exception ex)
                        {
                            Log.Warning(ex, "Error during MxAccess unregister");
                        }
                        finally
                        {
                            // Force-release COM object
                            Marshal.ReleaseComObject(_lmxProxy);
                            _lmxProxy = null;
                            _connectionHandle = 0;
                        }
                    }
                });

                SetState(ConnectionState.Disconnected);
                Log.Information("Disconnected from MxAccess");
            }
            catch (Exception ex)
            {
                Log.Error(ex, "Error during disconnect");
                SetState(ConnectionState.Error, ex.Message);
            }
        }

        /// <summary>
        ///     Starts the auto-reconnect monitor loop.
        ///     Call this after initial ConnectAsync succeeds.
        /// </summary>
        public void StartMonitorLoop()
        {
            if (!_autoReconnect) return;

            _reconnectCts = new CancellationTokenSource();
            Task.Run(() => MonitorConnectionAsync(_reconnectCts.Token));
        }

        /// <summary>
        ///     Stops the auto-reconnect monitor loop.
        /// </summary>
        public void StopMonitorLoop()
        {
            _reconnectCts?.Cancel();
        }

        /// <summary>
        ///     Auto-reconnect monitor loop. Checks connection every monitorInterval.
        ///     On disconnect, attempts reconnect. On failure, retries at next interval.
        /// </summary>
        private async Task MonitorConnectionAsync(CancellationToken ct)
        {
            Log.Information("Connection monitor loop started (interval={IntervalMs}ms)", _monitorIntervalMs);

            while (!ct.IsCancellationRequested)
            {
                try
                {
                    await Task.Delay(_monitorIntervalMs, ct);
                }
                catch (OperationCanceledException)
                {
                    break;
                }

                if (IsConnected) continue;

                Log.Information("MxAccess disconnected, attempting reconnect...");
                SetState(ConnectionState.Reconnecting);

                try
                {
                    await ConnectAsync(ct);
                    Log.Information("Reconnected to MxAccess successfully");
                }
                catch (OperationCanceledException)
                {
                    break;
                }
                catch (Exception ex)
                {
                    Log.Warning(ex, "Reconnect attempt failed, will retry in {IntervalMs}ms", _monitorIntervalMs);
                }
            }

            Log.Information("Connection monitor loop exited");
        }

        /// <summary>
        ///     Cleans up COM objects on the STA thread after a failed connection.
        /// </summary>
        private async Task CleanupComObjectsAsync()
        {
            try
            {
                await _staThread.DispatchAsync(() =>
                {
                    if (_lmxProxy != null)
                    {
                        try { _lmxProxy.OnDataChange -= OnDataChange; } catch { }
                        try { _lmxProxy.OnWriteComplete -= OnWriteComplete; } catch { }
                        try { Marshal.ReleaseComObject(_lmxProxy); } catch { }
                        _lmxProxy = null;
                    }
                    _connectionHandle = 0;
                });
            }
            catch (Exception ex)
            {
                Log.Warning(ex, "Error during COM object cleanup");
            }
        }

        /// <summary>Gets the UTC time when the connection was established.</summary>
        public DateTime ConnectedSince
        {
            get { lock (_lock) { return _connectedSince; } }
        }
    }
}