using System;
using System.Threading;
using System.Threading.Tasks;
using ZB.MOM.WW.OtOpcUa.Host.Domain;

namespace ZB.MOM.WW.OtOpcUa.Host.MxAccess
{
    public sealed partial class MxAccessClient
    {
        private Task? _monitorTask;

        /// <summary>
        ///     Starts the background monitor that reconnects dropped sessions and watches the probe tag for staleness.
        /// </summary>
        public void StartMonitor()
        {
            if (_monitorCts != null)
                StopMonitor();

            _monitorCts = new CancellationTokenSource();
            _monitorTask = Task.Run(() => MonitorLoopAsync(_monitorCts.Token));
            Log.Information("MxAccess monitor started (interval={Interval}s)", _config.MonitorIntervalSeconds);
        }

        /// <summary>
        ///     Stops the background monitor loop.
        /// </summary>
        public void StopMonitor()
        {
            _monitorCts?.Cancel();
            try { _monitorTask?.Wait(TimeSpan.FromSeconds(5)); } catch { /* timeout or faulted */ }
            _monitorTask = null;
        }

        private async Task MonitorLoopAsync(CancellationToken ct)
        {
            while (!ct.IsCancellationRequested)
            {
                try
                {
                    await Task.Delay(TimeSpan.FromSeconds(_config.MonitorIntervalSeconds), ct);
                }
                catch (OperationCanceledException)
                {
                    break;
                }

                try
                {
                    if ((_state == ConnectionState.Disconnected || _state == ConnectionState.Error) &&
                        _config.AutoReconnect)
                    {
                        Log.Information("Monitor: connection lost (state={State}), attempting reconnect", _state);
                        await ReconnectAsync();
                        continue;
                    }

                    if (_state == ConnectionState.Connected && _probeTag != null)
                    {
                        var elapsed = DateTime.UtcNow - _lastProbeValueTime;
                        if (elapsed.TotalSeconds > _config.ProbeStaleThresholdSeconds)
                        {
                            Log.Warning("Monitor: probe stale ({Elapsed:F0}s > {Threshold}s), forcing reconnect",
                                elapsed.TotalSeconds, _config.ProbeStaleThresholdSeconds);
                            await ReconnectAsync();
                        }
                    }
                }
                catch (Exception ex)
                {
                    Log.Error(ex, "Monitor loop error");
                }
            }

            Log.Information("MxAccess monitor stopped");
        }
    }
}