using System.Reactive.Linq;
using System.Reactive.Subjects;
using System.Threading.Channels;
using Microsoft.Extensions.Logging;
using TeamsISO.Engine.Discovery;
using TeamsISO.Engine.Domain;
using TeamsISO.Engine.Interop;
using TeamsISO.Engine.Persistence;
using TeamsISO.Engine.Pipeline;

namespace TeamsISO.Engine.Controller;

/// <summary>
/// Default implementation of <see cref="IIsoController"/>.
/// Holds the participant tracker, the discovery service, the pipeline dictionary, the config store,
/// and the runtime probe. Exposes participant and alert observables for the host UI.
/// </summary>
public sealed class IsoController : IIsoController
{
    private readonly INdiInterop _interop;
    private readonly Func<IsoPipelineConfig, IsoPipeline> _pipelineFactory;
    private readonly ConfigStore _configStore;
    private readonly NdiRuntimeProbe _runtimeProbe;
    private readonly ILogger<IsoController> _logger;
    private readonly TimeSpan _renameWindow;
    private readonly TimeSpan _discoveryInterval;

    private readonly ParticipantTracker _tracker;
    private readonly Channel<DiscoveryEvent> _discoveryChannel;
    private readonly NdiDiscoveryService _discovery;
    private readonly Dictionary<Guid, IsoPipeline> _pipelines = new();
    private readonly BehaviorSubject<IReadOnlyList<Participant>> _participants =
        new(Array.Empty<Participant>());
    private readonly Subject<EngineAlert> _alerts = new();
    private readonly object _gate = new();

    private FrameProcessingSettings _settings;
    private CancellationTokenSource? _cts;
    private Task? _discoveryTask;
    private Task? _eventPumpTask;

    public IObservable<IReadOnlyList<Participant>> Participants => _participants.AsObservable();
    public IObservable<EngineAlert> Alerts => _alerts.AsObservable();
    public FrameProcessingSettings GlobalSettings { get { lock (_gate) return _settings; } }

    public IsoController(
        INdiInterop interop,
        Func<IsoPipelineConfig, IsoPipeline> pipelineFactory,
        ConfigStore configStore,
        NdiRuntimeProbe runtimeProbe,
        ILoggerFactory loggerFactory,
        TimeSpan? renameWindow = null,
        TimeSpan? discoveryInterval = null,
        Func<DateTimeOffset>? clock = null)
    {
        _interop = interop;
        _pipelineFactory = pipelineFactory;
        _configStore = configStore;
        _runtimeProbe = runtimeProbe;
        _logger = loggerFactory.CreateLogger<IsoController>();
        _renameWindow = renameWindow ?? TimeSpan.FromSeconds(5);
        _discoveryInterval = discoveryInterval ?? TimeSpan.FromMilliseconds(500);

        var loaded = configStore.Load();
        _settings = loaded.Global;

        _tracker = new ParticipantTracker(_renameWindow, clock ?? (() => DateTimeOffset.UtcNow));
        _discoveryChannel = Channel.CreateUnbounded<DiscoveryEvent>();
        _discovery = new NdiDiscoveryService(
            interop, _discoveryChannel.Writer,
            loggerFactory.CreateLogger<NdiDiscoveryService>());
    }

    public async Task StartAsync(CancellationToken cancellationToken)
    {
        if (_cts is not null)
            throw new InvalidOperationException("Controller already started.");
        _cts = CancellationTokenSource.CreateLinkedTokenSource(cancellationToken);

        // Runtime probe — surface alert if mismatch but don't fail startup.
        var probeResult = _runtimeProbe.Probe();
        if (probeResult is NdiRuntimeProbeResult.Mismatch mismatch)
        {
            _alerts.OnNext(new EngineAlert.NdiRuntimeMismatch(mismatch.Detected, mismatch.Expected));
            _logger.LogWarning("NDI runtime mismatch: detected {Detected}, expected {Expected}.",
                mismatch.Detected, mismatch.Expected);
        }

        _discoveryTask = _discovery.RunAsync(_discoveryInterval, _cts.Token);
        _eventPumpTask = PumpDiscoveryEventsAsync(_cts.Token);
        await Task.CompletedTask;
    }

    public IsoHealthStats GetStats(Guid participantId)
    {
        lock (_gate)
        {
            return _pipelines.TryGetValue(participantId, out var pipeline)
                ? IsoHealthStats.Empty // production wires pipeline.Stats; Phase B-1 leaves this stub
                : IsoHealthStats.Empty;
        }
    }

    public async Task EnableIsoAsync(Guid participantId, string? customName, CancellationToken cancellationToken)
    {
        Participant? p;
        lock (_gate)
        {
            if (_pipelines.ContainsKey(participantId)) return;
            p = _tracker.Participants.FirstOrDefault(x => x.Id == participantId);
        }
        if (p is null || p.CurrentSource is null)
            throw new InvalidOperationException($"Participant {participantId} not currently visible on the network.");

        var output = customName ?? DefaultOutputName(participantId);
        var config = new IsoPipelineConfig(participantId, p.CurrentSource.FullName, output, _settings);
        var pipeline = _pipelineFactory(config);

        lock (_gate) _pipelines[participantId] = pipeline;
        await pipeline.StartAsync();
        await PersistAssignmentsAsync(cancellationToken);
    }

    public async Task DisableIsoAsync(Guid participantId, CancellationToken cancellationToken)
    {
        IsoPipeline? pipeline;
        lock (_gate)
        {
            if (!_pipelines.Remove(participantId, out pipeline)) return;
        }
        await pipeline.StopAsync();
        await pipeline.DisposeAsync();
        await PersistAssignmentsAsync(cancellationToken);
    }

    public Task SetGlobalSettingsAsync(FrameProcessingSettings settings, CancellationToken cancellationToken)
    {
        lock (_gate) _settings = settings;
        return PersistAssignmentsAsync(cancellationToken);
    }

    private Task PersistAssignmentsAsync(CancellationToken cancellationToken)
    {
        try
        {
            FrameProcessingSettings settings;
            IReadOnlyList<IsoAssignment> assignments;
            lock (_gate)
            {
                settings = _settings;
                assignments = _pipelines.Keys.Select(id =>
                    new IsoAssignment(id, IsEnabled: true, CustomOutputName: null)).ToArray();
            }
            _configStore.Save(new EngineConfig(settings, assignments));
        }
        catch (Exception ex)
        {
            _alerts.OnNext(new EngineAlert.ConfigSaveFailed(ex.Message));
            _logger.LogWarning(ex, "Failed to persist engine config.");
        }
        return Task.CompletedTask;
    }

    private async Task PumpDiscoveryEventsAsync(CancellationToken cancellationToken)
    {
        try
        {
            await foreach (var ev in _discoveryChannel.Reader.ReadAllAsync(cancellationToken))
            {
                lock (_gate)
                {
                    _tracker.Apply(ev);
                    _participants.OnNext(_tracker.Participants);
                }
            }
        }
        catch (OperationCanceledException) { }
    }

    private static string DefaultOutputName(Guid participantId) =>
        $"TEAMSISO_{participantId.ToString("N")[..8].ToUpperInvariant()}";

    public async ValueTask DisposeAsync()
    {
        _cts?.Cancel();
        if (_eventPumpTask is not null)
        {
            try { await _eventPumpTask; } catch { /* swallow */ }
        }
        if (_discoveryTask is not null)
        {
            try { await _discoveryTask; } catch { /* swallow */ }
        }
        IsoPipeline[] toDispose;
        lock (_gate)
        {
            toDispose = _pipelines.Values.ToArray();
            _pipelines.Clear();
        }
        foreach (var p in toDispose) await p.DisposeAsync();
        _alerts.OnCompleted();
        _participants.OnCompleted();
        _cts?.Dispose();
    }
}