using System.Collections.Concurrent;
using ZB.MOM.WW.OtOpcUa.Core.Abstractions;

namespace ZB.MOM.WW.OtOpcUa.Driver.TwinCAT;

/// <summary>
///     TwinCAT ADS driver — talks to Beckhoff PLC runtimes (TC2 + TC3) via AMS / ADS. PR 1 ships
///     the <see cref="IDriver"/> skeleton; read / write / discover / subscribe / probe / host-
///     resolver land in PRs 2 and 3.
/// </summary>
public sealed class TwinCATDriver : IDriver, IReadable, IWritable, ITagDiscovery, ISubscribable,
    IHostConnectivityProbe, IPerCallHostResolver, IDisposable, IAsyncDisposable
{
    private readonly TwinCATDriverOptions _options;
    private readonly string _driverInstanceId;
    private readonly ITwinCATClientFactory _clientFactory;
    private readonly PollGroupEngine _poll;
    private readonly Dictionary<string, DeviceState> _devices = new(StringComparer.OrdinalIgnoreCase);
    private readonly Dictionary<string, TwinCATTagDefinition> _tagsByName = new(StringComparer.OrdinalIgnoreCase);
    private DriverHealth _health = new(DriverState.Unknown, null, null);

    public event EventHandler<DataChangeEventArgs>? OnDataChange;
    public event EventHandler<HostStatusChangedEventArgs>? OnHostStatusChanged;

    public TwinCATDriver(TwinCATDriverOptions options, string driverInstanceId,
        ITwinCATClientFactory? clientFactory = null)
    {
        ArgumentNullException.ThrowIfNull(options);
        _options = options;
        _driverInstanceId = driverInstanceId;
        _clientFactory = clientFactory ?? new AdsTwinCATClientFactory();
        _poll = new PollGroupEngine(
            reader: ReadAsync,
            onChange: (handle, tagRef, snapshot) =>
                OnDataChange?.Invoke(this, new DataChangeEventArgs(handle, tagRef, snapshot)));
    }

    public string DriverInstanceId => _driverInstanceId;
    public string DriverType => "TwinCAT";

    public Task InitializeAsync(string driverConfigJson, CancellationToken cancellationToken)
    {
        _health = new DriverHealth(DriverState.Initializing, null, null);
        try
        {
            foreach (var device in _options.Devices)
            {
                var addr = TwinCATAmsAddress.TryParse(device.HostAddress)
                    ?? throw new InvalidOperationException(
                        $"TwinCAT device has invalid HostAddress '{device.HostAddress}' — expected 'ads://{{netId}}:{{port}}'.");
                _devices[device.HostAddress] = new DeviceState(addr, device);
            }
            foreach (var tag in _options.Tags) _tagsByName[tag.Name] = tag;

            if (_options.Probe.Enabled)
            {
                foreach (var state in _devices.Values)
                {
                    state.ProbeCts = new CancellationTokenSource();
                    var ct = state.ProbeCts.Token;
                    _ = Task.Run(() => ProbeLoopAsync(state, ct), ct);
                }
            }
            _health = new DriverHealth(DriverState.Healthy, DateTime.UtcNow, null);
        }
        catch (Exception ex)
        {
            _health = new DriverHealth(DriverState.Faulted, null, ex.Message);
            throw;
        }
        return Task.CompletedTask;
    }

    public async Task ReinitializeAsync(string driverConfigJson, CancellationToken cancellationToken)
    {
        await ShutdownAsync(cancellationToken).ConfigureAwait(false);
        await InitializeAsync(driverConfigJson, cancellationToken).ConfigureAwait(false);
    }

    public async Task ShutdownAsync(CancellationToken cancellationToken)
    {
        // Native subs first — disposing the handles is cheap + lets the client close its
        // notifications before the AdsClient itself goes away.
        foreach (var sub in _nativeSubs.Values)
            foreach (var r in sub.Registrations) { try { r.Dispose(); } catch { } }
        _nativeSubs.Clear();

        await _poll.DisposeAsync().ConfigureAwait(false);
        foreach (var state in _devices.Values)
        {
            try { state.ProbeCts?.Cancel(); } catch { }
            state.ProbeCts?.Dispose();
            state.ProbeCts = null;
            state.DisposeClient();
        }
        _devices.Clear();
        _tagsByName.Clear();
        _health = new DriverHealth(DriverState.Unknown, _health.LastSuccessfulRead, null);
    }

    public DriverHealth GetHealth() => _health;
    public long GetMemoryFootprint() => 0;
    public Task FlushOptionalCachesAsync(CancellationToken cancellationToken) => Task.CompletedTask;

    internal int DeviceCount => _devices.Count;
    internal DeviceState? GetDeviceState(string hostAddress) =>
        _devices.TryGetValue(hostAddress, out var s) ? s : null;

    // ---- IReadable ----

    public async Task<IReadOnlyList<DataValueSnapshot>> ReadAsync(
        IReadOnlyList<string> fullReferences, CancellationToken cancellationToken)
    {
        ArgumentNullException.ThrowIfNull(fullReferences);
        var now = DateTime.UtcNow;
        var results = new DataValueSnapshot[fullReferences.Count];

        for (var i = 0; i < fullReferences.Count; i++)
        {
            var reference = fullReferences[i];
            if (!_tagsByName.TryGetValue(reference, out var def))
            {
                results[i] = new DataValueSnapshot(null, TwinCATStatusMapper.BadNodeIdUnknown, null, now);
                continue;
            }
            if (!_devices.TryGetValue(def.DeviceHostAddress, out var device))
            {
                results[i] = new DataValueSnapshot(null, TwinCATStatusMapper.BadNodeIdUnknown, null, now);
                continue;
            }

            try
            {
                var client = await EnsureConnectedAsync(device, cancellationToken).ConfigureAwait(false);
                var parsed = TwinCATSymbolPath.TryParse(def.SymbolPath);
                var symbolName = parsed?.ToAdsSymbolName() ?? def.SymbolPath;
                var (value, status) = await client.ReadValueAsync(
                    symbolName, def.DataType, parsed?.BitIndex, cancellationToken).ConfigureAwait(false);

                results[i] = new DataValueSnapshot(value, status, now, now);
                if (status == TwinCATStatusMapper.Good)
                    _health = new DriverHealth(DriverState.Healthy, now, null);
                else
                    _health = new DriverHealth(DriverState.Degraded, _health.LastSuccessfulRead,
                        $"ADS status {status:X8} reading {reference}");
            }
            catch (OperationCanceledException) { throw; }
            catch (Exception ex)
            {
                results[i] = new DataValueSnapshot(null, TwinCATStatusMapper.BadCommunicationError, null, now);
                _health = new DriverHealth(DriverState.Degraded, _health.LastSuccessfulRead, ex.Message);
            }
        }

        return results;
    }

    // ---- IWritable ----

    public async Task<IReadOnlyList<WriteResult>> WriteAsync(
        IReadOnlyList<WriteRequest> writes, CancellationToken cancellationToken)
    {
        ArgumentNullException.ThrowIfNull(writes);
        var results = new WriteResult[writes.Count];

        for (var i = 0; i < writes.Count; i++)
        {
            var w = writes[i];
            if (!_tagsByName.TryGetValue(w.FullReference, out var def))
            {
                results[i] = new WriteResult(TwinCATStatusMapper.BadNodeIdUnknown);
                continue;
            }
            if (!def.Writable)
            {
                results[i] = new WriteResult(TwinCATStatusMapper.BadNotWritable);
                continue;
            }
            if (!_devices.TryGetValue(def.DeviceHostAddress, out var device))
            {
                results[i] = new WriteResult(TwinCATStatusMapper.BadNodeIdUnknown);
                continue;
            }

            try
            {
                var client = await EnsureConnectedAsync(device, cancellationToken).ConfigureAwait(false);
                var parsed = TwinCATSymbolPath.TryParse(def.SymbolPath);
                var symbolName = parsed?.ToAdsSymbolName() ?? def.SymbolPath;
                var status = await client.WriteValueAsync(
                    symbolName, def.DataType, parsed?.BitIndex, w.Value, cancellationToken).ConfigureAwait(false);
                results[i] = new WriteResult(status);
            }
            catch (OperationCanceledException) { throw; }
            catch (NotSupportedException nse)
            {
                results[i] = new WriteResult(TwinCATStatusMapper.BadNotSupported);
                _health = new DriverHealth(DriverState.Degraded, _health.LastSuccessfulRead, nse.Message);
            }
            catch (Exception ex) when (ex is FormatException or InvalidCastException)
            {
                results[i] = new WriteResult(TwinCATStatusMapper.BadTypeMismatch);
            }
            catch (OverflowException)
            {
                results[i] = new WriteResult(TwinCATStatusMapper.BadOutOfRange);
            }
            catch (Exception ex)
            {
                results[i] = new WriteResult(TwinCATStatusMapper.BadCommunicationError);
                _health = new DriverHealth(DriverState.Degraded, _health.LastSuccessfulRead, ex.Message);
            }
        }

        return results;
    }

    // ---- ITagDiscovery ----

    public async Task DiscoverAsync(IAddressSpaceBuilder builder, CancellationToken cancellationToken)
    {
        ArgumentNullException.ThrowIfNull(builder);
        var root = builder.Folder("TwinCAT", "TwinCAT");
        foreach (var device in _options.Devices)
        {
            var label = device.DeviceName ?? device.HostAddress;
            var deviceFolder = root.Folder(device.HostAddress, label);

            // Pre-declared tags — always emitted as the authoritative config path.
            var tagsForDevice = _options.Tags.Where(t =>
                string.Equals(t.DeviceHostAddress, device.HostAddress, StringComparison.OrdinalIgnoreCase));
            foreach (var tag in tagsForDevice)
            {
                deviceFolder.Variable(tag.Name, tag.Name, new DriverAttributeInfo(
                    FullName: tag.Name,
                    DriverDataType: tag.DataType.ToDriverDataType(),
                    IsArray: false,
                    ArrayDim: null,
                    SecurityClass: tag.Writable
                        ? SecurityClassification.Operate
                        : SecurityClassification.ViewOnly,
                    IsHistorized: false,
                    IsAlarm: false,
                    WriteIdempotent: tag.WriteIdempotent));
            }

            // Controller-side symbol browse — opt-in. Falls back to pre-declared-only on any
            // client-side error so a flaky symbol-table download doesn't block discovery.
            if (_options.EnableControllerBrowse && _devices.TryGetValue(device.HostAddress, out var state))
            {
                IAddressSpaceBuilder? discoveredFolder = null;
                try
                {
                    var client = await EnsureConnectedAsync(state, cancellationToken).ConfigureAwait(false);
                    await foreach (var sym in client.BrowseSymbolsAsync(cancellationToken).ConfigureAwait(false))
                    {
                        if (TwinCATSystemSymbolFilter.IsSystemSymbol(sym.InstancePath)) continue;
                        if (sym.DataType is not TwinCATDataType dt) continue; // unsupported type

                        discoveredFolder ??= deviceFolder.Folder("Discovered", "Discovered");
                        discoveredFolder.Variable(sym.InstancePath, sym.InstancePath, new DriverAttributeInfo(
                            FullName: sym.InstancePath,
                            DriverDataType: dt.ToDriverDataType(),
                            IsArray: false,
                            ArrayDim: null,
                            SecurityClass: sym.ReadOnly
                                ? SecurityClassification.ViewOnly
                                : SecurityClassification.Operate,
                            IsHistorized: false,
                            IsAlarm: false,
                            WriteIdempotent: false));
                    }
                }
                catch (OperationCanceledException) { throw; }
                catch
                {
                    // Symbol-loader failure is non-fatal to discovery — pre-declared tags already
                    // shipped + operators see the failure in driver health on next read.
                }
            }
        }
    }

    // ---- ISubscribable (native ADS notifications with poll fallback) ----

    private readonly ConcurrentDictionary<long, NativeSubscription> _nativeSubs = new();
    private long _nextNativeSubId;

    /// <summary>
    ///     Subscribe via native ADS notifications when <see cref="TwinCATDriverOptions.UseNativeNotifications"/>
    ///     is <c>true</c>, otherwise fall through to the shared <see cref="PollGroupEngine"/>.
    ///     Native path registers one <see cref="ITwinCATNotificationHandle"/> per tag against the
    ///     target's PLC runtime — the PLC pushes changes on its own cycle so we skip the poll
    ///     loop entirely. Unsub path disposes the handles.
    /// </summary>
    public async Task<ISubscriptionHandle> SubscribeAsync(
        IReadOnlyList<string> fullReferences, TimeSpan publishingInterval, CancellationToken cancellationToken)
    {
        if (!_options.UseNativeNotifications)
            return _poll.Subscribe(fullReferences, publishingInterval);

        var id = Interlocked.Increment(ref _nextNativeSubId);
        var handle = new NativeSubscriptionHandle(id);
        var registrations = new List<ITwinCATNotificationHandle>(fullReferences.Count);
        var now = DateTime.UtcNow;

        try
        {
            foreach (var reference in fullReferences)
            {
                if (!_tagsByName.TryGetValue(reference, out var def)) continue;
                if (!_devices.TryGetValue(def.DeviceHostAddress, out var device)) continue;

                var client = await EnsureConnectedAsync(device, cancellationToken).ConfigureAwait(false);
                var parsed = TwinCATSymbolPath.TryParse(def.SymbolPath);
                var symbolName = parsed?.ToAdsSymbolName() ?? def.SymbolPath;
                var bitIndex = parsed?.BitIndex;

                var reg = await client.AddNotificationAsync(
                    symbolName, def.DataType, bitIndex, publishingInterval,
                    (_, value) => OnDataChange?.Invoke(this,
                        new DataChangeEventArgs(handle, reference, new DataValueSnapshot(
                            value, TwinCATStatusMapper.Good, DateTime.UtcNow, DateTime.UtcNow))),
                    cancellationToken).ConfigureAwait(false);
                registrations.Add(reg);
            }
        }
        catch
        {
            // On any registration failure, tear down everything we got so far + rethrow. Leaves
            // the subscription in a clean "never existed" state rather than a half-registered
            // state the caller has to clean up.
            foreach (var r in registrations) { try { r.Dispose(); } catch { } }
            throw;
        }

        _nativeSubs[id] = new NativeSubscription(handle, registrations);
        return handle;
    }

    public Task UnsubscribeAsync(ISubscriptionHandle handle, CancellationToken cancellationToken)
    {
        if (handle is NativeSubscriptionHandle native && _nativeSubs.TryRemove(native.Id, out var sub))
        {
            foreach (var r in sub.Registrations) { try { r.Dispose(); } catch { } }
            return Task.CompletedTask;
        }
        _poll.Unsubscribe(handle);
        return Task.CompletedTask;
    }

    private sealed record NativeSubscriptionHandle(long Id) : ISubscriptionHandle
    {
        public string DiagnosticId => $"twincat-native-sub-{Id}";
    }

    private sealed record NativeSubscription(
        NativeSubscriptionHandle Handle,
        IReadOnlyList<ITwinCATNotificationHandle> Registrations);

    // ---- IHostConnectivityProbe ----

    public IReadOnlyList<HostConnectivityStatus> GetHostStatuses() =>
        [.. _devices.Values.Select(s => new HostConnectivityStatus(s.Options.HostAddress, s.HostState, s.HostStateChangedUtc))];

    private async Task ProbeLoopAsync(DeviceState state, CancellationToken ct)
    {
        while (!ct.IsCancellationRequested)
        {
            var success = false;
            try
            {
                var client = await EnsureConnectedAsync(state, ct).ConfigureAwait(false);
                success = await client.ProbeAsync(ct).ConfigureAwait(false);
            }
            catch (OperationCanceledException) when (ct.IsCancellationRequested) { break; }
            catch
            {
                // Probe failure — EnsureConnectedAsync's connect-failure path already disposed
                // + cleared the client, so next tick will reconnect.
            }

            TransitionDeviceState(state, success ? HostState.Running : HostState.Stopped);

            try { await Task.Delay(_options.Probe.Interval, ct).ConfigureAwait(false); }
            catch (OperationCanceledException) { break; }
        }
    }

    private void TransitionDeviceState(DeviceState state, HostState newState)
    {
        HostState old;
        lock (state.ProbeLock)
        {
            old = state.HostState;
            if (old == newState) return;
            state.HostState = newState;
            state.HostStateChangedUtc = DateTime.UtcNow;
        }
        OnHostStatusChanged?.Invoke(this,
            new HostStatusChangedEventArgs(state.Options.HostAddress, old, newState));
    }

    // ---- IPerCallHostResolver ----

    public string ResolveHost(string fullReference)
    {
        if (_tagsByName.TryGetValue(fullReference, out var def))
            return def.DeviceHostAddress;
        return _options.Devices.FirstOrDefault()?.HostAddress ?? DriverInstanceId;
    }

    private async Task<ITwinCATClient> EnsureConnectedAsync(DeviceState device, CancellationToken ct)
    {
        if (device.Client is { IsConnected: true } c) return c;
        device.Client ??= _clientFactory.Create();
        try
        {
            await device.Client.ConnectAsync(device.ParsedAddress, _options.Timeout, ct)
                .ConfigureAwait(false);
        }
        catch
        {
            device.Client.Dispose();
            device.Client = null;
            throw;
        }
        return device.Client;
    }

    public void Dispose() => DisposeAsync().AsTask().GetAwaiter().GetResult();
    public async ValueTask DisposeAsync() => await ShutdownAsync(CancellationToken.None).ConfigureAwait(false);

    internal sealed class DeviceState(TwinCATAmsAddress parsedAddress, TwinCATDeviceOptions options)
    {
        public TwinCATAmsAddress ParsedAddress { get; } = parsedAddress;
        public TwinCATDeviceOptions Options { get; } = options;
        public ITwinCATClient? Client { get; set; }

        public object ProbeLock { get; } = new();
        public HostState HostState { get; set; } = HostState.Unknown;
        public DateTime HostStateChangedUtc { get; set; } = DateTime.UtcNow;
        public CancellationTokenSource? ProbeCts { get; set; }

        public void DisposeClient()
        {
            Client?.Dispose();
            Client = null;
        }
    }
}