using System.Net.Http;
using Grpc.Core;
using Grpc.Net.Client;
using ScadaLink.DataConnectionLayer.Adapters.LmxProxy.Grpc;

namespace ScadaLink.DataConnectionLayer.Adapters;

/// <summary>
/// Production ILmxProxyClient that talks to the LmxProxy gRPC service
/// using proto-generated client stubs with x-api-key header injection.
/// </summary>
internal class RealLmxProxyClient : ILmxProxyClient
{
    private readonly string _host;
    private readonly int _port;
    private readonly string? _apiKey;
    private readonly int _samplingIntervalMs;
    private readonly bool _useTls;
    private GrpcChannel? _channel;
    private ScadaService.ScadaServiceClient? _client;
    private string? _sessionId;
    private Metadata? _headers;

    public RealLmxProxyClient(string host, int port, string? apiKey, int samplingIntervalMs = 0, bool useTls = false)
    {
        _host = host;
        _port = port;
        _apiKey = apiKey;
        _samplingIntervalMs = samplingIntervalMs;
        _useTls = useTls;
    }

    public bool IsConnected => _client != null && !string.IsNullOrEmpty(_sessionId);

    public async Task ConnectAsync(CancellationToken cancellationToken = default)
    {
        if (!_useTls)
            AppContext.SetSwitch("System.Net.Http.SocketsHttpHandler.Http2UnencryptedSupport", true);

        var scheme = _useTls ? "https" : "http";
        _channel = GrpcChannel.ForAddress($"{scheme}://{_host}:{_port}");
        _client = new ScadaService.ScadaServiceClient(_channel);

        _headers = new Metadata();
        if (!string.IsNullOrEmpty(_apiKey))
            _headers.Add("x-api-key", _apiKey);

        var response = await _client.ConnectAsync(new ConnectRequest
        {
            ClientId = $"ScadaLink-{Guid.NewGuid():N}",
            ApiKey = _apiKey ?? string.Empty
        }, _headers, cancellationToken: cancellationToken);

        if (!response.Success)
            throw new InvalidOperationException($"LmxProxy connect failed: {response.Message}");

        _sessionId = response.SessionId;
    }

    public async Task DisconnectAsync()
    {
        if (_client != null && !string.IsNullOrEmpty(_sessionId))
        {
            try { await _client.DisconnectAsync(new DisconnectRequest { SessionId = _sessionId }, _headers); }
            catch { /* best-effort */ }
        }
        _client = null;
        _sessionId = null;
    }

    public async Task<LmxVtq> ReadAsync(string address, CancellationToken cancellationToken = default)
    {
        EnsureConnected();
        var response = await _client!.ReadAsync(
            new ReadRequest { SessionId = _sessionId!, Tag = address },
            _headers, cancellationToken: cancellationToken);
        if (!response.Success)
            throw new InvalidOperationException($"Read failed for '{address}': {response.Message}");
        return ConvertVtq(response.Vtq);
    }

    public async Task<IDictionary<string, LmxVtq>> ReadBatchAsync(IEnumerable<string> addresses, CancellationToken cancellationToken = default)
    {
        EnsureConnected();
        var request = new ReadBatchRequest { SessionId = _sessionId! };
        request.Tags.AddRange(addresses);
        var response = await _client!.ReadBatchAsync(request, _headers, cancellationToken: cancellationToken);
        if (!response.Success)
            throw new InvalidOperationException($"ReadBatch failed: {response.Message}");
        return response.Vtqs.ToDictionary(v => v.Tag, v => ConvertVtq(v));
    }

    public async Task WriteAsync(string address, object value, CancellationToken cancellationToken = default)
    {
        EnsureConnected();
        var response = await _client!.WriteAsync(new WriteRequest
        {
            SessionId = _sessionId!,
            Tag = address,
            Value = value?.ToString() ?? string.Empty
        }, _headers, cancellationToken: cancellationToken);
        if (!response.Success)
            throw new InvalidOperationException($"Write failed for '{address}': {response.Message}");
    }

    public async Task WriteBatchAsync(IDictionary<string, object> values, CancellationToken cancellationToken = default)
    {
        EnsureConnected();
        var request = new WriteBatchRequest { SessionId = _sessionId! };
        request.Items.AddRange(values.Select(kv => new WriteItem
        {
            Tag = kv.Key,
            Value = kv.Value?.ToString() ?? string.Empty
        }));
        var response = await _client!.WriteBatchAsync(request, _headers, cancellationToken: cancellationToken);
        if (!response.Success)
            throw new InvalidOperationException($"WriteBatch failed: {response.Message}");
    }

    public Task<ILmxSubscription> SubscribeAsync(IEnumerable<string> addresses, Action<string, LmxVtq> onUpdate, Action? onStreamError = null, CancellationToken cancellationToken = default)
    {
        EnsureConnected();
        var tags = addresses.ToList();
        var cts = CancellationTokenSource.CreateLinkedTokenSource(cancellationToken);

        var request = new SubscribeRequest { SessionId = _sessionId!, SamplingMs = _samplingIntervalMs };
        request.Tags.AddRange(tags);

        var call = _client!.Subscribe(request, _headers, cancellationToken: cts.Token);

        _ = Task.Run(async () =>
        {
            try
            {
                while (await call.ResponseStream.MoveNext(cts.Token))
                {
                    var msg = call.ResponseStream.Current;
                    onUpdate(msg.Tag, ConvertVtq(msg));
                }
                // Stream ended normally (server closed) — treat as disconnect
                _sessionId = null;
                onStreamError?.Invoke();
            }
            catch (OperationCanceledException) { }
            catch (RpcException ex) when (ex.StatusCode == StatusCode.Cancelled) { }
            catch (RpcException)
            {
                // gRPC error (server offline, network failure) — signal disconnect
                _sessionId = null;
                onStreamError?.Invoke();
            }
        }, cts.Token);

        return Task.FromResult<ILmxSubscription>(new CtsSubscription(cts));
    }

    public async ValueTask DisposeAsync()
    {
        await DisconnectAsync();
        _channel?.Dispose();
        _channel = null;
    }

    private void EnsureConnected()
    {
        if (_client == null || string.IsNullOrEmpty(_sessionId))
            throw new InvalidOperationException("LmxProxy client is not connected.");
    }

    private static LmxVtq ConvertVtq(VtqMessage? msg)
    {
        if (msg == null)
            return new LmxVtq(null, DateTime.UtcNow, LmxQuality.Bad);

        object? value = msg.Value;
        if (!string.IsNullOrEmpty(msg.Value))
        {
            if (double.TryParse(msg.Value, out var d)) value = d;
            else if (bool.TryParse(msg.Value, out var b)) value = b;
            else value = msg.Value;
        }

        var timestamp = new DateTime(msg.TimestampUtcTicks, DateTimeKind.Utc);
        var quality = msg.Quality?.ToUpperInvariant() switch
        {
            "GOOD" => LmxQuality.Good,
            "UNCERTAIN" => LmxQuality.Uncertain,
            _ => LmxQuality.Bad
        };
        return new LmxVtq(value, timestamp, quality);
    }

    private sealed class CtsSubscription(CancellationTokenSource cts) : ILmxSubscription
    {
        public ValueTask DisposeAsync()
        {
            cts.Cancel();
            cts.Dispose();
            return ValueTask.CompletedTask;
        }
    }
}

/// <summary>
/// Production factory that creates real LmxProxy gRPC clients.
/// </summary>
public class RealLmxProxyClientFactory : ILmxProxyClientFactory
{
    public ILmxProxyClient Create(string host, int port, string? apiKey, int samplingIntervalMs = 0, bool useTls = false)
        => new RealLmxProxyClient(host, port, apiKey, samplingIntervalMs, useTls);
}