using System;
using System.Collections.Generic;
using System.Threading;
using System.Threading.Tasks;
using Grpc.Net.Client;
using Microsoft.Extensions.Logging;
using ProtoBuf.Grpc.Client;
using ZB.MOM.WW.LmxProxy.Client.Domain;
using ZB.MOM.WW.LmxProxy.Client.Security;

namespace ZB.MOM.WW.LmxProxy.Client
{
    public partial class LmxProxyClient
    {
        /// <summary>
        /// Connects to the LmxProxy service and establishes a session
        /// </summary>
        /// <param name="cancellationToken">Cancellation token.</param>
        public async Task ConnectAsync(CancellationToken cancellationToken = default)
        {
            GrpcChannel? provisionalChannel = null;

            await _connectionLock.WaitAsync(cancellationToken);
            try
            {
                if (_disposed)
                {
                    throw new ObjectDisposedException(nameof(LmxProxyClient));
                }

                if (_isConnected && _client != null && !string.IsNullOrEmpty(_sessionId))
                {
                    _logger.LogDebug("LmxProxyClient already connected to {Host}:{Port} with session {SessionId}",
                        _host, _port, _sessionId);
                    return;
                }

                string securityMode = _tlsConfiguration?.UseTls == true ? "TLS/SSL" : "INSECURE";
                _logger.LogInformation("Creating new {SecurityMode} connection to LmxProxy at {Host}:{Port}",
                    securityMode, _host, _port);

                Uri endpoint = BuildEndpointUri();
                provisionalChannel = GrpcChannelFactory.CreateChannel(endpoint, _tlsConfiguration, _logger);

                // Create code-first gRPC client
                IScadaService provisionalClient = provisionalChannel.CreateGrpcService<IScadaService>();

                // Establish session with the server
                var connectRequest = new ConnectRequest
                {
                    ClientId = $"ScadaBridge-{Guid.NewGuid():N}",
                    ApiKey = _apiKey ?? string.Empty
                };

                ConnectResponse connectResponse = await provisionalClient.ConnectAsync(connectRequest);

                if (!connectResponse.Success)
                {
                    provisionalChannel.Dispose();
                    throw new InvalidOperationException($"Failed to establish session: {connectResponse.Message}");
                }

                // Dispose any existing channel before replacing it
                _channel?.Dispose();

                _channel = provisionalChannel;
                _client = provisionalClient;
                _sessionId = connectResponse.SessionId;
                _isConnected = true;

                provisionalChannel = null;

                StartKeepAlive();

                _logger.LogInformation("Successfully connected to LmxProxy with session {SessionId}", _sessionId);
            }
            catch (Exception ex)
            {
                _isConnected = false;
                _client = null;
                _sessionId = string.Empty;
                _logger.LogError(ex, "Failed to connect to LmxProxy");
                throw;
            }
            finally
            {
                provisionalChannel?.Dispose();
                _connectionLock.Release();
            }
        }

        private void StartKeepAlive()
        {
            StopKeepAlive();

            _keepAliveTimer = new Timer(async _ =>
            {
                try
                {
                    if (_isConnected && _client != null && !string.IsNullOrEmpty(_sessionId))
                    {
                        // Send a lightweight ping to keep session alive
                        var request = new GetConnectionStateRequest { SessionId = _sessionId };
                        await _client.GetConnectionStateAsync(request);

                        _logger.LogDebug("Keep-alive ping sent successfully for session {SessionId}", _sessionId);
                    }
                }
                catch (Exception ex)
                {
                    _logger.LogDebug(ex, "Keep-alive ping failed");
                    StopKeepAlive();
                    await MarkDisconnectedAsync(ex).ConfigureAwait(false);
                }
            }, null, _keepAliveInterval, _keepAliveInterval);
        }

        private void StopKeepAlive()
        {
            _keepAliveTimer?.Dispose();
            _keepAliveTimer = null;
        }

        /// <summary>
        /// Disconnects from the LmxProxy service
        /// </summary>
        public async Task DisconnectAsync()
        {
            await _connectionLock.WaitAsync();
            try
            {
                StopKeepAlive();

                if (_client != null && !string.IsNullOrEmpty(_sessionId))
                {
                    try
                    {
                        var request = new DisconnectRequest { SessionId = _sessionId };
                        await _client.DisconnectAsync(request);
                        _logger.LogInformation("Session {SessionId} disconnected", _sessionId);
                    }
                    catch (Exception ex)
                    {
                        _logger.LogWarning(ex, "Error during disconnect");
                    }
                }

                _client = null;
                _sessionId = string.Empty;
                _isConnected = false;

                _channel?.Dispose();
                _channel = null;
            }
            finally
            {
                _connectionLock.Release();
            }
        }

        /// <summary>
        /// Connects the LmxProxy to MxAccess (legacy method - session now established in ConnectAsync)
        /// </summary>
        /// <param name="cancellationToken">Cancellation token.</param>
        public Task<(bool Success, string? ErrorMessage)> ConnectToMxAccessAsync(CancellationToken cancellationToken = default)
        {
            // Session is now established in ConnectAsync
            if (IsConnected)
                return Task.FromResult((true, (string?)null));

            return Task.FromResult<(bool Success, string? ErrorMessage)>((false, "Not connected. Call ConnectAsync first."));
        }

        /// <summary>
        /// Disconnects the LmxProxy from MxAccess (legacy method)
        /// </summary>
        /// <param name="cancellationToken">Cancellation token.</param>
        public async Task<(bool Success, string? ErrorMessage)> DisconnectFromMxAccessAsync(CancellationToken cancellationToken = default)
        {
            try
            {
                await DisconnectAsync();
                return (true, null);
            }
            catch (Exception ex)
            {
                return (false, ex.Message);
            }
        }

        /// <summary>
        /// Gets the connection state of the LmxProxy
        /// </summary>
        /// <param name="cancellationToken">Cancellation token.</param>
        public async Task<(bool IsConnected, string? ClientId)> GetConnectionStateAsync(CancellationToken cancellationToken = default)
        {
            EnsureConnected();

            var request = new GetConnectionStateRequest { SessionId = _sessionId };
            GetConnectionStateResponse response = await _client!.GetConnectionStateAsync(request);
            return (response.IsConnected, response.ClientId);
        }

        /// <summary>
        /// Builds the gRPC endpoint URI (http/https) based on TLS configuration.
        /// </summary>
        private Uri BuildEndpointUri()
        {
            string scheme = _tlsConfiguration?.UseTls == true ? Uri.UriSchemeHttps : Uri.UriSchemeHttp;
            return new UriBuilder
            {
                Scheme = scheme,
                Host = _host,
                Port = _port
            }.Uri;
        }

        private async Task MarkDisconnectedAsync(Exception? ex = null)
        {
            if (_disposed)
                return;

            await _connectionLock.WaitAsync().ConfigureAwait(false);
            try
            {
                _isConnected = false;
                _client = null;
                _sessionId = string.Empty;
                _channel?.Dispose();
                _channel = null;
            }
            finally
            {
                _connectionLock.Release();
            }

            List<ISubscription> subsToDispose;
            lock (_subscriptionLock)
            {
                subsToDispose = new List<ISubscription>(_activeSubscriptions);
                _activeSubscriptions.Clear();
            }

            foreach (ISubscription sub in subsToDispose)
            {
                try
                {
                    await sub.DisposeAsync().ConfigureAwait(false);
                }
                catch (Exception disposeEx)
                {
                    _logger.LogWarning(disposeEx, "Error disposing subscription after disconnect");
                }
            }

            if (ex != null)
            {
                _logger.LogWarning(ex, "Connection marked disconnected due to keep-alive failure");
            }
        }
    }
}