using System;
using System.Collections.Generic;
using System.Globalization;
using System.Linq;
using System.Text.Json;
using System.Threading;
using System.Threading.Channels;
using System.Threading.Tasks;
using Grpc.Core;
using Serilog;
using ZB.MOM.WW.LmxProxy.Host.Domain;
using ZB.MOM.WW.LmxProxy.Host.Security;
using ZB.MOM.WW.LmxProxy.Host.Services;
using ZB.MOM.WW.LmxProxy.Host.Grpc;

namespace ZB.MOM.WW.LmxProxy.Host.Grpc.Services
{
    /// <summary>
    ///     gRPC service implementation for SCADA operations.
    ///     Provides methods for connecting, reading, writing, batch operations, and subscriptions.
    /// </summary>
    public class ScadaGrpcService : ScadaService.ScadaServiceBase
    {
        private static readonly ILogger Logger = Log.ForContext<ScadaGrpcService>();

        private readonly PerformanceMetrics _performanceMetrics;
        private readonly IScadaClient _scadaClient;
        private readonly SessionManager _sessionManager;
        private readonly SubscriptionManager _subscriptionManager;

        /// <summary>
        ///     Initializes a new instance of the <see cref="ScadaGrpcService" /> class.
        /// </summary>
        /// <param name="scadaClient">The SCADA client instance.</param>
        /// <param name="subscriptionManager">The subscription manager instance.</param>
        /// <param name="sessionManager">The session manager instance.</param>
        /// <param name="performanceMetrics">Optional performance metrics service for tracking operations.</param>
        /// <exception cref="ArgumentNullException">Thrown if any required argument is null.</exception>
        public ScadaGrpcService(
            IScadaClient scadaClient,
            SubscriptionManager subscriptionManager,
            SessionManager sessionManager,
            PerformanceMetrics performanceMetrics = null)
        {
            _scadaClient = scadaClient ?? throw new ArgumentNullException(nameof(scadaClient));
            _subscriptionManager = subscriptionManager ?? throw new ArgumentNullException(nameof(subscriptionManager));
            _sessionManager = sessionManager ?? throw new ArgumentNullException(nameof(sessionManager));
            _performanceMetrics = performanceMetrics;
        }

        #region Connection Management

        /// <summary>
        ///     Creates a new session for a client.
        ///     The MxAccess connection is managed separately at server startup.
        /// </summary>
        /// <param name="request">The connection request with client ID and API key.</param>
        /// <param name="context">The gRPC server call context.</param>
        /// <returns>A <see cref="ConnectResponse" /> with session ID.</returns>
        public override Task<ConnectResponse> Connect(ConnectRequest request, ServerCallContext context)
        {
            try
            {
                Logger.Information("Connect request from {Peer} - ClientId: {ClientId}",
                    context.Peer, request.ClientId);

                // Validate that MxAccess is connected
                if (!_scadaClient.IsConnected)
                {
                    return Task.FromResult(new ConnectResponse
                    {
                        Success = false,
                        Message = "SCADA server is not connected to MxAccess",
                        SessionId = string.Empty
                    });
                }

                // Create a new session
                var sessionId = _sessionManager.CreateSession(request.ClientId, request.ApiKey);

                return Task.FromResult(new ConnectResponse
                {
                    Success = true,
                    Message = "Session created successfully",
                    SessionId = sessionId
                });
            }
            catch (Exception ex)
            {
                Logger.Error(ex, "Failed to create session for client {ClientId}", request.ClientId);
                return Task.FromResult(new ConnectResponse
                {
                    Success = false,
                    Message = ex.Message,
                    SessionId = string.Empty
                });
            }
        }

        /// <summary>
        ///     Terminates a client session.
        /// </summary>
        /// <param name="request">The disconnect request with session ID.</param>
        /// <param name="context">The gRPC server call context.</param>
        /// <returns>A <see cref="DisconnectResponse" /> indicating success or failure.</returns>
        public override Task<DisconnectResponse> Disconnect(DisconnectRequest request, ServerCallContext context)
        {
            try
            {
                Logger.Information("Disconnect request from {Peer} - SessionId: {SessionId}",
                    context.Peer, request.SessionId);

                var terminated = _sessionManager.TerminateSession(request.SessionId);

                return Task.FromResult(new DisconnectResponse
                {
                    Success = terminated,
                    Message = terminated ? "Session terminated successfully" : "Session not found"
                });
            }
            catch (Exception ex)
            {
                Logger.Error(ex, "Failed to disconnect session {SessionId}", request.SessionId);
                return Task.FromResult(new DisconnectResponse
                {
                    Success = false,
                    Message = ex.Message
                });
            }
        }

        /// <summary>
        ///     Gets the connection state for a session.
        /// </summary>
        /// <param name="request">The connection state request with session ID.</param>
        /// <param name="context">The gRPC server call context.</param>
        /// <returns>A <see cref="GetConnectionStateResponse" /> with connection details.</returns>
        public override Task<GetConnectionStateResponse> GetConnectionState(GetConnectionStateRequest request,
            ServerCallContext context)
        {
            var session = _sessionManager.GetSession(request.SessionId);

            if (session == null)
            {
                return Task.FromResult(new GetConnectionStateResponse
                {
                    IsConnected = false,
                    ClientId = string.Empty,
                    ConnectedSinceUtcTicks = 0
                });
            }

            return Task.FromResult(new GetConnectionStateResponse
            {
                IsConnected = _scadaClient.IsConnected,
                ClientId = session.ClientId,
                ConnectedSinceUtcTicks = session.ConnectedSinceUtcTicks
            });
        }

        #endregion

        #region Read Operations

        /// <summary>
        ///     Reads a single tag value from the SCADA system.
        /// </summary>
        /// <param name="request">The read request with session ID and tag.</param>
        /// <param name="context">The gRPC server call context.</param>
        /// <returns>A <see cref="ReadResponse" /> with the VTQ data.</returns>
        public override async Task<ReadResponse> Read(ReadRequest request, ServerCallContext context)
        {
            using (PerformanceMetrics.ITimingScope scope = _performanceMetrics?.BeginOperation("Read"))
            {
                try
                {
                    // Validate session
                    if (!_sessionManager.ValidateSession(request.SessionId))
                    {
                        return new ReadResponse
                        {
                            Success = false,
                            Message = "Invalid session ID",
                            Vtq = CreateBadVtqMessage(request.Tag)
                        };
                    }

                    Logger.Debug("Read request from {Peer} for {Tag}", context.Peer, request.Tag);

                    Vtq vtq = await _scadaClient.ReadAsync(request.Tag, context.CancellationToken);

                    scope?.SetSuccess(true);
                    return new ReadResponse
                    {
                        Success = true,
                        Message = string.Empty,
                        Vtq = ConvertToVtqMessage(request.Tag, vtq)
                    };
                }
                catch (Exception ex)
                {
                    Logger.Error(ex, "Failed to read {Tag}", request.Tag);
                    scope?.SetSuccess(false);
                    return new ReadResponse
                    {
                        Success = false,
                        Message = ex.Message,
                        Vtq = CreateBadVtqMessage(request.Tag)
                    };
                }
            }
        }

        /// <summary>
        ///     Reads multiple tag values from the SCADA system.
        /// </summary>
        /// <param name="request">The batch read request with session ID and tags.</param>
        /// <param name="context">The gRPC server call context.</param>
        /// <returns>A <see cref="ReadBatchResponse" /> with VTQ data for each tag.</returns>
        public override async Task<ReadBatchResponse> ReadBatch(ReadBatchRequest request, ServerCallContext context)
        {
            using (PerformanceMetrics.ITimingScope scope = _performanceMetrics?.BeginOperation("ReadBatch"))
            {
                try
                {
                    // Validate session
                    if (!_sessionManager.ValidateSession(request.SessionId))
                    {
                        var badResponse = new ReadBatchResponse
                        {
                            Success = false,
                            Message = "Invalid session ID"
                        };
                        foreach (var tag in request.Tags)
                        {
                            badResponse.Vtqs.Add(CreateBadVtqMessage(tag));
                        }
                        return badResponse;
                    }

                    Logger.Debug("ReadBatch request from {Peer} for {Count} tags", context.Peer, request.Tags.Count);

                    IReadOnlyDictionary<string, Vtq> results =
                        await _scadaClient.ReadBatchAsync(request.Tags, context.CancellationToken);

                    var response = new ReadBatchResponse
                    {
                        Success = true,
                        Message = string.Empty
                    };

                    // Return results in the same order as the request tags
                    foreach (var tag in request.Tags)
                    {
                        if (results.TryGetValue(tag, out Vtq vtq))
                        {
                            response.Vtqs.Add(ConvertToVtqMessage(tag, vtq));
                        }
                        else
                        {
                            response.Vtqs.Add(CreateBadVtqMessage(tag));
                        }
                    }

                    scope?.SetSuccess(true);
                    return response;
                }
                catch (Exception ex)
                {
                    Logger.Error(ex, "Failed to read batch");
                    scope?.SetSuccess(false);

                    var response = new ReadBatchResponse
                    {
                        Success = false,
                        Message = ex.Message
                    };

                    foreach (var tag in request.Tags)
                    {
                        response.Vtqs.Add(CreateBadVtqMessage(tag));
                    }

                    return response;
                }
            }
        }

        #endregion

        #region Write Operations

        /// <summary>
        ///     Writes a single tag value to the SCADA system.
        /// </summary>
        /// <param name="request">The write request with session ID, tag, and value.</param>
        /// <param name="context">The gRPC server call context.</param>
        /// <returns>A <see cref="WriteResponse" /> indicating success or failure.</returns>
        public override async Task<WriteResponse> Write(WriteRequest request, ServerCallContext context)
        {
            using (PerformanceMetrics.ITimingScope scope = _performanceMetrics?.BeginOperation("Write"))
            {
                try
                {
                    // Validate session
                    if (!_sessionManager.ValidateSession(request.SessionId))
                    {
                        return new WriteResponse
                        {
                            Success = false,
                            Message = "Invalid session ID"
                        };
                    }

                    Logger.Debug("Write request from {Peer} for {Tag}", context.Peer, request.Tag);

                    // Parse the string value to an appropriate type
                    var value = ParseValue(request.Value);

                    await _scadaClient.WriteAsync(request.Tag, value, context.CancellationToken);

                    scope?.SetSuccess(true);
                    return new WriteResponse
                    {
                        Success = true,
                        Message = string.Empty
                    };
                }
                catch (Exception ex)
                {
                    Logger.Error(ex, "Failed to write to {Tag}", request.Tag);
                    scope?.SetSuccess(false);
                    return new WriteResponse
                    {
                        Success = false,
                        Message = ex.Message
                    };
                }
            }
        }

        /// <summary>
        ///     Writes multiple tag values to the SCADA system.
        /// </summary>
        /// <param name="request">The batch write request with session ID and items.</param>
        /// <param name="context">The gRPC server call context.</param>
        /// <returns>A <see cref="WriteBatchResponse" /> with results for each tag.</returns>
        public override async Task<WriteBatchResponse> WriteBatch(WriteBatchRequest request, ServerCallContext context)
        {
            using (PerformanceMetrics.ITimingScope scope = _performanceMetrics?.BeginOperation("WriteBatch"))
            {
                try
                {
                    // Validate session
                    if (!_sessionManager.ValidateSession(request.SessionId))
                    {
                        var badResponse = new WriteBatchResponse
                        {
                            Success = false,
                            Message = "Invalid session ID"
                        };
                        foreach (var item in request.Items)
                        {
                            badResponse.Results.Add(new WriteResult
                            {
                                Tag = item.Tag,
                                Success = false,
                                Message = "Invalid session ID"
                            });
                        }
                        return badResponse;
                    }

                    Logger.Debug("WriteBatch request from {Peer} for {Count} items", context.Peer, request.Items.Count);

                    var values = new Dictionary<string, object>();
                    foreach (var item in request.Items)
                    {
                        values[item.Tag] = ParseValue(item.Value);
                    }

                    await _scadaClient.WriteBatchAsync(values, context.CancellationToken);

                    scope?.SetSuccess(true);

                    var response = new WriteBatchResponse
                    {
                        Success = true,
                        Message = string.Empty
                    };

                    foreach (var item in request.Items)
                    {
                        response.Results.Add(new WriteResult
                        {
                            Tag = item.Tag,
                            Success = true,
                            Message = string.Empty
                        });
                    }

                    return response;
                }
                catch (Exception ex)
                {
                    Logger.Error(ex, "Failed to write batch");
                    scope?.SetSuccess(false);

                    var response = new WriteBatchResponse
                    {
                        Success = false,
                        Message = ex.Message
                    };

                    foreach (var item in request.Items)
                    {
                        response.Results.Add(new WriteResult
                        {
                            Tag = item.Tag,
                            Success = false,
                            Message = ex.Message
                        });
                    }

                    return response;
                }
            }
        }

        /// <summary>
        ///     Writes a batch of tag values and waits for a flag tag to reach a specific value.
        /// </summary>
        /// <param name="request">The batch write and wait request.</param>
        /// <param name="context">The gRPC server call context.</param>
        /// <returns>A <see cref="WriteBatchAndWaitResponse" /> with results and flag status.</returns>
        public override async Task<WriteBatchAndWaitResponse> WriteBatchAndWait(WriteBatchAndWaitRequest request,
            ServerCallContext context)
        {
            var startTime = DateTime.UtcNow;

            try
            {
                // Validate session
                if (!_sessionManager.ValidateSession(request.SessionId))
                {
                    var badResponse = new WriteBatchAndWaitResponse
                    {
                        Success = false,
                        Message = "Invalid session ID",
                        FlagReached = false,
                        ElapsedMs = 0
                    };
                    foreach (var item in request.Items)
                    {
                        badResponse.WriteResults.Add(new WriteResult
                        {
                            Tag = item.Tag,
                            Success = false,
                            Message = "Invalid session ID"
                        });
                    }
                    return badResponse;
                }

                Logger.Debug("WriteBatchAndWait request from {Peer}", context.Peer);

                var values = new Dictionary<string, object>();
                foreach (var item in request.Items)
                {
                    values[item.Tag] = ParseValue(item.Value);
                }

                var flagValue = ParseValue(request.FlagValue);
                var pollInterval = request.PollIntervalMs > 0 ? request.PollIntervalMs : 100;

                using var cts = CancellationTokenSource.CreateLinkedTokenSource(context.CancellationToken);
                cts.CancelAfter(TimeSpan.FromMilliseconds(request.TimeoutMs));

                // Write the batch first
                await _scadaClient.WriteBatchAsync(values, cts.Token);

                // Poll for the flag value
                var flagReached = false;
                while (!cts.Token.IsCancellationRequested)
                {
                    try
                    {
                        var flagVtq = await _scadaClient.ReadAsync(request.FlagTag, cts.Token);
                        if (flagVtq.Value != null && AreValuesEqual(flagVtq.Value, flagValue))
                        {
                            flagReached = true;
                            break;
                        }

                        await Task.Delay(pollInterval, cts.Token);
                    }
                    catch (OperationCanceledException)
                    {
                        break;
                    }
                }

                var elapsedMs = (int)(DateTime.UtcNow - startTime).TotalMilliseconds;

                var response = new WriteBatchAndWaitResponse
                {
                    Success = true,
                    Message = string.Empty,
                    FlagReached = flagReached,
                    ElapsedMs = elapsedMs
                };

                foreach (var item in request.Items)
                {
                    response.WriteResults.Add(new WriteResult
                    {
                        Tag = item.Tag,
                        Success = true,
                        Message = string.Empty
                    });
                }

                return response;
            }
            catch (Exception ex)
            {
                Logger.Error(ex, "Failed to write batch and wait");

                var elapsedMs = (int)(DateTime.UtcNow - startTime).TotalMilliseconds;

                var response = new WriteBatchAndWaitResponse
                {
                    Success = false,
                    Message = ex.Message,
                    FlagReached = false,
                    ElapsedMs = elapsedMs
                };

                foreach (var item in request.Items)
                {
                    response.WriteResults.Add(new WriteResult
                    {
                        Tag = item.Tag,
                        Success = false,
                        Message = ex.Message
                    });
                }

                return response;
            }
        }

        #endregion

        #region Subscription Operations

        /// <summary>
        ///     Subscribes to value changes for specified tags and streams updates to the client.
        /// </summary>
        /// <param name="request">The subscribe request with session ID and tags.</param>
        /// <param name="responseStream">The server stream writer for VTQ updates.</param>
        /// <param name="context">The gRPC server call context.</param>
        /// <returns>A task representing the asynchronous operation.</returns>
        public override async Task Subscribe(SubscribeRequest request,
            IServerStreamWriter<VtqMessage> responseStream, ServerCallContext context)
        {
            // Validate session
            if (!_sessionManager.ValidateSession(request.SessionId))
            {
                Logger.Warning("Subscribe failed: Invalid session ID {SessionId}", request.SessionId);
                throw new RpcException(new Status(StatusCode.Unauthenticated, "Invalid session ID"));
            }

            var clientId = Guid.NewGuid().ToString();

            try
            {
                Logger.Information("Subscribe request from {Peer} with client ID {ClientId} for {Count} tags",
                    context.Peer, clientId, request.Tags.Count);

                Channel<(string address, Vtq vtq)> channel = await _subscriptionManager.SubscribeAsync(
                    clientId,
                    request.Tags,
                    context.CancellationToken);

                // Stream updates to the client until cancelled
                while (!context.CancellationToken.IsCancellationRequested)
                {
                    try
                    {
                        while (await channel.Reader.WaitToReadAsync(context.CancellationToken))
                        {
                            if (channel.Reader.TryRead(out (string address, Vtq vtq) item))
                            {
                                var vtqMessage = ConvertToVtqMessage(item.address, item.vtq);
                                await responseStream.WriteAsync(vtqMessage);
                            }
                        }
                    }
                    catch (OperationCanceledException)
                    {
                        break;
                    }
                }
            }
            catch (OperationCanceledException)
            {
                Logger.Information("Subscription cancelled for client {ClientId}", clientId);
            }
            catch (Exception ex)
            {
                Logger.Error(ex, "Error in subscription for client {ClientId}", clientId);
                throw;
            }
            finally
            {
                _subscriptionManager.UnsubscribeClient(clientId);
            }
        }

        #endregion

        #region Authentication

        /// <summary>
        ///     Checks the validity of an API key.
        /// </summary>
        /// <param name="request">The API key check request.</param>
        /// <param name="context">The gRPC server call context.</param>
        /// <returns>A <see cref="CheckApiKeyResponse" /> with validity and details.</returns>
        public override Task<CheckApiKeyResponse> CheckApiKey(CheckApiKeyRequest request, ServerCallContext context)
        {
            var response = new CheckApiKeyResponse
            {
                IsValid = false,
                Message = "API key validation failed"
            };

            // Check if API key was validated by interceptor
            if (context.UserState.TryGetValue("ApiKey", out object apiKeyObj) && apiKeyObj is ApiKey apiKey)
            {
                response.IsValid = apiKey.IsValid();
                response.Message = apiKey.IsValid()
                    ? $"API key is valid (Role: {apiKey.Role})"
                    : "API key is disabled";

                Logger.Information("API key check - Valid: {IsValid}, Role: {Role}",
                    response.IsValid, apiKey.Role);
            }
            else
            {
                Logger.Warning("API key check failed - no API key in context");
            }

            return Task.FromResult(response);
        }

        #endregion

        #region Value Conversion Helpers

        /// <summary>
        ///     Converts a domain <see cref="Vtq" /> to a gRPC <see cref="VtqMessage" />.
        /// </summary>
        private static VtqMessage ConvertToVtqMessage(string tag, Vtq vtq)
        {
            return new VtqMessage
            {
                Tag = tag,
                Value = ConvertValueToString(vtq.Value),
                TimestampUtcTicks = vtq.Timestamp.Ticks,
                Quality = ConvertQualityToString(vtq.Quality)
            };
        }

        /// <summary>
        ///     Creates a bad quality VTQ message for error cases.
        /// </summary>
        private static VtqMessage CreateBadVtqMessage(string tag)
        {
            return new VtqMessage
            {
                Tag = tag,
                Value = string.Empty,
                TimestampUtcTicks = DateTime.UtcNow.Ticks,
                Quality = "Bad"
            };
        }

        /// <summary>
        ///     Converts a value to its string representation.
        /// </summary>
        private static string ConvertValueToString(object value)
        {
            if (value == null)
            {
                return string.Empty;
            }

            return value switch
            {
                bool b => b.ToString().ToLowerInvariant(),
                DateTime dt => dt.ToUniversalTime().ToString("O"),
                DateTimeOffset dto => dto.ToString("O"),
                float f => f.ToString(CultureInfo.InvariantCulture),
                double d => d.ToString(CultureInfo.InvariantCulture),
                decimal dec => dec.ToString(CultureInfo.InvariantCulture),
                Array => JsonSerializer.Serialize(value, value.GetType()),
                _ => value.ToString() ?? string.Empty
            };
        }

        /// <summary>
        ///     Converts a domain quality value to a string.
        /// </summary>
        private static string ConvertQualityToString(Domain.Quality quality)
        {
            // Simplified quality mapping for the new API
            var qualityValue = (int)quality;

            if (qualityValue >= 192) // Good family
            {
                return "Good";
            }

            if (qualityValue >= 64) // Uncertain family
            {
                return "Uncertain";
            }

            return "Bad"; // Bad family
        }

        /// <summary>
        ///     Parses a string value to an appropriate .NET type.
        /// </summary>
        private static object ParseValue(string value)
        {
            if (string.IsNullOrEmpty(value))
            {
                return string.Empty;
            }

            // Try to parse as boolean
            if (bool.TryParse(value, out bool boolResult))
            {
                return boolResult;
            }

            // Try to parse as integer
            if (int.TryParse(value, NumberStyles.Integer, CultureInfo.InvariantCulture, out int intResult))
            {
                return intResult;
            }

            // Try to parse as long
            if (long.TryParse(value, NumberStyles.Integer, CultureInfo.InvariantCulture, out long longResult))
            {
                return longResult;
            }

            // Try to parse as double
            if (double.TryParse(value, NumberStyles.Float | NumberStyles.AllowThousands, CultureInfo.InvariantCulture,
                    out double doubleResult))
            {
                return doubleResult;
            }

            // Try to parse as DateTime
            if (DateTime.TryParse(value, CultureInfo.InvariantCulture, DateTimeStyles.RoundtripKind,
                    out DateTime dateResult))
            {
                return dateResult;
            }

            // Return as string
            return value;
        }

        /// <summary>
        ///     Compares two values for equality.
        /// </summary>
        private static bool AreValuesEqual(object value1, object value2)
        {
            if (value1 == null && value2 == null)
            {
                return true;
            }

            if (value1 == null || value2 == null)
            {
                return false;
            }

            // Convert both to strings for comparison
            var str1 = ConvertValueToString(value1);
            var str2 = ConvertValueToString(value2);

            return string.Equals(str1, str2, StringComparison.OrdinalIgnoreCase);
        }

        #endregion
    }
}