using Common.Helpers;
using Common.Logging;
using Common.Messaging;
using CommunityToolkit.Mvvm.Messaging;
using MultiTerm.Protocols.Model;
using MultiTerm.Protocols.Types;
using System.Collections.Concurrent;

namespace MultiTerm.Protocols;

public abstract class CommunicationProtocol : ICommunicationProtocol
{
    protected readonly ILogger logger;
    protected readonly IMessenger messenger;
    private CancellationTokenSource cancellationTokenSource;
    private Thread? readingThread;
    private RecurringTimer? bufferHandlingTimer;
    private const int bufferHandlingTimerIntervalMs = 20;   // After x milliseconds the timer shall be called
    private const int eventBlockSize = 50;                  // Block size for Received/Sent Data events
    private ConcurrentQueue<ExtendedByte>? receivedDataQueue;
    private ConcurrentQueue<ExtendedByte>? sentDataQueue;

    public event EventHandler<ReceivedDataEventArgs>? ReceivedDataEvent;
    public event EventHandler<SentDataEventArgs>? SentDataEvent;
    public event EventHandler<ProtocolConnectionState>? ConnectionStateChangedEvent;

    public abstract ProtocolType ProtocolType { get; }
    public abstract string InstanceIdentifier { get; protected set; }
    public abstract string LongInstanceIdentifier { get; protected set; }

    private ProtocolConnectionState state = ProtocolConnectionState.NotConnected;
    public ProtocolConnectionState State
    {
        get { return state; }
        set
        {
            state = value;
            this.ConnectionStateChangedEvent?.Invoke(this, state);
        }
    }

    public CommunicationProtocol(ILogger logger, IMessenger messenger)
    {
        // initialize other
        this.cancellationTokenSource = new CancellationTokenSource();
        this.logger = logger;
        this.messenger = messenger;
    }

    /// <summary>
    /// To be called when data was received from the connected device.
    /// </summary>
    protected void OnReceivedData(ExtendedByte receivedByte) { this.receivedDataQueue?.Enqueue(receivedByte); }

    /// <summary>
    /// To be called when data was sent to the connected device.
    /// </summary>
    protected void OnSentData(ExtendedByte sentByte) { this.sentDataQueue?.Enqueue(sentByte); }

    /// <summary>
    /// To be called whenever the protocol detected that it is disconnected, but this is not a known fact.
    /// </summary>
    protected void OnUnintentionallyDisconnected()
    {
        // perform all steps in a task, to prevent deadlock when this method is called from a thread that is joined.
        Task.Run(() =>
        {
            this.CancelOngoingOperations();
            this.logger.LogError($"'{nameof(OnUnintentionallyDisconnected)}()' called.", nameof(CommunicationProtocol));

            // update state
            this.State = ProtocolConnectionState.UnintentionallyDisconnected;

            // inform user
            this.messenger.Send<IUserInterfaceMessage>(new GenericUserInterfaceMessage($"'{this.GetProtocolAndInstanceIdentifier()}' unintentionally disconnected.", MessageImportance.High));
        });
    }

    /// <summary>
    /// Allows to send bytes using the implemented protocol.
    /// </summary>
    /// <param name="bytes">data as bytes</param>
    /// <returns>true if the data was sent successfully</returns>
    protected abstract bool InternalSendBytes(byte[] bytes);

    public bool SendBytes(byte[] bytes)
    {
        bool success = true;

        // guard is not connected => log warning. user of this function shall only use SendBytes if IsConnected is true
        if (this.State != ProtocolConnectionState.Connected)
        {
            this.logger.LogWarn($"'{nameof(SendBytes)}()' was reached with wrong {nameof(ProtocolConnectionState)} of {this.State}", nameof(CommunicationProtocol));
            return false;  // return and do not send
        }

        // send bytes
        success = this.InternalSendBytes(bytes);

        // if the sending was cancelled report error
        if (success == false)
        {
            this.logger.LogError($"'{nameof(SendBytes)}()' failed to send during {nameof(InternalSendBytes)}.", nameof(CommunicationProtocol));
            this.messenger.Send<IUserInterfaceMessage>(new GenericUserInterfaceMessage("Failed to send data, for more information please check logfile.", MessageImportance.High));
        }

        return success;
    }

    /// <summary>
    /// Allows to connect to the selected device using the implemented protocol.
    /// </summary>
    /// <param name="settings">protocol settings required to connect</param>
    /// <returns>true on success</returns>
    protected abstract bool InternalConnect(IProtocolSettings settings);

    /// <summary>
    /// Reads from the connected device in an endless loop.
    /// The endless loop must be ended when the <paramref name="ct"/> has <see cref="CancellationToken.IsCancellationRequested"/> set.
    /// </summary>
    /// <param name="ct">cancellation token</param>
    protected abstract void InternalRead(CancellationToken ct);

    public bool Connect(IProtocolSettings settings)
    {
        // check if not already connected
        if (this.State == ProtocolConnectionState.Connected)
        {
            this.logger.LogWarn($"'{nameof(Connect)}()' was reached with wrong {nameof(ProtocolConnectionState)} of {this.State}", nameof(CommunicationProtocol));
            return true;
        }

        // check if settings are valid, cancel if not
        if (settings.AreValid() == false)
        {
            this.logger.LogError($"'{nameof(Connect)}()' failed since the provided protocol settings are invalid", nameof(CommunicationProtocol));
            return false;
        }

        // try connecting if settings are valid
        if (this.InternalConnect(settings))
        {
            // renew token source and data buffers
            this.cancellationTokenSource = new CancellationTokenSource();
            this.receivedDataQueue = new ConcurrentQueue<ExtendedByte>();
            this.sentDataQueue = new ConcurrentQueue<ExtendedByte>();
            // start interal buffer handling thread
            this.bufferHandlingTimer = new(bufferHandlingTimerIntervalMs, delegate() { this.HandleDataQueues(); });
            this.bufferHandlingTimer.Start();
            // start internal reading thread
            this.readingThread = new Thread(() => this.InternalRead(this.cancellationTokenSource.Token));
            this.readingThread.Start();
            // update state
            this.State = ProtocolConnectionState.Connected;
            return true;
        }
        else
        {
            this.logger.LogWarn($"'{nameof(Connect)}()' failed to connect to protocol, did not start reading thread.", nameof(CommunicationProtocol));
            this.messenger.Send<IUserInterfaceMessage>(new GenericUserInterfaceMessage($"Failed to connect to '{this.GetProtocolAndInstanceIdentifier()}'. For more information please check logfile.", MessageImportance.High));
            return false;
        }
    }

    /// <summary>
    /// Allows to disconnect from the connected device.
    /// </summary>
    protected abstract void InternalDisconnect();
    public void Disconnect()
    {
        this.CancelOngoingOperations();
        this.InternalDisconnect();

        this.State = ProtocolConnectionState.NotConnected;
    }

    /// <summary>
    /// Sets cancellation token and makes sure ongoing operations do not run anymore.
    /// </summary>
    private void CancelOngoingOperations()
    {
        this.cancellationTokenSource.Cancel();

        // stop thread and timer
        this.readingThread?.Join();
        this.bufferHandlingTimer?.Stop();
    }

    /// <summary>
    /// Internal handling of internal data queues.
    /// Arranges characters into blocks and raises <see cref="ReceivedDataEvent"/> and <see cref="SentDataEvent"/>.
    /// </summary>
    private void HandleDataQueues()
    {
        bool receivedDataAvailable = this.receivedDataQueue != null && this.receivedDataQueue.TryPeek(out _);
        bool sentDataAvailable = this.sentDataQueue != null && this.sentDataQueue.TryPeek(out _);
        List<ExtendedByte> internalList = new();

        List<ExtendedByte> duplicateInternalList()
        {
            // shallow copy of data
            var duplicatedList = internalList.Select(item => (ExtendedByte)item.Clone()).ToList();
            // clear internal list
            internalList.Clear();
            return duplicatedList;
        }

        // collect received data
        if (receivedDataAvailable)
        {
            // while data is available
            while (this.receivedDataQueue!.TryDequeue(out ExtendedByte? newReceivedByte))
            {
                // fill it into the internal list
                internalList.Add(newReceivedByte);
                if(internalList.Count > eventBlockSize)
                {
                    // raise event with block of data
                    this.ReceivedDataEvent?.Invoke(this, new ReceivedDataEventArgs(duplicateInternalList()));
                }
            }
            // no more new data but still some data in the list => send it
            if (internalList.Count > 0)
            {
                this.ReceivedDataEvent?.Invoke(this, new ReceivedDataEventArgs(duplicateInternalList()));
            }
            // reset list for sent data
            internalList = new();
        }        

        // collect sent data
        if (sentDataAvailable)
        {
            // while data is available
            while (this.sentDataQueue!.TryDequeue(out ExtendedByte? newSentByte))
            {
                // fill it into the internal list
                internalList.Add(newSentByte);
                if (internalList.Count > eventBlockSize)
                {
                    // raise event with block of data
                    this.SentDataEvent?.Invoke(this, new SentDataEventArgs(duplicateInternalList()));
                }
            }
            // no more new data but still some data in the list => send it
            if (internalList.Count > 0)
            {
                this.SentDataEvent?.Invoke(this, new SentDataEventArgs(duplicateInternalList()));
            }
        }
    }

    #region Helpers
    public string GetProtocolAndInstanceIdentifier()
    {
        return $"{EnumHelpers.GetEnumDescription(this.ProtocolType)} {this.InstanceIdentifier}";
    }
    #endregion
}