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 Thread? bufferHandlingThread;
    private ConcurrentQueue<ExtendedByte>? receivedDataQueue;
    private ConcurrentQueue<ExtendedByte>? sentDataQueue;

    public event EventHandler<ReceivedDataEventArgs>? ReceivedDataEvent;
    public event EventHandler<SentDataEventArgs>? SentDataEvent;
    public event EventHandler<DisconnectedEventArgs>? DisconnectedEvent;

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

    public bool IsConnected { get; private set; } = false;

    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(() =>
        {
            // update state
            this.IsConnected = false;

            this.CancelThreads();
            this.logger.LogError($"'{nameof(OnUnintentionallyDisconnected)}()' called.", nameof(CommunicationProtocol));

            // raise event indicating an unintentional disconnect
            this.DisconnectedEvent?.Invoke(this, new DisconnectedEventArgs(true));
        });
    }

    /// <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.IsConnected == false) 
        { 
            this.logger.LogWarn($"'{nameof(SendBytes)}()' was reached with {nameof(IsConnected)} being false", 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.IsConnected == true)
        {
            this.logger.LogWarn($"'{nameof(Connect)}()' was reached even if {nameof(IsConnected)} is already true.", 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.bufferHandlingThread = new Thread(() => this.HandleDataQueues(this.cancellationTokenSource.Token));
            this.bufferHandlingThread.Start();
            // start internal reading thread
            this.readingThread = new Thread(() => this.InternalRead(this.cancellationTokenSource.Token));
            this.readingThread.Start();
            // update state
            this.IsConnected = true;
            return true;
        }
        else
        {
            this.logger.LogWarn($"'{nameof(Connect)}()' failed to connect to protocol, did not start reading thread.", nameof(CommunicationProtocol));
            return false;
        }
    }

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

        // raise event indicating an intentional disconnect
        this.DisconnectedEvent?.Invoke(this, new DisconnectedEventArgs(false));
    }

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

        // join both threads if they exist
        this.readingThread?.Join();
        this.bufferHandlingThread?.Join();
    }

    /// <summary>
    /// Internal handling of internal data queues.
    /// </summary>
    /// <param name="ct">cancellation token</param>
    private void HandleDataQueues(CancellationToken ct)
    {
        while(ct.IsCancellationRequested == false)
        {
            bool receivedDataAvailable  = this.receivedDataQueue != null && this.receivedDataQueue.TryPeek(out _);
            bool sentDataAvailable      = this.sentDataQueue != null     && this.sentDataQueue.TryPeek(out _);

            // collect received data
            if (receivedDataAvailable)
            {
                // something is in the queue => block thread and try dequeue
                ExtendedByte? newReceivedData;
                while (this.receivedDataQueue!.TryDequeue(out newReceivedData) == false)
                {
                    Thread.Sleep(1);
                }
                // raise event
                this.ReceivedDataEvent?.Invoke(this, new ReceivedDataEventArgs(new ExtendedByte[] { newReceivedData }));
            }

            // collect sent data
            if (sentDataAvailable)
            {
                // something is in the queue => block thread and try dequeue
                ExtendedByte? newSentData;
                while (this.sentDataQueue!.TryDequeue(out newSentData) == false)
                {
                    Thread.Sleep(1);
                }
                // raise event
                this.SentDataEvent?.Invoke(this, new SentDataEventArgs(new ExtendedByte[] { newSentData }));
            }

            // generally wait some time to slow down thread, if no data available
            if (!receivedDataAvailable && !sentDataAvailable)
            {
                Thread.Sleep(5);
            }

            // always sleep 1ms to keep UI rolling
            Thread.Sleep(1);
        }
    }
}