using Common;
using Common.AppSettings;
using Common.Helpers;
using Common.Messaging;
using CommunityToolkit.Mvvm.ComponentModel;
using CommunityToolkit.Mvvm.Input;
using CommunityToolkit.Mvvm.Messaging;
using MultiTerm.Core.Types;
using MultiTerm.Protocols;
using MultiTerm.Protocols.Types;
using System.Text;

namespace MultiTerm.Core.ViewModel;

public abstract partial class TerminalViewModel : ObservableObject, ITerminalViewModel
{
    private const string defaultReceiveNewlineSeparatorAppSettingsKey = "DefaultReceiveNewlineSeparator";
    private const string defaultSendNewlineSeparatorAppSettingsKey = "DefaultSendNewlineSeparator";
    private readonly IAppSettingsProvider appSettings;
    private readonly IMessenger messenger;
    private readonly IContext context;

    public abstract string Title { get; }
    public abstract TerminalViewType ViewType { get; }  
    public ProtocolType ProtocolType { get; set; }

    /// <summary>
    /// Holds communication data, meaning data that was sent to or received over the communication protocol.
    /// </summary>
    [ObservableProperty]
    private CommunicationDataViewModel? communicationData;

    /// <summary>
    /// Newline Separator Type that is selected for receival data of this Terminal. Defaults to none.
    /// </summary>
    [ObservableProperty]
    private NewlineSeparatorType receiveNewlineSeparatorType = NewlineSeparatorType.None;

    /// <summary>
    /// Newline Separator Type that is selected for sent out data of this Terminal. Defaults to none.
    /// </summary>
    [ObservableProperty]
    private NewlineSeparatorType sendNewlineSeparatorType = NewlineSeparatorType.None;

    private ICommunicationProtocol? communicationProtocol;
    public ICommunicationProtocol? CommunicationProtocol
    {
        get { return this.communicationProtocol; }
        set 
        { 
            this.communicationProtocol = value;
            // register communication protocol in the Communication Data View Model
            this.CommunicationData = new CommunicationDataViewModel(this.communicationProtocol, this.context);

            // initializes default newline separators, requires communicationData to be not null
            this.InitializeNewlineSeparatorsFromAppSettings();

            // initialize both newline Separators. initializes with null if they are not available.
            this.CommunicationData.ConfigureNewlineSeparators(this.ReceiveNewlineSeparatorType, this.SendNewlineSeparatorType);
        }
    }

    private IProtocolSettingsViewModel? protocolSettings;
    public IProtocolSettingsViewModel? ProtocolSettings
    {
        get { return this.protocolSettings; }
        set 
        {
            this.protocolSettings = value; 
            // register event handler for connection request from viewmodel
            if(value != null)
            {
                this.protocolSettings!.ConnectRequested += OnViewModelRequestedConnect;
                this.protocolSettings!.DisconnectRequested += OnViewModelRequestedDisconnect;
            }
        }
    }

    public TerminalViewModel(IAppSettingsProvider appSettings, IMessenger messenger, IContext context)
    {
        this.appSettings = appSettings;
        this.messenger = messenger;
        this.context = context;
    }

    /// <summary>
    /// Sends the given string to this instances <see cref="CommunicationProtocol"/>, UTF-16 encoded. 
    /// Appends configured <see cref="SendNewlineSeparatorType"/> to the end of string.
    /// </summary>
    /// <param name="data">data string</param>
    protected void SendToCommunicationProtocol(string data)
    {
        // guard communication protocol null
        if(this.CommunicationProtocol == null) { throw new NullReferenceException($"'{nameof(SendToCommunicationProtocol)}()' was called but {nameof(CommunicationProtocol)} is null."); }

        // inform user and quit if communication protocol is not connected
        if (this.CommunicationProtocol.IsConnected == false)
        {
            this.messenger.Send<IUserInterfaceMessage>(new ProtocolNotConnectedMessage("Cannot send message"));
            return;
        }

        // add newline sequence to end of data
        string newlineSequence = this.SendNewlineSeparatorType switch
        {
            NewlineSeparatorType.None => String.Empty,
            NewlineSeparatorType.CR => "\r",
            NewlineSeparatorType.LF => "\n",
            NewlineSeparatorType.CR_LF => "\r\n",
            _ => throw new NotImplementedException($"'{nameof(SendToCommunicationProtocol)}()' " +
            $"does not implement handling for {nameof(NewlineSeparatorType)} {this.SendNewlineSeparatorType}.")
        };
        string modifiedData = data + newlineSequence;

        // extract unicode byte array
        var byteArray = Encoding.Unicode.GetBytes(modifiedData);

        // send
        this.CommunicationProtocol.SendBytes(byteArray);
    }

    #region Connect/Disconnect
    private void OnViewModelRequestedConnect(object? sender, ConnectionRequestEventArgs e)
    {
        // guard uninitialized CommunicationProtocol
        if (CommunicationProtocol == null) { throw new Exception($"To call '{nameof(OnViewModelRequestedConnect)}()', CommunicationProtocol must not be null!"); }

        e.Success = this.CommunicationProtocol.Connect(e.Settings);
    }

    private void OnViewModelRequestedDisconnect(object? sender, EventArgs e)
    {
        // guard uninitialized CommunicationProtocol
        if (CommunicationProtocol == null) { throw new Exception($"To call '{nameof(OnViewModelRequestedConnect)}()', CommunicationProtocol must not be null!"); }

        this.CommunicationProtocol.Disconnect();
    }
    #endregion

    #region Closing handling
    public event EventHandler? ClosingEvent;

    /// <summary>
    /// Method to override if any closing actions are required.
    /// Closing can be cancelled using the return value.
    /// </summary>
    /// <returns>true if closing is allowed. false if it shall be cancelled.</returns>
    protected virtual bool ClosingActions() { return true; }

    [RelayCommand]
    public void CloseRequest()
    {
        if (this.ClosingActions() == true)
        {
            ClosingEvent?.Invoke(this, EventArgs.Empty);
        }
    }
    #endregion

    #region Newline Separator handling
    /// <summary>
    /// Gets the default settings for both newline separators from the AppSettings Provider.
    /// Writes them to the local variables <see cref="ReceiveNewlineSeparatorType"/> and <see cref="SendNewlineSeparatorType"/>.
    /// In case there are no default settings, it does not overwrite the local variables.
    /// In case the Communication Data is null, nothing is done.
    /// </summary>
    private void InitializeNewlineSeparatorsFromAppSettings()
    {
        // guard null objects
        if(this.CommunicationData == null) { return; }

        // get newline separators from persistent settings, if not available catch exceptions
        this.appSettings.TryReadSetting(defaultReceiveNewlineSeparatorAppSettingsKey, out string settingValueReceiveNLSep);
        try
        {
            this.ReceiveNewlineSeparatorType = EnumHelpers.ParseEnum<NewlineSeparatorType>(settingValueReceiveNLSep);
        }
        catch { }
        this.appSettings.TryReadSetting(defaultSendNewlineSeparatorAppSettingsKey, out string settingValueSendNLSep);
        try
        {
            this.SendNewlineSeparatorType = EnumHelpers.ParseEnum<NewlineSeparatorType>(settingValueSendNLSep);
        }
        catch { }
    }

    partial void OnReceiveNewlineSeparatorTypeChanged(NewlineSeparatorType value)
    {
        // triggers rearranging the received data with the new NewlineSeparatorType
        this.CommunicationData?.ConfigureNewlineSeparators(value, null);
    }

    partial void OnSendNewlineSeparatorTypeChanged(NewlineSeparatorType value)
    {
        // triggers rearranging the sent data with the new NewlineSeparatorType
        this.CommunicationData?.ConfigureNewlineSeparators(null, value);
    }
    #endregion

}