MultiTerm/MultiTerm.Core/ViewModel/ConsoleViewModel.cs

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

namespace MultiTerm.Core.ViewModel;

public partial class ConsoleViewModel : TerminalViewModel
{
    public override TerminalViewType ViewType => TerminalViewType.Console;

    private readonly ILogger logger;
    private Encoding currentEncoding;

    /* settings */
    private readonly Encoding defaultEncoding = Encoding.ASCII;              // default encoding instance
    private const EncodingType defaultEncodingType = EncodingType.ASCII;     // default encoding type
    private const int DataMaxLength = 5000;                                  // maximum amount of characters stored int the data textbox

    #region Observable Properties
    /// <summary>
    /// Holds Console content.
    /// </summary>
    [ObservableProperty]
    private string data = string.Empty;

    /// <summary>
    /// Encoding type of the sent and received messages.
    /// </summary>
    [ObservableProperty]
    private EncodingType selectedEncodingType = defaultEncodingType;

    /// <summary>
    /// Holds message that is to be sent next. E.g. currently being typed in.
    /// </summary>
    [ObservableProperty]
    private string sendableMessage = string.Empty;
    #endregion

    public ConsoleViewModel(IAppSettingsProvider appSettings, IMessenger messenger, ILogger logger) : base(appSettings, messenger)
    {
        this.logger = logger;
        this.currentEncoding = this.GetEncoding(this.SelectedEncodingType);
    }

    public override void DisplayNewReceivedData(IEnumerable<ExtendedByte> newData)
    {
        // extract bytes
        var bytes = newData.Select(b => b.Byte).ToArray();
        string newDataDecoded = currentEncoding.GetString(bytes);
        // calculate new legth
        int newTotalLength = this.Data.Length + newDataDecoded.Length;
        // trim current data at the beginning if new length is too long
        if (newTotalLength > DataMaxLength)
        {
            // trim overshoot from start of string
            this.Data = this.Data[(newTotalLength - DataMaxLength)..];
        }
        // append data
        this.Data += newDataDecoded;
    }

    /// <summary>
    /// Command to send a prepared message.
    /// </summary>
    [RelayCommand]
    public void Send()
    {
        // encode
        var encodedBytes = this.currentEncoding.GetBytes(this.SendableMessage);

        // send
        if (this.SendToCommunicationProtocol(encodedBytes))
        {
            // add to history
            this.AddToSendHistory(new StringHistoryElement(this.SendableMessage));
            // clear if sending was successful
            this.SendableMessage = string.Empty;
        }
    }

    protected override void HandleInsertElementFromHistory(object element)
    {
        if(element is not StringHistoryElement elementString) { throw new Exception($"'{HandleInsertElementFromHistory}()' in {nameof(ConsoleViewModel)} got wrong type of element. Got Type: {element.GetType()}"); }
        // overwrite sendable message with history element
        this.SendableMessage = elementString.Text;
    }

    /// <summary>
    /// Command to clear the data that was received.
    /// </summary>
    [RelayCommand]
    public void ClearData()
    {
        this.Data = string.Empty;
    }

    /// <summary>
    /// Handles changing of encoding type.
    /// </summary>
    /// <param name="value">new value</param>
    partial void OnSelectedEncodingTypeChanged(EncodingType value)
    {
        this.currentEncoding = this.GetEncoding(value);
    }

    #region Unused Methods
    public override void DisplayNewSentData(IEnumerable<ExtendedByte> newData)
    {
        // no display of sent data
    }

    protected override void ActOnDataDisplayNewlineSeparatorTypeChanged(NewlineSeparatorType newType)
    {
        // No change when data display newline separator type changed
    }

    #endregion

    #region Helpers
    /// <summary>
    /// Returns <see cref="Encoding"/> instance of <paramref name="encodingType"/>.
    /// If the <paramref name="encodingType"/> is not supported or any issue arrived, the <see cref="SelectedEncodingType"/> is set to ASCII and ASCII <see cref="Encoding"/> is returned.
    /// </summary>
    /// <param name="encodingType">type of encoding</param>
    /// <returns>encoding instance</returns>
    private Encoding GetEncoding(EncodingType encodingType)
    {
        Encoding? encoding;

        try
        {
            // Encoding Type value corresponds to codepage number, therefore can be get by cast to int
            encoding = Encoding.GetEncoding(Convert.ToInt32(encodingType));
        }
        catch (Exception)
        {
            // log exception and set encoding to null
            this.logger.LogWarn($"'{nameof(GetEncoding)}()' failed to resolve encoding type {encodingType} (codepage {Convert.ToInt32(encodingType)}). Reverted to default.", nameof(ConsoleViewModel));
            encoding = null;
        }

        // failed to get encoding or got null encoding
        if (encoding == null)
        {
            // set selected encoding type to default and return default encoding
            this.SelectedEncodingType = defaultEncodingType;
            encoding = defaultEncoding;
        }

        return encoding!;
    }
    #endregion
}