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.Collections.ObjectModel;
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;
    private List<char>? listOfPrevCharacters;

    /* settings */
    private readonly Encoding defaultEncoding = Encoding.ASCII;              // default encoding instance
    private const EncodingType defaultEncodingType = EncodingType.ASCII;     // default encoding type
    private const int DataMaxLength = 20000;                                 // limit of maximum shown characters

    /// <summary>
    /// Newline Sequence string inserted on every newline in the <see cref="Data"/>.
    /// </summary>
    public static readonly string NewlineSequence = Environment.NewLine;

    #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);
        // replace newlines 
        newDataDecoded = ReplaceNewlineCharacters(newDataDecoded, ref this.listOfPrevCharacters, this.DataDisplayNewlineSeparatorType, currentEncoding);
        // calculate new lnegth
        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)
    {
        // null element received => insert empty
        if (element == null)
        {
            this.SendableMessage = string.Empty;
            return;
        }

        // otherwise check type
        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 Newline Insertion
    /// <summary>
    /// Returns if the <paramref name="character"/> is a known newline characters.
    /// </summary>
    /// <param name="character">character to test if it is a known newline characters</param>
    /// <returns>true if the character is a newline character</returns>
    private static bool IsKnownNewlineCharacter(char character)
    {
        // must be extended if new newline characters shall be detected!
        const string knownNewlineCharacters = "\n\r";

        return knownNewlineCharacters.Contains(character);
    }

    /// <summary>
    /// Searches <paramref name="text"/> for known Newline characters (using <see cref="IsKnownNewlineCharacter(char)"/>. Removes all known Newline characters from the text.
    /// If the newline sequence according to <paramref name="newlineSeparatorType"/> is found, the configured <see cref="NewlineSequence"/> is introduced.
    /// </summary>
    /// <param name="text">text to search for newline characters</param>
    /// <param name="previousCharacters">list of previous characters, managed by this method. to identify newline sequences over multiple calls of this method</param>
    /// <param name="newlineSeparatorType">separator type</param>
    /// <param name="encoding">encoding to use</param>
    /// <returns>string with replaced newline characters</returns>
    private static string ReplaceNewlineCharacters(
        string text,
        ref List<char>? previousCharacters,
        NewlineSeparatorType newlineSeparatorType,
        Encoding encoding)
    {
        StringBuilder stringBuilder = new();

        // go through characters
        foreach (char character in text)
        {
            // add to collection if the character is not a known newline character
            if (IsKnownNewlineCharacter(character) == false)
            {
                stringBuilder.Append(character);
            }

            // check if a newline should be introduced after this character
            switch (ShouldIntroduceNewlineAfterThisCharacter(character, previousCharacters, newlineSeparatorType, encoding))
            {
                case ShouldIntroduceNewlineAfterThisCharacterResult.NoNewline:
                    // a decision could be made, previousCharacters can be cleared
                    if (previousCharacters != null) { previousCharacters = null; }
                    // nothing to do
                    break;

                case ShouldIntroduceNewlineAfterThisCharacterResult.IntroduceNewline:
                    // a decision could be made, previousCharacters can be cleared
                    if (previousCharacters != null) { previousCharacters = null; }
                    // append line in string
                    stringBuilder.Append(NewlineSequence);
                    break;

                case ShouldIntroduceNewlineAfterThisCharacterResult.RequiresMoreCharacters:
                    // first time that more characters are required => create new list
                    previousCharacters ??= new List<char>();
                    // add current character to list
                    previousCharacters.Add(character);
                    break;

                default:
                    throw new Exception($"'{nameof(ReplaceNewlineCharacters)}()' failed because of error when checking if a newline should be introduced.");
            }
        }

        return stringBuilder.ToString();
    }

    /// <summary>
    /// Result type for <see cref="ShouldIntroduceNewlineAfterThisCharacter"/>
    /// </summary>
    public enum ShouldIntroduceNewlineAfterThisCharacterResult
    {
        /// <summary>
        /// No newline is required.
        /// </summary>
        NoNewline,

        /// <summary>
        /// A newline shall be introduced after this byte.
        /// </summary>
        IntroduceNewline,

        /// <summary>
        /// Following characters are required to finalize result wether a newline shall be introduced or not.
        /// </summary>
        RequiresMoreCharacters
    }

    /// <summary>
    /// Function to check wether a newline shall be introduced after the given <paramref name="character"/>.
    /// Since some newline sequences will require multiple characters in correct order, a more complex handling is required, which is possible using this function.
    /// </summary>
    /// <param name="character">the current character in the collection</param>
    /// <param name="previousCharacters">list of previous character, newest at the last position of the list, null if not required</param>
    /// <param name="newlineSeparatorType">separator type</param>
    /// <param name="encoding">encoding to be used to check if the characters are equal</param>
    /// <returns>enum result of type <see cref="ShouldIntroduceNewlineAfterThisCharacterResult"/></returns>
    /// <exception cref="NotImplementedException">if the handling for the <paramref name="newlineSeparatorType"/> is not implemented</exception>
    private static ShouldIntroduceNewlineAfterThisCharacterResult ShouldIntroduceNewlineAfterThisCharacter(
        char character,
        List<char>? previousCharacters,
        NewlineSeparatorType newlineSeparatorType,
        Encoding encoding)
    {
        var result = ShouldIntroduceNewlineAfterThisCharacterResult.NoNewline;

        switch (newlineSeparatorType)
        {
            case NewlineSeparatorType.None:
                break;

            case NewlineSeparatorType.CR:
                if (EncodedCharacterEqualsAsciiCharacter(character, '\r', encoding))
                {
                    result = ShouldIntroduceNewlineAfterThisCharacterResult.IntroduceNewline;
                }
                break;

            case NewlineSeparatorType.LF:
                if (EncodedCharacterEqualsAsciiCharacter(character, '\n', encoding))
                {
                    result = ShouldIntroduceNewlineAfterThisCharacterResult.IntroduceNewline;
                }
                break;

            case NewlineSeparatorType.CR_LF:
                if (EncodedCharacterEqualsAsciiCharacter(character, '\r', encoding))
                {
                    result = ShouldIntroduceNewlineAfterThisCharacterResult.RequiresMoreCharacters;
                }
                if (EncodedCharacterEqualsAsciiCharacter(character, '\n', encoding))
                {
                    if (previousCharacters != null && EncodedCharacterEqualsAsciiCharacter(previousCharacters.Last(), '\r', encoding))
                    {
                        result = ShouldIntroduceNewlineAfterThisCharacterResult.IntroduceNewline;
                    }
                }
                break;

            default:
                throw new NotImplementedException($"'{nameof(ShouldIntroduceNewlineAfterThisCharacter)}()' does not implement handling for {nameof(NewlineSeparatorType)} {newlineSeparatorType}");
        }

        return result;
    }

    #endregion

    #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!;
    }

    /// <summary>
    /// Returns wether the <paramref name="encodedChar"/> equals the <paramref name="asciiChar"/>.
    /// <paramref name="encodedChar"/> must be encoded with <paramref name="encoding"/>.
    /// </summary>
    /// <returns>true if equal</returns>
    private static bool EncodedCharacterEqualsAsciiCharacter(char encodedChar, char asciiChar, Encoding encoding)
    {
        return encodedChar.ToString() == encoding.GetString(Encoding.ASCII.GetBytes(new char[] { asciiChar }));
    }
    #endregion
}