MultiTerm/MultiTerm.Wpf.CustomControl/ValueConverter/DataViewModelToStringConverter.cs

using MultiTerm.Core.ViewModel;
using System;
using System.Collections.Generic;
using System.Globalization;
using System.Linq;
using System.Windows.Data;

namespace MultiTerm.Wpf.CustomControl.ValueConverter;


[ValueConversion(typeof(IEnumerable<DataViewModel>), typeof(string))]
public class DataViewModelToStringConverter : IValueConverter
{
    /// <summary>
    /// Newline Sequence that is introduced whenever a new line begins in the DataViewModel.
    /// </summary>
    public static readonly char NewlineSequence = '\n';

    /// <summary>
    /// Convert from IEnumerable<DataViewModel> to string
    /// </summary>
    /// <param name="value"></param>
    /// <param name="targetType"></param>
    /// <param name="parameter"></param>
    /// <param name="culture"></param>
    /// <returns></returns>
    /// <exception cref="NotImplementedException"></exception>
    public object Convert(object value, Type targetType, object parameter, CultureInfo culture)
    {
        // guard null
        if(value is null) { return string.Empty; }

        // guard type
        if (value is not IEnumerable<DataViewModel> enumerable) { throw new ArgumentException($"Can only convert from {nameof(IEnumerable<DataViewModel>)} value"); }

        // guard empty enumerable
        if (enumerable.Count() == 0) { return string.Empty; }

        string returnString = string.Empty;

        // iterate through data, adding content to textbox
        int prevCounter = enumerable.First().LineIdentifier;
        for (int i = 0; i < enumerable.Count(); i++)
        {
            DataViewModel item = enumerable.ElementAt(i);

            // newline if previous counter is lower than this
            if (item.LineIdentifier > prevCounter)
            {
                returnString += NewlineSequence;
                prevCounter = item.LineIdentifier;
            }

            // add character (text)
            returnString += item.DisplayStringUtf16;
        }

        return returnString;
    }

    public object ConvertBack(object value, Type targetType, object parameter, CultureInfo culture)
    {
        throw new NotImplementedException();
    }
}