MultiTerm/MultiTerm.Wpf/ValueConverters/EnumValueToEnumDescriptionConverter.cs

using System;
using System.Collections;
using System.Collections.Generic;
using System.Globalization;
using System.Windows.Data;
using Common.Helpers;

namespace MultiTerm.Wpf.ValueConverters;

/// <summary>
/// Can convert an enum value to a human readable string. Therefore it uses the Description attribute if set.
/// </summary>
[ValueConversion(typeof(Enum), typeof(Enum))]
public class EnumValueToEnumDescriptionConverter : IValueConverter
{
    /// <summary>
    /// Converts complete enum to <see cref="IEnumerable"/> of <see cref="string"/>.
    /// Also converts single enum values to <see cref="string"/>.
    /// </summary>
    /// <returns>description or humanized string of the enum value</returns>
    /// <exception cref="NotImplementedException">if <paramref name="value"/> is another type than an <see cref="IEnumerable"/> or <see cref="Enum"/></exception>
    public object Convert(object value, Type targetType, object parameter, CultureInfo culture)
    {
        if(value is IEnumerable arrayOfEnumValues)
        {
            List<string> outputValues = new();
            foreach (var item in arrayOfEnumValues)
            {
                outputValues.Add(EnumHelpers.GetEnumDescription((Enum)item));
            }
            return outputValues;
        }
        else if(value is Enum)
        {
            return EnumHelpers.GetEnumDescription((Enum)value);
        }
        else
        {
            throw new NotImplementedException();
        }
    }

    /// <summary>
    /// Converts single string values to Enum of <paramref name="targetType"/>.
    /// </summary>
    /// <returns>enum value or empty object if no matching enum value was found</returns>
    /// <exception cref="ArgumentException">if value is not a string</exception>
    public object ConvertBack(object value, Type targetType, object parameter, CultureInfo culture)
    {
        // guard that it is a string, cannot be a collection
        if (value is not string stringValue) { throw new ArgumentException("Can only convert string values."); }

        // find value by description
        var objOfEnumType = EnumHelpers.CreateInstanceOfEnumType(targetType);
        var enumObjectWithMatchingDescription = EnumHelpers.GetEnumValueByDescription(objOfEnumType, stringValue);

        // return new object if none found
        if(enumObjectWithMatchingDescription == null)
        { return new object(); }

        return enumObjectWithMatchingDescription;
    }
}