MultiTerm/MultiTerm.Wpf/ValueConverters/EnumDescriptionToMenuItemConverter.cs

using System;
using System.Globalization;
using System.Windows.Data;
using System.Windows.Controls;
using Common.Helpers;

namespace MultiTerm.Wpf.ValueConverters;

/// <summary>
/// Converts an Enum (using its Description Attribute) to a Menu Item.
/// The Menu Item has the Description assigned to its Header.
/// If the Enum has no Description, it will convert the Enum Value to string and use this.
/// </summary>
[ValueConversion(typeof(Enum), typeof(MenuItem))]
public class EnumDescriptionToMenuItemConverter : IValueConverter
{
    /// <summary>
    /// Convert from Data Source to Dependency Object type.
    /// Here: Enum type to MenuItem.
    /// </summary>
    /// <param name="value">value to convert</param>
    /// <param name="targetType">type to convert to</param>
    /// <param name="parameter">no parameter required</param>
    /// <param name="culture">most likely CultureInfo.CurrentCulture</param>
    /// <returns>New MenuItem with Enum description in Header property</returns>
    public object Convert(object value, Type targetType, object parameter, CultureInfo culture)
    {
        Enum enumValue = (Enum)value;
        string description = EnumHelpers.GetEnumDescription(enumValue);
        MenuItem newMenuItem = new()
        {
            Header = description
        };
        return newMenuItem;
    }

    /// <summary>
    /// Convert from Dependency Object type to Data Source type.
    /// Here: MenuItem to Enum type.
    /// </summary>
    /// <param name="value">value to convert</param>
    /// <param name="targetType">type to convert to</param>
    /// <param name="parameter">no parameter required</param>
    /// <param name="culture">most likely CultureInfo.CurrentCulture</param>
    /// <returns>Enum value of the MenuItem that was converted</returns>
    public object ConvertBack(object value, Type targetType, object parameter, CultureInfo culture)
    {
        // guard argument null
        if (targetType == null) { throw new ArgumentNullException(nameof(targetType)); }
        if (value == null) { throw new ArgumentNullException(nameof(value)); }

        // extract menu item and guard null
        if (value is not MenuItem menuObject)
        {
            throw new Exception($"Cannot convert value that is not of type {nameof(MenuItem)} with {nameof(EnumDescriptionToMenuItemConverter)}");
        }

        // get all enum descriptions and iterate
        var enumObj = EnumHelpers.CreateInstanceOfEnumType(targetType);
        var descriptionToEnumValue = EnumHelpers.GetAllEnumDescriptions(enumObj);
        foreach (var kvp in descriptionToEnumValue)
        {
            // compare key (enum description) to menu header
            if(String.Compare(kvp.Key, menuObject.Header.ToString(), true) == 0)
            {
                // if correct description is found, return according enum value
                return kvp.Value;
            }
        }

        // if nothing worked => return value 
        return value;
    }
}