Plane.Libraries/Plane.Windows/Converters/NullableBooleanConverter.cs

using System;
using System.Collections.Generic;
using System.Globalization;
using System.Linq;
using System.Text;
using System.Windows;
using System.Windows.Data;

namespace Plane.Windows.Converters
{
    public class NullableBooleanConverter<T> : IValueConverter
    {
        public NullableBooleanConverter(T trueValue, T falseValue, T nullValue)
        {
            True = trueValue;
            False = falseValue;
            Null = nullValue;
        }

        public T True { get; set; }
        public T False { get; set; }
        public T Null { get; set; }

        public virtual object Convert(object value, Type targetType, object parameter, CultureInfo culture)
        {
            if (value != null && !(value is bool?))
                throw new InvalidOperationException("The target must be a Nullable<bool>");
            var val = (bool?)value;
            return
                val == null
                ? Null
                : val.Value
                  ? True
                  : False;
        }

        public virtual object ConvertBack(object value, Type targetType, object parameter, CultureInfo culture)
        {
            if (!(value is T))
                throw new InvalidOperationException($"The target must be a {typeof(T).Name}");
            var comparer = EqualityComparer<T>.Default;
            var val = (T)value;
            return
                comparer.Equals(val, True)
                ? true
                : comparer.Equals(val, False)
                  ? false
                  : (bool?)null;
        }
    }
}