Add NullableDefaultNumericConverter

StabilityMatrix.Avalonia/Converters/NullableDefaultNumericConverter.cs

@@ -0,0 +1,84 @@
+using System;
+using System.ComponentModel;
+using System.Diagnostics.CodeAnalysis;
+using System.Globalization;
+using System.Numerics;
+using Avalonia.Data.Converters;
+
+namespace StabilityMatrix.Avalonia.Converters;
+
+/// <summary>
+/// Converts a possibly boxed nullable value type to its default value
+/// </summary>
+public class NullableDefaultNumericConverter<TSource, TTarget> : IValueConverter
+    where TSource : unmanaged, INumber<TSource>
+    where TTarget : unmanaged, INumber<TTarget>
+{
+    public ReturnBehavior NanHandling { get; set; } = ReturnBehavior.DefaultValue;
+
+    /// <summary>
+    /// Unboxes a nullable value type
+    /// </summary>
+    private TSource Unbox(TTarget? value)
+    {
+        if (!value.HasValue)
+        {
+            return default;
+        }
+
+        if (TTarget.IsNaN(value.Value))
+        {
+            return NanHandling switch
+            {
+                ReturnBehavior.DefaultValue => default,
+                ReturnBehavior.Throw => throw new InvalidCastException("Cannot convert NaN to a numeric type"),
+                _
+                    => throw new InvalidEnumArgumentException(
+                        nameof(NanHandling),
+                        (int)NanHandling,
+                        typeof(ReturnBehavior)
+                    )
+            };
+        }
+
+        return (TSource)System.Convert.ChangeType(value.Value, typeof(TSource));
+    }
+
+    /// <summary>
+    /// Convert a value type to a nullable value type
+    /// </summary>
+    public object? Convert(object? value, Type targetType, object? parameter, CultureInfo culture)
+    {
+        if (targetType != typeof(TTarget?) && !targetType.IsAssignableTo(typeof(TTarget)))
+        {
+            // ReSharper disable once LocalizableElement
+            throw new ArgumentException(
+                $"Convert Target type {targetType.Name} must be assignable to {typeof(TTarget).Name}"
+            );
+        }
+
+        return (TTarget?)System.Convert.ChangeType(value, typeof(TTarget));
+    }
+
+    /// <summary>
+    /// Convert a nullable value type to a value type
+    /// </summary>
+    public object ConvertBack(object? value, Type targetType, object? parameter, CultureInfo culture)
+    {
+        if (!targetType.IsAssignableTo(typeof(TSource)))
+        {
+            // ReSharper disable once LocalizableElement
+            throw new ArgumentException(
+                $"ConvertBack Target type {targetType.Name} must be assignable to {typeof(TSource).Name}"
+            );
+        }
+
+        return Unbox((TTarget?)value);
+    }
+
+    public enum ReturnBehavior
+    {
+        DefaultValue,
+        Throw
+    }
+}

StabilityMatrix.Avalonia/Converters/NullableDefaultNumericConverters.cs

@@ -0,0 +1,6 @@
+namespace StabilityMatrix.Avalonia.Converters;
+
+public static class NullableDefaultNumericConverters
+{
+    public static readonly NullableDefaultNumericConverter<int, decimal> IntToDecimal = new();
+}