using System.Linq.Expressions;
using System.Reflection;

namespace Connected.Interop
{
	public static class Nullables
	{
		public static bool IsNullableType(this Type type)
		{
			return type is not null && type.GetTypeInfo().IsGenericType && type.GetGenericTypeDefinition() == typeof(Nullable<>);
		}

		public static bool IsNullAssignable(this Type type)
		{
			return !type.GetTypeInfo().IsValueType || type.IsNullableType();
		}

		public static Type GetNonNullableType(this Type type)
		{
			if (type.IsNullableType())
				return type.GetTypeInfo().GenericTypeArguments[0];

			return type;
		}

		public static Type GetNullAssignableType(this Type type)
		{
			if (!type.IsNullAssignable())
				return typeof(Nullable<>).MakeGenericType(type);

			return type;
		}

		public static ConstantExpression GetNullConstant(this Type type)
		{
			return Expression.Constant(null, type.GetNullAssignableType());
		}
	}
}