gaemstone/src/gaemstone/Utility/ReflectionExtensions.cs

using System;
using System.Collections.Generic;
using System.Collections.ObjectModel;
using System.Linq;
using System.Reflection;
using System.Text;

namespace gaemstone.Utility;

public static class ReflectionExtensions
{
	public static string GetFriendlyName(this Type type)
	{
		if (!type.IsGenericType) return type.Name;
		var name = type.Name;
		var sb = new StringBuilder(name[..name.IndexOf('`')]);
		sb.Append('<');
		sb.AppendJoin(",", type.GenericTypeArguments.Select(GetFriendlyName));
		sb.Append('>');
		return sb.ToString();
	}

	public static T? Get<T>(this MemberInfo member)
		where T : Attribute => member.GetCustomAttribute<T>();
	public static IEnumerable<T> GetMultiple<T>(this MemberInfo member)
		where T : Attribute => member.GetCustomAttributes<T>();
	public static bool Has<T>(this MemberInfo member)
		where T : Attribute => member.GetCustomAttribute<T>() != null;

	public static T? Get<T>(this ParameterInfo member)
		where T : Attribute => member.GetCustomAttribute<T>();
	public static IEnumerable<T> GetMultiple<T>(this ParameterInfo member)
		where T : Attribute => member.GetCustomAttributes<T>();
	public static bool Has<T>(this ParameterInfo member)
		where T : Attribute => member.GetCustomAttribute<T>() != null;


	public static bool IsNullable(this PropertyInfo property) =>
		IsNullable(property.PropertyType, property.DeclaringType, property.CustomAttributes);
	public static bool IsNullable(this FieldInfo field) =>
		IsNullable(field.FieldType, field.DeclaringType, field.CustomAttributes);
	public static bool IsNullable(this ParameterInfo parameter) =>
		IsNullable(parameter.ParameterType, parameter.Member, parameter.CustomAttributes);

	// https://stackoverflow.com/a/58454489
	static bool IsNullable(Type memberType, MemberInfo? declaringType, IEnumerable<CustomAttributeData> customAttributes)
	{
		if (memberType.IsValueType) return (Nullable.GetUnderlyingType(memberType) != null);

		var nullable = customAttributes.FirstOrDefault(
			x => (x.AttributeType.FullName == "System.Runtime.CompilerServices.NullableAttribute"));
		if ((nullable != null) && (nullable.ConstructorArguments.Count == 1)) {
			var attributeArgument = nullable.ConstructorArguments[0];
			if (attributeArgument.ArgumentType == typeof(byte[])) {
				var args = (ReadOnlyCollection<CustomAttributeTypedArgument>)attributeArgument.Value!;
				if ((args.Count > 0) && (args[0].ArgumentType == typeof(byte)))
					return (byte)args[0].Value! == 2;
			} else if (attributeArgument.ArgumentType == typeof(byte))
				return (byte)attributeArgument.Value! == 2;
		}

		for (var type = declaringType; type != null; type = type.DeclaringType) {
			var context = type.CustomAttributes.FirstOrDefault(
				x => (x.AttributeType.FullName == "System.Runtime.CompilerServices.NullableContextAttribute"));
			if ((context != null) && (context.ConstructorArguments.Count == 1) &&
				(context.ConstructorArguments[0].ArgumentType == typeof(byte)))
				return (byte)context.ConstructorArguments[0].Value! == 2;
		}

		// Couldn't find a suitable attribute.
		return false;
	}
}