Avalonia/src/Markup/Perspex.Markup.Xaml/MarkupExtensions/StaticExtension.cs

// Copyright (c) The Perspex Project. All rights reserved.
// Licensed under the MIT license. See licence.md file in the project root for full license information.

using System;
using System.Linq;
using System.Reflection;
using Glass;
using OmniXaml;

namespace Perspex.Markup.Xaml.MarkupExtensions
{
    public class StaticExtension : MarkupExtension
    {
        public StaticExtension()
        {
        }

        public StaticExtension(string identifier)
        {
            Identifier = identifier;
        }

        public string Identifier { get; set; }

        public override object ProvideValue(MarkupExtensionContext markupExtensionContext)
        {
            var typeRepository = markupExtensionContext.TypeRepository;
            var typeAndMember = GetTypeAndMember(Identifier);
            var prefixAndType = GetPrefixAndType(typeAndMember.Item1);
            var xamlType = typeRepository.GetByPrefix(prefixAndType.Item1, prefixAndType.Item2);
            return GetValue(xamlType.UnderlyingType, typeAndMember.Item2);
        }

        private static Tuple<string, string> GetTypeAndMember(string s)
        {
            var parts = s.Split('.');

            if (parts.Length != 2)
            {
                throw new ArgumentException("Static member must be in the form Type.Member.");
            }

            return Tuple.Create(parts[0], parts[1]);
        }

        private static Tuple<string, string> GetPrefixAndType(string s)
        {
            if (s.Contains(":"))
            {
                return s.Dicotomize(':');
            }
            else
            {
                return new Tuple<string, string>(string.Empty, s);
            }
        }

        private object GetValue(Type type, string name)
        {
            var t = type;

            while (t != null)
            {
                var result = t.GetTypeInfo().DeclaredMembers.FirstOrDefault(x => x.Name == name);

                if (result is PropertyInfo)
                {
                    var property = ((PropertyInfo)result);
                    
                    if (property.GetMethod.IsStatic)
                    {
                        return ((PropertyInfo)result).GetValue(null);
                    }
                }
                else if (result is FieldInfo)
                {
                    return ((FieldInfo)result).GetValue(null);
                }

                t = t.GetTypeInfo().BaseType;
            }

            throw new ArgumentException($"Static member '{type}.{name}' not found.");
        }
    }
}