DynamicEventHandler for C# Metro Apps / WinRT / Universal

using System;
using System.Reflection;
using System.Linq;
using Singularity.Core;

#if NETFX_CORE

using Windows.UI.Xaml;
using System.Runtime.InteropServices.WindowsRuntime;

#else

using System.Windows;
using System.Windows.Markup;

#endif

/// <summary>
/// By: Caino MDK
/// </summary>
namespace Singularity.Core
{
    public sealed class DynamicEventHandler : DisposableBase
    {
        private EventInfo eventInfo;
        private Delegate handler;

#if NETFX_CORE
        private Action<EventRegistrationToken> remove;
#endif

        public string EventName { get; private set; }

        public object AssociatedObject { get; private set; }

        public Action<object, object> EventHandler { get; private set; }

        public DynamicEventHandler(object associatedObject, string eventName, Action<object, object> eventHandler)
        {
            this.EventName = eventName;
            this.AssociatedObject = associatedObject;
            this.EventHandler = eventHandler;

            this.AttachEvent();
        }

        private void AttachEvent()
        {
            this.eventInfo = this.AssociatedObject.GetType().GetRuntimeEvent(this.EventName);

            if (eventInfo == null)
                return;

#if NETFX_CORE

            var addMethodInfo = eventInfo.AddMethod;
            var removeMethodInfo = eventInfo.RemoveMethod;

            var eventHandlerType = addMethodInfo.GetParameters()[0].ParameterType;

            this.remove = x => removeMethodInfo.Invoke(this.AssociatedObject, new object[] { x });

            var method = this.GetType().GetRuntimeMethods().First(x => x.Name == "ExecuteCommand");
            this.handler = method.CreateDelegate(eventInfo.EventHandlerType, this);

            WindowsRuntimeMarshal.AddEventHandler(x => this.AddEventHandler(addMethodInfo, x), remove, this.handler);
#else
            var method = this.GetType().GetRuntimeMethods().First(x => x.Name == "ExecuteCommand");
            this.handler = method.CreateDelegate(eventInfo.EventHandlerType, this);
            this.eventInfo.AddEventHandler(this.AssociatedObject, this.handler);

#endif
        }

#if NETFX_CORE

        private EventRegistrationToken AddEventHandler(MethodInfo addMethodInfo, Delegate method)
        {
            var token = addMethodInfo.Invoke(this.AssociatedObject, new object[] { method });

            // in some conditions (I never found out why) the "get" of the event does not return a
            // EventRegistrationToken. In this case we have to use our workaround
            // If someone has an idea why this is happening... please notify me
            if (token == null)
            {
                var eventTokenTable = this.AssociatedObject.GetType().GetTypeInfo().GetDeclaredField("_" + this.EventName);

                // maybe the tokentable is named camelcase
                if (eventTokenTable == null)
                {
                    eventTokenTable = this.AssociatedObject.GetType().GetTypeInfo().GetDeclaredField(this.EventName.ToCamelCase());
                }

                // still no table? maybe camelcased with underscore
                if (eventTokenTable == null)
                {
                    eventTokenTable = this.AssociatedObject.GetType().GetTypeInfo().GetDeclaredField("_" + this.EventName.ToCamelCase());
                }

                // still no table? fuck this... I don't know
                if (eventTokenTable == null)
                    throw new Exception("No token for event found");

                var eventTokenTableInstance = eventTokenTable.GetValue(this.AssociatedObject);
                var getTokenMethod = eventTokenTableInstance.GetType().GetTypeInfo().GetDeclaredMethod("GetToken");
                token = getTokenMethod.Invoke(eventTokenTableInstance, new object[] { method });
            }

            return (EventRegistrationToken)token;
        }

#endif

        private void DetachEvent()
        {
#if NETFX_CORE
            if (this.remove == null || this.handler == null)
                return;

            WindowsRuntimeMarshal.RemoveEventHandler(this.remove, this.handler);

#else
            if (this.eventInfo == null || this.handler == null)
                return;

            this.eventInfo.RemoveEventHandler(this.AssociatedObject, this.handler);
#endif
            this.eventInfo = null;
            this.handler = null;
        }

        protected override void OnDispose(bool disposeManaged)
        {
            if (disposeManaged)
            {
                this.DetachEvent();
                this.AssociatedObject = null;
                this.EventHandler = null;
            }
        }

        private void ExecuteCommand(object sender, object args)
        {
            if (this.EventHandler != null)
            {
                this.EventHandler(sender, args);
            }

#if NETFX_CORE
            var handledProperty = args.GetType().GetRuntimeProperty("Handled");
#else
            var handledProperty = args.GetType().GetProperty("Handled");
#endif
            if (handledProperty != null)
            {
                handledProperty.SetValue(args, true);
            }
        }
    }
}