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using System;

using System.Collections.Generic;

using System.Collections.ObjectModel;

using System.Diagnostics;

using System.Linq;

using System.Reactive;

using System.Reactive.Linq;

using System.Reflection;

using System.Reflection.Emit;

namespace UnitTests

{

internal class EventListener

{

#region static helpers fields

private static readonly ConstructorInfo _dictionaryCto =

typeof(Dictionary<string, object>).GetConstructor(Type.EmptyTypes);

private static readonly MethodInfo _dictionarySetItemMethod =

typeof(Dictionary<string, object>).GetProperty("Item").GetSetMethod();

private static readonly MethodInfo _listAddMethod = typeof(ObservableCollection<Dictionary<string, object>>).GetMethod("Add");

#endregion

private readonly ObservableCollection<Dictionary<string, object>> _savedArgs = new ObservableCollection<Dictionary<string, object>>();

private List<dynamic> _dynamicSavedArgs;

public EventListener(object raiser, string eventName)

{

EventInfo eventInfo = raiser.GetType().GetEvent(eventName);

var handler = CreateCompatibleListener(eventInfo);

eventInfo.AddEventHandler(raiser, handler);

}

private Delegate CreateCompatibleListener(EventInfo eventInfo)

{

string methodName = eventInfo.Name + "_handler_";

var delegateType = eventInfo.EventHandlerType;

var invokeMethod = delegateType.GetMethod("Invoke");

if (invokeMethod.ReturnType != typeof(void))

throw new NotSupportedException();

var delegateParameters = invokeMethod.GetParameters();

var args = new List<Type> {typeof (EventListener)};

args.AddRange(delegateParameters.Select(p=>p.ParameterType));

var dm = new DynamicMethod(methodName,

typeof (void),

args.ToArray(),

typeof(EventListener));

var generator = dm.GetILGenerator(256);

generator.DeclareLocal(typeof (Dictionary<string, object>));

generator.Emit(OpCodes.Newobj, _dictionaryCto);

generator.Emit(OpCodes.Stloc_0);

var savedArgsField = GetType().GetField("_savedArgs", BindingFlags.Instance | BindingFlags.NonPublic);

Debug.Assert(savedArgsField != null);

// add the arguments received to the dictionary

for (var idx = 0; idx < delegateParameters.Length; idx++)

{

var parameter = delegateParameters[idx];

dm.DefineParameter(idx + 2, ParameterAttributes.In, parameter.Name);

generator.Emit(OpCodes.Ldloc_0);

generator.Emit(OpCodes.Ldstr, parameter.Name);

generator.Emit(OpCodes.Ldarg, idx + 1);

if (parameter.ParameterType.IsValueType)

{

generator.Emit(OpCodes.Box, parameter.ParameterType);

}

generator.Emit(OpCodes.Callvirt, _dictionarySetItemMethod);

}

// add the dictionary to the list

generator.Emit(OpCodes.Ldarg_0);

generator.Emit(OpCodes.Ldfld, savedArgsField);

generator.Emit(OpCodes.Ldloc_0);

generator.Emit(OpCodes.Callvirt, _listAddMethod);

generator.Emit(OpCodes.Ret);

return dm.CreateDelegate(delegateType, this);

}

public ObservableCollection<Dictionary<string, object>> SavedArgs

{

get

{

return _savedArgs;

}

}

public IList<dynamic> DynamicSavedArgs

{

get

{

return _dynamicSavedArgs ??

(_dynamicSavedArgs = _savedArgs.Select(dict => (dynamic) dict.ToExpando()).ToList());

}

}

}

}