using System;

using System.ComponentModel;

using System.Reactive.Linq;

using System.Reflection;

namespace ReactiveUI

{

/// <summary>

/// Generates Observables based on observing INotifyPropertyChanged objects

/// </summary>

public class INPCObservableForProperty : ICreatesObservableForProperty

{

public int GetAffinityForObject(Type type, string propertyName, bool beforeChanged)

{

var target = beforeChanged ? typeof (INotifyPropertyChanging) : typeof (INotifyPropertyChanged);

return target.GetTypeInfo().IsAssignableFrom(type.GetTypeInfo()) ? 5 : 0;

}

public IObservable<IObservedChange<object, object>> GetNotificationForProperty(object sender, string propertyName, bool beforeChanged)

{

var before = sender as INotifyPropertyChanging;

var after = sender as INotifyPropertyChanged;

if (beforeChanged ? before == null : after == null) {

return Observable.Never<IObservedChange<object, object>>();

}

return Observable.Create<IObservedChange<object, object>>(subj => {

if (beforeChanged) {

var obs = Observable.FromEventPattern<PropertyChangingEventHandler, PropertyChangingEventArgs>(

x => before.PropertyChanging += x, x => before.PropertyChanging -= x);

return obs.Where(x => x.EventArgs.PropertyName == propertyName)

.Select(x => (IObservedChange<object, object>) new ObservedChange<object, object>() { Sender = sender, PropertyName = x.EventArgs.PropertyName })

.Subscribe(subj);

} else {

var obs = Observable.FromEventPattern<PropertyChangedEventHandler, PropertyChangedEventArgs>(

x => after.PropertyChanged += x, x => after.PropertyChanged -= x);

return obs.Where(x => x.EventArgs.PropertyName == propertyName)

.Select(x => (IObservedChange<object, object>) new ObservedChange<object, object>() { Sender = sender, PropertyName = x.EventArgs.PropertyName })

.Subscribe(subj);

}

});

}

}

}