using System;

using System.ComponentModel;

using System.Linq.Expressions;

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, Expression expression, bool beforeChanged)

{

var before = sender as INotifyPropertyChanging;

var after = sender as INotifyPropertyChanged;

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

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

}

var memberInfo = expression.GetMemberInfo();

if (beforeChanged) {

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

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

if (expression.NodeType == ExpressionType.Index) {

return obs.Where(x => string.IsNullOrEmpty(x.EventArgs.PropertyName)

|| x.EventArgs.PropertyName.Equals(memberInfo.Name + "[]"))

.Select(x => new ObservedChange<object, object>(sender, expression));

} else {

return obs.Where(x => string.IsNullOrEmpty(x.EventArgs.PropertyName)

|| x.EventArgs.PropertyName.Equals(memberInfo.Name))

.Select(x => new ObservedChange<object, object>(sender, expression));

}

} else {

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

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

if (expression.NodeType == ExpressionType.Index) {

return obs.Where(x => string.IsNullOrEmpty(x.EventArgs.PropertyName)

|| x.EventArgs.PropertyName.Equals(memberInfo.Name + "[]"))

.Select(x => new ObservedChange<object, object>(sender, expression));

} else {

return obs.Where(x => string.IsNullOrEmpty(x.EventArgs.PropertyName)

|| x.EventArgs.PropertyName.Equals(memberInfo.Name))

.Select(x => new ObservedChange<object, object>(sender, expression));

}

}

}

}

}