public IObservable <IChangeSet <T> > Run()
{
return(Observable.Create <IChangeSet <T> >(observer =>
{
var locker = new object();
Func <T, bool> predicate = t => false;
var all = new List <ItemWithMatch>();
var filtered = new ChangeAwareList <ItemWithMatch>();
//requery when predicate changes
var predicateChanged = _predicates.Synchronize(locker)
.Select(newPredicate =>
{
predicate = newPredicate;
Requery(predicate, all, filtered);
return filtered.CaptureChanges();
});
/*
* Apply the transform operator so 'IsMatch' state can be evalutated and captured one time only
* This is to eliminate the need to re-apply the predicate when determining whether an item was previously matched
*/
var filteredResult = _source.Synchronize(locker)
.Transform(t => new ItemWithMatch(t, predicate(t)))
.Select(changes =>
{
all.Clone(changes); //keep track of all changes
filtered.Filter(changes, iwm => iwm.IsMatch); //maintain filtered result
return filtered.CaptureChanges();
});
return predicateChanged.Merge(filteredResult)
.NotEmpty()
.Select(changes => changes.Transform(iwm => iwm.Item))
.SubscribeSafe(observer);
}));
}