/// <summary>
/// Creates an observable with two pairwise notification channels by combining the latest values of the specified
/// observable sequences and choosing which channels will receive values based on the specified function.
/// </summary>
/// <typeparam name="TLeft">Type of the left notification channel.</typeparam>
/// <typeparam name="TRight">Type of the right notification channel.</typeparam>
/// <param name="leftSource">The observable sequence that provides notifications for the left channel.</param>
/// <param name="rightSource">The observable sequence that provides notifications for the right channel.</param>
/// <param name="directionSelector">Selects the channels that will receive notifications for every pair.</param>
/// <returns>A new observable sequence containing the latest values in the specified observable sequences.</returns>
public static IObservable <Either <TLeft, TRight> > Pair <TLeft, TRight>(
this IObservable <TLeft> leftSource,
IObservable <TRight> rightSource,
Func <TLeft, TRight, PairDirection> directionSelector)
{
Contract.Requires(leftSource != null);
Contract.Requires(rightSource != null);
Contract.Requires(directionSelector != null);
Contract.Ensures(Contract.Result <IObservable <Either <TLeft, TRight> > >() != null);
return(EitherObservable.Create <TLeft, TRight>(
observer =>
leftSource.Always().StartWith(Maybe.Empty <TLeft>())
.CombineLatest(
rightSource.Always().StartWith(Maybe.Empty <TRight>()),
(left, right) => new
{
left,
right
})
.SubscribeSafe(
pair =>
{
if (!pair.left.HasValue)
{
if (pair.right.HasValue)
{
observer.OnNextRight(pair.right.Value);
}
}
else if (!pair.right.HasValue)
{
observer.OnNextLeft(pair.left.Value);
}
else
{
var left = pair.left.Value;
var right = pair.right.Value;
switch (directionSelector(left, right))
{
case PairDirection.Left:
observer.OnNextLeft(left);
break;
case PairDirection.Right:
observer.OnNextRight(right);
break;
case PairDirection.Both:
observer.OnNextLeft(left);
observer.OnNextRight(right);
break;
case PairDirection.Neither:
break;
default:
throw new InvalidOperationException(Errors.InvalidPairDirectionValue);
}
}
},
observer.OnError,
observer.OnCompleted)));
}
