public StockObserver(StockObservable stockObservable, TextWriter writer)
{
_writer = writer;
var priceChangedEvents = Observable.FromEventPattern <EventHandler <PriceChangedEventData>, PriceChangedEventData>(
h => stockObservable.PriceChanged += h,
h => stockObservable.PriceChanged -= h)
.Select(e => e.EventArgs)
.Synchronize();
var drasticChanges = from priceChange in priceChangedEvents
group priceChange by priceChange.QuoteSymbol
into company
from priceChangePair in company.Buffer(2, 1)
let changeRatio = CalculateChangeRatio(priceChangePair)
where changeRatio > MaxChangeRatio
select new DrasticChange
{
Symbol = company.Key,
ChangeRatio = changeRatio,
OldPrice = priceChangePair[0].Price,
NewPrice = priceChangePair[1].Price
};
_subscriptions = drasticChanges.Subscribe(OnDrasticChange);
}
public void should_process_ticks()
{
using (TextWriter writer = new StringWriter())
{
Console.SetOut(writer);
var stockTicker = new StockObservable();
var sut = new StockObserver(stockTicker, writer);
stockTicker.Notify("yahoo", 100);
stockTicker.Notify("amazon", 100);
stockTicker.Notify("amazon", 125);
stockTicker.Notify("yahoo", 200);
writer.Flush();
writer.ToString().Should().Contain("Stock: yahoo has changed price from 100 to 200, that is a ratio of 1");
writer.ToString().Should().Contain("Stock: amazon has changed price from 100 to 125, that is a ratio of 0.25");
}
}
