// FIXME:
// 1) JUST FOR WARM UP: .map() incoming Dictionary<string, object> to MessageDTO. For that purpose use MessageDTO.price()
// NOTE: Incoming Dictionary<string, object> contains keys PRICE_KEY and CURRENCY_KEY
// NOTE: Use MessageMapper utility class for message validation and transformation
// Visible for testing
IObservable <Dictionary <string, object> > SelectOnlyPriceUpdateEvents(IObservable <Dictionary <string, object> > input)
{
// TODO: filter only Price messages
// TODO: verify that price message are valid
// HINT: Use MessageMapper methods to perform filtering and validation
return(input.Where(m => MessageMapper.IsPriceMessageType(m) && MessageMapper.IsValidPriceMessage(m)));
}