Handles a Decision according to SWF docs.
        See: http://docs.aws.amazon.com/amazonswf/latest/apireference/API_Decision.html

def handle_decisions(self, event_id, decisions):
        """
        Handles a Decision according to SWF docs.
        See: http://docs.aws.amazon.com/amazonswf/latest/apireference/API_Decision.html
        """
        # handle each decision separately, in order
        for decision in decisions:
            decision_type = decision["decisionType"]
            attributes_key = "{0}DecisionAttributes".format(
                decapitalize(decision_type))
            attributes = decision.get(attributes_key, {})
            if decision_type == "CompleteWorkflowExecution":
                self.complete(event_id, attributes.get("result"))
            elif decision_type == "FailWorkflowExecution":
                self.fail(event_id, attributes.get(
                    "details"), attributes.get("reason"))
            elif decision_type == "ScheduleActivityTask":
                self.schedule_activity_task(event_id, attributes)
            else:
                # TODO: implement Decision type: CancelTimer
                # TODO: implement Decision type: CancelWorkflowExecution
                # TODO: implement Decision type: ContinueAsNewWorkflowExecution
                # TODO: implement Decision type: RecordMarker
                # TODO: implement Decision type: RequestCancelActivityTask
                # TODO: implement Decision type: RequestCancelExternalWorkflowExecution
                # TODO: implement Decision type: ScheduleLambdaFunction
                # TODO: implement Decision type: SignalExternalWorkflowExecution
                # TODO: implement Decision type: StartChildWorkflowExecution
                # TODO: implement Decision type: StartTimer
                raise NotImplementedError(
                    "Cannot handle decision: {0}".format(decision_type))

        # finally decrement counter if and only if everything went well
        self.open_counts["openDecisionTasks"] -= 1