private List collectBranchOperatorsStartingFrom()

in wayang-commons/wayang-core/src/main/java/org/apache/wayang/core/optimizer/enumeration/PlanEnumerator.java [394:445]
43 lines of code
12 McCabe index (conditional complexity)

    private List<Operator> collectBranchOperatorsStartingFrom(Operator startOperator) {
        List<Operator> branch = new LinkedList<>();
        Operator currentOperator = startOperator;
        while (true) {
            boolean isEnumeratable = currentOperator.isExecutionOperator() ||
                    currentOperator.isAlternative() ||
                    currentOperator.isLoopSubplan();
            if (!isEnumeratable) {
                this.logger.trace("Cannot enumerate branch with {}.", currentOperator);
                return null;
            }
            branch.add(currentOperator);

            // Cut branches if requested.
            if (!this.isEnumeratingBranchesFirst) break;

            // Try to advance. This requires certain conditions, though.
            OutputSlot<?> followableOutput;
            if (currentOperator.isLoopHead()) {
                LoopHeadOperator loopHeadOperator = (LoopHeadOperator) currentOperator;
                if (loopHeadOperator.getLoopBodyOutputs().size() != 1) {
                    break;
                }
                followableOutput = WayangCollections.getSingle(loopHeadOperator.getLoopBodyOutputs());

            } else {
                if (currentOperator.getNumOutputs() != 1) {
                    break;
                }
                followableOutput = currentOperator.getOutput(0);
            }

            if (followableOutput.getOccupiedSlots().size() != 1) {
                this.logger.trace("Stopping branch, because operator does not feed exactly one operator.");
                break;
            }
            Operator nextOperator = currentOperator.getOutput(0).getOccupiedSlots().get(0).getOwner();
            if (nextOperator.getNumInputs() != 1) {
                this.logger.trace("Stopping branch, because next operator does not have exactly one input.");
                break;
            }

            if (nextOperator == startOperator) {
                break;
            }

            currentOperator = nextOperator;
        }
        this.logger.trace("Determined branch: {}.", currentOperator);

        return branch;
    }