| /* |
| * Licensed to the Apache Software Foundation (ASF) under one |
| * or more contributor license agreements. See the NOTICE file |
| * distributed with this work for additional information |
| * regarding copyright ownership. The ASF licenses this file |
| * to you under the Apache License, Version 2.0 (the |
| * "License"); you may not use this file except in compliance |
| * with the License. You may obtain a copy of the License at |
| * |
| * http://www.apache.org/licenses/LICENSE-2.0 |
| * |
| * Unless required by applicable law or agreed to in writing, software |
| * distributed under the License is distributed on an "AS IS" BASIS, |
| * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. |
| * See the License for the specific language governing permissions and |
| * limitations under the License. |
| */ |
| |
| package org.apache.wayang.core.plan.wayangplan; |
| |
| import java.util.Optional; |
| |
| /** |
| * Visitor (as in the Visitor Pattern) for {@link WayangPlan}s. |
| */ |
| public abstract class TopDownPlanVisitor<Payload, Return> { |
| |
| public Return process(Operator operator, OutputSlot<?> fromOutputSlot, Payload payload) { |
| final Optional<Return> returnOptional = this.prepareVisit(operator, fromOutputSlot, payload); |
| if (returnOptional != null) { |
| return returnOptional.orElse(null); |
| } |
| Return result = operator.accept(this, fromOutputSlot, payload); |
| this.followUp(operator, fromOutputSlot, payload, result); |
| |
| return result; |
| } |
| |
| protected abstract Optional<Return> prepareVisit(Operator operator, OutputSlot<?> fromOutputSlot, Payload payload); |
| |
| protected abstract void followUp(Operator operator, OutputSlot<?> fromOutputSlot, Payload payload, Return result); |
| |
| /** |
| * todo |
| * |
| * @param operatorAlternative |
| */ |
| public abstract Return visit(OperatorAlternative operatorAlternative, OutputSlot<?> fromOutputSlot, Payload payload); |
| |
| public Return visit(Subplan subplan, OutputSlot<?> fromOutputSlot, Payload payload) { |
| if (fromOutputSlot == null) { |
| return subplan.getSink().accept(this, fromOutputSlot, payload); |
| } else { |
| final OutputSlot<Object> innerOutputSlot = subplan.traceOutput(fromOutputSlot).unchecked(); |
| return innerOutputSlot.getOwner().accept(this, innerOutputSlot, payload); |
| } |
| } |
| |
| /** |
| * todo |
| */ |
| public abstract Return visit(ActualOperator operator, OutputSlot<?> fromOutputSlot, Payload payload); |
| |
| protected Optional<Return> proceed(Operator operator, int inputIndex, Payload payload) { |
| final InputSlot<Object> outerInputSlot = operator |
| .getOutermostInputSlot(operator.getInput(inputIndex)) |
| .unchecked(); |
| final OutputSlot<Object> occupant = outerInputSlot.getOccupant(); |
| if (occupant != null) { |
| return Optional.ofNullable(this.process(occupant.getOwner(), occupant, payload)); |
| } else { |
| return null; |
| } |
| } |
| |
| } |