    001/*
    002 * Copyright (c) 2016 Chris K Wensel <chris@wensel.net>. All Rights Reserved.
    003 *
    004 * Project and contact information: http://www.cascading.org/
    005 *
    006 * This file is part of the Cascading project.
    007 *
    008 * Licensed under the Apache License, Version 2.0 (the "License");
    009 * you may not use this file except in compliance with the License.
    010 * You may obtain a copy of the License at
    011 *
    012 *     http://www.apache.org/licenses/LICENSE-2.0
    013 *
    014 * Unless required by applicable law or agreed to in writing, software
    015 * distributed under the License is distributed on an "AS IS" BASIS,
    016 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
    017 * See the License for the specific language governing permissions and
    018 * limitations under the License.
    019 */
    020
    021package cascading.flow.planner.rule.expression;
    022
    023import cascading.flow.planner.iso.expression.ElementCapture;
    024import cascading.flow.planner.iso.expression.ElementExpression;
    025import cascading.flow.planner.iso.expression.ExpressionGraph;
    026import cascading.flow.planner.iso.expression.FlowElementExpression;
    027import cascading.flow.planner.rule.RuleExpression;
    028import cascading.flow.planner.rule.expressiongraph.ConsecutiveNoOpPipesExpressionGraph;
    029import cascading.pipe.Pipe;
    030import cascading.tap.Tap;
    031
    032import static cascading.flow.planner.iso.expression.OrElementExpression.or;
    033
    034/**
    035 * This rule prevents a multi-graph from being formed when all no-op Pipe instances are removed from the assembly.
    036 * <p>
    037 * Adding support for multi-graphs in the FlowElementGraph is the better long term solution.
    038 */
    039public class NoOpPipeMultiGraphExpression extends RuleExpression
    040  {
    041  public static final ElementExpression SPLIT = or(
    042    new FlowElementExpression( Pipe.class ), new FlowElementExpression( Tap.class )
    043  );
    044
    045  public static final ElementExpression JOIN = or(
    046    new FlowElementExpression( Pipe.class ), new FlowElementExpression( Tap.class )
    047  );
    048
    049  public NoOpPipeMultiGraphExpression()
    050    {
    051    super(
    052      new ConsecutiveNoOpPipesExpressionGraph(),
    053      new ExpressionGraph()
    054        .arcs(
    055          SPLIT,
    056          new FlowElementExpression( ElementCapture.Primary, true, Pipe.class ),
    057          JOIN
    058        )
    059        .arcs(
    060          SPLIT,
    061          new FlowElementExpression( ElementCapture.Secondary, true, Pipe.class ),
    062          JOIN
    063        )
    064    );
    065    }
    066  }