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  }