com.tinkerpop.gremlin.hadoop.process.graph.strategy.HadoopElementStepStrategy Maven / Gradle / Ivy

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package com.tinkerpop.gremlin.hadoop.process.graph.strategy;

import com.tinkerpop.gremlin.hadoop.structure.HadoopElement;
import com.tinkerpop.gremlin.process.Step;
import com.tinkerpop.gremlin.process.Traversal;
import com.tinkerpop.gremlin.process.TraversalEngine;
import com.tinkerpop.gremlin.process.graph.step.sideEffect.GraphStep;
import com.tinkerpop.gremlin.process.graph.step.sideEffect.IdentityStep;
import com.tinkerpop.gremlin.process.graph.step.sideEffect.StartStep;
import com.tinkerpop.gremlin.process.graph.strategy.AbstractTraversalStrategy;
import com.tinkerpop.gremlin.process.util.TraversalHelper;
import com.tinkerpop.gremlin.structure.Edge;
import com.tinkerpop.gremlin.structure.Element;
import com.tinkerpop.gremlin.structure.Vertex;
import com.tinkerpop.gremlin.structure.util.empty.EmptyGraph;

/**
 * @author Marko A. Rodriguez (http://markorodriguez.com)
 */
public class HadoopElementStepStrategy extends AbstractTraversalStrategy {

    private static final HadoopElementStepStrategy INSTANCE = new HadoopElementStepStrategy();

    private HadoopElementStepStrategy() {
    }

    @Override
    public void apply(final Traversal.Admin traversal, final TraversalEngine engine) {
        if (engine.equals(TraversalEngine.STANDARD))
            return;

        final StartStep startStep = (StartStep) TraversalHelper.getStart(traversal);
        if (startStep.startAssignableTo(Vertex.class, Edge.class)) {
            final HadoopElement element = ((StartStep) startStep).getStart();
            traversal.removeStep(0);
            TraversalHelper.getStart(traversal).getLabel().ifPresent(label -> {
                final Step identityStep = new IdentityStep(traversal);
                identityStep.setLabel(label);
                traversal.addStep(0, identityStep);
            });
            traversal.addStep(0, new GraphStep<>(traversal, EmptyGraph.instance(), element.getClass(), element.id()));
        }
    }

    public static HadoopElementStepStrategy instance() {
        return INSTANCE;
    }
}