gremlin-core/src/main/java/org/apache/tinkerpop/gremlin/process/traversal/util/TraversalUtil.java

/*
 * 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.tinkerpop.gremlin.process.traversal.util;

import org.apache.tinkerpop.gremlin.process.traversal.Step;
import org.apache.tinkerpop.gremlin.process.traversal.Traversal;
import org.apache.tinkerpop.gremlin.process.traversal.Traverser;
import org.apache.tinkerpop.gremlin.structure.util.CloseableIterator;

import java.util.Iterator;
import java.util.NoSuchElementException;

/**
 * @author Marko A. Rodriguez (http://markorodriguez.com)
 */
public final class TraversalUtil {

    private TraversalUtil() {
    }

    public static <S, E> E apply(final Traverser.Admin<S> traverser, final Traversal.Admin<S, E> traversal) {
        final Traverser<S> split = prepare(traverser, traversal);
        try {
            return traversal.next(); // map
        } catch (final NoSuchElementException e) {
            final String clazzOfTraverserValue = null == split.get() ? "null" : split.get().getClass().getSimpleName();
            throw new IllegalArgumentException(String.format("The provided traverser does not map to a value: %s[%s]->%s[%s] parent[%s]",
                    split, clazzOfTraverserValue, traversal, traversal.getClass().getSimpleName(), traversal.getParent().asStep().getTraversal()));
        } finally {
            //Close the traversal to release any underlying resources.
            CloseableIterator.closeIterator(traversal);
        }
    }

    public static <S, E> E apply(final S start, final Traversal.Admin<S, E> traversal) {
        traversal.reset();
        traversal.addStart(traversal.getTraverserGenerator().generate(start, traversal.getStartStep(), 1l));
        try {
            return traversal.next(); // map
        } catch (final NoSuchElementException e) {
            throw new IllegalArgumentException("The provided start does not map to a value: " + start + "->" + traversal);
        } finally {
            //Close the traversal to release any underlying resources.
            CloseableIterator.closeIterator(traversal);
        }
    }

    public static <S, E> E applyNullable(final S start, final Traversal.Admin<S, E> traversal) {
        return null == traversal ? (E) start : TraversalUtil.apply(start, traversal);
    }

    public static <S, E> E applyNullable(final Traverser.Admin<S> traverser, final Traversal.Admin<S, E> traversal) {
        return null == traversal ? (E) traverser.get() : TraversalUtil.apply(traverser, traversal);
    }

    public static <S, E> Iterator<E> applyAll(final Traverser.Admin<S> traverser, final Traversal.Admin<S, E> traversal) {
        prepare(traverser, traversal);
        return traversal; // flatmap
    }

    public static <S, E> Iterator<E> applyAll(final S start, final Traversal.Admin<S, E> traversal) {
        traversal.reset();
        traversal.addStart(traversal.getTraverserGenerator().generate(start, traversal.getStartStep(), 1l));
        return traversal; // flatMap
    }

    public static <S, E> boolean test(final Traverser.Admin<S> traverser, final Traversal.Admin<S, E> traversal, E end) {
        if (null == end) return TraversalUtil.test(traverser, traversal);

        prepare(traverser, traversal);

        final Step<?, E> endStep = traversal.getEndStep();
        boolean result = false;
        while (traversal.hasNext()) {
            if (endStep.next().get().equals(end)) {
                result = true;
                break;
            }
        }

        // The traversal might not have been fully consumed in the loop above. Close the traversal to release any underlying
        // resources.
        CloseableIterator.closeIterator(traversal);

        return result;
    }

    public static <S, E> TraversalProduct produce(final Traverser.Admin<S> traverser, final Traversal.Admin<S, E> traversal) {
        if (null == traversal) {
            return new TraversalProduct(traverser.get());
        } else {
            prepare(traverser, traversal);
            try {
                if (traversal.hasNext()) {
                    return new TraversalProduct(traversal.next());
                } else {
                    return TraversalProduct.UNPRODUCTIVE;
                }
            } finally {
                CloseableIterator.closeIterator(traversal);
            }
        }
    }

    public static <S, E> TraversalProduct produce(final S start, final Traversal.Admin<S, E> traversal) {
        if (null == traversal) {
            return new TraversalProduct(start);
        } else {
            traversal.reset();
            traversal.addStart(traversal.getTraverserGenerator().generate(start, traversal.getStartStep(), 1L));
            try {
                if (traversal.hasNext()) {
                    return new TraversalProduct(traversal.next());
                } else {
                    return TraversalProduct.UNPRODUCTIVE;
                }
            } finally {
                CloseableIterator.closeIterator(traversal);
            }
        }
    }

    public static <S, E> boolean test(final Traverser.Admin<S> traverser, final Traversal.Admin<S, E> traversal) {
        prepare(traverser, traversal);
        final boolean val =  traversal.hasNext(); // filter

        //Close the traversal to release any underlying resources.
        CloseableIterator.closeIterator(traversal);

        return val;
    }

    public static <S, E> boolean test(final S start, final Traversal.Admin<S, E> traversal, final E end) {
        if (null == end) return TraversalUtil.test(start, traversal);

        traversal.reset();
        traversal.addStart(traversal.getTraverserGenerator().generate(start, traversal.getStartStep(), 1l));
        final Step<?, E> endStep = traversal.getEndStep();

        boolean result = false;
        while (traversal.hasNext()) {
            if (endStep.next().get().equals(end)) {
                result = true;
                break;
            }
        }

        //Close the traversal to release any underlying resources.
        CloseableIterator.closeIterator(traversal);

        return result;
    }

    public static <S, E> boolean test(final S start, final Traversal.Admin<S, E> traversal) {
        traversal.reset();
        traversal.addStart(traversal.getTraverserGenerator().generate(start, traversal.getStartStep(), 1l));
        boolean result = traversal.hasNext(); // filter

        //Close the traversal to release any underlying resources.
        CloseableIterator.closeIterator(traversal);

        return result;
    }

    public static <S, E> Traverser<S> prepare(final Traverser.Admin<S> traverser, final Traversal.Admin<S, E> traversal) {
        final Traverser.Admin<S> split = traverser.split();
        split.setSideEffects(traversal.getSideEffects());
        split.setBulk(1L);
        traversal.reset();
        traversal.addStart(split);
        return split;
    }
}