/*
 * 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.step.filter;

import org.apache.tinkerpop.gremlin.process.traversal.P;
import org.apache.tinkerpop.gremlin.process.traversal.Pop;
import org.apache.tinkerpop.gremlin.process.traversal.Traversal;
import org.apache.tinkerpop.gremlin.process.traversal.Traverser;
import org.apache.tinkerpop.gremlin.process.traversal.step.ByModulating;
import org.apache.tinkerpop.gremlin.process.traversal.step.PathProcessor;
import org.apache.tinkerpop.gremlin.process.traversal.step.Scoping;
import org.apache.tinkerpop.gremlin.process.traversal.step.TraversalParent;
import org.apache.tinkerpop.gremlin.process.traversal.traverser.TraverserRequirement;
import org.apache.tinkerpop.gremlin.process.traversal.util.ConnectiveP;
import org.apache.tinkerpop.gremlin.process.traversal.util.TraversalHelper;
import org.apache.tinkerpop.gremlin.process.traversal.util.TraversalRing;
import org.apache.tinkerpop.gremlin.process.traversal.util.TraversalUtil;
import org.apache.tinkerpop.gremlin.structure.util.StringFactory;

import java.util.ArrayList;
import java.util.Collection;
import java.util.Collections;
import java.util.HashSet;
import java.util.Iterator;
import java.util.List;
import java.util.Optional;
import java.util.Set;

/**
 * @author Marko A. Rodriguez (http://markorodriguez.com)
 */
public final class WherePredicateStep<S> extends FilterStep<S> implements Scoping, PathProcessor, ByModulating, TraversalParent {

    protected String startKey;
    protected List<String> selectKeys;
    protected P<Object> predicate;
    protected final Set<String> scopeKeys = new HashSet<>();
    protected Set<String> keepLabels;

    protected TraversalRing<S, ?> traversalRing = new TraversalRing<>();

    public WherePredicateStep(final Traversal.Admin traversal, final Optional<String> startKey, final P<String> predicate) {
        super(traversal);
        this.startKey = startKey.orElse(null);
        if (null != this.startKey)
            this.scopeKeys.add(this.startKey);
        this.predicate = (P) predicate;
        this.selectKeys = new ArrayList<>();
        this.configurePredicates(this.predicate);
    }

    private void configurePredicates(final P<Object> predicate) {
        if (predicate instanceof ConnectiveP)
            ((ConnectiveP<Object>) predicate).getPredicates().forEach(this::configurePredicates);
        else {
            final String selectKey = (String) (predicate.getValue() instanceof Collection ? ((Collection) predicate.getValue()).iterator().next() : predicate.getValue()); // hack for within("x"))
            this.selectKeys.add(selectKey);
            this.scopeKeys.add(selectKey);
        }
    }

    private void setPredicateValues(final P<Object> predicate, final Traverser.Admin<S> traverser, final Iterator<String> selectKeysIterator) {
        if (predicate instanceof ConnectiveP)
            ((ConnectiveP<Object>) predicate).getPredicates().forEach(p -> this.setPredicateValues(p, traverser, selectKeysIterator));
        else
            predicate.setValue(TraversalUtil.applyNullable((S) this.getScopeValue(Pop.last, selectKeysIterator.next(), traverser), this.traversalRing.next()));
    }

    public Optional<P<?>> getPredicate() {
        return Optional.ofNullable(this.predicate);
    }

    public Optional<String> getStartKey() {
        return Optional.ofNullable(this.startKey);
    }

    public void removeStartKey() {
        this.selectKeys.remove(this.startKey);
        this.startKey = null;
    }

    @Override
    protected boolean filter(final Traverser.Admin<S> traverser) {
        final Object value = null == this.startKey ?
                TraversalUtil.applyNullable(traverser, this.traversalRing.next()) :
                TraversalUtil.applyNullable((S) this.getScopeValue(Pop.last, this.startKey, traverser), this.traversalRing.next());
        this.setPredicateValues(this.predicate, traverser, this.selectKeys.iterator());
        this.traversalRing.reset();
        return this.predicate.test(value);
    }

    @Override
    public String toString() {
        // TODO: revert the predicates to their string form?
        return StringFactory.stepString(this, this.startKey, this.predicate, this.traversalRing);
    }

    @Override
    public Set<String> getScopeKeys() {
        return Collections.unmodifiableSet(this.scopeKeys);
    }

    @Override
    public WherePredicateStep<S> clone() {
        final WherePredicateStep<S> clone = (WherePredicateStep<S>) super.clone();
        clone.predicate = this.predicate.clone();
        clone.traversalRing = this.traversalRing.clone();
        return clone;
    }

    @Override
    public void setTraversal(final Traversal.Admin<?, ?> parentTraversal) {
        super.setTraversal(parentTraversal);
        this.traversalRing.getTraversals().forEach(this::integrateChild);
    }

    @Override
    public int hashCode() {
        return super.hashCode() ^ this.traversalRing.hashCode() ^ (null == this.startKey ? "null".hashCode() : this.startKey.hashCode()) ^ this.predicate.hashCode();
    }

    @Override
    public Set<TraverserRequirement> getRequirements() {
        return this.getSelfAndChildRequirements(TraverserRequirement.OBJECT, TraverserRequirement.SIDE_EFFECTS);
    }

    @Override
    public List<Traversal.Admin<S, ?>> getLocalChildren() {
        return (List) this.traversalRing.getTraversals();
    }

    @Override
    protected Traverser.Admin<S> processNextStart() {
        return PathProcessor.processTraverserPathLabels(super.processNextStart(), this.keepLabels);
    }

    @Override
    public void setKeepLabels(final Set<String> keepLabels) {
        this.keepLabels = new HashSet<>(keepLabels);
    }

    @Override
    public Set<String> getKeepLabels() {
        return this.keepLabels;
    }

    @Override
    public void modulateBy(final Traversal.Admin<?, ?> traversal) throws UnsupportedOperationException {
        this.traversalRing.addTraversal(this.integrateChild(traversal));
    }
}

@@ -3231,166 +3231,32 @@
 y = 
-(String) (predicate.getValue() instanceof Collection ? ((Collection) predicate.getValue()).iterator().next() : predicate.getValue()); // hack for within(%22x%22))
+getSelectKey(predicate);
 %0A   
@@ -4057,32 +4057,289 @@
 artKey);%0A    %7D%0A%0A
+    public String getSelectKey(final P%3CObject%3E predicate) %7B%0A        return (String) (predicate.getValue() instanceof Collection ? ((Collection) predicate.getValue()).iterator().next()%0A                : predicate.getValue()); // hack for within(%22x%22))%0A    %7D%0A%0A
     public void 

add a public helper method to retrieve select key from WherePredicateStep