extras/indexing/src/main/java/org/apache/rya/indexing/external/matching/QueryNodesToTupleExpr.java

package org.apache.rya.indexing.external.matching;

/*
 * 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.
 */

import java.util.ArrayList;
import java.util.HashSet;
import java.util.List;
import java.util.Set;

import org.eclipse.rdf4j.query.algebra.Filter;
import org.eclipse.rdf4j.query.algebra.Join;
import org.eclipse.rdf4j.query.algebra.LeftJoin;
import org.eclipse.rdf4j.query.algebra.QueryModelNode;
import org.eclipse.rdf4j.query.algebra.TupleExpr;

import com.google.common.collect.Lists;

/**
 * This class converts a given collection of {@link QueryModelNode}s into a
 * {@link TupleExpr}. The primary purpose of this class is to reconstruct a
 * TupleExpr representation of a {@link QuerySegment} from its List view.
 *
 */
public class QueryNodesToTupleExpr {

    private List<QueryModelNode> queryNodes;
    private Set<Filter> filters;

    public QueryNodesToTupleExpr(List<QueryModelNode> queryNodes, Set<Filter> filters) {
        this.queryNodes = queryNodes;
        this.filters = filters;
    }

    /**
     *
     * @return - a TupleExprAndNodes object that consists of the the TupleExpr
     *         representation of the List of QueryModelNodes and the nodes used
     *         to build the TupleExpr.
     */
    public TupleExprAndNodes getTupleAndNodes() {
        List<QueryModelNode> nodeCopy = new ArrayList<>();
        Set<Filter> setCopy = new HashSet<>();
        for (QueryModelNode q : queryNodes) {
            nodeCopy.add(q.clone());
        }
        for (Filter f : filters) {
            setCopy.add(f.clone());
        }
        TupleExpr te = buildQuery(nodeCopy, setCopy);

        return new TupleExprAndNodes(te, nodeCopy, setCopy);
    }

    private TupleExpr buildQuery(List<QueryModelNode> queryNodes, Set<Filter> filters) {
        List<Filter> chain = getFilterChain(filters);
        return getNewJoin(queryNodes, chain);
    }

    // chain filters together and return front and back of chain
    private static List<Filter> getFilterChain(Set<Filter> filters) {
        final List<Filter> filterTopBottom = Lists.newArrayList();
        Filter filterChainTop = null;
        Filter filterChainBottom = null;

        for (final Filter filter : filters) {
            if (filterChainTop == null) {
                filterChainTop = filter;
                filter.setParentNode(null);
            } else if (filterChainBottom == null) {
                filterChainBottom = filter;
                filterChainTop.setArg(filterChainBottom);
            } else {
                filterChainBottom.setArg(filter);
                filterChainBottom = filter;
            }
        }
        if (filterChainTop != null) {
            filterTopBottom.add(filterChainTop);
        }
        if (filterChainBottom != null) {
            filterTopBottom.add(filterChainBottom);
        }
        return filterTopBottom;
    }

    // build newJoin node given remaining joinArgs and chain of filters
    private static TupleExpr getNewJoin(List<QueryModelNode> args, List<Filter> filterChain) {
        TupleExpr newJoin;
        TupleExpr tempJoin;
        final List<TupleExpr> joinArgs = Lists.newArrayList();
        for (QueryModelNode q : args) {
            if (q instanceof TupleExpr) {
                joinArgs.add(0, (TupleExpr) q);
            } else {
                throw new IllegalArgumentException("Invalid query node!");
            }
        }

        if (joinArgs.size() > 1) {
            TupleExpr left = joinArgs.remove(0);
            TupleExpr right = joinArgs.remove(0);
            tempJoin = getJoin(left, right);
            for (int i = joinArgs.size() - 1; i >= 0; i--) {
                tempJoin = getJoin(tempJoin, joinArgs.get(i));
            }
            if (filterChain.size() == 0) {
                newJoin = tempJoin;
            } else if (filterChain.size() == 1) {
                newJoin = filterChain.get(0);
                ((Filter) newJoin).setArg(tempJoin);
            } else {
                newJoin = filterChain.get(0);
                filterChain.get(1).setArg(tempJoin);
            }
        } else if (joinArgs.size() == 1) {
            tempJoin = joinArgs.get(0);
            if (filterChain.size() == 0) {
                newJoin = tempJoin;
            } else if (filterChain.size() == 1) {
                newJoin = filterChain.get(0);
                ((Filter) newJoin).setArg(tempJoin);
            } else {
                newJoin = filterChain.get(0);
                filterChain.get(1).setArg(tempJoin);
            }
        } else {
            throw new IllegalStateException("JoinArgs size cannot be zero.");
        }
        return newJoin;
    }

    private static TupleExpr getJoin(TupleExpr oldJoin, TupleExpr newArg) {
        if (newArg instanceof FlattenedOptional) {
            return new LeftJoin(oldJoin, ((FlattenedOptional) newArg).getRightArg());
        } else {
            return new Join(oldJoin, newArg);
        }
    }

    public static class TupleExprAndNodes {

        private TupleExpr te;
        private List<QueryModelNode> nodes;
        private Set<Filter> filters;

        public TupleExprAndNodes(TupleExpr te, List<QueryModelNode> nodes, Set<Filter> filters) {
            this.te = te;
            this.nodes = nodes;
            this.filters = filters;
        }

        public TupleExpr getTupleExpr() {
            return te;
        }

        public List<QueryModelNode> getNodes() {
            return nodes;
        }

        public Set<Filter> getFilters() {
            return filters;
        }

        @Override
        public String toString() {
            return "Query: " + te + "   Nodes: " + nodes;
        }

    }

}