extras/rya.pcj.fluo/pcj.fluo.app/src/main/java/org/apache/rya/indexing/pcj/fluo/app/FilterResultUpdater.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.rya.indexing.pcj.fluo.app;

import static com.google.common.base.Preconditions.checkNotNull;

import org.apache.fluo.api.client.TransactionBase;
import org.apache.fluo.api.data.Bytes;
import org.apache.rya.api.model.VisibilityBindingSet;
import org.apache.rya.indexing.pcj.fluo.app.query.FilterMetadata;
import org.apache.rya.indexing.pcj.fluo.app.query.FluoQueryColumns;
import org.apache.rya.indexing.pcj.fluo.app.util.FilterSerializer;
import org.apache.rya.indexing.pcj.storage.accumulo.VariableOrder;
import org.apache.rya.indexing.pcj.storage.accumulo.VisibilityBindingSetSerDe;
import org.eclipse.rdf4j.common.iteration.CloseableIteration;
import org.eclipse.rdf4j.model.IRI;
import org.eclipse.rdf4j.model.Resource;
import org.eclipse.rdf4j.model.Statement;
import org.eclipse.rdf4j.model.Value;
import org.eclipse.rdf4j.model.ValueFactory;
import org.eclipse.rdf4j.model.impl.SimpleValueFactory;
import org.eclipse.rdf4j.query.BindingSet;
import org.eclipse.rdf4j.query.QueryEvaluationException;
import org.eclipse.rdf4j.query.algebra.Filter;
import org.eclipse.rdf4j.query.algebra.FunctionCall;
import org.eclipse.rdf4j.query.algebra.ValueExpr;
import org.eclipse.rdf4j.query.algebra.evaluation.TripleSource;
import org.eclipse.rdf4j.query.algebra.evaluation.ValueExprEvaluationException;
import org.eclipse.rdf4j.query.algebra.evaluation.function.FunctionRegistry;
import org.eclipse.rdf4j.query.algebra.evaluation.impl.StrictEvaluationStrategy;
import org.eclipse.rdf4j.query.algebra.evaluation.util.QueryEvaluationUtil;
import org.slf4j.Logger;
import org.slf4j.LoggerFactory;

import edu.umd.cs.findbugs.annotations.DefaultAnnotation;
import edu.umd.cs.findbugs.annotations.NonNull;

/**
 * Updates the results of a Filter node when its child has added a new Binding
 * Set to its results.
 */
@DefaultAnnotation(NonNull.class)
public class FilterResultUpdater extends AbstractNodeUpdater {

    private static final Logger log = LoggerFactory.getLogger(FilterResultUpdater.class);

    private static final VisibilityBindingSetSerDe BS_SERDE = new VisibilityBindingSetSerDe();

    /**
     * Is used to evaluate the conditions of a {@link Filter}.
     */
    private static final StrictEvaluationStrategy evaluator = new StrictEvaluationStrategy(
            new TripleSource() {
                private final ValueFactory valueFactory = SimpleValueFactory.getInstance();

                @Override
                public ValueFactory getValueFactory() {
                    return valueFactory;
                }

                @Override
                public CloseableIteration<? extends Statement, QueryEvaluationException> getStatements(
                        final Resource arg0,
                        final IRI arg1,
                        final Value arg2,
                        final Resource... arg3) throws QueryEvaluationException {
                    throw new UnsupportedOperationException();
                }
            },null);

    /**
     * Updates the results of a Filter node when one of its child has added a
     * new Binding Set to its results.
     *
     * @param tx - The transaction all Fluo queries will use. (not null)
     * @param childBindingSet - A binding set that the query's child node has emitted. (not null)
     * @param filterMetadata - The metadata of the Filter whose results will be updated. (not null)
     * @throws Exception Something caused the update to fail.
     */
    public void updateFilterResults(
            final TransactionBase tx,
            final VisibilityBindingSet childBindingSet,
            final FilterMetadata filterMetadata) throws Exception {
        checkNotNull(tx);
        checkNotNull(childBindingSet);
        checkNotNull(filterMetadata);

        log.trace("Transaction ID: {}\nFilter Node ID: {}\nBinding Set:\n{}\n", tx.getStartTimestamp(), filterMetadata.getNodeId(), childBindingSet);

        // Parse the original query and find the Filter that represents filterId.
        final String sparql = filterMetadata.getFilterSparql();
        final Filter filter = FilterSerializer.deserialize(sparql);

        // Evaluate whether the child BindingSet satisfies the filter's condition.
        final ValueExpr condition = filter.getCondition();
        if (isTrue(condition, childBindingSet)) {

            // Create the Row Key for the emitted binding set. It does not contain visibilities.
            final VariableOrder filterVarOrder = filterMetadata.getVariableOrder();
            final Bytes resultRow = makeRowKey(filterMetadata.getNodeId(), filterVarOrder, childBindingSet);

            // Serialize and emit BindingSet
            final Bytes nodeValueBytes = BS_SERDE.serialize(childBindingSet);
            log.trace("Transaction ID: {}\nNew Binding Set: {}\n", tx.getStartTimestamp(), childBindingSet);

            tx.set(resultRow, FluoQueryColumns.FILTER_BINDING_SET, nodeValueBytes);
        }
    }

    /**
     * Evaluate a {@link BindingSet} to see if it is accepted by a filter's condition.
     *
     * @param condition - The filter condition. (not null)
     * @param bindings - The binding set to evaluate. (not null)
     * @return {@code true} if the binding set is accepted by the filter; otherwise {@code false}.
     * @throws QueryEvaluationException The condition couldn't be evaluated. In the case that the ValueExpr is a
     *             {@link FunctionCall}, this Exception is thrown because the Function could not be found in the
     *             {@link FunctionRegistry}.
     */
    private static boolean isTrue(final ValueExpr condition, final BindingSet bindings) throws QueryEvaluationException {
        try {
            final Value value = evaluator.evaluate(condition, bindings);
            return QueryEvaluationUtil.getEffectiveBooleanValue(value);
        } catch (final ValueExprEvaluationException e) {
            //False returned because for whatever reason, the ValueExpr could not be evaluated.
            //In the event that the ValueExpr is a FunctionCall, this Exception will be generated if
            //the Function URI is a valid URI that was found in the FunctionRegistry, but the arguments
            //for that Function could not be parsed.
            return false;
        }
    }
}