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 * to you under the Apache License, Version 2.0 (the
 * "License"); you may not use this file except in compliance
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 *     http://www.apache.org/licenses/LICENSE-2.0
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package org.apache.jena.tdb2.solver;


import org.apache.jena.atlas.lib.Lib ;
import org.apache.jena.query.Query ;
import org.apache.jena.sparql.algebra.Algebra ;
import org.apache.jena.sparql.algebra.Op ;
import org.apache.jena.sparql.algebra.OpLib;
import org.apache.jena.sparql.core.DatasetDescription ;
import org.apache.jena.sparql.core.DatasetGraph ;
import org.apache.jena.sparql.core.DynamicDatasets ;
import org.apache.jena.sparql.core.Substitute ;
import org.apache.jena.sparql.engine.Plan ;
import org.apache.jena.sparql.engine.QueryEngineFactory ;
import org.apache.jena.sparql.engine.QueryEngineRegistry ;
import org.apache.jena.sparql.engine.QueryIterator ;
import org.apache.jena.sparql.engine.binding.Binding ;
import org.apache.jena.sparql.engine.main.QueryEngineMain ;
import org.apache.jena.sparql.mgt.Explain ;
import org.apache.jena.sparql.util.Context ;
import org.apache.jena.tdb2.TDB2;
import org.apache.jena.tdb2.TDBException;
import org.apache.jena.tdb2.store.DatasetGraphTDB;
import org.apache.jena.tdb2.sys.TDBInternal;

// This exists to intercept the query execution setup.
//  e.g choose the transformation optimizations
// then to make the quad form.
// TDB also uses a custom OpExecutor to intercept certain parts
// of the Op evaluations

public class QueryEngineTDB extends QueryEngineMain
{
    // ---- Wiring
    static public QueryEngineFactory getFactory() { return factory; }
    static public void register()       { QueryEngineRegistry.addFactory(factory); }
    static public void unregister()     { QueryEngineRegistry.removeFactory(factory); }

    // ---- Object

    protected QueryEngineTDB(Op op, DatasetGraphTDB dataset, Binding input, Context context)
    {
        super(op, dataset, input, context);
    }

    protected QueryEngineTDB(Query query, DatasetGraphTDB dataset, Binding input, Context cxt)
    {
        super(query, dataset, input, cxt);
    }

    private static boolean isUnionDefaultGraph(Context cxt) {
        return cxt.isTrue(TDB2.symUnionDefaultGraph1) || cxt.isTrue(TDB2.symUnionDefaultGraph2);
    }

    @Override
    protected DatasetGraph dynamicDataset(DatasetDescription dsDesc, DatasetGraph dataset, boolean unionDftGraph) {
        boolean union = unionDftGraph || isUnionDefaultGraph(context);
        return DynamicDatasets.dynamicDataset(dsDesc, dataset, union );
    }

    // Choose the algebra-level optimizations to invoke.
    @Override
    protected Op modifyOp(Op op)
    {
        op = Substitute.substitute(op, getStartBinding());
        // Optimize (high-level)
        op = super.modifyOp(op);

        // Quadification
        // Only apply if not a rewritten DynamicDataset
        if ( ! isDynamicDataset() )
            op = Algebra.toQuadForm(op);

        // Record it.
        setOp(op);
        return op;
    }

    @Override
    public QueryIterator eval(Op op, DatasetGraph dsg, Binding input, Context context)
    {
        // Top of execution of a query.
        // Op is quad'ed by now but there still may be some (graph ....) forms e.g. paths

        // Fix DatasetGraph for global union.
        if ( isUnionDefaultGraph(context) && ! isDynamicDataset() ) {
            op = OpLib.unionDefaultGraphQuads(op) ;
            Explain.explain("REWRITE(Union default graph)", op, context);
        }
        QueryIterator results = super.eval(op, dsg, input, context);
        return results;
    }

    // ---- Factory
    protected static QueryEngineFactory factory = new QueryEngineFactoryTDB();

    protected static class QueryEngineFactoryTDB implements QueryEngineFactory
    {
        private static boolean isHandledByTDB(DatasetGraph dataset) {
            return TDBInternal.isBackedByTDB(dataset);
        }

        protected DatasetGraphTDB dsgToQuery(DatasetGraph dataset) {
            try {
                return TDBInternal.requireStorage(dataset);
            } catch (TDBException ex) {
                // Check to a more specific message.
                throw new TDBException("Internal inconsistency: trying to execute query on unrecognized kind of DatasetGraph: "+Lib.className(dataset));
            }
        }

        @Override
        public boolean accept(Query query, DatasetGraph dataset, Context context)
        { return isHandledByTDB(dataset); }

        @Override
        public Plan create(Query query, DatasetGraph dataset, Binding input, Context context)
        {
            QueryEngineTDB engine = new QueryEngineTDB(query, dsgToQuery(dataset), input, context);
            return engine.getPlan();
        }

        @Override
        public boolean accept(Op op, DatasetGraph dataset, Context context)
        { return isHandledByTDB(dataset); }

        @Override
        public Plan create(Op op, DatasetGraph dataset, Binding binding, Context context)
        {
            QueryEngineTDB engine = new QueryEngineTDB(op, dsgToQuery(dataset), binding, context);
            return engine.getPlan();
        }
    }
}