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/*
 * Copyright 2015, The Querydsl Team (http://www.querydsl.com/team)
 *
 * Licensed 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 com.querydsl.jpa;

import java.io.Closeable;
import java.io.IOException;
import java.util.Iterator;

import javax.persistence.PersistenceException;
import javax.persistence.Query;

import org.eclipse.persistence.config.HintValues;
import org.eclipse.persistence.config.QueryHints;
import org.eclipse.persistence.jpa.JpaQuery;
import org.eclipse.persistence.queries.Cursor;

import com.mysema.commons.lang.CloseableIterator;
import com.mysema.commons.lang.IteratorAdapter;
import com.querydsl.core.types.FactoryExpression;

/**
 * {@code EclipseLinkHandler} is the {@link QueryHandler} implementation for EclipseLink
 *
 * @author tiwe
 *
 */
class EclipseLinkHandler implements QueryHandler {

    @Override
    public void addEntity(Query query, String alias, Class type) {
        // do nothing
    }

    @Override
    public void addScalar(Query query, String alias, Class type) {
        // do nothing
    }

    @Override
    public boolean createNativeQueryTyped() {
        return true;
    }

    @SuppressWarnings("unchecked")
    @Override
    public  CloseableIterator iterate(Query query, FactoryExpression projection) {
        boolean canUseCursor = false;
        try {
            canUseCursor = query.unwrap(Query.class) instanceof JpaQuery;
        } catch (PersistenceException e) { } // can't unwrap, just ignore the exception

        Iterator iterator = null;
        Closeable closeable = null;
        if (canUseCursor) {
            query.setHint(QueryHints.CURSOR, HintValues.TRUE);
            final Cursor cursor = (Cursor) query.getSingleResult();
            final int pageSize = cursor.getPageSize();
            closeable = new Closeable() {
                @Override
                public void close() throws IOException {
                    cursor.close();
                }
            };
            iterator = new Iterator() {
                private int rowsSinceLastClear = 0;

                @Override
                public boolean hasNext() {
                    return cursor.hasNext();
                }

                @Override
                public T next() {
                    if (rowsSinceLastClear++ == pageSize) {
                        rowsSinceLastClear = 0;
                        cursor.clear();
                    }
                    return (T) cursor.next();
                }
            };
        } else {
            iterator = query.getResultList().iterator();
        }
        if (projection != null) {
            return new TransformingIterator(iterator, closeable, projection);
        } else {
            return new IteratorAdapter(iterator, closeable);
        }
    }

    @Override
    public boolean transform(Query query, FactoryExpression projection) {
        return false;
    }

    @Override
    public boolean wrapEntityProjections() {
        return false;
    }

}