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 *   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
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 *  KIND, either express or implied.  See the License for the
 *  specific language governing permissions and limitations
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package org.apache.cayenne.lifecycle.relationship;

import java.util.Collections;
import java.util.HashMap;
import java.util.List;
import java.util.Map;

import org.apache.cayenne.Cayenne;
import org.apache.cayenne.DataObject;
import org.apache.cayenne.ObjectContext;
import org.apache.cayenne.ObjectId;
import org.apache.cayenne.exp.Expression;
import org.apache.cayenne.exp.ExpressionFactory;
import org.apache.cayenne.lifecycle.id.EntityIdCoder;
import org.apache.cayenne.map.EntityResolver;
import org.apache.cayenne.map.ObjEntity;
import org.apache.cayenne.query.ObjectIdQuery;
import org.apache.cayenne.query.SelectQuery;

/**
 * Provides lazy faulting functionality for a map of objects identified by String
 * ObjectId.
 * 
 * @since 3.1
 */
class ObjectIdBatchFault {

    private ObjectContext context;
    private List sources;
    private volatile Map resolved;

    ObjectIdBatchFault(ObjectContext context, List sources) {
        this.context = context;
        this.sources = sources;
    }

    Map getObjects() {

        if (resolved == null) {

            synchronized (this) {

                if (resolved == null) {
                    resolved = fetchObjects();
                }
            }
        }

        return resolved;
    }

    private Map fetchObjects() {

        if (sources == null) {
            return Collections.EMPTY_MAP;
        }

        EntityResolver resolver = context.getEntityResolver();

        // simple case of one query, handle it separately for performance reasons
        if (sources.size() == 1) {

            String uuid = sources.get(0).getId();
            String entityName = EntityIdCoder.getEntityName(uuid);

            ObjEntity entity = resolver.getObjEntity(entityName);
            ObjectId id = new EntityIdCoder(entity).toObjectId(uuid);

            Object object = Cayenne.objectForQuery(context, new ObjectIdQuery(id));
            if (object == null) {
                return Collections.EMPTY_MAP;
            }
            else {
                return Collections.singletonMap(uuid, object);
            }
        }

        Map queriesByEntity = new HashMap();
        Map codersByEntity = new HashMap();

        for (ObjectIdBatchSourceItem source : sources) {

            String uuid = source.getId();
            String entityName = EntityIdCoder.getEntityName(uuid);
            EntityIdCoder coder = codersByEntity.get(entityName);
            SelectQuery query;

            if (coder == null) {
                coder = new EntityIdCoder(resolver.getObjEntity(entityName));
                codersByEntity.put(entityName, coder);

                query = new SelectQuery(entityName);
                queriesByEntity.put(entityName, query);
            }
            else {
                query = queriesByEntity.get(entityName);
            }

            ObjectId id = coder.toObjectId(uuid);
            Expression idExp = ExpressionFactory.matchAllDbExp(
                    id.getIdSnapshot(),
                    Expression.EQUAL_TO);
            query.orQualifier(idExp);
        }

        int capacity = (int) Math.ceil(sources.size() / 0.75d);
        Map results = new HashMap(capacity);

        for (SelectQuery query : queriesByEntity.values()) {

            EntityIdCoder coder = codersByEntity.get(query.getRoot());
            List objects = context.performQuery(query);
            for (DataObject object : objects) {
                String uuid = coder.toStringId(object.getObjectId());
                results.put(uuid, object);
            }
        }

        return results;
    }
}