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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
 *  "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.
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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<ObjectIdBatchSourceItem> sources;
	private volatile Map<String, Object> resolved;

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

	Map<String, Object> getObjects() {

		if (resolved == null) {

			synchronized (this) {

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

		return resolved;
	}

	private Map<String, Object> fetchObjects() {

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

		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.emptyMap();
			} else {
				return Collections.singletonMap(uuid, object);
			}
		}

		Map<String, SelectQuery<DataObject>> queriesByEntity = new HashMap<>();
		Map<String, EntityIdCoder> codersByEntity = new HashMap<>();

		for (ObjectIdBatchSourceItem source : sources) {

			String uuid = source.getId();
			String entityName = EntityIdCoder.getEntityName(uuid);
			EntityIdCoder coder = codersByEntity.get(entityName);
			SelectQuery<DataObject> 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<String, Object> results = new HashMap<>(capacity);

		for (SelectQuery<DataObject> query : queriesByEntity.values()) {

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

		return results;
	}
}