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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.util;

import java.util.ArrayList;
import java.util.Collection;
import java.util.HashMap;
import java.util.Iterator;
import java.util.Map;

import org.apache.cayenne.CayenneRuntimeException;
import org.apache.cayenne.ObjectId;
import org.apache.cayenne.Persistent;
import org.apache.cayenne.map.EntityResolver;
import org.apache.cayenne.query.PrefetchTreeNode;
import org.apache.cayenne.reflect.AttributeProperty;
import org.apache.cayenne.reflect.ClassDescriptor;
import org.apache.cayenne.reflect.Property;
import org.apache.cayenne.reflect.PropertyVisitor;
import org.apache.cayenne.reflect.ToManyProperty;
import org.apache.cayenne.reflect.ToOneProperty;

/**
 * An operation that creates a subgraph of detached objects, using the PrefetchTree to
 * delineate the graph boundaries. Target objects can be described by a different set of
 * descriptors, thus allowing server-to-client conversion to happen in the process.
 * 
 * @since 1.2
 */
public class ObjectDetachOperation {

    protected EntityResolver targetResolver;
    protected Map<ObjectId, Persistent> seen;

    public ObjectDetachOperation(EntityResolver targetResolver) {
        this.targetResolver = targetResolver;
        this.seen = new HashMap<ObjectId, Persistent>();
    }

    public void reset() {
        seen.clear();
    }

    /**
     * "Detaches" an object from its context by creating an unattached copy. The copy is
     * created using target descriptor of this operation that may be different from the
     * object descriptor passed to this method.
     */
    public Object detach(
            Object object,
            ClassDescriptor descriptor,
            final PrefetchTreeNode prefetchTree) {
        if (!(object instanceof Persistent)) {
            throw new CayenneRuntimeException("Expected Persistent, got: " + object);
        }

        final Persistent source = (Persistent) object;
        ObjectId id = source.getObjectId();

        // sanity check
        if (id == null) {
            throw new CayenneRuntimeException("Server returned an object without an id: "
                    + source);
        }

        Object seenTarget = seen.get(id);
        if (seenTarget != null) {
            return seenTarget;
        }

        descriptor = descriptor.getSubclassDescriptor(source.getClass());

        // presumably id's entity name should be of the right subclass.
        final ClassDescriptor targetDescriptor = targetResolver.getClassDescriptor(id
                .getEntityName());

        final Persistent target = (Persistent) targetDescriptor.createObject();
        target.setObjectId(id);
        seen.put(id, target);

        descriptor.visitProperties(new PropertyVisitor() {

            public boolean visitToOne(ToOneProperty property) {
                if (prefetchTree != null) {

                    PrefetchTreeNode child = prefetchTree.getNode(property.getName());

                    if (child != null) {
                        Object destinationSource = property.readProperty(source);

                        Object destinationTarget = destinationSource != null ? detach(
                                destinationSource,
                                property.getTargetDescriptor(),
                                child) : null;

                        ToOneProperty targetProperty = (ToOneProperty) targetDescriptor
                                .getProperty(property.getName());
                        Object oldTarget = targetProperty.isFault(target)
                                ? null
                                : targetProperty.readProperty(target);
                        targetProperty
                                .writeProperty(target, oldTarget, destinationTarget);
                    }
                }

                return true;
            }

            public boolean visitToMany(ToManyProperty property) {
                if (prefetchTree != null) {
                    PrefetchTreeNode child = prefetchTree.getNode(property.getName());

                    if (child != null) {
                        Collection collection = (Collection) property
                                .readProperty(source);

                        Collection targetCollection = new ArrayList(collection.size());

                        Iterator it = collection.iterator();
                        while (it.hasNext()) {
                            Object destinationSource = it.next();
                            Object destinationTarget = destinationSource != null
                                    ? detach(destinationSource, property
                                            .getTargetDescriptor(), child)
                                    : null;

                            targetCollection.add(destinationTarget);
                        }

                        ToManyProperty targetProperty = (ToManyProperty) targetDescriptor
                                .getProperty(property.getName());
                        targetProperty.writeProperty(target, null, targetCollection);
                    }
                }

                return true;
            }

            public boolean visitAttribute(AttributeProperty property) {
                Property targetProperty = targetDescriptor
                        .getProperty(property.getName());
                targetProperty.writeProperty(target, null, property.readProperty(source));
                return true;
            }
        });

        return target;
    }
}
