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package org.apache.cayenne.lifecycle.relationship;

import org.apache.cayenne.DataObject;

import java.util.ArrayList;
import java.util.List;

/**
 * A faulting strategy that does batch-faulting of related objects whenever a first
 * ObjectId relationship is accessed.
 * 
 * @since 3.1
 */
public class ObjectIdRelationshipBatchFaultingStrategy implements
        ObjectIdRelationshipFaultingStrategy {

    private ThreadLocal> batchSources;

    public ObjectIdRelationshipBatchFaultingStrategy() {
        this.batchSources = new ThreadLocal<>();
    }

    public void afterObjectLoaded(DataObject object) {

        String uuidProperty = objectIdPropertyName(object);
        String uuidRelationship = objectIdRelationshipName(uuidProperty);
        String uuid = (String) object.readProperty(uuidProperty);
        if (uuid == null) {
            object.writePropertyDirectly(uuidRelationship, null);
        }
        else {
            List sources = batchSources.get();

            if (sources == null) {
                sources = new ArrayList<>();
                batchSources.set(sources);
            }

            sources.add(new ObjectIdBatchSourceItem(object, uuid, uuidRelationship));
        }
    }

    public void afterQuery() {

        List sources = batchSources.get();
        if (sources != null) {
            batchSources.set(null);

            ObjectIdBatchFault batchFault = new ObjectIdBatchFault(sources
                    .get(0)
                    .getObject()
                    .getObjectContext(), sources);

            for (ObjectIdBatchSourceItem source : sources) {
                source.getObject().writePropertyDirectly(
                        source.getObjectIdRelationship(),
                        new ObjectIdFault(batchFault, source.getId()));
            }
        }
    }

    String objectIdRelationshipName(String uuidPropertyName) {
        return "cay:related:" + uuidPropertyName;
    }

    String objectIdPropertyName(DataObject object) {

        ObjectIdRelationship annotation = object.getClass().getAnnotation(
                ObjectIdRelationship.class);

        if (annotation == null) {
            throw new IllegalArgumentException(
                    "Object class is not annotated with @UuidRelationship: "
                            + object.getClass().getName());
        }

        // TODO: I guess we'll need to cache this metadata for performance if we are to
        // support inheritance lookups, etc.

        return annotation.value();
    }

}