/*******************************************************************************
 * Copyright (c) 2007, 2010 Association for Decentralized Information Management
 * in Industry THTH ry.
 * All rights reserved. This program and the accompanying materials
 * are made available under the terms of the Eclipse Public License v1.0
 * which accompanies this distribution, and is available at
 * http://www.eclipse.org/legal/epl-v10.html
 *
 * Contributors:
 *     VTT Technical Research Centre of Finland - initial API and implementation
 *******************************************************************************/
package org.simantics.db.common.changeset;

import java.lang.reflect.Constructor;
import java.lang.reflect.InvocationTargetException;

import org.simantics.db.ChangeSet;
import org.simantics.db.MetadataI;
import org.simantics.db.ReadGraph;
import org.simantics.db.Session;
import org.simantics.db.common.procedure.adapter.TransientCacheListener;
import org.simantics.db.event.ChangeEvent;
import org.simantics.db.event.ChangeListener;
import org.simantics.db.exception.DatabaseException;
import org.simantics.db.request.Read;
import org.simantics.utils.ReflectionUtils;
import org.slf4j.LoggerFactory;

/**
 * A listener added to a Session for receiving notifications for completed
 * write transactions.
 * 
 * @see GraphChangeEvent
 * @see Session
 */
abstract public class GenericChangeListener<Request, Result> implements ChangeListener {

    private final Constructor<Read<Result>> constructor;

    public GenericChangeListener() {

        try {
            Class<Read<Result>> clazz = ReflectionUtils.getSingleParameterTypeExtending(getClass());
            this.constructor = clazz.getConstructor(ChangeSet.class);
            return;
        } catch (SecurityException | NoSuchMethodException e) {
            LoggerFactory.getLogger(getClass()).error("Could not get constructor with param {}", ChangeSet.class.getSimpleName(), e);
            throw new IllegalArgumentException(e);
        }
    }

    public final void graphChanged(ChangeEvent e) throws DatabaseException {

        try {
            if (!preEventRequest())
                return;

            Result event = e.getGraph().syncRequest(constructor.newInstance(e.getChanges()), TransientCacheListener.<Result>instance());
            onEvent(e.getGraph(), e.getMetadataI(), event);
        } catch (IllegalArgumentException | InstantiationException | IllegalAccessException | InvocationTargetException ex) {
            LoggerFactory.getLogger(getClass()).error("Could not construct new instance with {}", e.getChanges(), ex);
            throw new DatabaseException(ex);
        }

    }

    /**
     * Invoked before performing the event request with the received change
     * event and sending the result to {@link #onEvent(ReadGraph, Object)}. Can
     * be used to veto processing of an event.
     *
     * @return <code>true</code> if the event request shall be performed and the
     *         result sent to {@link #onEvent(ReadGraph, Object)},
     *         <code>false</code> to disable any further processing of the
     *         received db {@link ChangeEvent}
     * @since 1.8
     */
    public boolean preEventRequest() {
        return true;
    }

    public abstract void onEvent(ReadGraph graph, MetadataI metadata, Result event) throws DatabaseException;

}