/*******************************************************************************
 * Copyright (c) 2009, 2017 IBM Corporation and others.
 * This program and the accompanying materials are made available under the
 * terms of the Eclipse Public License v. 2.0 which is available at
 * http://www.eclipse.org/legal/epl-2.0.
 * 
 * SPDX-License-Identifier: EPL-2.0
 *
 * Contributors:
 *     IBM Corporation - initial API and implementation
 *     Zend Technologies
 *******************************************************************************/
package org.eclipse.dltk.core.index.sql;

import java.sql.Connection;
import java.sql.SQLException;

import org.eclipse.core.runtime.IConfigurationElement;
import org.eclipse.core.runtime.Platform;
import org.eclipse.core.runtime.jobs.ILock;
import org.eclipse.core.runtime.jobs.Job;

/**
 * Abstract database access factory
 * 
 * @author michael
 * 
 */
public abstract class DbFactory {

	private static final String EXTPOINT = SqlIndex.PLUGIN_ID + ".dbFactory"; //$NON-NLS-1$
	private static final String FACTORY_ELEM = "factory"; //$NON-NLS-1$
	private static final String CLASS_ATTR = "class"; //$NON-NLS-1$

	private static ILock instanceLock = Job.getJobManager().newLock();
	private static DbFactory instance;

	/**
	 * Returns current DAO factory provided through extension point
	 * 
	 * @return
	 */
	public static DbFactory getInstance() {
		if (instance == null) {
			try {
				instanceLock.acquire();
				if (instance == null) {
					try {
						for (IConfigurationElement element : Platform
								.getExtensionRegistry()
								.getConfigurationElementsFor(EXTPOINT)) {
							if (FACTORY_ELEM.equals(element.getName())) {
								instance = (DbFactory) element
										.createExecutableExtension(CLASS_ATTR);
								/*
								 * Explicitly register shutdown handler, so it
								 * would be disposed only if class was loaded.
								 * 
								 * We don't want static initialization code to
								 * be executed during framework shutdown.
								 */
								SqlIndex.addShutdownListener(() -> {
									if (instance != null) {
										try {
											instance.dispose();
										} catch (SQLException e) {
											SqlIndex.error(
													"DbFactory.dispose() error",
													e);
										}
										instance = null;
									}
								});
							}
						}
					} catch (Exception e) {
						SqlIndex.error(
								"An exception has occurred while creating database factory",
								e);
					}
				}
			} finally {
				instanceLock.release();
			}
		}
		return instance;
	}

	/**
	 * Creates connection to the database. Clients are responsible for closing
	 * this connection when not needed anymore.
	 * 
	 * @return connection Database connection
	 * @throws SQLException
	 */
	public abstract Connection createConnection() throws SQLException;

	/**
	 * Dispose connection pool
	 * 
	 * @throws SQLException
	 */
	public abstract void dispose() throws SQLException;

	/**
	 * Returns concrete DBMS implementation of element DAO
	 * 
	 * @return element DAO
	 */
	public abstract IElementDao getElementDao();

	/**
	 * Returns concrete DBMS implementation of file DAO
	 * 
	 * @return file DAO
	 */
	public abstract IFileDao getFileDao();

	/**
	 * Returns concrete DBMS implementation of container DAO
	 * 
	 * @return container DAO
	 */
	public abstract IContainerDao getContainerDao();

}