import org.apache.logging.log4j.LogManager;
import org.apache.logging.log4j.Logger;
import org.h2.jdbcx.JdbcConnectionPool;

import java.io.IOException;
import java.io.InputStream;
import java.sql.Connection;
import java.sql.SQLException;
import java.util.Properties;

public class ConnectionManager {

    private static final Logger log = LogManager
            .getLogger(ConnectionManager.class.getName());

    private static volatile JdbcConnectionPool instance;

    public static Connection getConnection() throws SQLException {
        log.traceEntry();
        log.traceExit();
        return getInstance().getConnection();
    }

    public static JdbcConnectionPool getInstance() {
        log.traceEntry();
        JdbcConnectionPool localInstance = instance;
        if (localInstance == null) {
            synchronized (JdbcConnectionPool.class) {
                localInstance = instance;
                if (localInstance == null) {
                    Properties properties = new Properties();
                    try (InputStream input = getClass()
                            .getResourceAsStream("/jdbc.properties")) {
                        properties.load(input);
                    } catch (IOException e) {
                        log.catching(e);
                    }

                    String url = properties.getProperty("jdbc.url");
                    String username = properties.getProperty("jdbc.username");
                    String password = properties.getProperty("jdbc.password");

                    instance = localInstance = JdbcConnectionPool
                            .create(url, username, password);
                }
            }
        }
        log.traceExit();
        return localInstance;
    }
}