/*
 * Copyright 2007-2010 Sun Microsystems, Inc.
 *
 * This file is part of Project Darkstar Server.
 *
 * Project Darkstar Server is free software: you can redistribute it
 * and/or modify it under the terms of the GNU General Public License
 * version 2 as published by the Free Software Foundation and
 * distributed hereunder to you.
 *
 * Project Darkstar Server is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 * GNU General Public License for more details.
 *
 * You should have received a copy of the GNU General Public License
 * along with this program.  If not, see <http://www.gnu.org/licenses/>.
 *
 * Sun designates this particular file as subject to the "Classpath"
 * exception as provided by Sun in the LICENSE file that accompanied
 * this code.
 *
 * --
 */

package com.sun.sgs.internal;

/**
 * Provides a pluggable mechanism for replacing the {@link ManagerLocator}
 * used by the application to get Managers from the Project Darkstar stack
 * through the {@link com.sun.sgs.app.AppContext AppContext}.  This class
 * should not be instantiated.
 */
public final class InternalContext {
    
    // the current locator for this context
    private static volatile ManagerLocator managerLocator;
    
    /** This class should not be instantiated. */
    private InternalContext() { }
    
    /**
     * Returns the {@code ManagerLocator} for use by the current
     * application.  This method is used by the 
     * {@link com.sun.sgs.app.AppContext AppContext} to retrieve Managers
     * from the Project Darkstar stack.  Generally, it should not need to be 
     * called by an application.
     *
     * @return	the {@code ManagerLocator} for the current application
     * @throws	IllegalStateException if the {@code ManagerLocator}
     *          is uninitialized
     */
    public static ManagerLocator getManagerLocator() {
        ManagerLocator locator = managerLocator;
        if (locator == null) {
            throw new IllegalStateException("ManagerLocator is not set");
        }
        return locator;
    }
    
    /**
     * Sets the {@code ManagerLocator} which is used to retrieve
     * managers for the application.  <p>
     * 
     * In most situations, this method
     * should only be called once upon bootup of a Project Darkstar
     * container.  It is also useful for swapping out implementations
     * of the Project Darkstar stack for testing purposes.
     * Typically, an application should never have a reason
     * to call this method, and doing so could cause unexpected
     * results. <p>
     * 
     * Specifying {@code null} for {@code managerLocator} sets the 
     * {@code ManagerLocator} back to its original, uninitialized state.
     * 
     * @param managerLocator the {@code ManagerLocator} that the 
     *        {@code InternalContext} should use to retrieve managers
     *        or {@code null} to make it uninitialized
     */
    public static synchronized void 
            setManagerLocator(ManagerLocator managerLocator) {
        InternalContext.managerLocator = managerLocator;
    }
}