SquirrelJME/SquirrelJME

// -*- Mode: Java; indent-tabs-mode: t; tab-width: 4 -*-
// ---------------------------------------------------------------------------
// SquirrelJME
//     Copyright (C) Stephanie Gawroriski <xer@multiphasicapps.net>
// ---------------------------------------------------------------------------
// SquirrelJME is under the Mozilla Public License Version 2.0.
// See license.mkd for licensing and copyright information.
// ---------------------------------------------------------------------------

package cc.squirreljme.runtime.midlet;

import javax.microedition.midlet.MIDlet;

/**
 * This is used to store the current MIDlet which is being run in the current
 * process.
 *
 * @since 2017/02/26
 */
public final class ActiveMidlet
{
    /** Lock to prevent multiple midlets from running. */
    private static final Object _ACTIVE_LOCK =
        new Object();
    
    /** Only a single midlet may run at a time. */
    private static volatile MIDlet _ACTIVE_MIDLET;
    
    /**
     * Not used.
     *
     * @since 2017/02/26
     */
    private ActiveMidlet()
    {
    }
    
    /**
     * Returns the currently active midlet.
     *
     * @return The active midlet.
     * @throws IllegalStateException If no midlet is set.
     * @since 2017/02/26
     */
    public static MIDlet get()
        throws IllegalStateException
    {
        MIDlet rv = ActiveMidlet.optional();
        
        /* {@squirreljme.error AD01 No MIDlet is currently active.} */
        if (rv == null)
            throw new IllegalStateException("AD01");
        
        return rv;
    }
    
    /**
     * Returns the currently active midlet.
     *
     * @return The active midlet or {@code null} if none is active.
     * @since 2019/04/14
     */
    public static MIDlet optional()
        throws IllegalStateException
    {
        // Lock
        synchronized (ActiveMidlet._ACTIVE_LOCK)
        {
            return ActiveMidlet._ACTIVE_MIDLET;
        }
    }
    
    /**
     * Sets the currently active midlet.
     *
     * @param __m The midlet to set.
     * @throws IllegalStateException If a midlet is already set.
     * @throws NullPointerException On null arguments.
     * @since 2017/02/26
     */
    public static void set(MIDlet __m)
        throws IllegalStateException, NullPointerException
    {
        // Check
        if (__m == null)
            throw new NullPointerException("NARG");
        
        // Prevent multiple MIDlet instantiations
        synchronized (ActiveMidlet._ACTIVE_LOCK)
        {
            /* {@squirreljme.error AD02 Only a single MIDlet may be active at
            a time.} */
            MIDlet active = ActiveMidlet._ACTIVE_MIDLET;
            if (active != null &&
                !(__m instanceof OverrideActiveMidletRestriction))
                throw new IllegalStateException("AD02");
            
            // Set active midlet
            ActiveMidlet._ACTIVE_MIDLET = __m;
        }
    }
}