//******************************************************************************
//
// File:    JobGenerator.java
// Package: edu.rit.pj.job
// Unit:    Class edu.rit.pj.job.JobGenerator
//
// This Java source file is copyright (C) 2010 by Alan Kaminsky. All rights
// reserved. For further information, contact the author, Alan Kaminsky, at
// ark@cs.rit.edu.
//
// This Java source file is part of the Parallel Java Library ("PJ"). PJ is free
// software; you can redistribute it and/or modify it under the terms of the GNU
// General Public License as published by the Free Software Foundation; either
// version 3 of the License, or (at your option) any later version.
//
// PJ 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.
//
// A copy of the GNU General Public License is provided in the file gpl.txt. You
// may also obtain a copy of the GNU General Public License on the World Wide
// Web at http://www.gnu.org/licenses/gpl.html.
//
//******************************************************************************

package edu.rit.pj.job;

import java.util.HashSet;
import java.util.Iterator;
import java.util.NoSuchElementException;
import java.util.Set;

/**
 * Class JobGenerator is the abstract base class for an object that generates a
 * group of {@linkplain Job}s.
 * 

 * Jobs are numbered from 0 to N−1, where N is the number of
 * jobs in the group. A subclass must override the jobCount() method to
 * return N. A subclass must override the createJob() method to
 * create and return the job corresponding to a given job number. The job
 * generator need not create all the jobs in the group, and it need not create
 * them in any particular order.
 * 

 * Class JobGenerator provides the omit() method to omit generating
 * certain job numbers. This is used for checkpointing. For further information,
 * see class {@linkplain Runner}.
 *
 * @author  Alan Kaminsky
 * @version 08-Oct-2010
 */
public abstract class JobGenerator
	implements Iterable
	{

// Hidden data members.

	private Set myOmittedJobNumbers;

// Exported constructors.

	/**
	 * Construct a new job generator.
	 */
	public JobGenerator()
		{
		myOmittedJobNumbers = new HashSet();
		}

// Exported operations.

	/**
	 * Omit the job numbers in the given set when generating jobs. To be
	 * effective, omit() must be called before calling
	 * iterator(). A snapshot of the given set is taken; changing the
	 * set's contents thereafter will not affect the job numbers to be omitted.
	 *
	 * @param  theOmittedJobNumbers  Set of job numbers to be omitted.
	 *
	 * @exception  NullPointerException
	 *     (unchecked exception) Thrown if theOmittedJobNumbers is
	 *     null.
	 */
	public void omit
		(Set theOmittedJobNumbers)
		{
		myOmittedJobNumbers.clear();
		myOmittedJobNumbers.addAll (theOmittedJobNumbers);
		}

	/**
	 * Get an iterator for generating the jobs in the job group.
	 *
	 * @return  Iterator.
	 */
	public Iterator iterator()
		{
		return new Iterator()
			{
			private int N = jobCount();
			private int myJobNumber = -1;
			private boolean generated = true;

			public boolean hasNext()
				{
				advance();
				return myJobNumber < N;
				}

			public Job next()
				{
				advance();
				if (myJobNumber >= N)
					{
					throw new NoSuchElementException();
					}
				generated = true;
				return createJob (myJobNumber);
				}

			public void remove()
				{
				throw new UnsupportedOperationException();
				}

			private void advance()
				{
				if (generated)
					{
					generated = false;
					do
						{
						++ myJobNumber;
						}
					while (myJobNumber < N &&
							myOmittedJobNumbers.contains (myJobNumber));
					}
				}
			};
		}

// Hidden operations.

	/**
	 * Returns the number of jobs in the job group, N.
	 *
	 * @return  Number of jobs.
	 */
	protected abstract int jobCount();

	/**
	 * Create the job with the given job number. This method must create and
	 * return an instance of class {@linkplain Job} whose job number is
	 * theJobNumber.
	 *
	 * @param  theJobNumber  Job number (0 .. N−1).
	 */
	protected abstract Job createJob
		(int theJobNumber);

	}