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/*
 * Copyright (C) 2014 Dell, Inc.
 * 
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 * 
 *     http://www.apache.org/licenses/LICENSE-2.0
 * 
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

package com.dell.doradus.utilities;

import java.util.Iterator;

import com.dell.doradus.olap.io.BSTR;

public class BigSetDiff implements Iterable {
    private Iterable m_plus;
    private Iterable m_minus;

    public BigSetDiff(Iterable plus, Iterable minus) {
    	m_plus = plus;
    	m_minus = minus;
    }
    
	@Override public Iterator iterator() {
		return new AndNotIterator();
	}
	
	public class AndNotIterator implements Iterator {
	    private Iterator m_plus;
	    private Iterator m_minus;
	    private BSTR m_next_plus;
	    private BSTR m_next_minus;
		
	    public AndNotIterator() {
	    	m_plus = BigSetDiff.this.m_plus.iterator();
	    	m_minus = BigSetDiff.this.m_minus.iterator();
	    	m_next_minus = m_minus.hasNext() ? m_minus.next() : null;
	        move();
	    }
	    
		@Override public boolean hasNext() {
			return m_next_plus != null;
		}

		@Override public BSTR next() {
			BSTR next = m_next_plus == null ? null : new BSTR(m_next_plus);
			if(next == null) throw new RuntimeException("Read past the end of the iterator");
			move();
			return next;
		}

		@Override public void remove() { throw new RuntimeException("Cannot remove"); }

		private void move() {
			do {
				if(!m_plus.hasNext()) {
					m_next_plus = null;
					if(m_next_minus != null) {
						while(m_minus.hasNext()) m_minus.next();
					}
					return;
				}
				m_next_plus = m_plus.next();
				while(m_next_minus != null && m_next_minus.compareTo(m_next_plus) < 0) {
					m_next_minus = m_minus.hasNext() ? m_minus.next() : null;
				}
			} while(m_next_plus.equals(m_next_minus));
		}
	}
	
}