/*
 * $Id$
 * Copyright (C) 2001 The Apache Software Foundation. All rights reserved.
 * For details on use and redistribution please refer to the
 * LICENSE file included with these sources.
 */

package org.apache.fop.layoutmgr;


import java.util.Iterator;
import java.util.NoSuchElementException;

public abstract class PositionIterator implements Iterator {
    Iterator m_parentIter;
    Object m_nextObj;
    LayoutManager m_childLM;
    boolean m_bHasNext;

    PositionIterator(Iterator parentIter) {
        m_parentIter = parentIter;
        lookAhead();
        //checkNext();
    }

    public LayoutManager getNextChildLM() {
        // Move to next "segment" of iterator, ie: new childLM
        if (m_childLM == null && m_nextObj != null) {
            m_childLM = getLM(m_nextObj);
            m_bHasNext = true;
        }
        return m_childLM;
    }

    protected abstract LayoutManager getLM(Object nextObj);

    protected abstract Position getPos(Object nextObj);

    private void lookAhead() {
        if (m_parentIter.hasNext()) {
            m_bHasNext = true;
            m_nextObj = m_parentIter.next();
        } else {
            endIter();
        }
    }

    protected boolean checkNext() {
        LayoutManager lm = getLM(m_nextObj);
        if (m_childLM == null) {
            m_childLM = lm;
        } else if (m_childLM != lm) {
            // End of this sub-sequence with same child LM
            m_bHasNext = false;
            m_childLM = null;
            return false;
        }
        return true;
    }

    protected void endIter() {
        m_bHasNext = false;
        m_nextObj = null;
        m_childLM = null;
    }

    public boolean hasNext() {
        return (m_bHasNext && checkNext());
    }


    public Object next() throws NoSuchElementException {
        if (m_bHasNext) {
            Object retObj = getPos(m_nextObj);
            lookAhead();
            return retObj;
        } else {
            throw new NoSuchElementException("PosIter");
        }
    }

    protected Object peekNext() {
        return m_nextObj;
    }

    public void remove() throws UnsupportedOperationException {
        throw new UnsupportedOperationException("PositionIterator doesn't support remove");
    }
}