fop/src/java/org/apache/fop/layoutmgr/ElementListUtils.java

/*
 * Licensed to the Apache Software Foundation (ASF) under one or more
 * contributor license agreements.  See the NOTICE file distributed with
 * this work for additional information regarding copyright ownership.
 * The ASF licenses this file to You 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.
 */

/* $Id$ */

package org.apache.fop.layoutmgr;

import java.util.List;
import java.util.ListIterator;

import org.apache.fop.traits.MinOptMax;
import org.apache.fop.util.ListUtil;

/**
 * Utilities for Knuth element lists.
 */
public final class ElementListUtils {
    
    private ElementListUtils() {
        // Utility class.
    }

    /**
     * Removes legal breaks in an element list. A constraint can be specified to limit the
     * range in which the breaks are removed. Legal breaks occuring before at least 
     * constraint.opt space is filled will be removed.
     * @param elements the element list
     * @param constraint min/opt/max value to restrict the range in which the breaks are removed.
     * @return true if the opt constraint is bigger than the list contents
     */
    public static boolean removeLegalBreaks(List elements, MinOptMax constraint) {
        return removeLegalBreaks(elements, constraint.opt);
    }

    /**
     * Removes legal breaks in an element list. A constraint can be specified to limit the
     * range in which the breaks are removed. Legal breaks occuring before at least 
     * constraint space is filled will be removed.
     * @param elements the element list
     * @param constraint value to restrict the range in which the breaks are removed.
     * @return true if the constraint is bigger than the list contents
     */
    public static boolean removeLegalBreaks(List elements, int constraint) {
        int len = 0;
        ListIterator iter = elements.listIterator();
        while (iter.hasNext()) {
            ListElement el = (ListElement)iter.next();
            if (el.isPenalty()) {
                KnuthPenalty penalty = (KnuthPenalty)el;
                //Convert all penalties to break inhibitors
                if (penalty.getP() < KnuthPenalty.INFINITE) {
                    iter.set(new KnuthPenalty(penalty.getW(), KnuthPenalty.INFINITE,
                            penalty.isFlagged(), penalty.getPosition(), penalty.isAuxiliary()));
                }
            } else if (el.isGlue()) {
                KnuthGlue glue = (KnuthGlue)el;
                len += glue.getW();
                iter.previous();
                el = (ListElement)iter.previous();
                iter.next();
                if (el.isBox()) {
                    iter.add(new KnuthPenalty(0, KnuthPenalty.INFINITE, false,
                            null, false));
                }
                iter.next();
            } else if (el instanceof BreakElement) {
                BreakElement breakEl = (BreakElement)el;
                if (breakEl.getPenaltyValue() < KnuthPenalty.INFINITE) {
                    breakEl.setPenaltyValue(KnuthPenalty.INFINITE);
                }
            } else {
                KnuthElement kel = (KnuthElement)el;
                len += kel.getW();
            }
            if (len >= constraint) {
                return false;
            }
        }
        return true;
    }

    /**
     * Removes legal breaks in an element list. A constraint can be specified to limit the
     * range in which the breaks are removed. Legal breaks within the space specified through the
     * constraint (starting from the end of the element list) will be removed.
     * @param elements the element list
     * @param constraint value to restrict the range in which the breaks are removed.
     * @return true if the constraint is bigger than the list contents
     */
    public static boolean removeLegalBreaksFromEnd(List elements, int constraint) {
        int len = 0;
        ListIterator i = elements.listIterator(elements.size());
        while (i.hasPrevious()) {
            ListElement el = (ListElement)i.previous();
            if (el.isPenalty()) {
                KnuthPenalty penalty = (KnuthPenalty)el;
                //Convert all penalties to break inhibitors
                if (penalty.getP() < KnuthPenalty.INFINITE) {
                    i.set(new KnuthPenalty(penalty.getW(), KnuthPenalty.INFINITE,
                            penalty.isFlagged(), penalty.getPosition(), penalty.isAuxiliary()));
                }
            } else if (el.isGlue()) {
                KnuthGlue glue = (KnuthGlue)el;
                len += glue.getW();
                el = (ListElement)i.previous();
                i.next();
                if (el.isBox()) {
                    i.add(new KnuthPenalty(0, KnuthPenalty.INFINITE, false,
                            null, false));
                }
            } else if (el.isUnresolvedElement()) {
                if (el instanceof BreakElement) {
                    BreakElement breakEl = (BreakElement)el;
                    if (breakEl.getPenaltyValue() < KnuthPenalty.INFINITE) {
                        breakEl.setPenaltyValue(KnuthPenalty.INFINITE);
                    }
                } else if (el instanceof UnresolvedListElementWithLength) {
                    UnresolvedListElementWithLength uel = (UnresolvedListElementWithLength)el;
                    len += uel.getLength().opt;
                }
            } else {
                KnuthElement kel = (KnuthElement)el;
                len += kel.getW();
            }
            if (len >= constraint) {
                return false;
            }
        }
        return true;
    }

    /**
     * Calculates the content length of the given element list. Warning: It doesn't take any
     * stretch and shrink possibilities into account.
     * @param elems the element list
     * @param start element at which to start
     * @param end element at which to stop
     * @return the content length
     */
    public static int calcContentLength(List elems, int start, int end) {
        ListIterator iter = elems.listIterator(start);
        int count = end - start + 1;
        int len = 0;
        while (iter.hasNext()) {
            ListElement el = (ListElement)iter.next();
            if (el.isBox()) {
                len += ((KnuthElement)el).getW();
            } else if (el.isGlue()) {
                len += ((KnuthElement)el).getW();
            } else {
                //log.debug("Ignoring penalty: " + el);
                //ignore penalties
            }
            count--;
            if (count == 0) {
                break;
            }
        }
        return len;
    }

    /**
     * Calculates the content length of the given element list. Warning: It doesn't take any
     * stretch and shrink possibilities into account.
     * @param elems the element list
     * @return the content length
     */
    public static int calcContentLength(List elems) {
        return calcContentLength(elems, 0, elems.size() - 1);
    }

    /**
     * Indicates whether the given element list ends with a forced break.
     * @param elems the element list
     * @return true if the list ends with a forced break
     */
    public static boolean endsWithForcedBreak(List elems) {
        ListElement last = (ListElement) ListUtil.getLast(elems);
        return last.isForcedBreak();
    }

    /**
     * Indicates whether the given element list ends with a penalty with a non-infinite penalty
     * value.
     * @param elems the element list
     * @return true if the list ends with a non-infinite penalty
     */
    public static boolean endsWithNonInfinitePenalty(List elems) {
        ListElement last = (ListElement) ListUtil.getLast(elems);
        if (last.isPenalty() && ((KnuthPenalty)last).getP() < KnuthElement.INFINITE) {
            return true;
        } else if (last instanceof BreakElement
                        && ((BreakElement)last).getPenaltyValue() < KnuthElement.INFINITE) {
            return true;
        }
        return false;
    }

    /**
     * Determines the position of the previous break before the start index on an
     * element list.
     * @param elems the element list
     * @param startIndex the start index
     * @return the position of the previous break, or -1 if there was no previous break
     */
    public static int determinePreviousBreak(List elems, int startIndex) {
        int prevBreak = startIndex - 1;
        while (prevBreak >= 0) {
            KnuthElement el = (KnuthElement)elems.get(prevBreak);
            if (el.isPenalty() && el.getP() < KnuthElement.INFINITE) {
                break;
            }
            prevBreak--;
        }
        return prevBreak;
    }

}