org.apache.wicket.markup.head.PriorityFirstComparator.java Source code

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Here is the source code for org.apache.wicket.markup.head.PriorityFirstComparator.java

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/*
 * 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.
 */
package org.apache.wicket.markup.head;

import java.io.Serializable;
import java.util.Comparator;

import org.apache.wicket.Page;
import org.apache.wicket.markup.head.ResourceAggregator.RecordedHeaderItem;
import org.apache.wicket.markup.head.ResourceAggregator.RecordedHeaderItemLocation;

/**
 * Implements the default sorting algorithm for {@link HeaderItem}s. {@link PriorityHeaderItem}s are
 * moved to the front, inverting the component order to convert the child-first into a parent-first
 * order. If {@code renderPageFirst} is true, the head from the markup of a page is moved to the
 * front of the header, directly after the priority header items.
 * 
 * @author papegaaij
 */
public class PriorityFirstComparator implements Comparator<RecordedHeaderItem>, Serializable {
    protected static enum HeaderItemType {
        PRIORITY, PAGE, COMPONENT;
    }

    private final boolean renderPageFirst;

    /**
     * Construct.
     * 
     * @param renderPageFirst
     *            when true, the header of the page is moved to the front.
     */
    public PriorityFirstComparator(boolean renderPageFirst) {
        this.renderPageFirst = renderPageFirst;
    }

    @Override
    public int compare(RecordedHeaderItem o1, RecordedHeaderItem o2) {
        HeaderItemType o1Type = getItemType(o1);
        HeaderItemType o2Type = getItemType(o2);

        if (o1Type != o2Type)
            return o1Type.ordinal() - o2Type.ordinal();

        if (o1Type == HeaderItemType.PRIORITY) {
            return inversedComponentOrder(o1, o2);
        }
        return compareWithinGroup(o1, o2);
    }

    /**
     * Compares two header items that belong in the same group.
     * 
     * @param o1
     * @param o2
     * @return 0 by default to preserve the order
     */
    protected int compareWithinGroup(RecordedHeaderItem o1, RecordedHeaderItem o2) {
        return 0;
    }

    /**
     * Compares two priority header items, converting the child-first order into parent-first.
     * 
     * @param o1
     * @param o2
     * @return -1, 0 or 1 if o1 needs to be rendered before, unchanged or after o2.
     */
    protected int inversedComponentOrder(RecordedHeaderItem o1, RecordedHeaderItem o2) {
        RecordedHeaderItemLocation lastO1Location = o1.getLocations().get(o1.getLocations().size() - 1);
        RecordedHeaderItemLocation lastO2Location = o2.getLocations().get(o2.getLocations().size() - 1);

        // within a component, preserve order
        if (lastO1Location.getRenderBase() == lastO2Location.getRenderBase())
            return 0;

        return lastO1Location.getIndexInRequest() < lastO2Location.getIndexInRequest() ? 1 : -1;
    }

    /**
     * Determines the type of the item: priority, page or component.
     * 
     * @param item
     * @return the type of the item
     */
    protected HeaderItemType getItemType(RecordedHeaderItem item) {
        if (item.getItem() instanceof PriorityHeaderItem)
            return HeaderItemType.PRIORITY;
        if (renderPageFirst) {
            if (item.getItem() instanceof PageHeaderItem)
                return HeaderItemType.PAGE;
            for (RecordedHeaderItemLocation curLocation : item.getLocations())
                if (curLocation.getRenderBase() instanceof Page)
                    return HeaderItemType.PAGE;
        }

        return HeaderItemType.COMPONENT;
    }
}