001/*
002 * This library is part of OpenCms -
003 * the Open Source Content Management System
004 *
005 * Copyright (c) Alkacon Software GmbH & Co. KG (http://www.alkacon.com)
006 *
007 * This library is free software; you can redistribute it and/or
008 * modify it under the terms of the GNU Lesser General Public
009 * License as published by the Free Software Foundation; either
010 * version 2.1 of the License, or (at your option) any later version.
011 *
012 * This library is distributed in the hope that it will be useful,
013 * but WITHOUT ANY WARRANTY; without even the implied warranty of
014 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
015 * Lesser General Public License for more details.
016 *
017 * For further information about Alkacon Software, please see the
018 * company website: http://www.alkacon.com
019 *
020 * For further information about OpenCms, please see the
021 * project website: http://www.opencms.org
022 *
023 * You should have received a copy of the GNU Lesser General Public
024 * License along with this library; if not, write to the Free Software
025 * Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA  02111-1307  USA
026 */
027
028package org.opencms.gwt.client.util;
029
030import java.util.List;
031
032import com.google.gwt.core.client.JavaScriptObject;
033import com.google.gwt.user.client.Timer;
034
035/**
036 * Helper class to append a stylesheet link to the head of the current page and run a callback when everything has been loaded.
037 */
038public class CmsStylesheetLoader {
039
040    /** The callback that should be called when everything has been loaded. */
041    private Runnable m_allLoadedCallback;
042
043    /** Indicates whether the all-loaded callback has already been called. */
044    private boolean m_callbackCalled;
045
046    /** The callback for the onload handlers of the stylesheets. */
047    private JavaScriptObject m_jsCallback;
048
049    /** The number of stylesheets that have been already loaded. */
050    private int m_loadCounter;
051
052    /** The list of stylesheets to load. */
053    private List<String> m_stylesheets;
054
055    /**
056     * Creates a new instance.<p>
057     *
058     * @param stylesheets the list of stylesheets to load
059     * @param allLoadedCallback the callback to call when everything has been loaded
060     */
061    public CmsStylesheetLoader(List<String> stylesheets, Runnable allLoadedCallback) {
062
063        m_stylesheets = stylesheets;
064        m_loadCounter = 0;
065        m_allLoadedCallback = allLoadedCallback;
066
067        m_jsCallback = createJsCallback();
068    }
069
070    /**
071     * Checks the window.document for given style-sheet.<p>
072     *
073     * @param styleSheetLink the style-sheet link
074     * @return true if the stylesheet is already present
075     */
076    private static native boolean checkStylesheet(String styleSheetLink)/*-{
077        var styles = $wnd.document.styleSheets;
078        for (var i = 0; i < styles.length; i++) {
079            if (styles[i].href != null
080                    && styles[i].href.indexOf(styleSheetLink) >= 0) {
081                // style-sheet is present
082                return true;
083            }
084        }
085        return false;
086    }-*/;
087
088    /**
089     * Starts the loading process and creates a timer that sets of the callback after a given tiime if it hasn't already been triggered.
090     *
091     * @param timeout number of milliseconds after which the callback should be called if it hasn't already been
092     */
093    public void loadWithTimeout(int timeout) {
094
095        for (String stylesheet : m_stylesheets) {
096            boolean alreadyLoaded = checkStylesheet(stylesheet);
097            if (alreadyLoaded) {
098                m_loadCounter += 1;
099            } else {
100                appendStylesheet(stylesheet, m_jsCallback);
101            }
102        }
103        checkAllLoaded();
104        if (timeout > 0) {
105            Timer timer = new Timer() {
106
107                @SuppressWarnings("synthetic-access")
108                @Override
109                public void run() {
110
111                    callCallback();
112                }
113            };
114
115            timer.schedule(timeout);
116        }
117    }
118
119    /**
120     * Appends a stylesheet to the page head.<p>
121     *
122     * @param stylesheet the stylesheet link
123     * @param callback the load handler for the stylesheet link element
124     */
125    private native void appendStylesheet(String stylesheet, JavaScriptObject callback) /*-{
126        var headID = $wnd.document.getElementsByTagName("head")[0];
127        var cssNode = $wnd.document.createElement('link');
128        cssNode.type = 'text/css';
129        cssNode.rel = 'stylesheet';
130        cssNode.href = stylesheet;
131        headID.appendChild(cssNode, callback);
132        cssNode.addEventListener("load", callback);
133    }-*/;
134
135    /**
136     * Calls the callback if it hasn't already been triggered.<p>
137     */
138    private void callCallback() {
139
140        if (!m_callbackCalled) {
141            m_callbackCalled = true;
142            m_allLoadedCallback.run();
143        }
144    }
145
146    /**
147     * Checks if all stylesheets have been loaded.<p>
148     */
149    private void checkAllLoaded() {
150
151        if (m_loadCounter == m_stylesheets.size()) {
152            callCallback();
153        }
154    }
155
156    /**
157     * Creates the callback for the onload handlers of the link elements.<p>
158     *
159     * @return the callback
160     */
161    private native JavaScriptObject createJsCallback() /*-{
162        var self = this;
163        return function() {
164            self.@org.opencms.gwt.client.util.CmsStylesheetLoader::onLoadCallback()();
165        }
166    }-*/;
167
168    /**
169     * The method which should be called by the onload handlers of the link elements.<p>
170     */
171    private void onLoadCallback() {
172
173        m_loadCounter += 1;
174        checkAllLoaded();
175    }
176
177}