CSSInjector.java

package kornell.gui.client.util;

import static kornell.core.util.StringUtils.mkurl;

import com.google.gwt.core.client.Callback;
import com.google.gwt.core.client.JavaScriptObject;

public class CSSInjector {
	
	public static void injectCSS(String path, Callback<Void, Exception>callback){
		JavaScriptObject styleElement = getStyleElement(path);
		if(callback != null){
			attachListeners(styleElement, callback);
		}
		
		updateSkin(styleElement);
	}

	public static void updateSkin(String skinName, Callback<Void, Exception>callback){
		String skinPath = mkurl(ClientConstants.CSS_PATH, "skin" + skinName + ".nocache.css");
		injectCSS(skinPath, callback);
	}

	private static native void updateSkin(JavaScriptObject styleElement) /*-{
		var oldLink = $wnd.document.getElementById('kornellSkin');
		if (oldLink) {
			$wnd.document.head.removeChild(oldLink);
		}

		// IE8 does not have document.head
		($wnd.document.head || $wnd.document.getElementsByTagName("head")[0])
				.appendChild(styleElement);
	}-*/;

	private static native JavaScriptObject getStyleElement(String skinPath) /*-{
		var link = $wnd.document.createElement('link'), oldLink = $wnd.document
				.getElementById('kornellSkin');
		link.id = 'kornellSkin';
		link.rel = 'stylesheet';
		link.type = 'text/css';
		link.href = skinPath;
		if (oldLink) {
			$wnd.document.head.removeChild(oldLink);
		}

		return link;
	}-*/;

	private static native void attachListeners(JavaScriptObject scriptElement, Callback<Void, Exception> callback) /*-{
	    function clearCallbacks() {
	      scriptElement.onerror = scriptElement.onreadystatechange = scriptElement.onload = null;
	    }
	    scriptElement.onload = $entry(function() {
	      clearCallbacks();
	      if (callback) {
	        callback.@com.google.gwt.core.client.Callback::onSuccess(Ljava/lang/Object;)(null);
	      }
	    });
	    // or possibly more portable script_tag.addEventListener('error', function(){...}, true);
	    scriptElement.onerror = $entry(function() {
	      clearCallbacks();
	      if (callback) {
	        var ex = @com.google.gwt.core.client.CodeDownloadException::new(Ljava/lang/String;)("onerror() called.");
	        callback.@com.google.gwt.core.client.Callback::onFailure(Ljava/lang/Object;)(ex);
	      }
	    });
	    scriptElement.onreadystatechange = $entry(function() {
	      if (/loaded|complete/.test(scriptElement.readyState)) {
	        scriptElement.onload();
	      }
	    });
	  }-*/;
	
}