/*******************************************************************************
 * Copyright (c) 2001, 2004 IBM Corporation and others.
 * All rights reserved. This program and the accompanying materials
 * are made available under the terms of the Eclipse Public License v1.0
 * which accompanies this distribution, and is available at
 * http://www.eclipse.org/legal/epl-v10.html
 * 
 * Contributors:
 *     IBM Corporation - initial API and implementation
 *     Jens Lukowski/Innoopract - initial renaming/restructuring
 *     
 *******************************************************************************/
package org.eclipse.wst.sse.ui.util;


import org.eclipse.core.runtime.IConfigurationElement;
import org.eclipse.core.runtime.IExtension;
import org.eclipse.core.runtime.IExtensionPoint;
import org.eclipse.core.runtime.IPluginDescriptor;
import org.eclipse.core.runtime.IPluginRegistry;
import org.eclipse.wst.sse.ui.Logger;


/**
 * Template implementation of a registry reader that creates objects
 * representing registry contents. Typically, an extension contains one
 * element, but this reader handles multiple elements per extension.
 * 
 * To start reading the extensions from the registry for an extension point,
 * call the method <code>readRegistry</code>.
 * 
 * To read children of an IConfigurationElement, call the method
 * <code>readElementChildren</code> from your implementation of the method
 * <code>readElement</code>, as it will not be done by default.
 */
public abstract class RegistryReader {


	protected static final String TAG_DESCRIPTION = "description"; //$NON-NLS-1$

	/**
	 * The constructor.
	 */
	protected RegistryReader() {
	}

	/**
	 * This method extracts description as a subelement of the given element.
	 * 
	 * @return description string if defined, or empty string if not.
	 */
	protected String getDescription(IConfigurationElement config) {
		IConfigurationElement[] children = config.getChildren(TAG_DESCRIPTION);
		if (children.length >= 1) {
			return children[0].getValue();
		}
		return ""; //$NON-NLS-1$
	}

	/**
	 * Logs the error in the workbench log using the provided text and the
	 * information in the configuration element.
	 */
	protected void logError(IConfigurationElement element, String text) {
		IExtension extension = element.getDeclaringExtension();
		IPluginDescriptor descriptor = extension.getDeclaringPluginDescriptor();
		StringBuffer buf = new StringBuffer();
		buf.append("Plugin " + descriptor.getUniqueIdentifier() + ", extension " + extension.getExtensionPointUniqueIdentifier()); //$NON-NLS-2$//$NON-NLS-1$
		buf.append("\n" + text); //$NON-NLS-1$
		Logger.log(Logger.ERROR, buf.toString());
	}

	/**
	 * Logs a very common registry error when a required attribute is missing.
	 */
	protected void logMissingAttribute(IConfigurationElement element, String attributeName) {
		logError(element, "Required attribute '" + attributeName + "' not defined"); //$NON-NLS-2$//$NON-NLS-1$
	}

	/**
	 * Logs a registry error when the configuration element is unknown.
	 */
	protected void logUnknownElement(IConfigurationElement element) {
		logError(element, "Unknown extension tag found: " + element.getName()); //$NON-NLS-1$
	}

	/**
	 * Apply a reproducable order to the list of extensions provided, such
	 * that the order will not change as extensions are added or removed.
	 */
	protected IExtension[] orderExtensions(IExtension[] extensions) {
		// By default, the order is based on plugin id sorted
		// in ascending order. The order for a plugin providing
		// more than one extension for an extension point is
		// dependent in the order listed in the XML file.
		Sorter sorter = new Sorter() {
			public boolean compare(Object extension1, Object extension2) {
				String s1 = ((IExtension) extension1).getDeclaringPluginDescriptor().getUniqueIdentifier().toUpperCase();
				String s2 = ((IExtension) extension2).getDeclaringPluginDescriptor().getUniqueIdentifier().toUpperCase();
				//Return true if elementTwo is 'greater than' elementOne
				return s2.compareTo(s1) > 0;
			}
		};

		Object[] sorted = sorter.sort(extensions);
		IExtension[] sortedExtension = new IExtension[sorted.length];
		System.arraycopy(sorted, 0, sortedExtension, 0, sorted.length);
		return sortedExtension;
	}

	/**
	 * Implement this method to read element's attributes. If children should
	 * also be read, then implementor is responsible for calling
	 * <code>readElementChildren</code>. Implementor is also responsible
	 * for logging missing attributes.
	 * 
	 * @return true if element was recognized, false if not.
	 */
	protected abstract boolean readElement(IConfigurationElement element);

	/**
	 * Read the element's children. This is called by the subclass'
	 * readElement method when it wants to read the children of the element.
	 */
	protected void readElementChildren(IConfigurationElement element) {
		readElements(element.getChildren());
	}

	/**
	 * Read each element one at a time by calling the subclass implementation
	 * of <code>readElement</code>.
	 * 
	 * Logs an error if the element was not recognized.
	 */
	protected void readElements(IConfigurationElement[] elements) {
		for (int i = 0; i < elements.length; i++) {
			if (!readElement(elements[i]))
				logUnknownElement(elements[i]);
		}
	}

	/**
	 * Read one extension by looping through its configuration elements.
	 */
	protected void readExtension(IExtension extension) {
		readElements(extension.getConfigurationElements());
	}

	/**
	 * Start the registry reading process using the supplied plugin ID and
	 * extension point.
	 */
	protected void readRegistry(IPluginRegistry registry, String pluginId, String extensionPoint) {
		IExtensionPoint point = registry.getExtensionPoint(pluginId, extensionPoint);
		if (point != null) {
			IExtension[] extensions = point.getExtensions();
			extensions = orderExtensions(extensions);
			for (int i = 0; i < extensions.length; i++)
				readExtension(extensions[i]);
		}
	}
}