/*******************************************************************************
 * Copyright (c) 2002, 2006 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
 *******************************************************************************/
package org.eclipse.ui.internal.cheatsheets.registry;

import org.eclipse.core.runtime.*;
import org.eclipse.ui.internal.cheatsheets.*;

/**
 *	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.
	 */
	/*package*/ RegistryReader() {
	}

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

	/**
	 * Logs the error in the workbench log using the provided
	 * text and the information in the configuration element.
	 */
	private void logError(IConfigurationElement element, String text) {
		IExtension extension = element.getDeclaringExtension();
		StringBuffer buf = new StringBuffer();
		buf.append("Plugin " + extension.getContributor().getName() + ", extension " + extension.getExtensionPointUniqueIdentifier()); //$NON-NLS-2$//$NON-NLS-1$
		buf.append("\n" + text); //$NON-NLS-1$

		IStatus status = new Status(IStatus.ERROR, ICheatSheetResource.CHEAT_SHEET_PLUGIN_ID, IStatus.OK, buf.toString(), null);
		CheatSheetPlugin.getPlugin().getLog().log(status);
	}

	/**
	 * Logs a very common registry error when a required attribute is missing.
	 */
	/*package*/ 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.
	 */
	private 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.
	 */
	private 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).getContributor().getName().toUpperCase();
				String s2 = ((IExtension) extension2).getContributor().getName().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.
	 */
	/*package*/ 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.
	 */
	/*package*/ 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.
	 */
	private 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.
	 */
	private void readExtension(IExtension extension) {
		readElements(extension.getConfigurationElements());
	}

	/**
	 *	Start the registry reading process using the
	 * supplied plugin ID and extension point.
	 */
	/*package*/ void readRegistry(IExtensionRegistry 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]);
		}
	}
}