/*******************************************************************************
 * Copyright (c) 2010 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.wst.sse.ui.internal.contentassist;

import java.util.ArrayList;
import java.util.Arrays;
import java.util.HashMap;
import java.util.Iterator;
import java.util.List;
import java.util.Map;

import org.eclipse.core.runtime.CoreException;
import org.eclipse.core.runtime.IConfigurationElement;
import org.eclipse.core.runtime.IExtensionRegistry;
import org.eclipse.core.runtime.IStatus;
import org.eclipse.core.runtime.InvalidRegistryObjectException;
import org.eclipse.core.runtime.Platform;
import org.eclipse.core.runtime.Status;
import org.eclipse.wst.sse.ui.internal.Logger;
import org.eclipse.wst.sse.ui.internal.SSEUIPlugin;
import org.eclipse.wst.sse.ui.preferences.ICompletionProposalCategoriesConfigurationReader;
import org.eclipse.wst.sse.ui.preferences.ICompletionProposalCategoriesConfigurationWriter;

/**
 * <p>A registry for all extensions to the
 * <code>org.eclipse.wst.sse.ui.completionProposalCategoriesConfiguration</code>
 * extension point.</p>
 */
public final class CompletionProposoalCatigoriesConfigurationRegistry {
	/** The extension schema name of the extension point */
	private static final String EXTENSION_POINT = "completionProposalCategoriesConfiguration"; //$NON-NLS-1$

	/** The extension schema name of categories properties child elements */
	private static final String ELEM_CATEGORIES_PROPERTIES = "categoriesConfiguration"; //$NON-NLS-1$
	
	/** The extension schema name of the content type id attribute */
	private static final String ATTR_CONTENT_TYPE_ID = "contentTypeID"; //$NON-NLS-1$
	
	/** The extension schema name of the class attribute */
	private static final String ATTR_CLASS = "class"; //$NON-NLS-1$
	
	/** The singleton instance. */
	private static CompletionProposoalCatigoriesConfigurationRegistry fgSingleton = null;
	
	/** <code>true</code> if this registry has been loaded. */
	private boolean fLoaded;
	
	/**
	 * <code>{@link Map}<{@link String}, {@link ICompletionProposalCategoriesConfigurationReader}></code>
	 * <ul>
	 * <li><b>key:</b> Content Type ID</li>
	 * <li><b>value:</b> Categories Properties</li>
	 */
	private Map fPropertiesByContentTypeID;
	
	/**
	 * @return the singleton instance of this registry
	 */
	public static synchronized CompletionProposoalCatigoriesConfigurationRegistry getDefault() {
		if (fgSingleton == null) {
			fgSingleton = new CompletionProposoalCatigoriesConfigurationRegistry();
		}

		return fgSingleton;
	}
	
	/**
	 * Private constructor to create singleton instance
	 */
	private CompletionProposoalCatigoriesConfigurationRegistry() {
		this.fLoaded = false;
		this.fPropertiesByContentTypeID = new HashMap();
	}
	
	/**
	 * @param contentTypeID get the {@link ICompletionProposalCategoriesConfigurationReader} associated
	 * with the given content type
	 * @return the {@link ICompletionProposalCategoriesConfigurationReader} associated
	 * with the given content type, or <code>null</code> if one does not exist.
	 */
	public ICompletionProposalCategoriesConfigurationReader getReadableConfiguration(String contentTypeID) {
		this.ensureLoaded();
		return (ICompletionProposalCategoriesConfigurationReader)this.fPropertiesByContentTypeID.get(contentTypeID);
	}
	
	/**
	 * @param contentTypeID get the {@link ICompletionProposalCategoriesConfigurationWriter} associated
	 * with the given content type
	 * @return the {@link ICompletionProposalCategoriesConfigurationWriter} associated
	 * with the given content type, or <code>null</code> if one does not exist.
	 */
	public ICompletionProposalCategoriesConfigurationWriter getWritableConfiguration(String contentTypeID) {
		this.ensureLoaded();
		
		ICompletionProposalCategoriesConfigurationReader reader = getReadableConfiguration(contentTypeID);
		ICompletionProposalCategoriesConfigurationWriter writer = null;
		if(reader instanceof ICompletionProposalCategoriesConfigurationWriter) {
			writer = (ICompletionProposalCategoriesConfigurationWriter)reader;
		}
		
		return writer;
	}
	
	/**
	 * Ensures the <code>org.eclipse.wst.sse.ui.completionProposalCategoriesConfiguration</code>
	 * extensions have been loaded
	 */
	private void ensureLoaded() {
		if(!this.fLoaded) {
			this.load();
			this.fLoaded = true;
		}
	}
	
	/**
	 * Loads the <code>org.eclipse.wst.sse.ui.completionProposalCategoriesConfiguration</code> extensions
	 */
	private void load() {
		//get the extensions
		IExtensionRegistry registry= Platform.getExtensionRegistry();
		List extensionElements= new ArrayList(Arrays.asList(registry.getConfigurationElementsFor(SSEUIPlugin.ID, EXTENSION_POINT)));
		
		//for each element get its attributes and add it to the map of properties
		Iterator elementsIter = extensionElements.iterator();
		while(elementsIter.hasNext()) {
			IConfigurationElement element = (IConfigurationElement)elementsIter.next();
			
			try {
				if(element.getName().equals(ELEM_CATEGORIES_PROPERTIES)) {				
					String contentTypeID = element.getAttribute(ATTR_CONTENT_TYPE_ID);
					ContentAssistUtils.checkExtensionAttributeNotNull(contentTypeID, ATTR_CONTENT_TYPE_ID, element);
					
					String pageClass = element.getAttribute(ATTR_CLASS);
					ContentAssistUtils.checkExtensionAttributeNotNull(pageClass, ATTR_CLASS, element);
					
					ICompletionProposalCategoriesConfigurationReader props =
						(ICompletionProposalCategoriesConfigurationReader)element.createExecutableExtension(ATTR_CLASS);
				
					if(!this.fPropertiesByContentTypeID.containsKey(contentTypeID)){
						this.fPropertiesByContentTypeID.put(contentTypeID, props);
					} else {
						Logger.log(Logger.ERROR, "Extension " + element.getDeclaringExtension() + //$NON-NLS-1$
								" is attempting to to define itself as the proposal cateigories" + //$NON-NLS-1$
								" configuration for content type " + contentTypeID + " when another" + //$NON-NLS-1$ //$NON-NLS-2$
								" extensions has already done so."); //$NON-NLS-1$
					}
				} else {
					//extension specified element that is not valid for this extension
					Logger.log(Logger.WARNING, "The element " + element + " is not valid for the" + //$NON-NLS-1$ //$NON-NLS-2$
							"org.eclipse.wst.sse.ui.completionProposalCategoriesConfiguration" + //$NON-NLS-1$
							" extension point.  Only " + ELEM_CATEGORIES_PROPERTIES + //$NON-NLS-1$
							" elements are valid."); //$NON-NLS-1$
				}
			} catch (InvalidRegistryObjectException x) {
				/*
				 * Element is not valid any longer as the contributing plug-in was unloaded
				 * or for some other reason. 
				 */
				String message = "The extension ''" + element.toString() + "'' has become invalid."; //$NON-NLS-1$ //$NON-NLS-2$
				IStatus status= new Status(IStatus.WARNING, SSEUIPlugin.ID, IStatus.OK, message, x);
				Logger.log(status);
			} catch (CoreException x) {
				Logger.log(x.getStatus());
			}
		}
	}
}