/*******************************************************************************
 * Copyright (c) 2006, 2010 Soyatec (http://www.soyatec.com) 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:
 *     Soyatec - initial API and implementation
 *******************************************************************************/
package org.eclipse.xwt.vex.contentassist;

import java.util.ArrayList;
import java.util.Collections;
import java.util.Comparator;
import java.util.List;

import org.eclipse.jface.text.IDocument;
import org.eclipse.jface.text.IRegion;
import org.eclipse.jface.text.ITextSelection;
import org.eclipse.jface.text.ITextViewer;
import org.eclipse.jface.text.Region;
import org.eclipse.jface.text.contentassist.ICompletionProposal;
import org.eclipse.jface.text.templates.ContextTypeRegistry;
import org.eclipse.jface.text.templates.Template;
import org.eclipse.jface.text.templates.TemplateCompletionProcessor;
import org.eclipse.jface.text.templates.TemplateContext;
import org.eclipse.jface.text.templates.TemplateContextType;
import org.eclipse.jface.text.templates.TemplateException;
import org.eclipse.jface.text.templates.TemplateProposal;
import org.eclipse.jface.text.templates.persistence.TemplateStore;
import org.eclipse.swt.graphics.Image;
import org.eclipse.wst.xml.ui.internal.XMLUIPlugin;
import org.eclipse.wst.xml.ui.internal.contentassist.ReplaceNameTemplateContext;
import org.eclipse.wst.xml.ui.internal.editor.XMLEditorPluginImageHelper;
import org.eclipse.wst.xml.ui.internal.editor.XMLEditorPluginImages;

/**
 * Completion processor for XML Templates. Most of the work is already done by the XML Content Assist processor, so by the time the XMLTemplateCompletionProcessor is asked for content assist proposals, the XML content assist processor has already set the context type for templates.
 */
public class VEXTemplateCompletionProcessor extends TemplateCompletionProcessor {
	private static final class ProposalComparator implements Comparator {
		public int compare(Object o1, Object o2) {
			return ((TemplateProposal) o2).getRelevance() - ((TemplateProposal) o1).getRelevance();
		}
	}

	private static final Comparator fgProposalComparator = new ProposalComparator();
	private String fContextTypeId = null;

	/*
	 * Copied from super class except instead of calling createContext(viewer, region) call createContext(viewer, region, offset) instead
	 */
	public ICompletionProposal[] computeCompletionProposals(ITextViewer viewer, int offset) {

		ITextSelection selection = (ITextSelection) viewer.getSelectionProvider().getSelection();

		// adjust offset to end of normalized selection
		if (selection.getOffset() == offset) {
			offset = selection.getOffset() + selection.getLength();
		}

		String prefix = extractPrefix(viewer, offset);
		Region region = new Region(offset - prefix.length(), prefix.length());
		TemplateContext context = createContext(viewer, region, offset);
		if (context == null) {
			return new ICompletionProposal[0];
		}

		// name of the selection variables {line, word}_selection
		context.setVariable("selection", selection.getText()); //$NON-NLS-1$

		Template[] templates = getTemplates(context.getContextType().getId());

		List matches = new ArrayList();
		for (int i = 0; i < templates.length; i++) {
			Template template = templates[i];
			try {
				context.getContextType().validate(template.getPattern());
			} catch (TemplateException e) {
				continue;
			}
			if (template.matches(prefix, context.getContextType().getId())) {
				matches.add(createProposal(template, context, (IRegion) region, getRelevance(template, prefix)));
			}
		}

		Collections.sort(matches, fgProposalComparator);

		return (ICompletionProposal[]) matches.toArray(new ICompletionProposal[matches.size()]);
	}

	/**
	 * Creates a concrete template context for the given region in the document. This involves finding out which context type is valid at the given location, and then creating a context of this type. The default implementation returns a <code>SmartReplaceTemplateContext</code> for the context type at the given location. This takes the offset at which content assist was invoked into consideration.
	 * 
	 * @param viewer
	 *            the viewer for which the context is created
	 * @param region
	 *            the region into <code>document</code> for which the context is created
	 * @param offset
	 *            the original offset where content assist was invoked
	 * @return a template context that can handle template insertion at the given location, or <code>null</code>
	 */
	private TemplateContext createContext(ITextViewer viewer, IRegion region, int offset) {
		// pretty much same code as super.createContext except create
		// SmartReplaceTemplateContext
		TemplateContextType contextType = getContextType(viewer, region);
		if (contextType != null) {
			IDocument document = viewer.getDocument();
			return new ReplaceNameTemplateContext(contextType, document, region.getOffset(), region.getLength(), offset);
		}
		return null;
	}

	protected ICompletionProposal createProposal(Template template, TemplateContext context, IRegion region, int relevance) {
		return new CustomTemplateProposal(template, context, region, getImage(template), relevance);
	}

	protected TemplateContextType getContextType(ITextViewer viewer, IRegion region) {
		TemplateContextType type = null;

		ContextTypeRegistry registry = getTemplateContextRegistry();
		if (registry != null) {
			type = registry.getContextType(fContextTypeId);
		}

		return type;
	}

	protected Image getImage(Template template) {
		// just return the same image for now
		return XMLEditorPluginImageHelper.getInstance().getImage(XMLEditorPluginImages.IMG_OBJ_TAG_MACRO);
	}

	private ContextTypeRegistry getTemplateContextRegistry() {
		return XMLUIPlugin.getDefault().getTemplateContextRegistry();
	}

	protected Template[] getTemplates(String contextTypeId) {
		Template templates[] = null;

		TemplateStore store = getTemplateStore();
		if (store != null) {
			templates = store.getTemplates(contextTypeId);
		}

		return templates;
	}

	private TemplateStore getTemplateStore() {
		return XMLUIPlugin.getDefault().getTemplateStore();
	}

	public void setContextType(String contextTypeId) {
		fContextTypeId = contextTypeId;
	}
}