/*******************************************************************************
 * Copyright (c) 2004, 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.jst.jsp.ui.internal.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.jst.jsp.ui.internal.JSPUIPlugin;
import org.eclipse.jst.jsp.ui.internal.editor.JSPEditorPluginImageHelper;
import org.eclipse.jst.jsp.ui.internal.editor.JSPEditorPluginImages;
import org.eclipse.swt.graphics.Image;

/**
 * Completion processor for JSP Templates. Most of the work is already done by
 * the JSP Content Assist processor, so by the time the
 * JSPTemplateCompletionProcessor is asked for content assist proposals, the
 * jsp content assist processor has already set the context type for
 * templates.
 */
class JSPTemplateCompletionProcessor 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 JSPEditorPluginImageHelper.getInstance().getImage(JSPEditorPluginImages.IMG_OBJ_TAG_JSP);
	}

	private ContextTypeRegistry getTemplateContextRegistry() {
		return JSPUIPlugin.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 JSPUIPlugin.getDefault().getTemplateStore();
	}

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