/*=============================================================================#
 # Copyright (c) 2007, 2021 Stephan Wahlbrink and others.
 # 
 # This program and the accompanying materials are made available under the
 # terms of the Eclipse Public License 2.0 which is available at
 # https://www.eclipse.org/legal/epl-2.0, or the Apache License, Version 2.0
 # which is available at https://www.apache.org/licenses/LICENSE-2.0.
 # 
 # SPDX-License-Identifier: EPL-2.0 OR Apache-2.0
 # 
 # Contributors:
 #     Stephan Wahlbrink <sw@wahlbrink.eu> - initial API and implementation
 #=============================================================================*/

package org.eclipse.statet.ltk.ui.sourceediting;

import org.eclipse.core.commands.AbstractHandler;
import org.eclipse.core.commands.ExecutionEvent;
import org.eclipse.core.commands.ExecutionException;
import org.eclipse.core.runtime.NullProgressMonitor;
import org.eclipse.jface.text.IRegion;
import org.eclipse.jface.text.ITextSelection;
import org.eclipse.jface.text.Region;

import org.eclipse.statet.ltk.ast.core.AstInfo;
import org.eclipse.statet.ltk.ast.core.AstNode;
import org.eclipse.statet.ltk.ast.core.util.AstSelection;
import org.eclipse.statet.ltk.model.core.element.SourceUnit;


/**
 * Command handler to expand the text selection according the AST.
 */
public abstract class StructureSelectHandler extends AbstractHandler {
	
	
	public static class Enclosing extends StructureSelectHandler {
		
		public Enclosing(final ISourceEditor editor, final StructureSelectionHistory history) {
			super(editor, history);
		}
		
		@Override
		IRegion concreteNewSelectionRange(final AstSelection selection) {
			final AstNode covering= selection.getCovering();
			return createRegion(covering.getStartOffset(), covering.getEndOffset());
		}
		
	}
	
	public static class Next extends StructureSelectHandler {
		
		public Next(final ISourceEditor editor, final StructureSelectionHistory history) {
			super(editor, history);
		}
		
		@Override
		IRegion concreteNewSelectionRange(final AstSelection selection) {
			final AstNode covering= selection.getCovering();
			AstNode child= selection.getChildLastTouching();
			if (child == null || selection.getStopOffset() >= child.getEndOffset()) {
				child= selection.getChildAfter();
			}
			if (child != null) {
				return createRegion(selection.getStartOffset(), child.getEndOffset());
			}
			return createRegion(covering.getStartOffset(), covering.getEndOffset());
		}
		
	}
	
	public static class Previous extends StructureSelectHandler {
		
		public Previous(final ISourceEditor editor, final StructureSelectionHistory history) {
			super(editor, history);
		}
		
		@Override
		IRegion concreteNewSelectionRange(final AstSelection selection) {
			final AstNode covering= selection.getCovering();
			AstNode child= selection.getChildFirstTouching();
			if (child == null || selection.getStartOffset() <= child.getStartOffset()) {
				child= selection.getChildBefore();
			}
			if (child != null) {
				return createRegion(selection.getStopOffset(), child.getStartOffset());
			}
			return createRegion(covering.getEndOffset(), covering.getStartOffset());
		}
		
	}
	
	
	private final ISourceEditor sourceEditor;
	private final StructureSelectionHistory selectionHistory;
	
	
	protected StructureSelectHandler(final ISourceEditor editor, final StructureSelectionHistory history) {
		super();
		assert (editor != null);
		assert (history != null);
		this.sourceEditor= editor;
		this.selectionHistory= history;
	}
	
	
	@Override
	public Object execute(final ExecutionEvent event) throws ExecutionException {
		final SourceUnit su= this.sourceEditor.getSourceUnit();
		if (su == null) {
			return null;
		}
		final AstInfo astInfo= su.getAstInfo(null, true, new NullProgressMonitor());
		if (astInfo == null) {
			return null;
		}
		
		final ITextSelection selection= getTextSelection();
		final IRegion newRange= getNewSelectionRange(selection.getOffset(), selection.getOffset()+selection.getLength(), astInfo);
		if (newRange != null) {
			this.selectionHistory.remember(new Region(selection.getOffset(), selection.getLength()));
			try {
				this.selectionHistory.ignoreSelectionChanges();
				this.sourceEditor.selectAndReveal(newRange.getOffset(), newRange.getLength());
			}
			finally {
				this.selectionHistory.listenToSelectionChanges();
			}
		}
		return null;
	}
	
	public final IRegion getNewSelectionRange(final int oldStart, final int oldStop, final AstInfo ast) {
		final AstSelection selection= AstSelection.search(ast.getRoot(),
				oldStart, oldStop, AstSelection.MODE_COVERING_GREATER );
		if (selection.getCovering() == null) {
			return null;
		}
		return concreteNewSelectionRange(selection);
	}
	
	/**
	 * Subclasses determine the actual new selection.
	 */
	abstract IRegion concreteNewSelectionRange(AstSelection selection);
	
	protected final ITextSelection getTextSelection() {
		return (ITextSelection) this.sourceEditor.getViewer().getSelectionProvider().getSelection();
	}
	
	protected final IRegion createRegion(int start, final int stop) {
		if (start < 0) {
			start= 0;
		}
		return new Region(start, stop-start);
	}
	
}