/*******************************************************************************
 * Copyright (c) 2000, 2017 IBM Corporation and others.
 *
 * This program and the accompanying materials
 * are made available under the terms of the Eclipse Public License 2.0
 * which accompanies this distribution, and is available at
 * https://www.eclipse.org/legal/epl-2.0/
 *
 * SPDX-License-Identifier: EPL-2.0
 *
 * Contributors:
 *     IBM Corporation - initial API and implementation
 *******************************************************************************/
package org.eclipse.jdt.internal.corext.refactoring.rename;

import org.eclipse.jface.text.IRegion;
import org.eclipse.jface.text.Region;

import org.eclipse.jdt.core.dom.ASTNode;
import org.eclipse.jdt.core.dom.CompilationUnit;
import org.eclipse.jdt.core.dom.IBinding;
import org.eclipse.jdt.core.dom.Name;
import org.eclipse.jdt.core.dom.SimpleName;
import org.eclipse.jdt.core.dom.VariableDeclaration;
import org.eclipse.jdt.core.dom.VariableDeclarationStatement;

import org.eclipse.jdt.internal.corext.dom.Selection;
import org.eclipse.jdt.internal.corext.dom.SelectionAnalyzer;

public class TempDeclarationFinder {

	//no instances
	private TempDeclarationFinder(){}

	/**
	 * @return <code>null</code> if the selection is invalid or does not cover a temp
	 * declaration or reference.
	 */
	public static VariableDeclaration findTempDeclaration(CompilationUnit cu, int selectionOffset, int selectionLength) {
		ASTNode selectedNode= getSelectedNode(cu, selectionOffset, selectionLength);

		if (selectedNode instanceof VariableDeclaration)
			return (VariableDeclaration) selectedNode;

		if (selectedNode instanceof Name) {
			Name reference= (Name) selectedNode;
			IBinding binding= reference.resolveBinding();
			if (binding == null)
				return null;
			ASTNode declaringNode= cu.findDeclaringNode(binding);
			if (declaringNode instanceof VariableDeclaration)
				return (VariableDeclaration) declaringNode;
			else
				return null;
		} else if (selectedNode instanceof VariableDeclarationStatement) {
			VariableDeclarationStatement vds= (VariableDeclarationStatement) selectedNode;
			if (vds.fragments().size() != 1)
				return null;
			return (VariableDeclaration) vds.fragments().get(0);
		}
		return null;
	}

	public static ASTNode getSelectedNode(CompilationUnit cu, int selectionOffset, int selectionLength) {
		TempSelectionAnalyzer analyzer= new TempSelectionAnalyzer(selectionOffset, selectionLength);
		cu.accept(analyzer);

		ASTNode[] selected= analyzer.getSelectedNodes();
		if (selected == null || selected.length != 1)
			return null;

		return selected[0];
	}

	/*
	 * Class used to extract selected nodes from an AST.
	 * Subclassing <code>SelectionAnalyzer</code> is needed to support activation
	 * when only a part of the <code>VariableDeclaration</code> node is selected
	 */
	private static class TempSelectionAnalyzer extends SelectionAnalyzer {

		private ASTNode fNode;

		TempSelectionAnalyzer(int selectionOffset, int selectionLength){
			super(Selection.createFromStartLength(selectionOffset, selectionLength), true);
		}

		//overridden
		@Override
		public boolean visitNode(ASTNode node) {
			if (node instanceof VariableDeclaration)
				return visitVariableDeclaration((VariableDeclaration)node);
			else if (node instanceof SimpleName)
					return visitSimpleName((SimpleName)node);
			else
				return super.visitNode(node);
		}

		private boolean addNodeAndStop(ASTNode node){
			fNode= node;
			return false;
		}

		private boolean visitSimpleName(SimpleName name) {
			if (getSelection().coveredBy(name))
				return addNodeAndStop(name);
			return super.visitNode(name);
		}

		private boolean visitVariableDeclaration(VariableDeclaration vd) {
			if (vd.getInitializer() != null){
				int start= vd.getStartPosition();
				IRegion declarationRange= new Region(start, vd.getInitializer().getStartPosition() - start);
				if (getSelection().coveredBy(declarationRange))
					return addNodeAndStop(vd);
				else
					return super.visitNode(vd);
			} else {
				if (getSelection().coveredBy(vd))
					return addNodeAndStop(vd);
				else
					return super.visitNode(vd);
			}
		}

		//overridden
		@Override
		public ASTNode[] getSelectedNodes() {
			if (fNode != null)
				return new ASTNode[] { fNode };
			return super.getSelectedNodes();
		}
	}

}
