FirstPrecursorNodeLocator.java

package org.rubypeople.rdt.internal.ti.util;

import org.jruby.ast.Node;

/**
 * Visitor to find the first node that precedes a given offset that satisfies a given condition.
 * @author Jason Morrison
 */
public class FirstPrecursorNodeLocator extends NodeLocator {

	//Singleton pattern
	private FirstPrecursorNodeLocator() {}
	private static FirstPrecursorNodeLocator staticInstance = new FirstPrecursorNodeLocator();
	public static FirstPrecursorNodeLocator Instance()
	{
		return staticInstance;
	}
	
	/** Offset to start searching backwards from. */
	private int offset;
	
	/** INodeAcceptor that defines the desired node. */
	private INodeAcceptor acceptor;
	
	/** Running best match for closest precursor */
	private Node locatedNode;

	/**
	 * Finds the first node preceding the given offset that is accepted by the acceptor.
	 * @param rootNode Root Node that contains all nodes to search.
	 * @param offset Offset to search backwards from; returned node must occur strictly before this (i.e. end before offset.)
	 * @param acceptor INodeAcceptor defining the condition which the desired node fulfills.
	 * @return First precursor or null.
	 */
	public Node findFirstPrecursor(Node rootNode, int offset, INodeAcceptor acceptor ) {
		locatedNode = null;
		this.offset = offset;
		this.acceptor = acceptor;
		
		// Traverse to find closest precursor
		rootNode.accept(this);
		
		// Return the match
		return locatedNode;
	}

	/**
	 * Searches via InOrderVisitor for the closest precursor.
	 */
	public Object handleNode(Node iVisited) {
// TODO This will include nodes that envelop nodeStart, not only those starting strictly before it.
//      If this behavior is unwanted, remove the || (iVisited.getPosition().getStartOffset() <= offset)
//		in the conditional		
		if (( iVisited.getPosition().getEndOffset() <= offset) || (iVisited.getPosition().getStartOffset() <= offset )) {
			if ( acceptor.doesAccept( iVisited ) ) {
				locatedNode = iVisited;
			}
		}		
		return super.handleNode(iVisited);
	}
	
	
}