
public class Runner {

	/** The root node from where validation should be started */
	INode fRoot;
	
	/** The query interface to our model */
	IModelQuery fModelQuery;
	
	/** empty list of problems */
	IProblem[] fProblems = {};

	
	/**
	 * Return a brand new shiny instance of a runner. The runner's purpose is to validate
	 * the nodes in the tree starting at node passed.
	 * 
	 * @param query the model query
	 * @param root the root node.
	 */
	
	public Runner ( IModelQuery query, INode root) {

		fRoot = root ;
		fModelQuery = query;
	}
	
	
	/**
	 * Perform the validation run.
	 * 
	 * @return list of problems found.
	 */
	
	
	public IProblem[] run () {

		// Create a depth first iteration from the root node
		ArrayList<INode> iteratorList = new ArrayList<INode>(32);
		ArrayList<Validator> validatorList = new ArrayList<Validator>(256);
		
		// start at the root node
		iteratorList.add(fRoot);
		
		// 1. Generate the list of validators to call, in order
		while (iteratorList.size() > 0) {
			
			INode nextNode = iteratorList.remove(0);
			
			Validator validator = nextNode.nodeValidator();
			
			if (validator != null) {				
				validatorList.add(validator);
				validator.setModelQuery(fModelQuery);
			}
			
			// the facaded object will tell us what children to include in the walk
			List<INode> children = nextNode.children();			
			if (children.size() > 0) {
				iteratorList.addAll(0, children);
			}			
		}
		
		
		// Pass 1
		for(Validator validator : validatorList) {
			validator.validate(Validator.PASS1);
		}
		
		ArrayList<IProblem> problems = new ArrayList<IProblem>( 64 );
		
		// Pass 2
		// On the validators that have been run, perform the final rule pass.
		for(Validator validator : validatorList) {
			validator.validate(Validator.PASS2);
			
			for(IProblem problem : validator.getProblems() ) {
				problems.add (problem);
			}
		}

		return problems.toArray( fProblems );
	}
}