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/*
 *
 *          Copyright (c) 2013,2019  AT&T Knowledge Ventures
 *                     SPDX-License-Identifier: MIT
 */
package com.att.research.xacmlatt.pdp.std.combiners;

import java.util.Iterator;
import java.util.List;

import com.att.research.xacml.api.Decision;
import com.att.research.xacml.api.Identifier;
import com.att.research.xacmlatt.pdp.eval.EvaluationContext;
import com.att.research.xacmlatt.pdp.eval.EvaluationException;
import com.att.research.xacmlatt.pdp.eval.EvaluationResult;
import com.att.research.xacmlatt.pdp.policy.CombinerParameter;
import com.att.research.xacmlatt.pdp.policy.CombiningElement;

/**
 * PermitOverrides extends {@link com.att.research.xacmlatt.pdp.std.combiners.CombiningAlgorithmBase} to implement the
 * XACML 3.0 Permit-overrides combining algorithm for policies and rules.
 * 
 * @author car
 * @version $Revision: 1.1 $
 * 
 * @param  the java class of the object to be combined
 */
public class PermitOverrides extends CombiningAlgorithmBase {

	public PermitOverrides(Identifier identifierIn) {
		super(identifierIn);
	}

	@Override
	public EvaluationResult combine(EvaluationContext evaluationContext,
			List> elements,
			List combinerParameters)
			throws EvaluationException {
		boolean atLeastOneDeny					= false;

		EvaluationResult combinedResult			= new EvaluationResult(Decision.DENY);
		
		EvaluationResult firstIndeterminateD	= null;
		EvaluationResult firstIndeterminateP	= null;
		EvaluationResult firstIndeterminateDP	= null;
		
		Iterator> iterElements	= elements.iterator();
		while (iterElements.hasNext()) {
			CombiningElement combiningElement		= iterElements.next();
			EvaluationResult evaluationResultElement	= combiningElement.evaluate(evaluationContext);
			
			assert(evaluationResultElement != null);
			switch(evaluationResultElement.getDecision()) {
			case DENY:
				atLeastOneDeny	= true;
				combinedResult.merge(evaluationResultElement);
				break;
			case INDETERMINATE:
			case INDETERMINATE_DENYPERMIT:
				if (firstIndeterminateDP == null) {
					firstIndeterminateDP	= evaluationResultElement;
				} else {
					firstIndeterminateDP.merge(evaluationResultElement);
				}
				break;
			case INDETERMINATE_DENY:
				if (firstIndeterminateD == null) {
					firstIndeterminateD		= evaluationResultElement;
				} else {
					firstIndeterminateD.merge(evaluationResultElement);
				}
				break;
			case INDETERMINATE_PERMIT:
				if (firstIndeterminateP == null) {
					firstIndeterminateP		= evaluationResultElement;
				} else {
					firstIndeterminateP.merge(evaluationResultElement);
				}
				break;
			case NOTAPPLICABLE:
				break;
			case PERMIT:
				return evaluationResultElement;
			default:
				throw new EvaluationException("Illegal Decision: \"" + evaluationResultElement.getDecision().toString());
			}
		}
		
		if (firstIndeterminateDP != null) {
			return firstIndeterminateDP;
		} else if (firstIndeterminateP != null && (firstIndeterminateD != null || atLeastOneDeny)) {
			return new EvaluationResult(Decision.INDETERMINATE_DENYPERMIT, firstIndeterminateD.getStatus());
		} else if (firstIndeterminateP != null) {
			return firstIndeterminateP;
		} else if (atLeastOneDeny) {
			return combinedResult;
		} else if (firstIndeterminateD != null) {
			return firstIndeterminateD;
		} else {
			return new EvaluationResult(Decision.NOTAPPLICABLE);
		}
	}

}