SecureBPMN/designer/src/com.sun.xacml/src/main/java/com/sun/xacml/combine/OnlyOneApplicablePolicyAlg.java

/*
 * @(#)OnlyOneApplicablePolicyAlg.java
 *
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 * 
 * This software is provided "AS IS," without a warranty of any kind. ALL
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package com.sun.xacml.combine;

import com.sun.xacml.AbstractPolicy;
import com.sun.xacml.EvaluationCtx;
import com.sun.xacml.MatchResult;

import com.sun.xacml.ctx.Result;
import com.sun.xacml.ctx.Status;

import java.net.URI;

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


/**
 * This is the standard Only One Applicable Policy combining algorithm. This
 * is a special algorithm used at the root of a policy/pdp to make sure that
 * pdp only selects one policy per request.
 *
 * @since 1.0
 * @author Seth Proctor
 */
public class OnlyOneApplicablePolicyAlg extends PolicyCombiningAlgorithm
{

    /**
     * The standard URN used to identify this algorithm
     */
    public static final String algId =
        "urn:oasis:names:tc:xacml:1.0:policy-combining-algorithm:" +
        "only-one-applicable";

    // a URI form of the identifier
    private static URI identifierURI;
    // exception if the URI was invalid, which should never be a problem
    private static RuntimeException earlyException;

    static {
        try {
            identifierURI = URI.create(algId);
        } catch (IllegalArgumentException e) {
            earlyException = e;
        }
    }

    /**
     * Standard constructor.
     */
    public OnlyOneApplicablePolicyAlg() {
        super(identifierURI);

        if (earlyException != null) {
            throw earlyException;
        }
    }
    


    /**
     * Applies the combining rule to the set of policies based on the
     * evaluation context.
     *
     * @param context the context from the request
     * @param parameters a (possibly empty) non-null <code>List</code> of
     *                   <code>CombinerParameter<code>s
     * @param policyElements the policies to combine
     *
     * @return the result of running the combining algorithm
     */
    public Result combine(EvaluationCtx context, List<CombinerParameter> parameters,
                          List<CombinerElement> policyElements) {
        boolean atLeastOne = false;
        AbstractPolicy selectedPolicy = null;
        Iterator<CombinerElement> it = policyElements.iterator();

        while (it.hasNext()) {
            AbstractPolicy policy =
                ((PolicyCombinerElement)(it.next())).getPolicy();

            // see if the policy matches the context
            context.newEvent(policy);
            MatchResult match = policy.match(context);
           
            // if there is an error in trying to match any of the targets,
            // we always return INDETERMINATE immediately
            if (match.getResult() == MatchResult.INDETERMINATE) {
                Result result = new Result(Result.DECISION_INDETERMINATE,
                                           match.getStatus(),
                                           context);
                context.closeCurrentEvent(result);
                return result;
            }
            
            if (match.getResult() == MatchResult.NO_MATCH) {
                context.closeCurrentEvent(
                        new Result(Result.DECISION_NOT_APPLICABLE));
            }
            
            if (match.getResult() == MatchResult.MATCH) {
                // if this isn't the first match, then this is an error
                if (atLeastOne) {
                    List<String> code = new ArrayList<String>();
                    code.add(Status.STATUS_PROCESSING_ERROR);
                    String message = "Too many applicable policies";
                    Result result = new Result(Result.DECISION_INDETERMINATE,
                                               new Status(code, message),
                                               context);
                    context.closeCurrentEvent(result);
                    return result;
                }

                // if this was the first applicable policy in the set, then
                // remember it for later
                atLeastOne = true;
                selectedPolicy = policy;
                context.closeCurrentEvent("Evaluated later");
            }
        }

        // if we got through the loop and found exactly one match, then
        // we return the evaluation result of that policy
        if (atLeastOne) {
            context.newEvent(selectedPolicy);
            Result result = selectedPolicy.evaluate(context);
            context.closeCurrentEvent(result);
            // do not treat the discarded values
            if (result != null) {
                return result;
            }
        }

        // if we didn't find a matching policy, then we don't apply
        return new Result(Result.DECISION_NOT_APPLICABLE,
                          context);
    }

}