/*
 * @(#)FirstApplicablePolicyAlg.java
 *
 * Copyright 2003-2005 Sun Microsystems, Inc. All Rights Reserved.
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 * be used to endorse or promote products derived from this software without
 * specific prior written permission.
 * 
 * This software is provided "AS IS," without a warranty of any kind. ALL
 * EXPRESS OR IMPLIED CONDITIONS, REPRESENTATIONS AND WARRANTIES, INCLUDING
 * ANY IMPLIED WARRANTY OF MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE
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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 java.net.URI;

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


/**
 * This is the standard First Applicable policy combining algorithm. It looks
 * through the set of policies, finds the first one that applies, and returns
 * that evaluation result.
 *
 * @since 1.0
 * @author Seth Proctor
 */
public class FirstApplicablePolicyAlg 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:" +
        "first-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 FirstApplicablePolicyAlg() {
        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) {
        Iterator<CombinerElement> it = policyElements.iterator();
        
        while (it.hasNext()) {
            AbstractPolicy policy =
                ((PolicyCombinerElement)(it.next())).getPolicy();

            // make sure that the policy matches the context
            context.newEvent(policy);
            MatchResult match = policy.match(context);

            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) {
                // evaluate the policy
                Result result = policy.evaluate(context);
                context.closeCurrentEvent(result);
                // do not treat the discarded values
                if (result != null) {
                    int effect = result.getDecision();
                
                    // in the case of PERMIT, DENY, or INDETERMINATE, we always
                    // just return that result, so only on a rule that doesn't
                    // apply do we keep going...
                    if (effect != Result.DECISION_NOT_APPLICABLE) {
                        return result;
                    }
                }
            }
        }

        // if we got here, then none of the rules applied
        return new Result(Result.DECISION_NOT_APPLICABLE,
                          context);
    }

}