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package com.sun.xml.internal.ws.policy;

import com.sun.xml.internal.ws.policy.privateutil.PolicyLogger;

import java.util.Collection;

import java.util.LinkedList;

import java.util.List;

import java.util.Queue;

import com.sun.xml.internal.ws.policy.privateutil.LocalizationMessages;

import com.sun.xml.internal.ws.policy.sourcemodel.wspolicy.NamespaceVersion;

import java.util.ArrayList;

/**

 * The instance of this class is intended to provide policy intersection mechanism.

 *

 * @author Marek Potociar (marek.potociar@sun.com)

 */

public final class PolicyIntersector {

    static enum CompatibilityMode {

        STRICT,

        LAX

    }

    private static final PolicyIntersector STRICT_INTERSECTOR = new PolicyIntersector(CompatibilityMode.STRICT);

    private static final PolicyIntersector LAX_INTERSECTOR = new PolicyIntersector(CompatibilityMode.LAX);

    private static final PolicyLogger LOGGER = PolicyLogger.getLogger(PolicyIntersector.class);

    private CompatibilityMode mode;

    /**

     * Prevents direct instantiation of this class from outside

     * @param intersectionMode intersection mode

     */

    private PolicyIntersector(CompatibilityMode intersectionMode) {

        this.mode = intersectionMode;

    }

    /**

     * Returns a strict policy intersector that can be used to intersect group of policies.

     *

     * @return policy intersector instance.

     */

    public static PolicyIntersector createStrictPolicyIntersector() {

        return PolicyIntersector.STRICT_INTERSECTOR;

    }

    /**

     * Returns a strict policy intersector that can be used to intersect group of policies.

     *

     * @return policy intersector instance.

     */

    public static PolicyIntersector createLaxPolicyIntersector() {

        return PolicyIntersector.LAX_INTERSECTOR;

    }

    /**

     * Performs intersection on the input collection of policies and returns the resulting (intersected) policy. If input policy

     * collection contains only a single policy instance, no intersection is performed and the instance is directly returned

     * as a method call result.

     *

     * @param policies collection of policies to be intersected. Must not be {@code null} nor empty, otherwise exception is thrown.

     * @return intersected policy as a result of perfromed policy intersection. A {@code null} value is never returned.

     *

     * @throws IllegalArgumentException in case {@code policies} argument is either {@code null} or empty collection.

     */

    public Policy intersect(final Policy... policies) {

        if (policies == null || policies.length == 0) {

            throw LOGGER.logSevereException(new IllegalArgumentException(LocalizationMessages.WSP_0056_NEITHER_NULL_NOR_EMPTY_POLICY_COLLECTION_EXPECTED()));

        } else if (policies.length == 1) {

            return policies[0];

        }

        // check for "null" and "empty" policy: if such policy is found return "null" policy,

        // or if all policies are "empty", return "empty" policy

        boolean found = false;

        boolean allPoliciesEmpty = true;

        NamespaceVersion latestVersion = null;

        for (Policy tested : policies) {

            if (tested.isEmpty()) {

                found = true;

            } else {

                if (tested.isNull()) {

                    found = true;

                }

                allPoliciesEmpty = false;

            }

            if (latestVersion == null) {

                latestVersion = tested.getNamespaceVersion();

            } else if (latestVersion.compareTo(tested.getNamespaceVersion()) < 0) {

                latestVersion = tested.getNamespaceVersion();

            }

            if (found && !allPoliciesEmpty) {

                return Policy.createNullPolicy(latestVersion, null, null);

            }

        }

        latestVersion = (latestVersion != null) ? latestVersion : NamespaceVersion.getLatestVersion();

        if (allPoliciesEmpty) {

            return Policy.createEmptyPolicy(latestVersion, null, null);

        }

        // simple tests didn't lead to final answer => let's performe some intersecting ;)

        final List<AssertionSet> finalAlternatives = new LinkedList<AssertionSet>(policies[0].getContent());

        final Queue<AssertionSet> testedAlternatives = new LinkedList<AssertionSet>();

        final List<AssertionSet> alternativesToMerge = new ArrayList<AssertionSet>(2);

        for (int i = 1; i < policies.length; i++) {

            final Collection<AssertionSet> currentAlternatives = policies[i].getContent();

            testedAlternatives.clear();

            testedAlternatives.addAll(finalAlternatives);

            finalAlternatives.clear();

            AssertionSet testedAlternative;

            while ((testedAlternative = testedAlternatives.poll()) != null) {

                for (AssertionSet currentAlternative : currentAlternatives) {

                    if (testedAlternative.isCompatibleWith(currentAlternative, this.mode)) {

                        alternativesToMerge.add(testedAlternative);

                        alternativesToMerge.add(currentAlternative);

                        finalAlternatives.add(AssertionSet.createMergedAssertionSet(alternativesToMerge));

                        alternativesToMerge.clear();

                    }

                }

            }

        }

        return Policy.createPolicy(latestVersion, null, null, finalAlternatives);

    }

}