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/**
 * Licensed to the Apache Software Foundation (ASF) under one
 * or more contributor license agreements. See the NOTICE file
 * distributed with this work for additional information
 * regarding copyright ownership. The ASF licenses this file
 * to you under the Apache License, Version 2.0 (the
 * "License"); you may not use this file except in compliance
 * with the License. You may obtain a copy of the License at
 *
 * http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing,
 * software distributed under the License is distributed on an
 * "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
 * KIND, either express or implied. See the License for the
 * specific language governing permissions and limitations
 * under the License.
 */

package org.apache.neethi.util;

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

import org.apache.neethi.All;
import org.apache.neethi.Assertion;
import org.apache.neethi.ExactlyOne;
import org.apache.neethi.IntersectableAssertion;
import org.apache.neethi.Policy;
import org.apache.neethi.PolicyComponent;
import org.apache.neethi.PolicyContainingAssertion;

/**
 * This class contains methods dealing with policy intersection.
 * Intersection of two assertions, i.e. computation if a compatible assertion,
 * is domain specific and relies on AssertionBuilder.buildCompatible.
 * See Section 4.5 in http://www.w3.org/TR/2006/WD-ws-policy-20061117.
 */
public class PolicyIntersector {
    
    private boolean strict;
    
    public PolicyIntersector() {
        strict = true;
    }
    public PolicyIntersector(boolean s) {
        strict = s;
    }
    
    public boolean isStrict() {
        return strict;
    }

    public void setStrict(boolean s) {
        strict = s;
    }

    private Assertion intersect(Assertion a1, Assertion a2) {
        if (a1 instanceof IntersectableAssertion) {
            if (!((IntersectableAssertion)a1).isCompatible(a2, strict)) {
                return null;
            }
            return ((IntersectableAssertion)a1).intersect(a2, strict);
        }
        //the assertion doesn't implement IntersectableAssertion so we
        //need to try doing a basic intersect ourself
        if (a1.getName().equals(a2.getName())) {
            if (a1 instanceof PolicyContainingAssertion 
                && a2 instanceof PolicyContainingAssertion) {
                PolicyContainingAssertion pc1 = (PolicyContainingAssertion)a1;
                PolicyContainingAssertion pc2 = (PolicyContainingAssertion)a2;
                Policy p1 = pc1.getPolicy();
                Policy p2 = pc2.getPolicy();
                PolicyIntersector pi = new PolicyIntersector(strict);
                if (pi.compatiblePolicies(p1, p2)) {
                    return a1;
                }
            } else {
                return a1;
            }
        }
        return null;
    }
    private Assertion findCompatibleAssertion(Assertion assertion, 
                                              Collection alt,
                                              boolean remove) {
        Iterator iterator = alt.iterator();
        while (iterator.hasNext()) {
            PolicyComponent a = iterator.next();
            if (a instanceof Assertion) {
                Assertion compatible = intersect(assertion, (Assertion)a);
                if (null != compatible) {
                    if (remove) {
                        iterator.remove();
                    }
                    return compatible;
                }
            }
        }
        return null;
    } 
    
    
    boolean compatibleAlternatives(Collection alt1, 
                                   Collection alt2) {
        if (alt1.isEmpty() && alt2.isEmpty()) {
            return true;
        }
        
        All all = createCompatibleAlternatives(alt1, alt2, true);
        if (all == null) {
            return false;
        }
        return !all.getAssertions().isEmpty();
    }
    
    All createCompatibleAlternatives(Collection alt1, 
                                     Collection alt2,
                                     boolean remove) {
        All all = new All();
        if (alt1.isEmpty() && alt2.isEmpty()) {
            return all;
        }
        
        alt1 = new ArrayList(alt1);
        alt2 = new ArrayList(alt2);
        
        Iterator iterator = alt1.iterator();
        while (iterator.hasNext()) {
            PolicyComponent a1 = iterator.next();
            if (a1 instanceof Assertion) {
                Assertion assertion = findCompatibleAssertion((Assertion)a1, alt2, remove);
                if (assertion != null) {
                    if (remove) {
                        iterator.remove();
                    }
                    all.addPolicyComponent(assertion);
                } else if (!strict && ((Assertion)a1).isIgnorable()) {
                    all.addPolicyComponent(a1);
                } else if (strict || !((Assertion)a1).isIgnorable()) {
                    return null;
                }
            }
        }
        iterator = alt2.iterator();
        while (iterator.hasNext()) {
            PolicyComponent a2 = iterator.next();
            if (a2 instanceof Assertion) {
                Assertion assertion = findCompatibleAssertion((Assertion)a2, alt1, remove);
                if (assertion != null) { 
                    all.addPolicyComponent(assertion);
                } else if (!strict && ((Assertion)a2).isIgnorable()) {
                    all.addPolicyComponent(a2);
                } else if (strict || !((Assertion)a2).isIgnorable()) {
                    return null;
                }
            }
        }
        return all;
    }
    
    public boolean compatiblePolicies(Policy p1, Policy p2) {       
        Iterator> i1 = p1.getAlternatives();
        while (i1.hasNext()) {
            List alt1 = i1.next();
            Iterator> i2 = p2.getAlternatives();
            if (!i2.hasNext() && alt1.isEmpty()) {
                return true;
            }
            while (i2.hasNext()) {                
                List alt2 = i2.next();
                if (compatibleAlternatives(alt1, alt2)) {
                    return true;                    
                }
            }
        }        
        return false;
    }
    
    public Policy intersect(Policy p1, Policy p2) {
        return intersect(p1, p2, false);
    }
    public Policy intersect(Policy p1, Policy p2, boolean allowDups) {
        Policy compatible = new Policy(p1.getPolicyRegistry(), p1.getNamespace());
        ExactlyOne eo = new ExactlyOne(compatible);
        if (!compatiblePolicies(p1, p2)) {
            return compatible;
        }
        Iterator> i1 = p1.getAlternatives();
        while (i1.hasNext()) {
            List alt1 = i1.next();
            Iterator> i2 = p2.getAlternatives();
            while (i2.hasNext()) {                
                List alt2 = i2.next();
                All all = createCompatibleAlternatives(alt1, alt2, !allowDups);
                if (all != null) {
                    eo.addPolicyComponent(all);
                }
            }            
        }
        
        return compatible;
    }
    
}