content: /*
   * 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.ambari.server.controller.internal;
  
  import java.util.Arrays;
  import java.util.Collections;
  import java.util.LinkedList;
  import java.util.List;
  
  import org.apache.ambari.server.controller.predicate.AlwaysPredicate;
  import org.apache.ambari.server.controller.predicate.AndPredicate;
  import org.apache.ambari.server.controller.predicate.ArrayPredicate;
  import org.apache.ambari.server.controller.predicate.CategoryPredicate;
  import org.apache.ambari.server.controller.predicate.ComparisonPredicate;
  import org.apache.ambari.server.controller.predicate.EqualsPredicate;
  import org.apache.ambari.server.controller.predicate.OrPredicate;
  import org.apache.ambari.server.controller.predicate.PredicateVisitor;
  import org.apache.ambari.server.controller.predicate.UnaryPredicate;
  import org.apache.ambari.server.controller.spi.Predicate;
  import org.apache.ambari.server.controller.spi.ResourceProvider;
  import org.apache.ambari.server.controller.utilities.PredicateHelper;
  
  /**
   * A predicate visitor used to simplify by doing the following ...
   *
   * 1) distribute across OR (e.g. A && ( B || C ) becomes ( A && B ) || ( A && C )).
   * This is done because an individual back end request object can not handle OR.  Instead
   * we need to break up the predicate to form multiple requests and take the union of all
   * the responses.
   * 2) convert predicates based on unsupported properties to AlwaysPredicate.
   * Unsupported properties are those not returned by the resource provider.  For these
   * properties we need to wait until the property provider that handles the property has
   * been called.
   * 3) convert predicates based on any operator other than == to AlwaysPredicate.
   * The back end requests can not handle any operator other than equals.  The complete predicate
   * will get applied further down the line if necessary.
   *
   * After visiting a predicate, the visitor should be able to supply a list of predicates that can be
   * used to generate requests to the backend, working around the restrictions above.
   *
   * Note that the results acquired using the generated predicates may be a super set of what is actually
   * desired given the original predicate, but the original predicate will be applied at a suitable time
   * down the line if required.
   */
  public class SimplifyingPredicateVisitor implements PredicateVisitor {
    /**
     * Associated resource provider.
     */
    private ResourceProvider resourceProvider;
  
    /**
     * The last visited predicate.
     */
    private Predicate lastVisited = null;
  
  
    /**
     * Constructor.
     *
     * @param provider  associated resource provider
     */
    public SimplifyingPredicateVisitor(ResourceProvider provider) {
      resourceProvider = provider;
    }
  
    /**
     * Obtain a list of simplified predicates based on the rules described in the class documentation.
     *
     * @return a list of simplified predicates
     */
    public List<Predicate> getSimplifiedPredicates() {
      if (lastVisited == null) {
        return Collections.emptyList();
      }
      if (lastVisited instanceof OrPredicate) {
        return Arrays.asList(((OrPredicate) lastVisited).getPredicates());
      }
      return Collections.singletonList(lastVisited);
    }
  
    @Override
    public void acceptComparisonPredicate(ComparisonPredicate predicate) {
      if (predicate instanceof EqualsPredicate &&
          resourceProvider.checkPropertyIds(Collections.singleton(predicate.getPropertyId())).isEmpty()) {
        lastVisited = predicate;
      }
      else {
        lastVisited = AlwaysPredicate.INSTANCE;
      }
    }
  
    @Override
    public void acceptArrayPredicate(ArrayPredicate arrayPredicate) {
      List<Predicate> predicateList = new LinkedList<>();
      boolean hasOrs = false;
  
      Predicate[] predicates = arrayPredicate.getPredicates();
      if (predicates.length > 0) {
        for (Predicate predicate : predicates) {
          PredicateHelper.visit(predicate, this);
          predicateList.add(lastVisited);
          if (lastVisited instanceof OrPredicate) {
            hasOrs = true;
          }
        }
      }
      // distribute so that A && ( B || C ) becomes ( A && B ) || ( A && C )
      if (hasOrs && arrayPredicate instanceof AndPredicate) {
        int size = predicateList.size();
        List<Predicate> andPredicateList = new LinkedList<>();
  
        for (int i = 0; i < size; ++i) {
          for (int j = i + 1; j < size; ++j) {
            andPredicateList.addAll(distribute(predicateList.get(i), predicateList.get(j)));
          }
        }
        lastVisited = OrPredicate.instance(andPredicateList.toArray(new Predicate[andPredicateList.size()]));
      }
      else {
        lastVisited = arrayPredicate.create(predicateList.toArray(new Predicate[predicateList.size()]));
      }
    }
  
    @Override
    public void acceptUnaryPredicate(UnaryPredicate predicate) {
      lastVisited = predicate;
    }
  
    @Override
    public void acceptAlwaysPredicate(AlwaysPredicate predicate) {
      lastVisited = predicate;
    }
  
    private static List<Predicate> distribute(Predicate left, Predicate right) {
  
      if (left instanceof OrPredicate) {
        return distributeOr((OrPredicate) left, right);
      }
  
      if (right instanceof OrPredicate) {
        return distributeOr((OrPredicate) right, left);
      }
      return Collections.singletonList(left.equals(right) ?
          left : AndPredicate.instance(left, right));
    }
  
    private static List<Predicate> distributeOr(OrPredicate orPredicate, Predicate other) {
      List<Predicate> andPredicateList = new LinkedList<>();
      OrPredicate otherOr = null;
  
      if (other instanceof OrPredicate) {
        otherOr = (OrPredicate) other;
      }
  
      for (Predicate basePredicate : orPredicate.getPredicates()) {
  
        if (otherOr != null) {
          andPredicateList.addAll(distributeOr(otherOr, basePredicate));
        }
        else {
          andPredicateList.add(basePredicate.equals(other) ?
              basePredicate : AndPredicate.instance(basePredicate, other));
        }
      }
      return andPredicateList;
    }
  
    @Override
    public void acceptCategoryPredicate(CategoryPredicate predicate) {
      lastVisited = predicate;
    }
  }
  