/**
 * 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.hadoop.fs.permission;

import java.util.Collections;
import java.util.List;

import org.apache.hadoop.classification.InterfaceAudience;
import org.apache.hadoop.classification.InterfaceStability;
import org.apache.hadoop.fs.permission.AclEntry;
import org.apache.hadoop.fs.permission.AclEntryScope;

/**
 * Groups a list of ACL entries into separate lists for access entries vs.
 * default entries.
 */
@InterfaceAudience.LimitedPrivate({"HDFS", "MapReduce"})
@InterfaceStability.Unstable
public final class ScopedAclEntries {
  private static final int PIVOT_NOT_FOUND = -1;

  private final List<AclEntry> accessEntries;
  private final List<AclEntry> defaultEntries;

  /**
   * Creates a new ScopedAclEntries from the given list.  It is assumed that the
   * list is already sorted such that all access entries precede all default
   * entries.
   *
   * @param aclEntries List<AclEntry> to separate
   */
  public ScopedAclEntries(List<AclEntry> aclEntries) {
    int pivot = calculatePivotOnDefaultEntries(aclEntries);
    if (pivot != PIVOT_NOT_FOUND) {
      accessEntries = pivot != 0 ? aclEntries.subList(0, pivot) :
        Collections.<AclEntry>emptyList();
      defaultEntries = aclEntries.subList(pivot, aclEntries.size());
    } else {
      accessEntries = aclEntries;
      defaultEntries = Collections.emptyList();
    }
  }

  /**
   * Returns access entries.
   *
   * @return List<AclEntry> containing just access entries, or an empty list if
   *   there are no access entries
   */
  public List<AclEntry> getAccessEntries() {
    return accessEntries;
  }

  /**
   * Returns default entries.
   *
   * @return List<AclEntry> containing just default entries, or an empty list if
   *   there are no default entries
   */
  public List<AclEntry> getDefaultEntries() {
    return defaultEntries;
  }

  /**
   * Returns the pivot point in the list between the access entries and the
   * default entries.  This is the index of the first element in the list that is
   * a default entry.
   *
   * @param aclBuilder ArrayList<AclEntry> containing entries to build
   * @return int pivot point, or -1 if list contains no default entries
   */
  private static int calculatePivotOnDefaultEntries(List<AclEntry> aclBuilder) {
    for (int i = 0; i < aclBuilder.size(); ++i) {
      if (aclBuilder.get(i).getScope() == AclEntryScope.DEFAULT) {
        return i;
      }
    }
    return PIVOT_NOT_FOUND;
  }
}