/**
    * 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.hbase;
  
  import java.util.Collection;
  import java.util.Objects;
  
  import org.apache.hadoop.hbase.classification.InterfaceAudience;
  import org.apache.hadoop.hbase.client.RegionReplicaUtil;
  import org.apache.hadoop.hbase.util.Bytes;
  
  /**
   * Container for holding a list of {@link HRegionLocation}'s that correspond to the
   * same range. The list is indexed by the replicaId. This is an immutable list,
   * however mutation operations are provided which returns a new List via copy-on-write
   * (assuming small number of locations)
   */
  @InterfaceAudience.Private
  public class RegionLocations {
  
    private final int numNonNullElements;
  
    // locations array contains the HRL objects for known region replicas indexes by the replicaId.
    // elements can be null if the region replica is not known at all. A null value indicates
    // that there is a region replica with the index as replicaId, but the location is not known
    // in the cache.
    private final HRegionLocation[] locations; // replicaId -> HRegionLocation.
  
    /**
     * Constructs the region location list. The locations array should
     * contain all the locations for known replicas for the region, and should be
     * sorted in replicaId ascending order, although it can contain nulls indicating replicaIds
     * that the locations of which are not known.
     * @param locations an array of HRegionLocations for the same region range
     */
    public RegionLocations(HRegionLocation... locations) {
      int numNonNullElements = 0;
      int maxReplicaId = -1;
      int maxReplicaIdIndex = -1;
      int index = 0;
      for (HRegionLocation loc : locations) {
        if (loc != null) {
          if (loc.getServerName() != null) {
            numNonNullElements++;
          }
          if (loc.getRegionInfo().getReplicaId() >= maxReplicaId) {
            maxReplicaId = loc.getRegionInfo().getReplicaId();
            maxReplicaIdIndex = index;
          }
        }
        index++;
      }
      this.numNonNullElements = numNonNullElements;
  
      // account for the null elements in the array after maxReplicaIdIndex
      maxReplicaId = maxReplicaId + (locations.length - (maxReplicaIdIndex + 1) );
  
      if (maxReplicaId + 1 == locations.length) {
        this.locations = locations;
      } else {
        this.locations = new HRegionLocation[maxReplicaId + 1];
        for (HRegionLocation loc : locations) {
          if (loc != null) {
            this.locations[loc.getRegionInfo().getReplicaId()] = loc;
          }
        }
      }
    }
  
    public RegionLocations(Collection<HRegionLocation> locations) {
      this(locations.toArray(new HRegionLocation[locations.size()]));
    }
  
    /**
     * Returns the size of the list even if some of the elements
     * might be null.
     * @return the size of the list (corresponding to the max replicaId)
     */
    public int size() {
      return locations.length;
    }
  
    /**
    * Returns the size of not-null locations
    * @return the size of not-null locations
    */
   public int numNonNullElements() {
     return numNonNullElements;
   }
 
   /**
    * Returns whether there are non-null elements in the list
    * @return whether there are non-null elements in the list
    */
   public boolean isEmpty() {
     return numNonNullElements == 0;
   }
 
   /**
    * Returns a new RegionLocations with the locations removed (set to null)
    * which have the destination server as given.
    * @param serverName the serverName to remove locations of
    * @return an RegionLocations object with removed locations or the same object
    * if nothing is removed
    */
   public RegionLocations removeByServer(ServerName serverName) {
     HRegionLocation[] newLocations = null;
     for (int i = 0; i < locations.length; i++) {
       // check whether something to remove
       if (locations[i] != null && serverName.equals(locations[i].getServerName())) {
         if (newLocations == null) { //first time
           newLocations = new HRegionLocation[locations.length];
           System.arraycopy(locations, 0, newLocations, 0, i);
         }
         newLocations[i] = null;
       } else if (newLocations != null) {
         newLocations[i] = locations[i];
       }
     }
     return newLocations == null ? this : new RegionLocations(newLocations);
   }
 
   /**
    * Removes the given location from the list
    * @param location the location to remove
    * @return an RegionLocations object with removed locations or the same object
    * if nothing is removed
    */
   public RegionLocations remove(HRegionLocation location) {
     if (location == null) return this;
     if (location.getRegionInfo() == null) return this;
     int replicaId = location.getRegionInfo().getReplicaId();
     if (replicaId >= locations.length) return this;
 
     // check whether something to remove. HRL.compareTo() compares ONLY the
     // serverName. We want to compare the HRI's as well.
     if (locations[replicaId] == null
         || !location.getRegionInfo().equals(locations[replicaId].getRegionInfo())
         || !location.equals(locations[replicaId])) {
       return this;
     }
 
     HRegionLocation[] newLocations = new HRegionLocation[locations.length];
     System.arraycopy(locations, 0, newLocations, 0, locations.length);
     newLocations[replicaId] = null;
 
     return new RegionLocations(newLocations);
   }
 
   /**
    * Removes location of the given replicaId from the list
    * @param replicaId the replicaId of the location to remove
    * @return an RegionLocations object with removed locations or the same object
    * if nothing is removed
    */
   public RegionLocations remove(int replicaId) {
     if (getRegionLocation(replicaId) == null) {
       return this;
     }
 
     HRegionLocation[] newLocations = new HRegionLocation[locations.length];
 
     System.arraycopy(locations, 0, newLocations, 0, locations.length);
     if (replicaId < newLocations.length) {
       newLocations[replicaId] = null;
     }
 
     return new RegionLocations(newLocations);
   }
 
   /**
    * Merges this RegionLocations list with the given list assuming
    * same range, and keeping the most up to date version of the
    * HRegionLocation entries from either list according to seqNum. If seqNums
    * are equal, the location from the argument (other) is taken.
    * @param other the locations to merge with
    * @return an RegionLocations object with merged locations or the same object
    * if nothing is merged
    */
   public RegionLocations mergeLocations(RegionLocations other) {
     assert other != null;
 
     HRegionLocation[] newLocations = null;
 
     // Use the length from other, since it is coming from meta. Otherwise,
     // in case of region replication going down, we might have a leak here.
     int max = other.locations.length;
 
     HRegionInfo regionInfo = null;
     for (int i = 0; i < max; i++) {
       HRegionLocation thisLoc = this.getRegionLocation(i);
       HRegionLocation otherLoc = other.getRegionLocation(i);
       if (regionInfo == null && otherLoc != null && otherLoc.getRegionInfo() != null) {
         // regionInfo is the first non-null HRI from other RegionLocations. We use it to ensure that
         // all replica region infos belong to the same region with same region id.
         regionInfo = otherLoc.getRegionInfo();
       }
 
       HRegionLocation selectedLoc = selectRegionLocation(thisLoc,
         otherLoc, true, false);
 
       if (!Objects.equals(selectedLoc, thisLoc)) {
         if (newLocations == null) {
           newLocations = new HRegionLocation[max];
           System.arraycopy(locations, 0, newLocations, 0, i);
         }
       }
       if (newLocations != null) {
         newLocations[i] = selectedLoc;
       }
     }
 
     // ensure that all replicas share the same start code. Otherwise delete them
     if (newLocations != null && regionInfo != null) {
       for (int i=0; i < newLocations.length; i++) {
         if (newLocations[i] != null) {
           if (!RegionReplicaUtil.isReplicasForSameRegion(regionInfo,
             newLocations[i].getRegionInfo())) {
             newLocations[i] = null;
           }
         }
       }
     }
 
     return newLocations == null ? this : new RegionLocations(newLocations);
   }
 
   private HRegionLocation selectRegionLocation(HRegionLocation oldLocation,
       HRegionLocation location, boolean checkForEquals, boolean force) {
     if (location == null) {
       return oldLocation == null ? null : oldLocation;
     }
 
     if (oldLocation == null) {
       return location;
     }
 
     if (force
         || isGreaterThan(location.getSeqNum(), oldLocation.getSeqNum(), checkForEquals)) {
       return location;
     }
     return oldLocation;
   }
 
   /**
    * Updates the location with new only if the new location has a higher
    * seqNum than the old one or force is true.
    * @param location the location to add or update
    * @param checkForEquals whether to update the location if seqNums for the
    * HRegionLocations for the old and new location are the same
    * @param force whether to force update
    * @return an RegionLocations object with updated locations or the same object
    * if nothing is updated
    */
   public RegionLocations updateLocation(HRegionLocation location,
       boolean checkForEquals, boolean force) {
     assert location != null;
 
     int replicaId = location.getRegionInfo().getReplicaId();
 
     HRegionLocation oldLoc = getRegionLocation(location.getRegionInfo().getReplicaId());
     HRegionLocation selectedLoc = selectRegionLocation(oldLoc, location,
       checkForEquals, force);
 
     if (Objects.equals(selectedLoc, oldLoc)) {
       return this;
     }
     HRegionLocation[] newLocations = new HRegionLocation[Math.max(locations.length, replicaId +1)];
     System.arraycopy(locations, 0, newLocations, 0, locations.length);
     newLocations[replicaId] = location;
     // ensure that all replicas share the same start code. Otherwise delete them
     for (int i=0; i < newLocations.length; i++) {
       if (newLocations[i] != null) {
         if (!RegionReplicaUtil.isReplicasForSameRegion(location.getRegionInfo(),
           newLocations[i].getRegionInfo())) {
           newLocations[i] = null;
         }
       }
     }
     return new RegionLocations(newLocations);
   }
 
   private boolean isGreaterThan(long a, long b, boolean checkForEquals) {
     return a > b || (checkForEquals && (a == b));
   }
 
   public HRegionLocation getRegionLocation(int replicaId) {
     if (replicaId >= locations.length) {
       return null;
     }
     return locations[replicaId];
   }
 
   /**
    * Returns the region location from the list for matching regionName, which can
    * be regionName or encodedRegionName
    * @param regionName regionName or encodedRegionName
    * @return HRegionLocation found or null
    */
   public HRegionLocation getRegionLocationByRegionName(byte[] regionName) {
     for (HRegionLocation loc : locations) {
       if (loc != null) {
         if (Bytes.equals(loc.getRegionInfo().getRegionName(), regionName)
             || Bytes.equals(loc.getRegionInfo().getEncodedNameAsBytes(), regionName)) {
           return loc;
         }
       }
     }
     return null;
   }
 
   public HRegionLocation[] getRegionLocations() {
     return locations;
   }
 
   public HRegionLocation getDefaultRegionLocation() {
     return locations[HRegionInfo.DEFAULT_REPLICA_ID];
   }
 
   /**
    * Returns the first not-null region location in the list
    */
   public HRegionLocation getRegionLocation() {
     for (HRegionLocation loc : locations) {
       if (loc != null) {
         return loc;
       }
     }
     return null;
   }
 
   @Override
   public String toString() {
     StringBuilder builder = new StringBuilder("[");
     for (HRegionLocation loc : locations) {
       if (builder.length() > 1) {
         builder.append(", ");
       }
       builder.append(loc == null ? "null" : loc);
     }
     builder.append("]");
     return builder.toString();
   }
 
 }