/**
 * 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.hdfs.server.blockmanagement;

import java.util.Iterator;

import org.apache.hadoop.hdfs.protocol.Block;
import org.apache.hadoop.hdfs.server.namenode.INodeId;
import org.apache.hadoop.util.GSet;
import org.apache.hadoop.util.LightWeightGSet;

/**
 * This class maintains the map from a block to its metadata.
 * block's metadata currently includes blockCollection it belongs to and
 * the datanodes that store the block.
 */
class BlocksMap {
  private static class StorageIterator implements Iterator<DatanodeStorageInfo> {
    private final BlockInfo blockInfo;
    private int nextIdx = 0;
      
    StorageIterator(BlockInfo blkInfo) {
      this.blockInfo = blkInfo;
    }

    @Override
    public boolean hasNext() {
      return blockInfo != null && nextIdx < blockInfo.getCapacity()
              && blockInfo.getDatanode(nextIdx) != null;
    }

    @Override
    public DatanodeStorageInfo next() {
      return blockInfo.getStorageInfo(nextIdx++);
    }

    @Override
    public void remove()  {
      throw new UnsupportedOperationException("Sorry. can't remove.");
    }
  }

  /** Constant {@link LightWeightGSet} capacity. */
  private final int capacity;
  
  private GSet<Block, BlockInfo> blocks;

  BlocksMap(int capacity) {
    // Use 2% of total memory to size the GSet capacity
    this.capacity = capacity;
    this.blocks = new LightWeightGSet<Block, BlockInfo>(capacity) {
      @Override
      public Iterator<BlockInfo> iterator() {
        SetIterator iterator = new SetIterator();
        /*
         * Not tracking any modifications to set. As this set will be used
         * always under FSNameSystem lock, modifications will not cause any
         * ConcurrentModificationExceptions. But there is a chance of missing
         * newly added elements during iteration.
         */
        iterator.setTrackModification(false);
        return iterator;
      }
    };
  }


  void close() {
    clear();
    blocks = null;
  }
  
  void clear() {
    if (blocks != null) {
      blocks.clear();
    }
  }

  /**
   * Add block b belonging to the specified block collection to the map.
   */
  BlockInfo addBlockCollection(BlockInfo b, BlockCollection bc) {
    BlockInfo info = blocks.get(b);
    if (info != b) {
      info = b;
      blocks.put(info);
    }
    info.setBlockCollectionId(bc.getId());
    return info;
  }

  /**
   * Remove the block from the block map;
   * remove it from all data-node lists it belongs to;
   * and remove all data-node locations associated with the block.
   */
  void removeBlock(Block block) {
    BlockInfo blockInfo = blocks.remove(block);
    if (blockInfo == null)
      return;

    assert blockInfo.getBlockCollectionId() == INodeId.INVALID_INODE_ID;
    for(int idx = blockInfo.numNodes()-1; idx >= 0; idx--) {
      DatanodeDescriptor dn = blockInfo.getDatanode(idx);
      if (dn != null) {
        removeBlock(dn, blockInfo); // remove from the list and wipe the location
      }
    }
  }
  
  /** Returns the block object it it exists in the map. */
  BlockInfo getStoredBlock(Block b) {
    return blocks.get(b);
  }

  /**
   * Searches for the block in the BlocksMap and 
   * returns {@link Iterable} of the storages the block belongs to.
   */
  Iterable<DatanodeStorageInfo> getStorages(Block b) {
    return getStorages(blocks.get(b));
  }

  /**
   * For a block that has already been retrieved from the BlocksMap
   * returns {@link Iterable} of the storages the block belongs to.
   */
  Iterable<DatanodeStorageInfo> getStorages(final BlockInfo storedBlock) {
    return new Iterable<DatanodeStorageInfo>() {
      @Override
      public Iterator<DatanodeStorageInfo> iterator() {
        return new StorageIterator(storedBlock);
      }
    };
  }

  /** counts number of containing nodes. Better than using iterator. */
  int numNodes(Block b) {
    BlockInfo info = blocks.get(b);
    return info == null ? 0 : info.numNodes();
  }

  /**
   * Remove data-node reference from the block.
   * Remove the block from the block map
   * only if it does not belong to any file and data-nodes.
   */
  boolean removeNode(Block b, DatanodeDescriptor node) {
    BlockInfo info = blocks.get(b);
    if (info == null)
      return false;

    // remove block from the data-node list and the node from the block info
    boolean removed = removeBlock(node, info);

    if (info.getDatanode(0) == null     // no datanodes left
              && info.isDeleted()) {  // does not belong to a file
      blocks.remove(b);  // remove block from the map
    }
    return removed;
  }

  /**
   * Remove block from the list of blocks belonging to the data-node. Remove
   * data-node from the block.
   */
  static boolean removeBlock(DatanodeDescriptor dn, BlockInfo b) {
    final DatanodeStorageInfo s = b.findStorageInfo(dn);
    // if block exists on this datanode
    return s != null && s.removeBlock(b);
  }

  int size() {
    if (blocks != null) {
      return blocks.size();
    } else {
      return 0;
    }
  }

  Iterable<BlockInfo> getBlocks() {
    return blocks;
  }
  
  /** Get the capacity of the HashMap that stores blocks */
  int getCapacity() {
    return capacity;
  }
}