/**
    * 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.quotas;
  
  import java.io.Closeable;
  import java.io.IOException;
  import java.util.Iterator;
  import java.util.LinkedList;
  import java.util.Queue;
  
  import org.apache.commons.logging.Log;
  import org.apache.commons.logging.LogFactory;
  import org.apache.hadoop.conf.Configuration;
  import org.apache.hadoop.hbase.TableName;
  import org.apache.hadoop.hbase.classification.InterfaceAudience;
  import org.apache.hadoop.hbase.classification.InterfaceStability;
  import org.apache.hadoop.hbase.client.Connection;
  import org.apache.hadoop.hbase.client.ConnectionFactory;
  import org.apache.hadoop.hbase.client.Result;
  import org.apache.hadoop.hbase.client.ResultScanner;
  import org.apache.hadoop.hbase.client.Scan;
  import org.apache.hadoop.hbase.client.Table;
  import org.apache.hadoop.hbase.protobuf.generated.QuotaProtos.Quotas;
  import org.apache.hadoop.util.StringUtils;
  
  /**
   * Scanner to iterate over the quota settings.
   */
  @InterfaceAudience.Public
  @InterfaceStability.Evolving
  public final class QuotaRetriever implements Closeable, Iterable<QuotaSettings> {
    private static final Log LOG = LogFactory.getLog(QuotaRetriever.class);
  
    private final Queue<QuotaSettings> cache = new LinkedList<QuotaSettings>();
    private ResultScanner scanner;
    /**
     * Connection to use. Could pass one in and have this class use it but this class wants to be
     * standalone.
     */
    private Connection connection;
    private Table table;
  
    private QuotaRetriever() {
    }
  
    void init(final Configuration conf, final Scan scan) throws IOException {
      this.connection = ConnectionFactory.createConnection(conf);
      this.table = this.connection.getTable(QuotaTableUtil.QUOTA_TABLE_NAME);
      try {
        scanner = table.getScanner(scan);
      } catch (IOException e) {
        try {
          close();
        } catch (IOException ioe) {
          LOG.warn("Failed getting scanner and then failed close on cleanup", e);
        }
        throw e;
      }
    }
  
    @Override
    public void close() throws IOException {
      if (this.table != null) {
        this.table.close();
        this.table = null;
      }
      if (this.connection != null) {
        this.connection.close();
        this.connection = null;
      }
    }
  
    public QuotaSettings next() throws IOException {
      if (cache.isEmpty()) {
        Result result = scanner.next();
        if (result == null) return null;
  
        QuotaTableUtil.parseResult(result, new QuotaTableUtil.QuotasVisitor() {
          @Override
          public void visitUserQuotas(String userName, Quotas quotas) {
            cache.addAll(QuotaSettingsFactory.fromUserQuotas(userName, quotas));
          }
  
          @Override
          public void visitUserQuotas(String userName, TableName table, Quotas quotas) {
            cache.addAll(QuotaSettingsFactory.fromUserQuotas(userName, table, quotas));
          }
  
          @Override
          public void visitUserQuotas(String userName, String namespace, Quotas quotas) {
           cache.addAll(QuotaSettingsFactory.fromUserQuotas(userName, namespace, quotas));
         }
 
         @Override
         public void visitTableQuotas(TableName tableName, Quotas quotas) {
           cache.addAll(QuotaSettingsFactory.fromTableQuotas(tableName, quotas));
         }
 
         @Override
         public void visitNamespaceQuotas(String namespace, Quotas quotas) {
           cache.addAll(QuotaSettingsFactory.fromNamespaceQuotas(namespace, quotas));
         }
       });
     }
     return cache.poll();
   }
 
   @Override
   public Iterator<QuotaSettings> iterator() {
     return new Iter();
   }
 
   private class Iter implements Iterator<QuotaSettings> {
     private QuotaSettings cache;
 
     public Iter() {
       try {
         cache = QuotaRetriever.this.next();
       } catch (IOException e) {
         LOG.warn(StringUtils.stringifyException(e));
       }
     }
 
     @Override
     public boolean hasNext() {
       return cache != null;
     }
 
     @Override
     public QuotaSettings next() {
       QuotaSettings result = cache;
       try {
         cache = QuotaRetriever.this.next();
       } catch (IOException e) {
         LOG.warn(StringUtils.stringifyException(e));
       }
       return result;
     }
 
     @Override
     public void remove() {
       throw new RuntimeException("remove() not supported");
     }
   }
 
   /**
    * Open a QuotaRetriever with no filter, all the quota settings will be returned.
    * @param conf Configuration object to use.
    * @return the QuotaRetriever
    * @throws IOException if a remote or network exception occurs
    */
   public static QuotaRetriever open(final Configuration conf) throws IOException {
     return open(conf, null);
   }
 
   /**
    * Open a QuotaRetriever with the specified filter.
    * @param conf Configuration object to use.
    * @param filter the QuotaFilter
    * @return the QuotaRetriever
    * @throws IOException if a remote or network exception occurs
    */
   public static QuotaRetriever open(final Configuration conf, final QuotaFilter filter)
       throws IOException {
     Scan scan = QuotaTableUtil.makeScan(filter);
     QuotaRetriever scanner = new QuotaRetriever();
     scanner.init(conf, scan);
     return scanner;
   }
 }