/*
 * 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.client;

import java.io.Closeable;
import java.io.IOException;
import java.util.concurrent.ExecutorService;
import org.apache.hadoop.conf.Configuration;
import org.apache.hadoop.hbase.Abortable;
import org.apache.hadoop.hbase.HBaseInterfaceAudience;
import org.apache.hadoop.hbase.ServerName;
import org.apache.hadoop.hbase.TableName;
import org.apache.yetus.audience.InterfaceAudience;

/**
 * A cluster connection encapsulating lower level individual connections to actual servers and a
 * connection to zookeeper. Connections are instantiated through the {@link ConnectionFactory}
 * class. The lifecycle of the connection is managed by the caller, who has to {@link #close()} the
 * connection to release the resources.
 * <p>
 * The connection object contains logic to find the master, locate regions out on the cluster, keeps
 * a cache of locations and then knows how to re-calibrate after they move. The individual
 * connections to servers, meta cache, zookeeper connection, etc are all shared by the {@link Table}
 * and {@link Admin} instances obtained from this connection.
 * <p>
 * Connection creation is a heavy-weight operation. Connection implementations are thread-safe, so
 * that the client can create a connection once, and share it with different threads. {@link Table}
 * and {@link Admin} instances, on the other hand, are light-weight and are not thread-safe.
 * Typically, a single connection per client application is instantiated and every thread will
 * obtain its own Table instance. Caching or pooling of {@link Table} and {@link Admin} is not
 * recommended.
 * @see ConnectionFactory
 * @since 0.99.0
 */
@InterfaceAudience.Public
public interface Connection extends Abortable, Closeable {

  /*
   * Implementation notes: - Only allow new style of interfaces: -- All table names are passed as
   * TableName. No more byte[] and string arguments -- Most of the classes with names H is
   * deprecated in favor of non-H versions (Table, Connection, etc) -- Only real client-facing
   * public methods are allowed - Connection should contain only getTable(), getAdmin() kind of
   * general methods.
   */

  /** Returns Configuration instance being used by this Connection instance. */
  Configuration getConfiguration();

  /**
   * Retrieve a Table implementation for accessing a table. The returned Table is not thread safe, a
   * new instance should be created for each using thread. This is a lightweight operation, pooling
   * or caching of the returned Table is neither required nor desired.
   * <p>
   * The caller is responsible for calling {@link Table#close()} on the returned table instance.
   * <p>
   * Since 0.98.1 this method no longer checks table existence. An exception will be thrown if the
   * table does not exist only when the first operation is attempted.
   * @param tableName the name of the table
   * @return a Table to use for interactions with this table
   */
  default Table getTable(TableName tableName) throws IOException {
    return getTable(tableName, null);
  }

  /**
   * Retrieve a Table implementation for accessing a table. The returned Table is not thread safe, a
   * new instance should be created for each using thread. This is a lightweight operation, pooling
   * or caching of the returned Table is neither required nor desired.
   * <p>
   * The caller is responsible for calling {@link Table#close()} on the returned table instance.
   * <p>
   * Since 0.98.1 this method no longer checks table existence. An exception will be thrown if the
   * table does not exist only when the first operation is attempted.
   * @param tableName the name of the table
   * @param pool      The thread pool to use for batch operations, null to use a default pool.
   * @return a Table to use for interactions with this table
   */
  default Table getTable(TableName tableName, ExecutorService pool) throws IOException {
    return getTableBuilder(tableName, pool).build();
  }

  /**
   * <p>
   * Retrieve a {@link BufferedMutator} for performing client-side buffering of writes. The
   * {@link BufferedMutator} returned by this method is thread-safe. This accessor will create a new
   * ThreadPoolExecutor and will be shutdown once we close the BufferedMutator. This object can be
   * used for long lived operations.
   * </p>
   * <p>
   * The caller is responsible for calling {@link BufferedMutator#close()} on the returned
   * {@link BufferedMutator} instance.
   * </p>
   * <p>
   * @param tableName the name of the table
   * @return a {@link BufferedMutator} for the supplied tableName.
   */
  BufferedMutator getBufferedMutator(TableName tableName) throws IOException;

  /**
   * Retrieve a {@link BufferedMutator} for performing client-side buffering of writes. The
   * {@link BufferedMutator} returned by this method is thread-safe. This object can be used for
   * long lived table operations. If user passes ThreadPool in BufferedMutatorParams then we will
   * use that otherwise we will create for the user. For user specified ThreadPool, it is the user's
   * responsibility to shutdown. For ThreadPool created by us, we will shutdown when user calls
   * {@link BufferedMutator#close()}. The caller is responsible for calling
   * {@link BufferedMutator#close()} on the returned {@link BufferedMutator} instance.
   * @param params details on how to instantiate the {@code BufferedMutator}.
   * @return a {@link BufferedMutator} for the supplied tableName.
   */
  BufferedMutator getBufferedMutator(BufferedMutatorParams params) throws IOException;

  /**
   * Retrieve a RegionLocator implementation to inspect region information on a table. The returned
   * RegionLocator is not thread-safe, so a new instance should be created for each using thread.
   * This is a lightweight operation. Pooling or caching of the returned RegionLocator is neither
   * required nor desired. <br>
   * The caller is responsible for calling {@link RegionLocator#close()} on the returned
   * RegionLocator instance. RegionLocator needs to be unmanaged
   * @param tableName Name of the table who's region is to be examined
   * @return A RegionLocator instance
   */
  RegionLocator getRegionLocator(TableName tableName) throws IOException;

  /**
   * Clear all the entries in the region location cache, for all the tables.
   * <p/>
   * If you only want to clear the cache for a specific table, use
   * {@link RegionLocator#clearRegionLocationCache()}.
   * <p/>
   * This may cause performance issue so use it with caution.
   */
  void clearRegionLocationCache();

  /**
   * Retrieve an Admin implementation to administer an HBase cluster. The returned Admin is not
   * guaranteed to be thread-safe. A new instance should be created for each using thread. This is a
   * lightweight operation. Pooling or caching of the returned Admin is not recommended. <br>
   * The caller is responsible for calling {@link Admin#close()} on the returned Admin instance.
   * @return an Admin instance for cluster administration
   */
  Admin getAdmin() throws IOException;

  @Override
  void close() throws IOException;

  /**
   * Returns whether the connection is closed or not.
   * @return true if this connection is closed
   */
  boolean isClosed();

  /**
   * Returns an {@link TableBuilder} for creating {@link Table}.
   * @param tableName the name of the table
   * @param pool      the thread pool to use for requests like batch and scan
   */
  TableBuilder getTableBuilder(TableName tableName, ExecutorService pool);

  /**
   * Returns the cluster ID unique to this HBase cluster. <br>
   * The default implementation is added to keep client compatibility.
   */
  default String getClusterId() {
    return null;
  }

  /**
   * Retrieve an Hbck implementation to fix an HBase cluster. The returned Hbck is not guaranteed to
   * be thread-safe. A new instance should be created by each thread. This is a lightweight
   * operation. Pooling or caching of the returned Hbck instance is not recommended. <br>
   * The caller is responsible for calling {@link Hbck#close()} on the returned Hbck instance. <br>
   * This will be used mostly by hbck tool.
   * @return an Hbck instance for active master. Active master is fetched from the zookeeper.
   */
  @InterfaceAudience.LimitedPrivate(HBaseInterfaceAudience.HBCK)
  default Hbck getHbck() throws IOException {
    throw new UnsupportedOperationException("Not implemented");
  }

  /**
   * Retrieve an Hbck implementation to fix an HBase cluster. The returned Hbck is not guaranteed to
   * be thread-safe. A new instance should be created by each thread. This is a lightweight
   * operation. Pooling or caching of the returned Hbck instance is not recommended. <br>
   * The caller is responsible for calling {@link Hbck#close()} on the returned Hbck instance. <br>
   * This will be used mostly by hbck tool. This may only be used to by pass getting registered
   * master from ZK. In situations where ZK is not available or active master is not registered with
   * ZK and user can get master address by other means, master can be explicitly specified.
   * @param masterServer explicit {@link ServerName} for master server
   * @return an Hbck instance for a specified master server
   */
  @InterfaceAudience.LimitedPrivate(HBaseInterfaceAudience.HBCK)
  default Hbck getHbck(ServerName masterServer) throws IOException {
    throw new UnsupportedOperationException("Not implemented");
  }
}