/*
 *
 * 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.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.
   */

  /**
   * @return 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 BufferedMutator will
   * use the Connection's ExecutorService. 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>
   * This accessor will use the connection's ExecutorService and will throw an
   * exception in the main thread when an asynchronous exception occurs.
   *
   * @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. 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;

  /**
   * 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);
}