/*
 * Copyright (c) 2014 DataTorrent, Inc. ALL Rights Reserved.
 *
 * Licensed 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 com.datatorrent.lib.db.jdbc;

import java.sql.ResultSet;
import java.sql.SQLException;
import java.sql.Statement;

import org.slf4j.Logger;
import org.slf4j.LoggerFactory;

import com.datatorrent.api.Context.OperatorContext;
import com.datatorrent.api.DefaultOutputPort;

import com.datatorrent.lib.db.AbstractStoreInputOperator;

/**
 * This is a base implementation of a JDBC input operator.&nbsp;
 * This operator reads data from a database through the JAVA DataBase Connectivity (JDBC) API
 * and emits the data as tuples.&nbsp;
 * Subclasses should implement the methods required to read the data from the database.
 * <p>
 * This is an abstract class. Sub-classes need to implement {@link #queryToRetrieveData()} and {@link #getTuple(ResultSet)}.
 * </p>
 * @displayName Abstract JDBC Input
 * @category Database
 * @tags input operator
 *
 * @param <T> The tuple type
 * @since 0.9.4
 */
public abstract class AbstractJdbcInputOperator<T> extends AbstractStoreInputOperator<T, JdbcStore>
{
  private static final Logger logger = LoggerFactory.getLogger(AbstractJdbcInputOperator.class);
  Statement queryStatement = null;

  /**
   * Any concrete class has to override this method to convert a Database row into Tuple.
   *
   * @param result a single row that has been read from database.
   * @return Tuple a tuples created from row which can be any Java object.
   */
  public abstract T getTuple(ResultSet result);

  /**
   * Any concrete class has to override this method to return the query string which will be used to
   * retrieve data from database.
   *
   * @return Query string
   */
  public abstract String queryToRetrieveData();

  /**
   * The output port that will emit tuples read from the database.
   */
  public final transient DefaultOutputPort<T> outputPort = new DefaultOutputPort<T>();

  /**
   * This executes the query to retrieve result from database.
   * It then converts each row into tuple and emit that into output port.
   */
  @Override
  public void emitTuples()
  {
    String query = queryToRetrieveData();
    logger.debug(String.format("select statement: %s", query));

    try {
      ResultSet result = queryStatement.executeQuery(query);
      while (result.next()) {
        T tuple = getTuple(result);
        outputPort.emit(tuple);
      }
    }
    catch (SQLException ex) {
      store.disconnect();
      throw new RuntimeException(String.format("Error while running query: %s", query), ex);
    }
  }

  @Override
  public void setup(OperatorContext context)
  {
    super.setup(context);
    try {
      queryStatement = store.getConnection().createStatement();
    }
    catch (SQLException e) {
      throw new RuntimeException("creating query", e);
    }
  }
}