content: /*
   * 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.arrow.adapter.jdbc;
  
  import static org.apache.arrow.adapter.jdbc.JdbcToArrowUtils.isColumnNullable;
  
  import java.sql.ResultSet;
  import java.sql.ResultSetMetaData;
  import java.sql.SQLException;
  import java.util.Iterator;
  import org.apache.arrow.adapter.jdbc.consumer.CompositeJdbcConsumer;
  import org.apache.arrow.adapter.jdbc.consumer.JdbcConsumer;
  import org.apache.arrow.adapter.jdbc.consumer.exceptions.JdbcConsumerException;
  import org.apache.arrow.util.AutoCloseables;
  import org.apache.arrow.util.Preconditions;
  import org.apache.arrow.vector.FieldVector;
  import org.apache.arrow.vector.VectorSchemaRoot;
  import org.apache.arrow.vector.types.pojo.ArrowType;
  import org.apache.arrow.vector.types.pojo.Schema;
  import org.apache.arrow.vector.util.ValueVectorUtility;
  
  /** VectorSchemaRoot iterator for partially converting JDBC data. */
  public class ArrowVectorIterator implements Iterator<VectorSchemaRoot>, AutoCloseable {
  
    private final ResultSet resultSet;
    private final JdbcToArrowConfig config;
  
    private final Schema schema;
    private final ResultSetMetaData rsmd;
  
    private final JdbcConsumer[] consumers;
    final CompositeJdbcConsumer compositeConsumer;
  
    // this is used only if resuing vector schema root is enabled.
    private VectorSchemaRoot nextBatch;
  
    private final int targetBatchSize;
  
    // This is used to track whether the ResultSet has been fully read, and is needed specifically for
    // cases where there
    // is a ResultSet having zero rows (empty):
    private boolean readComplete = false;
  
    /** Construct an instance. */
    private ArrowVectorIterator(ResultSet resultSet, JdbcToArrowConfig config) throws SQLException {
      this.resultSet = resultSet;
      this.config = config;
      this.schema = JdbcToArrowUtils.jdbcToArrowSchema(resultSet.getMetaData(), config);
      this.targetBatchSize = config.getTargetBatchSize();
  
      rsmd = resultSet.getMetaData();
      consumers = new JdbcConsumer[rsmd.getColumnCount()];
      this.compositeConsumer = new CompositeJdbcConsumer(consumers);
      this.nextBatch = config.isReuseVectorSchemaRoot() ? createVectorSchemaRoot() : null;
    }
  
    /** Create a ArrowVectorIterator to partially convert data. */
    public static ArrowVectorIterator create(ResultSet resultSet, JdbcToArrowConfig config)
        throws SQLException {
      ArrowVectorIterator iterator = null;
      try {
        iterator = new ArrowVectorIterator(resultSet, config);
      } catch (Throwable e) {
        AutoCloseables.close(e, iterator);
        throw new RuntimeException("Error occurred while creating iterator.", e);
      }
      return iterator;
    }
  
    private void consumeData(VectorSchemaRoot root) {
      // consume data
      try {
        int readRowCount = 0;
        if (targetBatchSize == JdbcToArrowConfig.NO_LIMIT_BATCH_SIZE) {
          while (resultSet.next()) {
            ValueVectorUtility.ensureCapacity(root, readRowCount + 1);
            compositeConsumer.consume(resultSet);
            readRowCount++;
          }
          readComplete = true;
        } else {
          while ((readRowCount < targetBatchSize) && !readComplete) {
            if (resultSet.next()) {
              compositeConsumer.consume(resultSet);
              readRowCount++;
            } else {
              readComplete = true;
            }
          }
        }
  
        root.setRowCount(readRowCount);
      } catch (Throwable e) {
        compositeConsumer.close();
        if (e instanceof JdbcConsumerException) {
          throw (JdbcConsumerException) e;
        } else {
          throw new RuntimeException("Error occurred while consuming data.", e);
        }
      }
    }
  
    private VectorSchemaRoot createVectorSchemaRoot() throws SQLException {
      VectorSchemaRoot root = null;
      try {
        root = VectorSchemaRoot.create(schema, config.getAllocator());
        if (config.getTargetBatchSize() != JdbcToArrowConfig.NO_LIMIT_BATCH_SIZE) {
          ValueVectorUtility.preAllocate(root, config.getTargetBatchSize());
        }
      } catch (Throwable e) {
        if (root != null) {
          root.close();
        }
        throw new RuntimeException("Error occurred while creating schema root.", e);
      }
      initialize(root);
      return root;
    }
  
    private void initialize(VectorSchemaRoot root) throws SQLException {
      for (int i = 1; i <= consumers.length; i++) {
        final JdbcFieldInfo columnFieldInfo =
            JdbcToArrowUtils.getJdbcFieldInfoForColumn(rsmd, i, config);
        ArrowType arrowType = config.getJdbcToArrowTypeConverter().apply(columnFieldInfo);
        consumers[i - 1] =
            config
                .getJdbcConsumerGetter()
                .apply(
                    arrowType,
                    i,
                    isColumnNullable(resultSet.getMetaData(), i, columnFieldInfo),
                    root.getVector(i - 1),
                    config);
      }
    }
  
    // Loads the next schema root or null if no more rows are available.
    private void load(VectorSchemaRoot root) {
      for (int i = 0; i < consumers.length; i++) {
        FieldVector vec = root.getVector(i);
        if (config.isReuseVectorSchemaRoot()) {
          // if we are reusing the vector schema root,
          // we must reset the vector before populating it with data.
          vec.reset();
        }
        consumers[i].resetValueVector(vec);
      }
  
      consumeData(root);
    }
  
    @Override
    public boolean hasNext() {
      return !readComplete;
    }
  
    /**
     * Gets the next vector. If {@link JdbcToArrowConfig#isReuseVectorSchemaRoot()} is false, the
     * client is responsible for freeing its resources.
     *
     * @throws JdbcConsumerException on error from VectorConsumer
     */
    @Override
    public VectorSchemaRoot next() {
      Preconditions.checkArgument(hasNext());
      try {
        VectorSchemaRoot ret =
            config.isReuseVectorSchemaRoot() ? nextBatch : createVectorSchemaRoot();
        load(ret);
        return ret;
      } catch (Exception e) {
        close();
        if (e instanceof JdbcConsumerException) {
          throw (JdbcConsumerException) e;
        } else {
          throw new RuntimeException("Error occurred while getting next schema root.", e);
        }
      }
    }
  
    /**
     * Clean up resources ONLY WHEN THE {@link VectorSchemaRoot} HOLDING EACH BATCH IS REUSED. If a
     * new VectorSchemaRoot is created for each batch, each root must be closed manually by the client
     * code.
     */
    @Override
    public void close() {
      if (config.isReuseVectorSchemaRoot()) {
        nextBatch.close();
        compositeConsumer.close();
      }
    }
  }
  