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/**
 * Copyright 2012 Twitter, Inc.
 *
 * 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 parquet.thrift;
import java.util.HashMap;
import java.util.Map;
import java.util.Set;

import org.apache.thrift.TBase;

import parquet.Log;
import parquet.hadoop.BadConfigurationException;
import parquet.thrift.struct.ThriftType;
import parquet.thrift.struct.ThriftType.StructType;

/**
 *
 * Metadata for thrift stored in the file footer
 *
 * @author Julien Le Dem
 *
 */
public class ThriftMetaData {
  private static final Log LOG = Log.getLog(ThriftMetaData.class);

  private static final String THRIFT_CLASS = "thrift.class";
  private static final String THRIFT_DESCRIPTOR = "thrift.descriptor";
  private Class thriftClass;
  private final String thriftClassName;
  private final StructType descriptor;

  /**
   * @param thriftClassName the class used to serialize
   * @param descriptor the json representation of the thrift structure
   */
  public ThriftMetaData(String thriftClassName, StructType descriptor) {
    this.thriftClassName = thriftClassName;
    this.descriptor = descriptor;
  }

  /**
   * Get the Thrift Class encoded in the metadata.
   * @return Thrift Class encoded in the metadata.
   * @throws BadConfigurationException if the encoded class does not
   * extend TBase or is not available in the current classloader.
   */
  public Class getThriftClass() {
    if (thriftClass == null) {
      thriftClass = getThriftClass(thriftClassName);
    }
    return thriftClass;
  }

  /**
   * @param thriftClassName the name of the thrift class
   * @return the class
   */
  public static Class getThriftClass(String thriftClassName) {
    try {
      Class thriftClass = Class.forName(thriftClassName);
      if (!TBase.class.isAssignableFrom(thriftClass)) {
        throw new BadConfigurationException("Provided class " + thriftClassName + " does not extend TBase");
      }
      return thriftClass;
    } catch (ClassNotFoundException e) {
      throw new BadConfigurationException("Could not instantiate thrift class " + thriftClassName, e);
    }
  }

  /**
   * @return the thrift descriptor
   */
  public StructType getDescriptor() {
    return descriptor;
  }

  /**
   * Reads ThriftMetadata from the parquet file footer.
   *
   * @param extraMetaData  extraMetaData field of the parquet footer
   * @return
   */
  public static ThriftMetaData fromExtraMetaData(
      Map extraMetaData) {
    final String thriftClassName = extraMetaData.get(THRIFT_CLASS);
    final String thriftDescriptorString = extraMetaData.get(THRIFT_DESCRIPTOR);
    if (thriftClassName == null && thriftDescriptorString == null) {
      return null;
    }
    final StructType descriptor;
    try {
      descriptor = (StructType)ThriftType.fromJSON(thriftDescriptorString);
    } catch (RuntimeException e) {
      throw new BadConfigurationException("Could not read the thrift descriptor " + thriftDescriptorString, e);
    }
    return new ThriftMetaData(thriftClassName, descriptor);
  }

  /**
   * generates a map of key values to store in the footer
   * @return the key values
   */
  public Map toExtraMetaData() {
    final Map map = new HashMap();
    map.put(THRIFT_CLASS, getThriftClass().getName());
    map.put(THRIFT_DESCRIPTOR, descriptor.toJSON());
    return map;
  }

  /**
   * @param fileMetadata the merged metadata from ultiple files
   * @return the list of thrift classes used to write them
   */
  public static Set getThriftClassNames(Map> fileMetadata) {
    return fileMetadata.get(THRIFT_CLASS);
  }

  @Override
  public String toString() {
    return "ThriftMetaData" + toExtraMetaData();
  }

}