/*
 * 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.flink.api.java.hadoop.common;

import org.apache.flink.annotation.Internal;
import org.apache.flink.api.common.io.RichInputFormat;
import org.apache.flink.core.io.InputSplit;
import org.apache.hadoop.security.Credentials;
import org.apache.hadoop.security.UserGroupInformation;

import java.io.IOException;
import java.io.ObjectInputStream;
import java.io.ObjectOutputStream;
import java.lang.reflect.InvocationTargetException;
import java.lang.reflect.Method;

/**
 * A common base for both "mapred" and "mapreduce" Hadoop input formats.
 */
@Internal
public abstract class HadoopInputFormatCommonBase<T, SPITTYPE extends InputSplit> extends RichInputFormat<T, SPITTYPE> {
	protected transient Credentials credentials;

	protected HadoopInputFormatCommonBase(Credentials creds) {
		this.credentials = creds;
	}

	protected void write(ObjectOutputStream out) throws IOException {
		this.credentials.write(out);
	}

	public void read(ObjectInputStream in) throws IOException {
		this.credentials = new Credentials();
		credentials.readFields(in);
	}

	/**
	 * This method only exists because there is no UserGroupInformation.getCredentials() method
	 * in Hadoop 1.x
	 *
	 * Note that this method returns "null" in Hadoop 1.x environments.
	 *
	 * @param ugi The user information
	 * @return new credentials object from the user information. MAY RETURN NULL!
	 */
	public static Credentials getCredentialsFromUGI(UserGroupInformation ugi) {
		Method getCredentialsMethod = null;
		for(Method m: ugi.getClass().getMethods()) {
			if(m.getName().equals("getCredentials")) {
				getCredentialsMethod = m;
				break;
			}
		}
		if(getCredentialsMethod == null) {
			return null;
		} else {
			try {
				return (Credentials) getCredentialsMethod.invoke(ugi);
			} catch (InvocationTargetException | IllegalAccessException e) {
				throw new RuntimeException("Unable to get credentials from UserGroupInformation. This is only supported by Hadoop 2.2.0+");
			}
		}
	}
}