/*
 * 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.mapred.utils;

import org.apache.flink.annotation.Internal;
import org.apache.flink.configuration.GlobalConfiguration;

import org.apache.hadoop.conf.Configuration;
import org.apache.hadoop.mapred.JobConf;
import org.slf4j.Logger;
import org.slf4j.LoggerFactory;

import java.io.File;
import java.util.Arrays;
import java.util.Map;
import java.util.Objects;

/** Utility class to work with Apache Hadoop MapRed classes. */
@Internal
public final class HadoopUtils {

    private static final Logger LOG = LoggerFactory.getLogger(HadoopUtils.class);

    /** Merge HadoopConfiguration into JobConf. This is necessary for the HDFS configuration. */
    public static void mergeHadoopConf(JobConf jobConf) {
        // we have to load the global configuration here, because the HadoopInputFormatBase does not
        // have access to a Flink configuration object
        org.apache.flink.configuration.Configuration flinkConfiguration =
                GlobalConfiguration.loadConfiguration();

        Configuration hadoopConf = getHadoopConfiguration(flinkConfiguration);
        for (Map.Entry<String, String> e : hadoopConf) {
            if (jobConf.get(e.getKey()) == null) {
                jobConf.set(e.getKey(), e.getValue());
            }
        }
    }

    /**
     * Returns a new Hadoop Configuration object using the path to the hadoop conf configured in the
     * main configuration (config.yaml). This method is public because its being used in the
     * HadoopDataSource.
     *
     * @param flinkConfiguration Flink configuration object
     * @return A Hadoop configuration instance
     */
    public static Configuration getHadoopConfiguration(
            org.apache.flink.configuration.Configuration flinkConfiguration) {

        Configuration retConf = new Configuration();

        // We need to load both core-site.xml and hdfs-site.xml to determine the default fs path and
        // the hdfs configuration
        // Try to load HDFS configuration from Hadoop's own configuration files

        // Approach environment variables
        for (String possibleHadoopConfPath : possibleHadoopConfPaths(flinkConfiguration)) {
            if (new File(possibleHadoopConfPath).exists()) {
                if (new File(possibleHadoopConfPath + "/core-site.xml").exists()) {
                    retConf.addResource(
                            new org.apache.hadoop.fs.Path(
                                    possibleHadoopConfPath + "/core-site.xml"));

                    if (LOG.isDebugEnabled()) {
                        LOG.debug(
                                "Adding "
                                        + possibleHadoopConfPath
                                        + "/core-site.xml to hadoop configuration");
                    }
                }
                if (new File(possibleHadoopConfPath + "/hdfs-site.xml").exists()) {
                    retConf.addResource(
                            new org.apache.hadoop.fs.Path(
                                    possibleHadoopConfPath + "/hdfs-site.xml"));

                    if (LOG.isDebugEnabled()) {
                        LOG.debug(
                                "Adding "
                                        + possibleHadoopConfPath
                                        + "/hdfs-site.xml to hadoop configuration");
                    }
                }
            }
        }
        return retConf;
    }

    /**
     * Get possible Hadoop conf dir paths, based on environment variables and flink configuration.
     *
     * @param flinkConfiguration The flink configuration that may contain the path to Hadoop conf
     *     dir.
     * @return an array of possible paths
     */
    public static String[] possibleHadoopConfPaths(
            org.apache.flink.configuration.Configuration flinkConfiguration) {
        String[] possiblePaths = new String[4];
        possiblePaths[0] = System.getenv("HADOOP_CONF_DIR");

        if (System.getenv("HADOOP_HOME") != null) {
            possiblePaths[1] = System.getenv("HADOOP_HOME") + "/conf";
            possiblePaths[2] = System.getenv("HADOOP_HOME") + "/etc/hadoop"; // hadoop 2.2
        }
        return Arrays.stream(possiblePaths).filter(Objects::nonNull).toArray(String[]::new);
    }

    /** Private constructor to prevent instantiation. */
    private HadoopUtils() {
        throw new RuntimeException();
    }
}
