/*
 * 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.beam.sdk.io.hadoop.format;

import java.io.DataInput;
import java.io.DataOutput;
import java.io.IOException;
import java.util.ArrayList;
import java.util.List;
import org.apache.beam.sdk.values.KV;
import org.apache.beam.vendor.guava.v20_0.com.google.common.base.Splitter;
import org.apache.hadoop.io.Text;
import org.apache.hadoop.io.Writable;
import org.apache.hadoop.mapreduce.InputFormat;
import org.apache.hadoop.mapreduce.InputSplit;
import org.apache.hadoop.mapreduce.JobContext;
import org.apache.hadoop.mapreduce.RecordReader;
import org.apache.hadoop.mapreduce.TaskAttemptContext;

/**
 * This is a valid InputFormat for reading employee data which is available in the form of {@code
 * List<KV>} as {@linkplain ReuseObjectsEmployeeRecordReader#employeeDataList employeeDataList}.
 * {@linkplain ReuseObjectsEmployeeRecordReader#employeeDataList employeeDataList} is populated
 * using {@linkplain TestEmployeeDataSet#populateEmployeeData()}.
 *
 * <p>{@linkplain ReuseObjectsEmployeeInputFormat} splits data into {@value
 * TestEmployeeDataSet#NUMBER_OF_SPLITS} splits, each split having {@value
 * TestEmployeeDataSet#NUMBER_OF_RECORDS_IN_EACH_SPLIT} records each. {@linkplain
 * ReuseObjectsEmployeeInputFormat} reads data from {@linkplain
 * ReuseObjectsEmployeeRecordReader#employeeDataList employeeDataList} and produces a key (employee
 * id) of type Text and value of type {@linkplain Employee Employee}.
 *
 * <p>{@linkplain ReuseObjectsEmployeeInputFormat} is also input to test whether {@linkplain
 * HadoopFormatIO } source returns immutable records for a scenario when RecordReader returns the
 * same key and value objects with updating values every time it reads data.
 */
class ReuseObjectsEmployeeInputFormat extends InputFormat<Text, Employee> {

  public ReuseObjectsEmployeeInputFormat() {}

  @Override
  public RecordReader<Text, Employee> createRecordReader(
      InputSplit split, TaskAttemptContext context) {
    return new ReuseObjectsEmployeeRecordReader();
  }

  @Override
  public List<InputSplit> getSplits(JobContext arg0) {
    List<InputSplit> inputSplitList = new ArrayList<>();
    for (int i = 1; i <= TestEmployeeDataSet.NUMBER_OF_SPLITS; i++) {
      InputSplit inputSplitObj =
          new ReuseEmployeeInputSplit(
              (i - 1) * TestEmployeeDataSet.NUMBER_OF_RECORDS_IN_EACH_SPLIT,
              i * TestEmployeeDataSet.NUMBER_OF_RECORDS_IN_EACH_SPLIT - 1);
      inputSplitList.add(inputSplitObj);
    }
    return inputSplitList;
  }

  /** InputSplit implementation for ReuseObjectsEmployeeInputFormat. */
  static class ReuseEmployeeInputSplit extends InputSplit implements Writable {
    // Start and end map index of each split of employeeData.
    private long startIndex;
    private long endIndex;

    public ReuseEmployeeInputSplit() {}

    ReuseEmployeeInputSplit(long startIndex, long endIndex) {
      this.startIndex = startIndex;
      this.endIndex = endIndex;
    }

    /** Returns number of records in each split. */
    @Override
    public long getLength() {
      return this.endIndex - this.startIndex + 1;
    }

    @Override
    public String[] getLocations() {
      return null;
    }

    long getStartIndex() {
      return startIndex;
    }

    public long getEndIndex() {
      return endIndex;
    }

    @Override
    public void readFields(DataInput dataIn) throws IOException {
      startIndex = dataIn.readLong();
      endIndex = dataIn.readLong();
    }

    @Override
    public void write(DataOutput dataOut) throws IOException {
      dataOut.writeLong(startIndex);
      dataOut.writeLong(endIndex);
    }
  }

  /** RecordReader for ReuseObjectsEmployeeInputFormat. */
  static class ReuseObjectsEmployeeRecordReader extends RecordReader<Text, Employee> {

    private ReuseEmployeeInputSplit split;
    private final Text currentKey = new Text();
    private final Employee currentValue = new Employee();
    private long employeeListIndex = 0L;
    private long recordsRead = 0L;
    private List<KV<String, String>> employeeDataList;

    ReuseObjectsEmployeeRecordReader() {}

    @Override
    public void close() {}

    @Override
    public Text getCurrentKey() {
      return currentKey;
    }

    @Override
    public Employee getCurrentValue() {
      return currentValue;
    }

    @Override
    public float getProgress() {
      return (float) recordsRead / split.getLength();
    }

    @Override
    public void initialize(InputSplit split, TaskAttemptContext arg1) {
      this.split = (ReuseEmployeeInputSplit) split;
      employeeListIndex = this.split.getStartIndex() - 1;
      recordsRead = 0;
      employeeDataList = TestEmployeeDataSet.populateEmployeeData();
    }

    @Override
    public boolean nextKeyValue() {
      if ((recordsRead++) >= split.getLength()) {
        return false;
      }
      employeeListIndex++;
      KV<String, String> employeeDetails = employeeDataList.get((int) employeeListIndex);
      List<String> empData = Splitter.on('_').splitToList(employeeDetails.getValue());
      // Updating the same key and value objects with new employee data.
      currentKey.set(employeeDetails.getKey());
      currentValue.setEmpName(empData.get(0));
      currentValue.setEmpAddress(empData.get(1));
      return true;
    }
  }
}