/*
 * 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.inputformat;

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.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#populateEmployeeDataNew()}.
 *
 * <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 HadoopInputFormatIO } source returns immutable records for a scenario when
 * RecordReader returns the same key and value objects with updating values every time it reads
 * data.
 */
public class ReuseObjectsEmployeeInputFormat extends InputFormat<Text, Employee> {

  public ReuseObjectsEmployeeInputFormat() {}

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

  @Override
  public List<InputSplit> getSplits(JobContext arg0) throws IOException, InterruptedException {
    List<InputSplit> inputSplitList = new ArrayList<InputSplit>();
    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.
   */
  public class ReuseEmployeeInputSplit extends InputSplit implements Writable {
    // Start and end map index of each split of employeeData.
    private long startIndex;
    private long endIndex;

    public ReuseEmployeeInputSplit() {}

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

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

    @Override
    public String[] getLocations() throws IOException, InterruptedException {
      return null;
    }


    public 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.
   */
  public class ReuseObjectsEmployeeRecordReader extends RecordReader<Text, Employee> {

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

    public ReuseObjectsEmployeeRecordReader() {}

    @Override
    public void close() throws IOException {}

    @Override
    public Text getCurrentKey() throws IOException, InterruptedException {
      return currentKey;
    }

    @Override
    public Employee getCurrentValue() throws IOException, InterruptedException {
      return currentValue;
    }

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

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

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