/**
 * 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.hadoop.hive.ql.udf;

import java.text.ParseException;
import java.text.SimpleDateFormat;
import java.util.Date;
import java.util.TimeZone;

import org.apache.hadoop.hive.ql.exec.Description;
import org.apache.hadoop.hive.ql.exec.UDF;
import org.apache.hadoop.hive.serde2.io.DateWritable;
import org.apache.hadoop.hive.serde2.io.TimestampWritable;
import org.apache.hadoop.io.IntWritable;
import org.apache.hadoop.io.Text;

/**
 * UDFDateDiff.
 *
 */
@Description(name = "datediff",
    value = "_FUNC_(date1, date2) - Returns the number of days between date1 and date2",
    extended = "date1 and date2 are strings in the format "
    + "'yyyy-MM-dd HH:mm:ss' or 'yyyy-MM-dd'. The time parts are ignored."
    + "If date1 is earlier than date2, the result is negative.\n"
    + "Example:\n "
    + "  > SELECT _FUNC_('2009-30-07', '2009-31-07') FROM src LIMIT 1;\n"
    + "  1")
public class UDFDateDiff extends UDF {
  private final SimpleDateFormat formatter = new SimpleDateFormat("yyyy-MM-dd");

  private final IntWritable result = new IntWritable();

  public UDFDateDiff() {
    formatter.setTimeZone(TimeZone.getTimeZone("UTC"));
  }

  /**
   * Calculate the difference in the number of days. The time part of the string
   * will be ignored. If dateString1 is earlier than dateString2, then the
   * result can be negative.
   *
   * @param dateString1
   *          the date string in the format of "yyyy-MM-dd HH:mm:ss" or
   *          "yyyy-MM-dd".
   * @param dateString2
   *          the date string in the format of "yyyy-MM-dd HH:mm:ss" or
   *          "yyyy-MM-dd".
   * @return the difference in days.
   */
  public IntWritable evaluate(Text dateString1, Text dateString2) {
    return evaluate(toDate(dateString1), toDate(dateString2));
  }

  public IntWritable evaluate(TimestampWritable t1, TimestampWritable t2) {
    return evaluate(toDate(t1), toDate(t2));
  }

  public IntWritable evaluate(TimestampWritable t, Text dateString) {
    return evaluate(toDate(t), toDate(dateString));
  }

  public IntWritable evaluate(Text dateString, TimestampWritable t) {
    return evaluate(toDate(dateString), toDate(t));
  }

  public IntWritable evaluate(Text dateString, DateWritable d) {
    return evaluate(toDate(dateString), d.get());
  }

  public IntWritable evaluate(TimestampWritable t, DateWritable d) {
    return evaluate(toDate(t), d.get());
  }

  public IntWritable evaluate(DateWritable d1, DateWritable d2) {
    return evaluate(d1.get(), d2.get());
  }

  public IntWritable evaluate(DateWritable d, Text dateString) {
    return evaluate(d.get(), toDate(dateString));
  }

  public IntWritable evaluate(DateWritable d, TimestampWritable t) {
    return evaluate(d.get(), toDate(t));
  }

  private IntWritable evaluate(Date date, Date date2) {
    if (date == null || date2 == null) {
      return null;
    }

    // NOTE: This implementation avoids the extra-second problem
    // by comparing with UTC epoch and integer division.
    // 86400 is the number of seconds in a day
    long diffInMilliSeconds = date.getTime() - date2.getTime();
    result.set((int) (diffInMilliSeconds / (86400 * 1000)));
    return result;
  }

  private Date format(String dateString) {
    try {
      return formatter.parse(dateString);
    } catch (ParseException e) {
      return null;
    }
  }

  private Date toDate(Text dateString) {
    if (dateString == null) {
      return null;
    }
    return format(dateString.toString());
  }

  private Date toDate(TimestampWritable t) {
    if (t == null) {
      return null;
    }
    return t.getTimestamp();
  }

}