/*
 * Copyright (C) The Apache Software Foundation. All rights reserved.
 *
 * This software is published under the terms of the Apache Software
 * License version 1.1, a copy of which has been included with this
 * distribution in the LICENSE.txt file.  */

package org.apache.log4j.helpers;

import java.util.Date;
import java.util.Calendar;
import java.util.TimeZone;
import java.text.FieldPosition;
import java.text.ParsePosition;
import java.text.DateFormat;


/**
   Formats a {@link Date} in the format "HH:mm:ss,SSS" for example,
   "15:49:37,459".
   
   @author Ceki Gülcü
   @author Andrew Vajoczki    

   @since 0.7.5
*/
public class AbsoluteTimeDateFormat extends DateFormat {

  /**
     String constant used to specify {@link
     org.apache.log4j.helpers.AbsoluteTimeDateFormat} in layouts. Current
     value is ABSOLUTE.  */
  public final static String ABS_TIME_DATE_FORMAT = "ABSOLUTE";

  /**
     String constant used to specify {@link
     org.apache.log4j.helpers.DateTimeDateFormat} in layouts.  Current
     value is DATE.
  */
  public final static String DATE_AND_TIME_DATE_FORMAT = "DATE";

  /**
     String constant used to specify {@link
     org.apache.log4j.helpers.ISO8601DateFormat} in layouts. Current
     value is ISO8601.
  */
  public final static String ISO8601_DATE_FORMAT = "ISO8601";

  public
  AbsoluteTimeDateFormat() {
    setCalendar(Calendar.getInstance());
  }
  
  public
  AbsoluteTimeDateFormat(TimeZone timeZone) {
    setCalendar(Calendar.getInstance(timeZone));
  }

  private static long   previousTime;
  private static char[] previousTimeWithoutMillis = new char[9]; // "HH:mm:ss."

  /**
     Appends to sbuf the time in the format
     "HH:mm:ss,SSS" for example, "15:49:37,459"

     @param date the date to format
     @param sbuf the string buffer to write to
     @param fieldPosition remains untouched
    */
  public
  StringBuffer format(Date date, StringBuffer sbuf,
		      FieldPosition fieldPosition) {

    long now = date.getTime();
    int millis = (int)(now % 1000);

    if ((now - millis) != previousTime) {
      // We reach this point at most once per second
      // across all threads instead of each time format()
      // is called. This saves considerable CPU time.

      calendar.setTime(date);

      int start = sbuf.length();
      
      int hour = calendar.get(Calendar.HOUR_OF_DAY);
      if(hour < 10) {
	sbuf.append('0');
      }
      sbuf.append(hour);
      sbuf.append(':');
      
      int mins = calendar.get(Calendar.MINUTE);
      if(mins < 10) {
	sbuf.append('0');
      }
      sbuf.append(mins);
      sbuf.append(':');
      
      int secs = calendar.get(Calendar.SECOND);
      if(secs < 10) {
	sbuf.append('0');
      }
      sbuf.append(secs);
      sbuf.append(',');      

      // store the time string for next time to avoid recomputation
      sbuf.getChars(start, sbuf.length(), previousTimeWithoutMillis, 0);
      
      previousTime = now - millis;
    }
    else {
      sbuf.append(previousTimeWithoutMillis);
    }
    

    
    if(millis < 100) 
      sbuf.append('0');
    if(millis < 10) 
      sbuf.append('0');
    
    sbuf.append(millis);
    return sbuf;
  }

  /**
     This method does not do anything but return null.
   */
  public
  Date parse(String s, ParsePosition pos) {
    return null;
  }  
}