/*
 * All content copyright Terracotta, Inc., unless otherwise indicated. All rights reserved.
 *
 * Licensed 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.eclipse.che.commons.schedule.executor;

import java.io.Serializable;
import java.text.ParseException;
import java.util.Calendar;
import java.util.Date;
import java.util.HashMap;
import java.util.Iterator;
import java.util.Locale;
import java.util.Map;
import java.util.SortedSet;
import java.util.StringTokenizer;
import java.util.TimeZone;
import java.util.TreeSet;

/**
 * Provides a parser and evaluator for unix-like cron expressions. Cron expressions provide the
 * ability to specify complex time combinations such as &quot;At 8:00am every Monday through
 * Friday&quot; or &quot;At 1:30am every last Friday of the month&quot;.
 *
 * <p>Cron expressions are comprised of 6 required fields and one optional field separated by white
 * space. The fields respectively are described as follows:
 *
 * <table cellspacing="8">
 * <tr>
 * <th align="left">Field Name</th>
 * <th align="left">&nbsp;</th>
 * <th align="left">Allowed Values</th>
 * <th align="left">&nbsp;</th>
 * <th align="left">Allowed Special Characters</th>
 * </tr>
 * <tr>
 * <td align="left"><code>Seconds</code></td>
 * <td align="left">&nbsp;</th>
 * <td align="left"><code>0-59</code></td>
 * <td align="left">&nbsp;</th>
 * <td align="left"><code>, - * /</code></td>
 * </tr>
 * <tr>
 * <td align="left"><code>Minutes</code></td>
 * <td align="left">&nbsp;</th>
 * <td align="left"><code>0-59</code></td>
 * <td align="left">&nbsp;</th>
 * <td align="left"><code>, - * /</code></td>
 * </tr>
 * <tr>
 * <td align="left"><code>Hours</code></td>
 * <td align="left">&nbsp;</th>
 * <td align="left"><code>0-23</code></td>
 * <td align="left">&nbsp;</th>
 * <td align="left"><code>, - * /</code></td>
 * </tr>
 * <tr>
 * <td align="left"><code>Day-of-month</code></td>
 * <td align="left">&nbsp;</th>
 * <td align="left"><code>1-31</code></td>
 * <td align="left">&nbsp;</th>
 * <td align="left"><code>, - * ? / L W</code></td>
 * </tr>
 * <tr>
 * <td align="left"><code>Month</code></td>
 * <td align="left">&nbsp;</th>
 * <td align="left"><code>1-12 or JAN-DEC</code></td>
 * <td align="left">&nbsp;</th>
 * <td align="left"><code>, - * /</code></td>
 * </tr>
 * <tr>
 * <td align="left"><code>Day-of-Week</code></td>
 * <td align="left">&nbsp;</th>
 * <td align="left"><code>1-7 or SUN-SAT</code></td>
 * <td align="left">&nbsp;</th>
 * <td align="left"><code>, - * ? / L #</code></td>
 * </tr>
 * <tr>
 * <td align="left"><code>Year (Optional)</code></td>
 * <td align="left">&nbsp;</th>
 * <td align="left"><code>empty, 1970-2199</code></td>
 * <td align="left">&nbsp;</th>
 * <td align="left"><code>, - * /</code></td>
 * </tr>
 * </table>
 *
 * <p>The '*' character is used to specify all values. For example, &quot;*&quot; in the minute
 * field means &quot;every minute&quot;.
 *
 * <p>The '?' character is allowed for the day-of-month and day-of-week fields. It is used to
 * specify 'no specific value'. This is useful when you need to specify something in one of the two
 * fields, but not the other.
 *
 * <p>The '-' character is used to specify ranges For example &quot;10-12&quot; in the hour field
 * means &quot;the hours 10, 11 and 12&quot;.
 *
 * <p>The ',' character is used to specify additional values. For example &quot;MON,WED,FRI&quot; in
 * the day-of-week field means &quot;the days Monday, Wednesday, and Friday&quot;.
 *
 * <p>The '/' character is used to specify increments. For example &quot;0/15&quot; in the seconds
 * field means &quot;the seconds 0, 15, 30, and 45&quot;. And &quot;5/15&quot; in the seconds field
 * means &quot;the seconds 5, 20, 35, and 50&quot;. Specifying '*' before the '/' is equivalent to
 * specifying 0 is the value to start with. Essentially, for each field in the expression, there is
 * a set of numbers that can be turned on or off. For seconds and minutes, the numbers range from 0
 * to 59. For hours 0 to 23, for days of the month 0 to 31, and for months 1 to 12. The
 * &quot;/&quot; character simply helps you turn on every &quot;nth&quot; value in the given set.
 * Thus &quot;7/6&quot; in the month field only turns on month &quot;7&quot;, it does NOT mean every
 * 6th month, please note that subtlety.
 *
 * <p>The 'L' character is allowed for the day-of-month and day-of-week fields. This character is
 * short-hand for &quot;last&quot;, but it has different meaning in each of the two fields. For
 * example, the value &quot;L&quot; in the day-of-month field means &quot;the last day of the
 * month&quot; - day 31 for January, day 28 for February on non-leap years. If used in the
 * day-of-week field by itself, it simply means &quot;7&quot; or &quot;SAT&quot;. But if used in the
 * day-of-week field after another value, it means &quot;the last xxx day of the month&quot; - for
 * example &quot;6L&quot; means &quot;the last friday of the month&quot;. You can also specify an
 * offset from the last day of the month, such as "L-3" which would mean the third-to-last day of
 * the calendar month. <i>When using the 'L' option, it is important not to specify lists, or ranges
 * of values, as you'll get confusing/unexpected results.</i>
 *
 * <p>The 'W' character is allowed for the day-of-month field. This character is used to specify the
 * weekday (Monday-Friday) nearest the given day. As an example, if you were to specify
 * &quot;15W&quot; as the value for the day-of-month field, the meaning is: &quot;the nearest
 * weekday to the 15th of the month&quot;. So if the 15th is a Saturday, the trigger will fire on
 * Friday the 14th. If the 15th is a Sunday, the trigger will fire on Monday the 16th. If the 15th
 * is a Tuesday, then it will fire on Tuesday the 15th. However if you specify &quot;1W&quot; as the
 * value for day-of-month, and the 1st is a Saturday, the trigger will fire on Monday the 3rd, as it
 * will not 'jump' over the boundary of a month's days. The 'W' character can only be specified when
 * the day-of-month is a single day, not a range or list of days.
 *
 * <p>The 'L' and 'W' characters can also be combined for the day-of-month expression to yield 'LW',
 * which translates to &quot;last weekday of the month&quot;.
 *
 * <p>The '#' character is allowed for the day-of-week field. This character is used to specify
 * &quot;the nth&quot; XXX day of the month. For example, the value of &quot;6#3&quot; in the
 * day-of-week field means the third Friday of the month (day 6 = Friday and &quot;#3&quot; = the
 * 3rd one in the month). Other examples: &quot;2#1&quot; = the first Monday of the month and
 * &quot;4#5&quot; = the fifth Wednesday of the month. Note that if you specify &quot;#5&quot; and
 * there is not 5 of the given day-of-week in the month, then no firing will occur that month. If
 * the '#' character is used, there can only be one expression in the day-of-week field
 * (&quot;3#1,6#3&quot; is not valid, since there are two expressions).
 *
 * <p>
 * <!--The 'C' character is allowed for the day-of-month and day-of-week fields.
 * This character is short-hand for "calendar". This means values are
 * calculated against the associated calendar, if any. If no calendar is
 * associated, then it is equivalent to having an all-inclusive calendar. A
 * value of "5C" in the day-of-month field means "the first day included by the
 * calendar on or after the 5th". A value of "1C" in the day-of-week field
 * means "the first day included by the calendar on or after Sunday".-->
 *
 * <p>The legal characters and the names of months and days of the week are not case sensitive.
 *
 * <p><b>NOTES:</b>
 *
 * <ul>
 *   <li>Support for specifying both a day-of-week and a day-of-month value is not complete (you'll
 *       need to use the '?' character in one of these fields).
 *   <li>Overflowing ranges is supported - that is, having a larger number on the left hand side
 *       than the right. You might do 22-2 to catch 10 o'clock at night until 2 o'clock in the
 *       morning, or you might have NOV-FEB. It is very important to note that overuse of
 *       overflowing ranges creates ranges that don't make sense and no effort has been made to
 *       determine which interpretation CronExpression chooses. An example would be "0 0 14-6 ? *
 *       FRI-MON".
 * </ul>
 *
 * @author Sharada Jambula, James House
 * @author Contributions from Mads Henderson
 * @author Refactoring from CronTrigger to CronExpression by Aaron Craven
 */
public final class CronExpression implements Serializable, Cloneable {

  private static final long serialVersionUID = 12423409423L;

  protected static final int SECOND = 0;
  protected static final int MINUTE = 1;
  protected static final int HOUR = 2;
  protected static final int DAY_OF_MONTH = 3;
  protected static final int MONTH = 4;
  protected static final int DAY_OF_WEEK = 5;
  protected static final int YEAR = 6;
  protected static final int ALL_SPEC_INT = 99; // '*'
  protected static final int NO_SPEC_INT = 98; // '?'
  protected static final Integer ALL_SPEC = ALL_SPEC_INT;
  protected static final Integer NO_SPEC = NO_SPEC_INT;

  protected static final Map<String, Integer> monthMap = new HashMap<String, Integer>(20);
  protected static final Map<String, Integer> dayMap = new HashMap<String, Integer>(60);

  static {
    monthMap.put("JAN", 0);
    monthMap.put("FEB", 1);
    monthMap.put("MAR", 2);
    monthMap.put("APR", 3);
    monthMap.put("MAY", 4);
    monthMap.put("JUN", 5);
    monthMap.put("JUL", 6);
    monthMap.put("AUG", 7);
    monthMap.put("SEP", 8);
    monthMap.put("OCT", 9);
    monthMap.put("NOV", 10);
    monthMap.put("DEC", 11);

    dayMap.put("SUN", 1);
    dayMap.put("MON", 2);
    dayMap.put("TUE", 3);
    dayMap.put("WED", 4);
    dayMap.put("THU", 5);
    dayMap.put("FRI", 6);
    dayMap.put("SAT", 7);
  }

  private final String cronExpression;
  private TimeZone timeZone = null;
  protected transient TreeSet<Integer> seconds;
  protected transient TreeSet<Integer> minutes;
  protected transient TreeSet<Integer> hours;
  protected transient TreeSet<Integer> daysOfMonth;
  protected transient TreeSet<Integer> months;
  protected transient TreeSet<Integer> daysOfWeek;
  protected transient TreeSet<Integer> years;

  protected transient boolean lastdayOfWeek = false;
  protected transient int nthdayOfWeek = 0;
  protected transient boolean lastdayOfMonth = false;
  protected transient boolean nearestWeekday = false;
  protected transient int lastdayOffset = 0;
  protected transient boolean expressionParsed = false;

  public static final int MAX_YEAR = Calendar.getInstance().get(Calendar.YEAR) + 100;

  /**
   * Constructs a new <CODE>CronExpression</CODE> based on the specified parameter.
   *
   * @param cronExpression String representation of the cron expression the new object should
   *     represent
   * @throws java.text.ParseException if the string expression cannot be parsed into a valid <CODE>
   *     CronExpression</CODE>
   */
  public CronExpression(String cronExpression) throws ParseException {
    if (cronExpression == null) {
      throw new IllegalArgumentException("cronExpression cannot be null");
    }

    this.cronExpression = cronExpression.toUpperCase(Locale.US);

    buildExpression(this.cronExpression);
  }

  /**
   * Constructs a new {@code CronExpression} as a copy of an existing instance.
   *
   * @param expression The existing cron expression to be copied
   */
  public CronExpression(CronExpression expression) {
    /*
     * We don't call the other constructor here since we need to swallow the
     * ParseException. We also elide some of the sanity checking as it is
     * not logically trippable.
     */
    this.cronExpression = expression.getCronExpression();
    try {
      buildExpression(cronExpression);
    } catch (ParseException ex) {
      throw new AssertionError();
    }
    if (expression.getTimeZone() != null) {
      setTimeZone((TimeZone) expression.getTimeZone().clone());
    }
  }

  /**
   * Indicates whether the given date satisfies the cron expression. Note that milliseconds are
   * ignored, so two Dates falling on different milliseconds of the same second will always have the
   * same result here.
   *
   * @param date the date to evaluate
   * @return a boolean indicating whether the given date satisfies the cron expression
   */
  public boolean isSatisfiedBy(Date date) {
    Calendar testDateCal = Calendar.getInstance(getTimeZone());
    testDateCal.setTime(date);
    testDateCal.set(Calendar.MILLISECOND, 0);
    Date originalDate = testDateCal.getTime();

    testDateCal.add(Calendar.SECOND, -1);

    Date timeAfter = getTimeAfter(testDateCal.getTime());

    return ((timeAfter != null) && (timeAfter.equals(originalDate)));
  }

  /**
   * Returns the next date/time <I>after</I> the given date/time which satisfies the cron
   * expression.
   *
   * @param date the date/time at which to begin the search for the next valid date/time
   * @return the next valid date/time
   */
  public Date getNextValidTimeAfter(Date date) {
    return getTimeAfter(date);
  }

  /**
   * Returns the next date/time <I>after</I> the given date/time which does <I>not</I> satisfy the
   * expression
   *
   * @param date the date/time at which to begin the search for the next invalid date/time
   * @return the next valid date/time
   */
  public Date getNextInvalidTimeAfter(Date date) {
    long difference = 1000;

    // move back to the nearest second so differences will be accurate
    Calendar adjustCal = Calendar.getInstance(getTimeZone());
    adjustCal.setTime(date);
    adjustCal.set(Calendar.MILLISECOND, 0);
    Date lastDate = adjustCal.getTime();

    Date newDate;

    // FUTURE_TODO: (QUARTZ-481) IMPROVE THIS! The following is a BAD solution to this problem.
    // Performance will be very bad here, depending on the cron expression. It is, however A
    // solution.

    // keep getting the next included time until it's farther than one second
    // apart. At that point, lastDate is the last valid fire time. We return
    // the second immediately following it.
    while (difference == 1000) {
      newDate = getTimeAfter(lastDate);
      if (newDate == null) break;

      difference = newDate.getTime() - lastDate.getTime();

      if (difference == 1000) {
        lastDate = newDate;
      }
    }

    return new Date(lastDate.getTime() + 1000);
  }

  /** Returns the time zone for which this <code>CronExpression</code> will be resolved. */
  public TimeZone getTimeZone() {
    if (timeZone == null) {
      timeZone = TimeZone.getDefault();
    }

    return timeZone;
  }

  /** Sets the time zone for which this <code>CronExpression</code> will be resolved. */
  public void setTimeZone(TimeZone timeZone) {
    this.timeZone = timeZone;
  }

  /**
   * Returns the string representation of the <CODE>CronExpression</CODE>
   *
   * @return a string representation of the <CODE>CronExpression</CODE>
   */
  @Override
  public String toString() {
    return cronExpression;
  }

  /**
   * Indicates whether the specified cron expression can be parsed into a valid cron expression
   *
   * @param cronExpression the expression to evaluate
   * @return a boolean indicating whether the given expression is a valid cron expression
   */
  public static boolean isValidExpression(String cronExpression) {

    try {
      new CronExpression(cronExpression);
    } catch (ParseException pe) {
      return false;
    }

    return true;
  }

  public static void validateExpression(String cronExpression) throws ParseException {

    new CronExpression(cronExpression);
  }

  ////////////////////////////////////////////////////////////////////////////
  //
  // Expression Parsing Functions
  //
  ////////////////////////////////////////////////////////////////////////////

  protected void buildExpression(String expression) throws ParseException {
    expressionParsed = true;

    try {

      if (seconds == null) {
        seconds = new TreeSet<Integer>();
      }
      if (minutes == null) {
        minutes = new TreeSet<Integer>();
      }
      if (hours == null) {
        hours = new TreeSet<Integer>();
      }
      if (daysOfMonth == null) {
        daysOfMonth = new TreeSet<Integer>();
      }
      if (months == null) {
        months = new TreeSet<Integer>();
      }
      if (daysOfWeek == null) {
        daysOfWeek = new TreeSet<Integer>();
      }
      if (years == null) {
        years = new TreeSet<Integer>();
      }

      int exprOn = SECOND;

      StringTokenizer exprsTok = new StringTokenizer(expression, " \t", false);

      while (exprsTok.hasMoreTokens() && exprOn <= YEAR) {
        String expr = exprsTok.nextToken().trim();

        // throw an exception if L is used with other days of the month
        if (exprOn == DAY_OF_MONTH
            && expr.indexOf('L') != -1
            && expr.length() > 1
            && expr.contains(",")) {
          throw new ParseException(
              "Support for specifying 'L' and 'LW' with other days of the month is not implemented",
              -1);
        }
        // throw an exception if L is used with other days of the week
        if (exprOn == DAY_OF_WEEK
            && expr.indexOf('L') != -1
            && expr.length() > 1
            && expr.contains(",")) {
          throw new ParseException(
              "Support for specifying 'L' with other days of the week is not implemented", -1);
        }
        if (exprOn == DAY_OF_WEEK
            && expr.indexOf('#') != -1
            && expr.indexOf('#', expr.indexOf('#') + 1) != -1) {
          throw new ParseException(
              "Support for specifying multiple \"nth\" days is not implemented.", -1);
        }

        StringTokenizer vTok = new StringTokenizer(expr, ",");
        while (vTok.hasMoreTokens()) {
          String v = vTok.nextToken();
          storeExpressionVals(0, v, exprOn);
        }

        exprOn++;
      }

      if (exprOn <= DAY_OF_WEEK) {
        throw new ParseException("Unexpected end of expression.", expression.length());
      }

      if (exprOn <= YEAR) {
        storeExpressionVals(0, "*", YEAR);
      }

      TreeSet<Integer> dow = getSet(DAY_OF_WEEK);
      TreeSet<Integer> dom = getSet(DAY_OF_MONTH);

      // Copying the logic from the UnsupportedOperationException below
      boolean dayOfMSpec = !dom.contains(NO_SPEC);
      boolean dayOfWSpec = !dow.contains(NO_SPEC);

      if (!dayOfMSpec || dayOfWSpec) {
        if (!dayOfWSpec || dayOfMSpec) {
          throw new ParseException(
              "Support for specifying both a day-of-week AND a day-of-month parameter is not implemented.",
              0);
        }
      }
    } catch (ParseException pe) {
      throw pe;
    } catch (Exception e) {
      throw new ParseException("Illegal cron expression format (" + e.toString() + ")", 0);
    }
  }

  protected int storeExpressionVals(int pos, String s, int type) throws ParseException {

    int incr = 0;
    int i = skipWhiteSpace(pos, s);
    if (i >= s.length()) {
      return i;
    }
    char c = s.charAt(i);
    if ((c >= 'A')
        && (c <= 'Z')
        && (!s.equals("L"))
        && (!s.equals("LW"))
        && (!s.matches("^L-[0-9]*[W]?"))) {
      String sub = s.substring(i, i + 3);
      int sval = -1;
      int eval = -1;
      if (type == MONTH) {
        sval = getMonthNumber(sub) + 1;
        if (sval <= 0) {
          throw new ParseException("Invalid Month value: '" + sub + "'", i);
        }
        if (s.length() > i + 3) {
          c = s.charAt(i + 3);
          if (c == '-') {
            i += 4;
            sub = s.substring(i, i + 3);
            eval = getMonthNumber(sub) + 1;
            if (eval <= 0) {
              throw new ParseException("Invalid Month value: '" + sub + "'", i);
            }
          }
        }
      } else if (type == DAY_OF_WEEK) {
        sval = getDayOfWeekNumber(sub);
        if (sval < 0) {
          throw new ParseException("Invalid Day-of-Week value: '" + sub + "'", i);
        }
        if (s.length() > i + 3) {
          c = s.charAt(i + 3);
          if (c == '-') {
            i += 4;
            sub = s.substring(i, i + 3);
            eval = getDayOfWeekNumber(sub);
            if (eval < 0) {
              throw new ParseException("Invalid Day-of-Week value: '" + sub + "'", i);
            }
          } else if (c == '#') {
            try {
              i += 4;
              nthdayOfWeek = Integer.parseInt(s.substring(i));
              if (nthdayOfWeek < 1 || nthdayOfWeek > 5) {
                throw new Exception();
              }
            } catch (Exception e) {
              throw new ParseException(
                  "A numeric value between 1 and 5 must follow the '#' option", i);
            }
          } else if (c == 'L') {
            lastdayOfWeek = true;
            i++;
          }
        }

      } else {
        throw new ParseException("Illegal characters for this position: '" + sub + "'", i);
      }
      if (eval != -1) {
        incr = 1;
      }
      addToSet(sval, eval, incr, type);
      return (i + 3);
    }

    if (c == '?') {
      i++;
      if ((i + 1) < s.length() && (s.charAt(i) != ' ' && s.charAt(i + 1) != '\t')) {
        throw new ParseException("Illegal character after '?': " + s.charAt(i), i);
      }
      if (type != DAY_OF_WEEK && type != DAY_OF_MONTH) {
        throw new ParseException("'?' can only be specfied for Day-of-Month or Day-of-Week.", i);
      }
      if (type == DAY_OF_WEEK && !lastdayOfMonth) {
        int val = daysOfMonth.last();
        if (val == NO_SPEC_INT) {
          throw new ParseException(
              "'?' can only be specfied for Day-of-Month -OR- Day-of-Week.", i);
        }
      }

      addToSet(NO_SPEC_INT, -1, 0, type);
      return i;
    }

    if (c == '*' || c == '/') {
      if (c == '*' && (i + 1) >= s.length()) {
        addToSet(ALL_SPEC_INT, -1, incr, type);
        return i + 1;
      } else if (c == '/'
          && ((i + 1) >= s.length() || s.charAt(i + 1) == ' ' || s.charAt(i + 1) == '\t')) {
        throw new ParseException("'/' must be followed by an integer.", i);
      } else if (c == '*') {
        i++;
      }
      c = s.charAt(i);
      if (c == '/') { // is an increment specified?
        i++;
        if (i >= s.length()) {
          throw new ParseException("Unexpected end of string.", i);
        }

        incr = getNumericValue(s, i);

        i++;
        if (incr > 10) {
          i++;
        }
        if (incr > 59 && (type == SECOND || type == MINUTE)) {
          throw new ParseException("Increment > 60 : " + incr, i);
        } else if (incr > 23 && (type == HOUR)) {
          throw new ParseException("Increment > 24 : " + incr, i);
        } else if (incr > 31 && (type == DAY_OF_MONTH)) {
          throw new ParseException("Increment > 31 : " + incr, i);
        } else if (incr > 7 && (type == DAY_OF_WEEK)) {
          throw new ParseException("Increment > 7 : " + incr, i);
        } else if (incr > 12 && (type == MONTH)) {
          throw new ParseException("Increment > 12 : " + incr, i);
        }
      } else {
        incr = 1;
      }

      addToSet(ALL_SPEC_INT, -1, incr, type);
      return i;
    } else if (c == 'L') {
      i++;
      if (type == DAY_OF_MONTH) {
        lastdayOfMonth = true;
      }
      if (type == DAY_OF_WEEK) {
        addToSet(7, 7, 0, type);
      }
      if (type == DAY_OF_MONTH && s.length() > i) {
        c = s.charAt(i);
        if (c == '-') {
          ValueSet vs = getValue(0, s, i + 1);
          lastdayOffset = vs.value;
          if (lastdayOffset > 30)
            throw new ParseException("Offset from last day must be <= 30", i + 1);
          i = vs.pos;
        }
        if (s.length() > i) {
          c = s.charAt(i);
          if (c == 'W') {
            nearestWeekday = true;
            i++;
          }
        }
      }
      return i;
    } else if (c >= '0' && c <= '9') {
      int val = Integer.parseInt(String.valueOf(c));
      i++;
      if (i >= s.length()) {
        addToSet(val, -1, -1, type);
      } else {
        c = s.charAt(i);
        if (c >= '0' && c <= '9') {
          ValueSet vs = getValue(val, s, i);
          val = vs.value;
          i = vs.pos;
        }
        i = checkNext(i, s, val, type);
        return i;
      }
    } else {
      throw new ParseException("Unexpected character: " + c, i);
    }

    return i;
  }

  protected int checkNext(int pos, String s, int val, int type) throws ParseException {

    int end = -1;
    int i = pos;

    if (i >= s.length()) {
      addToSet(val, end, -1, type);
      return i;
    }

    char c = s.charAt(pos);

    if (c == 'L') {
      if (type == DAY_OF_WEEK) {
        if (val < 1 || val > 7)
          throw new ParseException("Day-of-Week values must be between 1 and 7", -1);
        lastdayOfWeek = true;
      } else {
        throw new ParseException("'L' option is not valid here. (pos=" + i + ")", i);
      }
      TreeSet<Integer> set = getSet(type);
      set.add(val);
      i++;
      return i;
    }

    if (c == 'W') {
      if (type == DAY_OF_MONTH) {
        nearestWeekday = true;
      } else {
        throw new ParseException("'W' option is not valid here. (pos=" + i + ")", i);
      }
      if (val > 31)
        throw new ParseException(
            "The 'W' option does not make sense with values larger than 31 (max number of days in a month)",
            i);
      TreeSet<Integer> set = getSet(type);
      set.add(val);
      i++;
      return i;
    }

    if (c == '#') {
      if (type != DAY_OF_WEEK) {
        throw new ParseException("'#' option is not valid here. (pos=" + i + ")", i);
      }
      i++;
      try {
        nthdayOfWeek = Integer.parseInt(s.substring(i));
        if (nthdayOfWeek < 1 || nthdayOfWeek > 5) {
          throw new Exception();
        }
      } catch (Exception e) {
        throw new ParseException("A numeric value between 1 and 5 must follow the '#' option", i);
      }

      TreeSet<Integer> set = getSet(type);
      set.add(val);
      i++;
      return i;
    }

    if (c == '-') {
      i++;
      c = s.charAt(i);
      int v = Integer.parseInt(String.valueOf(c));
      end = v;
      i++;
      if (i >= s.length()) {
        addToSet(val, end, 1, type);
        return i;
      }
      c = s.charAt(i);
      if (c >= '0' && c <= '9') {
        ValueSet vs = getValue(v, s, i);
        end = vs.value;
        i = vs.pos;
      }
      if (i < s.length() && ((c = s.charAt(i)) == '/')) {
        i++;
        c = s.charAt(i);
        int v2 = Integer.parseInt(String.valueOf(c));
        i++;
        if (i >= s.length()) {
          addToSet(val, end, v2, type);
          return i;
        }
        c = s.charAt(i);
        if (c >= '0' && c <= '9') {
          ValueSet vs = getValue(v2, s, i);
          int v3 = vs.value;
          addToSet(val, end, v3, type);
          i = vs.pos;
          return i;
        } else {
          addToSet(val, end, v2, type);
          return i;
        }
      } else {
        addToSet(val, end, 1, type);
        return i;
      }
    }

    if (c == '/') {
      i++;
      c = s.charAt(i);
      int v2 = Integer.parseInt(String.valueOf(c));
      i++;
      if (i >= s.length()) {
        addToSet(val, end, v2, type);
        return i;
      }
      c = s.charAt(i);
      if (c >= '0' && c <= '9') {
        ValueSet vs = getValue(v2, s, i);
        int v3 = vs.value;
        addToSet(val, end, v3, type);
        i = vs.pos;
        return i;
      } else {
        throw new ParseException("Unexpected character '" + c + "' after '/'", i);
      }
    }

    addToSet(val, end, 0, type);
    i++;
    return i;
  }

  public String getCronExpression() {
    return cronExpression;
  }

  public String getExpressionSummary() {
    StringBuilder buf = new StringBuilder();

    buf.append("seconds: ");
    buf.append(getExpressionSetSummary(seconds));
    buf.append("\n");
    buf.append("minutes: ");
    buf.append(getExpressionSetSummary(minutes));
    buf.append("\n");
    buf.append("hours: ");
    buf.append(getExpressionSetSummary(hours));
    buf.append("\n");
    buf.append("daysOfMonth: ");
    buf.append(getExpressionSetSummary(daysOfMonth));
    buf.append("\n");
    buf.append("months: ");
    buf.append(getExpressionSetSummary(months));
    buf.append("\n");
    buf.append("daysOfWeek: ");
    buf.append(getExpressionSetSummary(daysOfWeek));
    buf.append("\n");
    buf.append("lastdayOfWeek: ");
    buf.append(lastdayOfWeek);
    buf.append("\n");
    buf.append("nearestWeekday: ");
    buf.append(nearestWeekday);
    buf.append("\n");
    buf.append("NthDayOfWeek: ");
    buf.append(nthdayOfWeek);
    buf.append("\n");
    buf.append("lastdayOfMonth: ");
    buf.append(lastdayOfMonth);
    buf.append("\n");
    buf.append("years: ");
    buf.append(getExpressionSetSummary(years));
    buf.append("\n");

    return buf.toString();
  }

  protected String getExpressionSetSummary(java.util.Set<Integer> set) {

    if (set.contains(NO_SPEC)) {
      return "?";
    }
    if (set.contains(ALL_SPEC)) {
      return "*";
    }

    StringBuilder buf = new StringBuilder();

    Iterator<Integer> itr = set.iterator();
    boolean first = true;
    while (itr.hasNext()) {
      Integer iVal = itr.next();
      String val = iVal.toString();
      if (!first) {
        buf.append(",");
      }
      buf.append(val);
      first = false;
    }

    return buf.toString();
  }

  protected String getExpressionSetSummary(java.util.ArrayList<Integer> list) {

    if (list.contains(NO_SPEC)) {
      return "?";
    }
    if (list.contains(ALL_SPEC)) {
      return "*";
    }

    StringBuilder buf = new StringBuilder();

    Iterator<Integer> itr = list.iterator();
    boolean first = true;
    while (itr.hasNext()) {
      Integer iVal = itr.next();
      String val = iVal.toString();
      if (!first) {
        buf.append(",");
      }
      buf.append(val);
      first = false;
    }

    return buf.toString();
  }

  protected int skipWhiteSpace(int i, String s) {
    for (; i < s.length() && (s.charAt(i) == ' ' || s.charAt(i) == '\t'); i++) {
      ;
    }

    return i;
  }

  protected int findNextWhiteSpace(int i, String s) {
    for (; i < s.length() && (s.charAt(i) != ' ' || s.charAt(i) != '\t'); i++) {
      ;
    }

    return i;
  }

  protected void addToSet(int val, int end, int incr, int type) throws ParseException {

    TreeSet<Integer> set = getSet(type);

    if (type == SECOND || type == MINUTE) {
      if ((val < 0 || val > 59 || end > 59) && (val != ALL_SPEC_INT)) {
        throw new ParseException("Minute and Second values must be between 0 and 59", -1);
      }
    } else if (type == HOUR) {
      if ((val < 0 || val > 23 || end > 23) && (val != ALL_SPEC_INT)) {
        throw new ParseException("Hour values must be between 0 and 23", -1);
      }
    } else if (type == DAY_OF_MONTH) {
      if ((val < 1 || val > 31 || end > 31) && (val != ALL_SPEC_INT) && (val != NO_SPEC_INT)) {
        throw new ParseException("Day of month values must be between 1 and 31", -1);
      }
    } else if (type == MONTH) {
      if ((val < 1 || val > 12 || end > 12) && (val != ALL_SPEC_INT)) {
        throw new ParseException("Month values must be between 1 and 12", -1);
      }
    } else if (type == DAY_OF_WEEK) {
      if ((val == 0 || val > 7 || end > 7) && (val != ALL_SPEC_INT) && (val != NO_SPEC_INT)) {
        throw new ParseException("Day-of-Week values must be between 1 and 7", -1);
      }
    }

    if ((incr == 0 || incr == -1) && val != ALL_SPEC_INT) {
      if (val != -1) {
        set.add(val);
      } else {
        set.add(NO_SPEC);
      }

      return;
    }

    int startAt = val;
    int stopAt = end;

    if (val == ALL_SPEC_INT && incr <= 0) {
      incr = 1;
      set.add(ALL_SPEC); // put in a marker, but also fill values
    }

    if (type == SECOND || type == MINUTE) {
      if (stopAt == -1) {
        stopAt = 59;
      }
      if (startAt == -1 || startAt == ALL_SPEC_INT) {
        startAt = 0;
      }
    } else if (type == HOUR) {
      if (stopAt == -1) {
        stopAt = 23;
      }
      if (startAt == -1 || startAt == ALL_SPEC_INT) {
        startAt = 0;
      }
    } else if (type == DAY_OF_MONTH) {
      if (stopAt == -1) {
        stopAt = 31;
      }
      if (startAt == -1 || startAt == ALL_SPEC_INT) {
        startAt = 1;
      }
    } else if (type == MONTH) {
      if (stopAt == -1) {
        stopAt = 12;
      }
      if (startAt == -1 || startAt == ALL_SPEC_INT) {
        startAt = 1;
      }
    } else if (type == DAY_OF_WEEK) {
      if (stopAt == -1) {
        stopAt = 7;
      }
      if (startAt == -1 || startAt == ALL_SPEC_INT) {
        startAt = 1;
      }
    } else if (type == YEAR) {
      if (stopAt == -1) {
        stopAt = MAX_YEAR;
      }
      if (startAt == -1 || startAt == ALL_SPEC_INT) {
        startAt = 1970;
      }
    }

    // if the end of the range is before the start, then we need to overflow into
    // the next day, month etc. This is done by adding the maximum amount for that
    // type, and using modulus max to determine the value being added.
    int max = -1;
    if (stopAt < startAt) {
      switch (type) {
        case SECOND:
          max = 60;
          break;
        case MINUTE:
          max = 60;
          break;
        case HOUR:
          max = 24;
          break;
        case MONTH:
          max = 12;
          break;
        case DAY_OF_WEEK:
          max = 7;
          break;
        case DAY_OF_MONTH:
          max = 31;
          break;
        case YEAR:
          throw new IllegalArgumentException("Start year must be less than stop year");
        default:
          throw new IllegalArgumentException("Unexpected type encountered");
      }
      stopAt += max;
    }

    for (int i = startAt; i <= stopAt; i += incr) {
      if (max == -1) {
        // ie: there's no max to overflow over
        set.add(i);
      } else {
        // take the modulus to get the real value
        int i2 = i % max;

        // 1-indexed ranges should not include 0, and should include their max
        if (i2 == 0 && (type == MONTH || type == DAY_OF_WEEK || type == DAY_OF_MONTH)) {
          i2 = max;
        }

        set.add(i2);
      }
    }
  }

  TreeSet<Integer> getSet(int type) {
    switch (type) {
      case SECOND:
        return seconds;
      case MINUTE:
        return minutes;
      case HOUR:
        return hours;
      case DAY_OF_MONTH:
        return daysOfMonth;
      case MONTH:
        return months;
      case DAY_OF_WEEK:
        return daysOfWeek;
      case YEAR:
        return years;
      default:
        return null;
    }
  }

  protected ValueSet getValue(int v, String s, int i) {
    char c = s.charAt(i);
    StringBuilder s1 = new StringBuilder(String.valueOf(v));
    while (c >= '0' && c <= '9') {
      s1.append(c);
      i++;
      if (i >= s.length()) {
        break;
      }
      c = s.charAt(i);
    }
    ValueSet val = new ValueSet();

    val.pos = (i < s.length()) ? i : i + 1;
    val.value = Integer.parseInt(s1.toString());
    return val;
  }

  protected int getNumericValue(String s, int i) {
    int endOfVal = findNextWhiteSpace(i, s);
    String val = s.substring(i, endOfVal);
    return Integer.parseInt(val);
  }

  protected int getMonthNumber(String s) {
    Integer integer = monthMap.get(s);

    if (integer == null) {
      return -1;
    }

    return integer;
  }

  protected int getDayOfWeekNumber(String s) {
    Integer integer = dayMap.get(s);

    if (integer == null) {
      return -1;
    }

    return integer;
  }

  ////////////////////////////////////////////////////////////////////////////
  //
  // Computation Functions
  //
  ////////////////////////////////////////////////////////////////////////////

  public Date getTimeAfter(Date afterTime) {

    // Computation is based on Gregorian year only.
    Calendar cl = new java.util.GregorianCalendar(getTimeZone());

    // move ahead one second, since we're computing the time *after* the
    // given time
    afterTime = new Date(afterTime.getTime() + 1000);
    // CronTrigger does not deal with milliseconds
    cl.setTime(afterTime);
    cl.set(Calendar.MILLISECOND, 0);

    boolean gotOne = false;
    // loop until we've computed the next time, or we've past the endTime
    while (!gotOne) {

      // if (endTime != null && cl.getTime().after(endTime)) return null;
      if (cl.get(Calendar.YEAR) > 2999) { // prevent endless loop...
        return null;
      }

      SortedSet<Integer> st = null;
      int t = 0;

      int sec = cl.get(Calendar.SECOND);
      int min = cl.get(Calendar.MINUTE);

      // get second.................................................
      st = seconds.tailSet(sec);
      if (st != null && st.size() != 0) {
        sec = st.first();
      } else {
        sec = seconds.first();
        min++;
        cl.set(Calendar.MINUTE, min);
      }
      cl.set(Calendar.SECOND, sec);

      min = cl.get(Calendar.MINUTE);
      int hr = cl.get(Calendar.HOUR_OF_DAY);
      t = -1;

      // get minute.................................................
      st = minutes.tailSet(min);
      if (st != null && st.size() != 0) {
        t = min;
        min = st.first();
      } else {
        min = minutes.first();
        hr++;
      }
      if (min != t) {
        cl.set(Calendar.SECOND, 0);
        cl.set(Calendar.MINUTE, min);
        setCalendarHour(cl, hr);
        continue;
      }
      cl.set(Calendar.MINUTE, min);

      hr = cl.get(Calendar.HOUR_OF_DAY);
      int day = cl.get(Calendar.DAY_OF_MONTH);
      t = -1;

      // get hour...................................................
      st = hours.tailSet(hr);
      if (st != null && st.size() != 0) {
        t = hr;
        hr = st.first();
      } else {
        hr = hours.first();
        day++;
      }
      if (hr != t) {
        cl.set(Calendar.SECOND, 0);
        cl.set(Calendar.MINUTE, 0);
        cl.set(Calendar.DAY_OF_MONTH, day);
        setCalendarHour(cl, hr);
        continue;
      }
      cl.set(Calendar.HOUR_OF_DAY, hr);

      day = cl.get(Calendar.DAY_OF_MONTH);
      int mon = cl.get(Calendar.MONTH) + 1;
      // '+ 1' because calendar is 0-based for this field, and we are
      // 1-based
      t = -1;
      int tmon = mon;

      // get day...................................................
      boolean dayOfMSpec = !daysOfMonth.contains(NO_SPEC);
      boolean dayOfWSpec = !daysOfWeek.contains(NO_SPEC);
      if (dayOfMSpec && !dayOfWSpec) { // get day by day of month rule
        st = daysOfMonth.tailSet(day);
        if (lastdayOfMonth) {
          if (!nearestWeekday) {
            t = day;
            day = getLastDayOfMonth(mon, cl.get(Calendar.YEAR));
            day -= lastdayOffset;
            if (t > day) {
              mon++;
              if (mon > 12) {
                mon = 1;
                tmon = 3333; // ensure test of mon != tmon further below fails
                cl.add(Calendar.YEAR, 1);
              }
              day = 1;
            }
          } else {
            t = day;
            day = getLastDayOfMonth(mon, cl.get(Calendar.YEAR));
            day -= lastdayOffset;

            java.util.Calendar tcal = java.util.Calendar.getInstance(getTimeZone());
            tcal.set(Calendar.SECOND, 0);
            tcal.set(Calendar.MINUTE, 0);
            tcal.set(Calendar.HOUR_OF_DAY, 0);
            tcal.set(Calendar.DAY_OF_MONTH, day);
            tcal.set(Calendar.MONTH, mon - 1);
            tcal.set(Calendar.YEAR, cl.get(Calendar.YEAR));

            int ldom = getLastDayOfMonth(mon, cl.get(Calendar.YEAR));
            int dow = tcal.get(Calendar.DAY_OF_WEEK);

            if (dow == Calendar.SATURDAY && day == 1) {
              day += 2;
            } else if (dow == Calendar.SATURDAY) {
              day -= 1;
            } else if (dow == Calendar.SUNDAY && day == ldom) {
              day -= 2;
            } else if (dow == Calendar.SUNDAY) {
              day += 1;
            }

            tcal.set(Calendar.SECOND, sec);
            tcal.set(Calendar.MINUTE, min);
            tcal.set(Calendar.HOUR_OF_DAY, hr);
            tcal.set(Calendar.DAY_OF_MONTH, day);
            tcal.set(Calendar.MONTH, mon - 1);
            Date nTime = tcal.getTime();
            if (nTime.before(afterTime)) {
              day = 1;
              mon++;
            }
          }
        } else if (nearestWeekday) {
          t = day;
          day = daysOfMonth.first();

          java.util.Calendar tcal = java.util.Calendar.getInstance(getTimeZone());
          tcal.set(Calendar.SECOND, 0);
          tcal.set(Calendar.MINUTE, 0);
          tcal.set(Calendar.HOUR_OF_DAY, 0);
          tcal.set(Calendar.DAY_OF_MONTH, day);
          tcal.set(Calendar.MONTH, mon - 1);
          tcal.set(Calendar.YEAR, cl.get(Calendar.YEAR));

          int ldom = getLastDayOfMonth(mon, cl.get(Calendar.YEAR));
          int dow = tcal.get(Calendar.DAY_OF_WEEK);

          if (dow == Calendar.SATURDAY && day == 1) {
            day += 2;
          } else if (dow == Calendar.SATURDAY) {
            day -= 1;
          } else if (dow == Calendar.SUNDAY && day == ldom) {
            day -= 2;
          } else if (dow == Calendar.SUNDAY) {
            day += 1;
          }

          tcal.set(Calendar.SECOND, sec);
          tcal.set(Calendar.MINUTE, min);
          tcal.set(Calendar.HOUR_OF_DAY, hr);
          tcal.set(Calendar.DAY_OF_MONTH, day);
          tcal.set(Calendar.MONTH, mon - 1);
          Date nTime = tcal.getTime();
          if (nTime.before(afterTime)) {
            day = daysOfMonth.first();
            mon++;
          }
        } else if (st != null && st.size() != 0) {
          t = day;
          day = st.first();
          // make sure we don't over-run a short month, such as february
          int lastDay = getLastDayOfMonth(mon, cl.get(Calendar.YEAR));
          if (day > lastDay) {
            day = daysOfMonth.first();
            mon++;
          }
        } else {
          day = daysOfMonth.first();
          mon++;
        }

        if (day != t || mon != tmon) {
          cl.set(Calendar.SECOND, 0);
          cl.set(Calendar.MINUTE, 0);
          cl.set(Calendar.HOUR_OF_DAY, 0);
          cl.set(Calendar.DAY_OF_MONTH, day);
          cl.set(Calendar.MONTH, mon - 1);
          // '- 1' because calendar is 0-based for this field, and we
          // are 1-based
          continue;
        }
      } else if (dayOfWSpec && !dayOfMSpec) { // get day by day of week rule
        if (lastdayOfWeek) { // are we looking for the last XXX day of
          // the month?
          int dow = daysOfWeek.first(); // desired
          // d-o-w
          int cDow = cl.get(Calendar.DAY_OF_WEEK); // current d-o-w
          int daysToAdd = 0;
          if (cDow < dow) {
            daysToAdd = dow - cDow;
          }
          if (cDow > dow) {
            daysToAdd = dow + (7 - cDow);
          }

          int lDay = getLastDayOfMonth(mon, cl.get(Calendar.YEAR));

          if (day + daysToAdd > lDay) { // did we already miss the
            // last one?
            cl.set(Calendar.SECOND, 0);
            cl.set(Calendar.MINUTE, 0);
            cl.set(Calendar.HOUR_OF_DAY, 0);
            cl.set(Calendar.DAY_OF_MONTH, 1);
            cl.set(Calendar.MONTH, mon);
            // no '- 1' here because we are promoting the month
            continue;
          }

          // find date of last occurrence of this day in this month...
          while ((day + daysToAdd + 7) <= lDay) {
            daysToAdd += 7;
          }

          day += daysToAdd;

          if (daysToAdd > 0) {
            cl.set(Calendar.SECOND, 0);
            cl.set(Calendar.MINUTE, 0);
            cl.set(Calendar.HOUR_OF_DAY, 0);
            cl.set(Calendar.DAY_OF_MONTH, day);
            cl.set(Calendar.MONTH, mon - 1);
            // '- 1' here because we are not promoting the month
            continue;
          }

        } else if (nthdayOfWeek != 0) {
          // are we looking for the Nth XXX day in the month?
          int dow = daysOfWeek.first(); // desired
          // d-o-w
          int cDow = cl.get(Calendar.DAY_OF_WEEK); // current d-o-w
          int daysToAdd = 0;
          if (cDow < dow) {
            daysToAdd = dow - cDow;
          } else if (cDow > dow) {
            daysToAdd = dow + (7 - cDow);
          }

          boolean dayShifted = false;
          if (daysToAdd > 0) {
            dayShifted = true;
          }

          day += daysToAdd;
          int weekOfMonth = day / 7;
          if (day % 7 > 0) {
            weekOfMonth++;
          }

          daysToAdd = (nthdayOfWeek - weekOfMonth) * 7;
          day += daysToAdd;
          if (daysToAdd < 0 || day > getLastDayOfMonth(mon, cl.get(Calendar.YEAR))) {
            cl.set(Calendar.SECOND, 0);
            cl.set(Calendar.MINUTE, 0);
            cl.set(Calendar.HOUR_OF_DAY, 0);
            cl.set(Calendar.DAY_OF_MONTH, 1);
            cl.set(Calendar.MONTH, mon);
            // no '- 1' here because we are promoting the month
            continue;
          } else if (daysToAdd > 0 || dayShifted) {
            cl.set(Calendar.SECOND, 0);
            cl.set(Calendar.MINUTE, 0);
            cl.set(Calendar.HOUR_OF_DAY, 0);
            cl.set(Calendar.DAY_OF_MONTH, day);
            cl.set(Calendar.MONTH, mon - 1);
            // '- 1' here because we are NOT promoting the month
            continue;
          }
        } else {
          int cDow = cl.get(Calendar.DAY_OF_WEEK); // current d-o-w
          int dow = daysOfWeek.first(); // desired
          // d-o-w
          st = daysOfWeek.tailSet(cDow);
          if (st != null && st.size() > 0) {
            dow = st.first();
          }

          int daysToAdd = 0;
          if (cDow < dow) {
            daysToAdd = dow - cDow;
          }
          if (cDow > dow) {
            daysToAdd = dow + (7 - cDow);
          }

          int lDay = getLastDayOfMonth(mon, cl.get(Calendar.YEAR));

          if (day + daysToAdd > lDay) { // will we pass the end of
            // the month?
            cl.set(Calendar.SECOND, 0);
            cl.set(Calendar.MINUTE, 0);
            cl.set(Calendar.HOUR_OF_DAY, 0);
            cl.set(Calendar.DAY_OF_MONTH, 1);
            cl.set(Calendar.MONTH, mon);
            // no '- 1' here because we are promoting the month
            continue;
          } else if (daysToAdd > 0) { // are we swithing days?
            cl.set(Calendar.SECOND, 0);
            cl.set(Calendar.MINUTE, 0);
            cl.set(Calendar.HOUR_OF_DAY, 0);
            cl.set(Calendar.DAY_OF_MONTH, day + daysToAdd);
            cl.set(Calendar.MONTH, mon - 1);
            // '- 1' because calendar is 0-based for this field,
            // and we are 1-based
            continue;
          }
        }
      } else { // dayOfWSpec && !dayOfMSpec
        throw new UnsupportedOperationException(
            "Support for specifying both a day-of-week AND a day-of-month parameter is not implemented.");
      }
      cl.set(Calendar.DAY_OF_MONTH, day);

      mon = cl.get(Calendar.MONTH) + 1;
      // '+ 1' because calendar is 0-based for this field, and we are
      // 1-based
      int year = cl.get(Calendar.YEAR);
      t = -1;

      // test for expressions that never generate a valid fire date,
      // but keep looping...
      if (year > MAX_YEAR) {
        return null;
      }

      // get month...................................................
      st = months.tailSet(mon);
      if (st != null && st.size() != 0) {
        t = mon;
        mon = st.first();
      } else {
        mon = months.first();
        year++;
      }
      if (mon != t) {
        cl.set(Calendar.SECOND, 0);
        cl.set(Calendar.MINUTE, 0);
        cl.set(Calendar.HOUR_OF_DAY, 0);
        cl.set(Calendar.DAY_OF_MONTH, 1);
        cl.set(Calendar.MONTH, mon - 1);
        // '- 1' because calendar is 0-based for this field, and we are
        // 1-based
        cl.set(Calendar.YEAR, year);
        continue;
      }
      cl.set(Calendar.MONTH, mon - 1);
      // '- 1' because calendar is 0-based for this field, and we are
      // 1-based

      year = cl.get(Calendar.YEAR);
      t = -1;

      // get year...................................................
      st = years.tailSet(year);
      if (st != null && st.size() != 0) {
        t = year;
        year = st.first();
      } else {
        return null; // ran out of years...
      }

      if (year != t) {
        cl.set(Calendar.SECOND, 0);
        cl.set(Calendar.MINUTE, 0);
        cl.set(Calendar.HOUR_OF_DAY, 0);
        cl.set(Calendar.DAY_OF_MONTH, 1);
        cl.set(Calendar.MONTH, 0);
        // '- 1' because calendar is 0-based for this field, and we are
        // 1-based
        cl.set(Calendar.YEAR, year);
        continue;
      }
      cl.set(Calendar.YEAR, year);

      gotOne = true;
    } // while( !done )

    return cl.getTime();
  }

  /**
   * Advance the calendar to the particular hour paying particular attention to daylight saving
   * problems.
   *
   * @param cal the calendar to operate on
   * @param hour the hour to set
   */
  protected void setCalendarHour(Calendar cal, int hour) {
    cal.set(java.util.Calendar.HOUR_OF_DAY, hour);
    if (cal.get(java.util.Calendar.HOUR_OF_DAY) != hour && hour != 24) {
      cal.set(java.util.Calendar.HOUR_OF_DAY, hour + 1);
    }
  }

  /**
   * NOT YET IMPLEMENTED: Returns the time before the given time that the <code>CronExpression
   * </code> matches.
   */
  public Date getTimeBefore(Date endTime) {
    // FUTURE_TODO: implement QUARTZ-423
    return null;
  }

  /**
   * NOT YET IMPLEMENTED: Returns the final time that the <code>CronExpression</code> will match.
   */
  public Date getFinalFireTime() {
    // FUTURE_TODO: implement QUARTZ-423
    return null;
  }

  protected boolean isLeapYear(int year) {
    return ((year % 4 == 0 && year % 100 != 0) || (year % 400 == 0));
  }

  protected int getLastDayOfMonth(int monthNum, int year) {

    switch (monthNum) {
      case 1:
        return 31;
      case 2:
        return (isLeapYear(year)) ? 29 : 28;
      case 3:
        return 31;
      case 4:
        return 30;
      case 5:
        return 31;
      case 6:
        return 30;
      case 7:
        return 31;
      case 8:
        return 31;
      case 9:
        return 30;
      case 10:
        return 31;
      case 11:
        return 30;
      case 12:
        return 31;
      default:
        throw new IllegalArgumentException("Illegal month number: " + monthNum);
    }
  }

  private void readObject(java.io.ObjectInputStream stream)
      throws java.io.IOException, ClassNotFoundException {

    stream.defaultReadObject();
    try {
      buildExpression(cronExpression);
    } catch (Exception ignore) {
    } // never happens
  }

  @Override
  @Deprecated
  public Object clone() {
    return new CronExpression(this);
  }
}

class ValueSet {
  public int value;

  public int pos;
}
