/*
 * 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.logging.log4j.core.util;

/*
 * This file originated from the Quartz scheduler with no change in licensing.
 * Copyright Terracotta, Inc.
 */

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:
 * <p/>
 * <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>0-11 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 0 to 11 (JAN to DEC). 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/>
 * <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>
 * <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". </li>
 * </ul>
 * </p>
 */
public final class CronExpression {

    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<>(20);
    protected static final Map<String, Integer> dayMap = new HashMap<>(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;
    public static final Calendar MIN_CAL = Calendar.getInstance();
    static {
        MIN_CAL.set(1970, 0, 1);
    }
    public static final Date MIN_DATE = MIN_CAL.getTime();

    /**
     * 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(final String cronExpression) throws ParseException {
        if (cronExpression == null) {
            throw new IllegalArgumentException("cronExpression cannot be null");
        }

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

        buildExpression(this.cronExpression);
    }

    /**
     * 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(final Date date) {
        final Calendar testDateCal = Calendar.getInstance(getTimeZone());
        testDateCal.setTime(date);
        testDateCal.set(Calendar.MILLISECOND, 0);
        final Date originalDate = testDateCal.getTime();

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

        final 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(final 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(final Date date) {
        long difference = 1000;

        //move back to the nearest second so differences will be accurate
        final 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(final 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(final String cronExpression) {

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

        return true;
    }

    public static void validateExpression(final String cronExpression) throws ParseException {

        new CronExpression(cronExpression);
    }


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

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

        try {

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

            int exprOn = SECOND;

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

            while (exprsTok.hasMoreTokens() && exprOn <= YEAR) {
                final 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);
                }

                final StringTokenizer vTok = new StringTokenizer(expr, ",");
                while (vTok.hasMoreTokens()) {
                    final 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);
            }

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

            // Copying the logic from the UnsupportedOperationException below
            final boolean dayOfMSpec = !dom.contains(NO_SPEC);
            final 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 (final ParseException pe) {
            throw pe;
        } catch (final Exception e) {
            throw new ParseException("Illegal cron expression format ("
                    + e.toString() + ")", 0);
        }
    }

    protected int storeExpressionVals(final int pos, final String s, final 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);
                    switch (c) {
                    case '-':
                        i += 4;
                        sub = s.substring(i, i + 3);
                        eval = getDayOfWeekNumber(sub);
                        if (eval < 0) {
                            throw new ParseException(
                                    "Invalid Day-of-Week value: '" + sub
                                            + "'", i);
                        }
                        break;
                    case '#':
                        try {
                            i += 4;
                            nthdayOfWeek = Integer.parseInt(s.substring(i));
                            if (nthdayOfWeek < 1 || nthdayOfWeek > 5) {
                                throw new Exception();
                            }
                        } catch (final Exception e) {
                            throw new ParseException(
                                    "A numeric value between 1 and 5 must follow the '#' option",
                                    i);
                        }
                        break;
                    case 'L':
                        lastdayOfWeek = true;
                        i++;
                        break;
                    default:
                        break;
                    }
                }

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

        switch (c) {
        case '?':
            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) {
                final 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;
        case '*':
        case '/':
            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;
        case '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 == '-') {
                    final 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;
        default:
            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') {
                        final 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);
            }
            break;
        }

        return i;
    }

    protected int checkNext(final int pos, final String s, final int val, final 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);
            }
            final 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);
            }
            final TreeSet<Integer> set = getSet(type);
            set.add(val);
            i++;
            return i;
        }

        switch (c) {
        case '#':
            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 (final Exception e) {
                throw new ParseException(
                        "A numeric value between 1 and 5 must follow the '#' option",
                        i);
            }
            final TreeSet<Integer> set = getSet(type);
            set.add(val);
            i++;
            return i;
        case '-':
            i++;
            c = s.charAt(i);
            final 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') {
                final 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);
                final 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') {
                    final ValueSet vs = getValue(v2, s, i);
                    final int v3 = vs.value;
                    addToSet(val, end, v3, type);
                    i = vs.pos;
                } else {
                    addToSet(val, end, v2, type);
                }
                return i;
            } else {
                addToSet(val, end, 1, type);
                return i;
            }
        case '/':
            i++;
            c = s.charAt(i);
            final 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') {
                final ValueSet vs = getValue(v2, s, i);
                final int v3 = vs.value;
                addToSet(val, end, v3, type);
                i = vs.pos;
                return i;
            } else {
                throw new ParseException("Unexpected character '" + c + "' after '/'", i);
            }
        default:
            break;
        }

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

    public String getCronExpression() {
        return cronExpression;
    }

    public String getExpressionSummary() {
        final 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(final java.util.Set<Integer> set) {

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

        final StringBuilder buf = new StringBuilder();

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

        return buf.toString();
    }

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

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

        final StringBuilder buf = new StringBuilder();

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

        return buf.toString();
    }

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

        return i;
    }

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

        return i;
    }

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

        final TreeSet<Integer> set = getSet(type);

        switch (type) {
        case SECOND:
        case 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);
            }
            break;
        case HOUR:
            if ((val < 0 || val > 23 || end > 23) && (val != ALL_SPEC_INT)) {
                throw new ParseException(
                        "Hour values must be between 0 and 23", -1);
            }
            break;
        case 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);
            }
            break;
        case MONTH:
            if ((val < 1 || val > 12 || end > 12) && (val != ALL_SPEC_INT)) {
                throw new ParseException(
                        "Month values must be between 1 and 12", -1);
            }
            break;
        case 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);
            }
            break;
        default:
            break;
        }

        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
        }

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

        // 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(final 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(final int v, final String s, int i) {
        char c = s.charAt(i);
        final 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);
        }
        final ValueSet val = new ValueSet();

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

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

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

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

        return integer;
    }

    protected int getDayOfWeekNumber(final String s) {
        final 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.
        final 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;
            }

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

            // get second.................................................
            SortedSet<Integer> 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);
            int 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...................................................
            final boolean dayOfMSpec = !daysOfMonth.contains(NO_SPEC);
            final 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;

                        final 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));

                        final int ldom = getLastDayOfMonth(mon, cl.get(Calendar.YEAR));
                        final 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);
                        final Date nTime = tcal.getTime();
                        if (nTime.before(afterTime)) {
                            day = 1;
                            mon++;
                        }
                    }
                } else if (nearestWeekday) {
                    t = day;
                    day = daysOfMonth.first();

                    final 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));

                    final int ldom = getLastDayOfMonth(mon, cl.get(Calendar.YEAR));
                    final 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);
                    final 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
                    final 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?
                    final int dow = daysOfWeek.first(); // desired
                    // d-o-w
                    final 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);
                    }

                    final 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?
                    final int dow = daysOfWeek.first(); // desired
                    // d-o-w
                    final 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 {
                    final 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);
                    }

                    final 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 switching 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(final Calendar cal, final 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);
        }
    }

    protected Date getTimeBefore(final Date targetDate) {
        final Calendar cl = Calendar.getInstance(getTimeZone());

        // CronTrigger does not deal with milliseconds, so truncate target
        cl.setTime(targetDate);
        cl.set(Calendar.MILLISECOND, 0);
        final Date targetDateNoMs = cl.getTime();

        // to match this
        Date start = targetDateNoMs;
        final long minIncrement = findMinIncrement();
        Date prevFireTime;
        do {
            final Date prevCheckDate = new Date(start.getTime() - minIncrement);
            prevFireTime = getTimeAfter(prevCheckDate);
            if (prevFireTime == null || prevFireTime.before(MIN_DATE)) {
                return null;
            }
            start = prevCheckDate;
        } while (prevFireTime.compareTo(targetDateNoMs) >= 0);
        return prevFireTime;
    }

    public Date getPrevFireTime(final Date targetDate) {
        return getTimeBefore(targetDate);
    }

    private long findMinIncrement() {
        if (seconds.size() != 1) {
            return minInSet(seconds) * 1000;
        } else if (seconds.first() == ALL_SPEC_INT) {
            return 1000;
        }
        if (minutes.size() != 1) {
            return minInSet(minutes) * 60000;
        } else if (minutes.first() == ALL_SPEC_INT) {
            return 60000;
        }
        if (hours.size() != 1) {
            return minInSet(hours) * 3600000;
        } else if (hours.first() == ALL_SPEC_INT) {
            return 3600000;
        }
        return 86400000;
    }

    private int minInSet(final TreeSet<Integer> set) {
        int previous = 0;
        int min = Integer.MAX_VALUE;
        boolean first = true;
        for (final int value : set) {
            if (first) {
                previous = value;
                first = false;
                continue;
            } else {
                final int diff = value - previous;
                if (diff < min) {
                    min = diff;
                }
            }
        }
        return min;
    }

    /**
     * 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(final int year) {
        return ((year % 4 == 0 && year % 100 != 0) || (year % 400 == 0));
    }

    protected int getLastDayOfMonth(final int monthNum, final 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 class ValueSet {
        public int value;

        public int pos;
    }


}
