/*
 * 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 com.njzscloud.common.sichen.support;

import java.text.ParseException;
import java.util.*;
/**
 * 提供类 Unix 风格 Cron 表达式的解析器和求值器。Cron 表达式能够指定复杂的时间组合，
 * 例如“每周一至周五的上午 8:00”或“每月最后一个周五的凌晨 1:30”。
 *
 * <P>
 * Cron 表达式由 6 个必填字段和 1 个可选字段组成，字段之间通过空格分隔。各字段的详细说明如下：
 *
 * <table cellspacing="8">
 * <tr>
 * <th align="left">字段名称</th>
 * <th align="left">&nbsp;</th>
 * <th align="left">允许值</th>
 * <th align="left">&nbsp;</th>
 * <th align="left">允许的特殊字符</th>
 * </tr>
 * <tr>
 * <td align="left"><code>秒（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>分（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>时（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>日（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>月（Month）</code></td>
 * <td align="left">&nbsp;</th>
 * <td align="left"><code>0-11 或 JAN-DEC（一月至十二月）</code></td>
 * <td align="left">&nbsp;</th>
 * <td align="left"><code>, - * /</code></td>
 * </tr>
 * <tr>
 * <td align="left"><code>周（Day-of-Week）</code></td>
 * <td align="left">&nbsp;</th>
 * <td align="left"><code>1-7 或 SUN-SAT（周日至周六）</code></td>
 * <td align="left">&nbsp;</th>
 * <td align="left"><code>, - * ? / L #</code></td>
 * </tr>
 * <tr>
 * <td align="left"><code>年（Year，可选）</code></td>
 * <td align="left">&nbsp;</th>
 * <td align="left"><code>空值、1970-2199</code></td>
 * <td align="left">&nbsp;</th>
 * <td align="left"><code>, - * /</code></td>
 * </tr>
 * </table>
 * <P>
 * '*' 字符用于指定“所有可能的值”。例如，在“分钟”字段中使用 "*" 表示“每分钟”。
 * <P>
 * '?' 字符仅允许在“日（Day-of-month）”和“周（Day-of-Week）”字段中使用，
 * 用于表示“不指定具体值”。当你需要在这两个字段中的一个指定条件，而另一个无需指定时，该字符非常有用。
 * <P>
 * '-' 字符用于指定时间范围。例如，在“小时”字段中使用 "10-12" 表示“上午 10 点、11 点和中午 12 点”。
 * <P>
 * ',' 字符用于指定多个额外的取值。例如，在“周”字段中使用 "MON,WED,FRI" 表示“周一、周三和周五”。
 * <P>
 * '/' 字符用于指定递增步长。例如，在“秒”字段中使用 "0/15" 表示“第 0 秒、15 秒、30 秒和 45 秒”；
 * 而 "5/15" 在“秒”字段中表示“第 5 秒、20 秒、35 秒和 50 秒”。在 '/' 前指定 '*' 等价于以 0 作为起始值。
 * 本质上，表达式的每个字段都对应一组可启用或禁用的数字集合：秒和分的范围是 0-59，小时是 0-23，
 * 日是 1-31，月是 0-11（对应 JAN 至 DEC）。'/' 字符的作用是在指定集合中启用“每隔 n 个”的取值。
 * 需要注意一个细节：在“月”字段中使用 "7/6" 仅会启用“7 月”，并不表示“每 6 个月”。
 * <P>
 * 'L' 字符仅允许在“日（Day-of-month）”和“周（Day-of-Week）”字段中使用，是“last（最后一个）”的缩写，
 * 但在两个字段中的含义有所不同。例如，在“日”字段中使用 "L" 表示“当月的最后一天”——1 月对应 31 日，
 * 非闰年的 2 月对应 28 日。若在“周”字段中单独使用 "L"，仅表示“7”或“SAT（周六）”；
 * 若在其他值后使用，则表示“当月最后一个指定星期几”，例如 "6L" 表示“当月最后一个周五”。
 * 你也可以指定相对于月末的偏移量，例如 "L-3" 表示“当月的倒数第三天”。
 * <i>注意：使用 'L' 选项时，请勿同时指定多个取值（列表）或范围，否则会得到混乱或不符合预期的结果。</i>
 * <P>
 * 'W' 字符仅允许在“日（Day-of-month）”字段中使用，用于指定“距离给定日期最近的工作日（周一至周五）”。
 * 例如，若在“日”字段中指定 "15W"，含义是“当月 15 日附近最近的工作日”：如果 15 日是周六，
 * 则触发时间为 14 日（周五）；如果 15 日是周日，则触发时间为 16 日（周一）；如果 15 日是周二，
 * 则触发时间为 15 日（周二）本身。若指定 "1W" 且 1 日是周六，触发时间会是 3 日（周一），
 * 因为该字符不会“跨越”月份的边界。'W' 字符仅能在“日”字段指定单个日期时使用，
 * 不能用于日期范围或多个日期列表。
 * <P>
 * 'L' 和 'W' 字符可在“日（Day-of-month）”字段中组合使用，形成 "LW"，含义是“当月的最后一个工作日”。
 * <P>
 * '#' 字符仅允许在“周（Day-of-Week）”字段中使用，用于指定“当月第 n 个星期几”。
 * 例如，在“周”字段中使用 "6#3" 表示“当月第三个周五”（6 对应周五，"#3" 对应第三个）。
 * 其他示例："2#1" 表示“当月第一个周一”，"4#5" 表示“当月第五个周三”。
 * 注意：若指定了 "#5" 但当月不存在对应的第 5 个星期几，则该月不会触发任务。
 * 此外，使用 '#' 字符时，“周”字段中只能包含一个表达式（例如 "3#1,6#3" 是无效的，因为它包含两个表达式）。
 * <P>
 * <!--'C' 字符仅允许在“日（Day-of-month）”和“周（Day-of-Week）”字段中使用，是“calendar（日历）”的缩写。
 * 这意味着取值会根据关联的日历（若有）进行计算；若未关联日历，则等价于使用全包含日历。
 * 在“日”字段中使用 "5C" 表示“日历中包含的、5 日或 5 日之后的第一天”；
 * 在“周”字段中使用 "1C" 表示“日历中包含的、周日或周日之后的第一天”。-->
 * <P>
 * 所有合法字符以及月份、星期几的名称均不区分大小写。
 *
 * <p>
 * <b>注意事项：</b>
 * <ul>
 * <li> 同时指定“日（Day-of-month）”和“周（Day-of-Week）”字段的功能尚未完善，
 * 你需要在其中一个字段中使用 '?' 字符。</li>
 * <li> 支持“溢出范围”（即范围左侧的数字大于右侧）：例如，你可以使用 22-2 表示“晚上 10 点至次日凌晨 2 点”，
 * 或使用 NOV-FEB 表示“11 月至次年 2 月”。但需要特别注意，过度使用溢出范围会产生无意义的时间范围，
 * 且 CronExpression 不会对这些无效范围进行特殊判断和处理（例如表达式 "0 0 14-6 ? * FRI-MON" 就是一个无意义的溢出范围示例）。</li>
 * </ul>
 * </p>
 *
 * @author 沙拉达·詹布拉、詹姆斯·豪斯
 * @author 贡献者：麦兹·亨德森
 * @author 重构者：艾伦·克雷文（将功能从 CronTrigger 重构为 CronExpression）
 * <p>
 * 源自 Quartz 框架 v2.3.1 版本
 */
public final class CronExpression {

    public static final int MAX_YEAR = Calendar.getInstance().get(Calendar.YEAR) + 100;
    private static final int SECOND = 0;
    private static final int MINUTE = 1;
    private static final int HOUR = 2;
    private static final int DAY_OF_MONTH = 3;
    private static final int MONTH = 4;
    private static final int DAY_OF_WEEK = 5;
    private static final int YEAR = 6;
    private static final int ALL_SPEC_INT = 99; // '*'
    private static final int NO_SPEC_INT = 98; // '?'
    private static final Integer ALL_SPEC = ALL_SPEC_INT;
    private static final Integer NO_SPEC = NO_SPEC_INT;

    private static final Map<String, Integer> monthMap = new HashMap<String, Integer>(20);
    private 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 TreeSet<Integer> seconds;
    private TreeSet<Integer> minutes;
    private TreeSet<Integer> hours;
    private TreeSet<Integer> daysOfMonth;
    private TreeSet<Integer> months;
    private TreeSet<Integer> daysOfWeek;
    private TreeSet<Integer> years;

    private boolean lastdayOfWeek = false;
    private int nthdayOfWeek = 0;
    private boolean lastdayOfMonth = false;
    private boolean nearestWeekday = false;
    private int lastdayOffset = 0;
    private boolean expressionParsed = false;
    private TimeZone timeZone = null;

    /**
     * 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 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 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);
    }

    /**
     * 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;
    }


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

    /// /////////////////////////////////////////////////////////////////////////

    private void buildExpression(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;

            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 + ")", 0);
        }
    }

    private 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 specified 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 specified 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++;
                }
                checkIncrementRange(incr, type, 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;
    }

    private void checkIncrementRange(int incr, int type, int idxPos) throws ParseException {
        if (incr > 59 && (type == SECOND || type == MINUTE)) {
            throw new ParseException("Increment > 60 : " + incr, idxPos);
        } else if (incr > 23 && (type == HOUR)) {
            throw new ParseException("Increment > 24 : " + incr, idxPos);
        } else if (incr > 31 && (type == DAY_OF_MONTH)) {
            throw new ParseException("Increment > 31 : " + incr, idxPos);
        } else if (incr > 7 && (type == DAY_OF_WEEK)) {
            throw new ParseException("Increment > 7 : " + incr, idxPos);
        } else if (incr > 12 && (type == MONTH)) {
            throw new ParseException("Increment > 12 : " + incr, idxPos);
        }
    }

    private 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 == '/') {
            if ((i + 1) >= s.length() || s.charAt(i + 1) == ' ' || s.charAt(i + 1) == '\t') {
                throw new ParseException("'/' must be followed by an integer.", i);
            }

            i++;
            c = s.charAt(i);
            int v2 = Integer.parseInt(String.valueOf(c));
            i++;
            if (i >= s.length()) {
                checkIncrementRange(v2, type, i);
                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;
                checkIncrementRange(v3, type, i);
                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() {

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

        return buf;
    }

    private 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();
    }

    private 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();
    }

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

        return i;
    }

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

        return i;
    }

    private 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;
        }
    }

    private 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;
    }

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

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

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

        return integer;
    }

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

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

        return integer;
    }

    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;

                        Calendar tcal = 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();

                    Calendar tcal = 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 = daysToAdd > 0;

                    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
     */
    private void setCalendarHour(Calendar cal, int hour) {
        cal.set(Calendar.HOUR_OF_DAY, hour);
        if (cal.get(Calendar.HOUR_OF_DAY) != hour && hour != 24) {
            cal.set(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;
    }

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

    private 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;
}
