/*
    * 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
    *
    *      https://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.commons.lang3.time;
  
  import java.text.SimpleDateFormat;
  import java.util.ArrayList;
  import java.util.Calendar;
  import java.util.Date;
  import java.util.GregorianCalendar;
  import java.util.Objects;
  import java.util.TimeZone;
  import java.util.stream.Stream;
  
  import org.apache.commons.lang3.StringUtils;
  import org.apache.commons.lang3.Strings;
  import org.apache.commons.lang3.Validate;
  
  /**
   * Duration formatting utilities and constants. The following table describes the tokens
   * used in the pattern language for formatting.
   * <table border="1">
   *  <caption>Pattern Tokens</caption>
   *  <tr><th>character</th><th>duration element</th></tr>
   *  <tr><td>y</td><td>years</td></tr>
   *  <tr><td>M</td><td>months</td></tr>
   *  <tr><td>d</td><td>days</td></tr>
   *  <tr><td>H</td><td>hours</td></tr>
   *  <tr><td>m</td><td>minutes</td></tr>
   *  <tr><td>s</td><td>seconds</td></tr>
   *  <tr><td>S</td><td>milliseconds</td></tr>
   *  <tr><td>'text'</td><td>arbitrary text content</td></tr>
   * </table>
   *
   * <strong>Note: It's not currently possible to include a single-quote in a format.</strong>
   * <br>
   * Token values are printed using decimal digits.
   * A token character can be repeated to ensure that the field occupies a certain minimum
   * size. Values will be left-padded with 0 unless padding is disabled in the method invocation.
   * <br>
   * Tokens can be marked as optional by surrounding them with brackets [ ]. These tokens will
   * only be printed if the token value is non-zero. Literals within optional blocks will only be
   * printed if the preceding non-literal token is non-zero. Leading optional literals will only
   * be printed if the following non-literal is non-zero.
   * Multiple optional blocks can be used to group literals with the desired token.
   * <p>
   * Notes on Optional Tokens:<br>
   * <strong>Multiple optional tokens without literals can result in impossible to understand output.</strong><br>
   * <strong>Patterns where all tokens are optional can produce empty strings.</strong><br>
   * (See examples below)
   * </p>
   * <br>
   * <table border="1">
   * <caption>Example Output</caption>
   * <tr><th>pattern</th><th>Duration.ofDays(1)</th><th>Duration.ofHours(1)</th><th>Duration.ofMinutes(1)</th><th>Duration.ZERO</th></tr>
   * <tr><td>d'd'H'h'm'm's's'</td><td>1d0h0m0s</td><td>0d1h0m0s</td><td>0d0h1m0s</td><td>0d0h0m0s</td></tr>
   * <tr><td>d'd'[H'h'm'm']s's'</td><td>1d0s</td><td>0d1h0s</td><td>0d1m0s</td><td>0d0s</td></tr>
   * <tr><td>[d'd'H'h'm'm']s's'</td><td>1d0s</td><td>1h0s</td><td>1m0s</td><td>0s</td></tr>
   * <tr><td>[d'd'H'h'm'm's's']</td><td>1d</td><td>1h</td><td>1m</td><td></td></tr>
   * <tr><td>['{'d'}']HH':'mm</td><td>{1}00:00</td><td>01:00</td><td>00:01</td><td>00:00</td></tr>
   * <tr><td>['{'dd'}']['&lt;'HH'&gt;']['('mm')']</td><td>{01}</td><td>&lt;01&gt;</td><td>(00)</td><td></td></tr>
   * <tr><td>[dHms]</td><td>1</td><td>1</td><td>1</td><td></td></tr>
   * </table>
   * <strong>Note: Optional blocks cannot be nested.</strong>
   *
   * @since 2.1
   */
  public class DurationFormatUtils {
  
      /**
       * Element that is parsed from the format pattern.
       */
      static final class Token {
  
          /** Empty array. */
          private static final Token[] EMPTY_ARRAY = {};
  
          /**
           * Helper method to determine if a set of tokens contain a value
           *
           * @param tokens set to look in
           * @param value to look for
           * @return boolean {@code true} if contained
           */
          static boolean containsTokenWithValue(final Token[] tokens, final Object value) {
              return Stream.of(tokens).anyMatch(token -> token.getValue() == value);
         }
 
         private final CharSequence value;
         private int count;
         private int optionalIndex = -1;
 
         /**
          * Wraps a token around a value. A value would be something like a 'Y'.
          *
          * @param value value to wrap, non-null.
          * @param optional whether the token is optional
          * @param optionalIndex the index of the optional token within the pattern
          */
         Token(final CharSequence value, final boolean optional, final int optionalIndex) {
             this.value = Objects.requireNonNull(value, "value");
             this.count = 1;
             if (optional) {
                 this.optionalIndex = optionalIndex;
             }
         }
 
         /**
          * Supports equality of this Token to another Token.
          *
          * @param obj2 Object to consider equality of
          * @return boolean {@code true} if equal
          */
         @Override
         public boolean equals(final Object obj2) {
             if (obj2 instanceof Token) {
                 final Token tok2 = (Token) obj2;
                 if (this.value.getClass() != tok2.value.getClass()) {
                     return false;
                 }
                 if (this.count != tok2.count) {
                     return false;
                 }
                 if (this.value instanceof StringBuilder) {
                     return this.value.toString().equals(tok2.value.toString());
                 }
                 if (this.value instanceof Number) {
                     return this.value.equals(tok2.value);
                 }
                 return this.value == tok2.value;
             }
             return false;
         }
 
         /**
          * Gets the current number of values represented
          *
          * @return int number of values represented
          */
         int getCount() {
             return count;
         }
 
         /**
          * Gets the particular value this token represents.
          *
          * @return Object value, non-null.
          */
         Object getValue() {
             return value;
         }
 
         /**
          * Returns a hash code for the token equal to the
          * hash code for the token's value. Thus 'TT' and 'TTTT'
          * will have the same hash code.
          *
          * @return The hash code for the token
          */
         @Override
         public int hashCode() {
             return this.value.hashCode();
         }
 
         /**
          * Adds another one of the value
          */
         void increment() {
             count++;
         }
 
         /**
          * Represents this token as a String.
          *
          * @return String representation of the token
          */
         @Override
         public String toString() {
             return StringUtils.repeat(this.value.toString(), this.count);
         }
     }
 
     private static final int MINUTES_PER_HOUR = 60;
 
     private static final int SECONDS_PER_MINUTES = 60;
 
     private static final int HOURS_PER_DAY = 24;
 
     /**
      * Pattern used with {@link FastDateFormat} and {@link SimpleDateFormat}
      * for the ISO 8601 period format used in durations.
      *
      * @see org.apache.commons.lang3.time.FastDateFormat
      * @see java.text.SimpleDateFormat
      */
     public static final String ISO_EXTENDED_FORMAT_PATTERN = "'P'yyyy'Y'M'M'd'DT'H'H'm'M's.SSS'S'";
 
     static final String y = "y";
 
     static final String M = "M";
 
     static final String d = "d";
 
     static final String H = "H";
 
     static final String m = "m";
 
     static final String s = "s";
 
     static final String S = "S";
 
     /**
      * The internal method to do the formatting.
      *
      * @param tokens  the tokens
      * @param years  the number of years
      * @param months  the number of months
      * @param days  the number of days
      * @param hours  the number of hours
      * @param minutes  the number of minutes
      * @param seconds  the number of seconds
      * @param milliseconds  the number of millis
      * @param padWithZeros  whether to pad
      * @return the formatted string
      */
     static String format(final Token[] tokens, final long years, final long months, final long days, final long hours, final long minutes,
             final long seconds,
             final long milliseconds, final boolean padWithZeros) {
         final StringBuilder buffer = new StringBuilder();
         boolean lastOutputSeconds = false;
         boolean lastOutputZero = false;
         int optionalStart = -1;
         boolean firstOptionalNonLiteral = false;
         int optionalIndex = -1;
         boolean inOptional = false;
         for (final Token token : tokens) {
             final Object value = token.getValue();
             final boolean isLiteral = value instanceof StringBuilder;
             final int count = token.getCount();
             if (optionalIndex != token.optionalIndex) {
               optionalIndex = token.optionalIndex;
               if (optionalIndex > -1) {
                 //entering new optional block
                 optionalStart = buffer.length();
                 lastOutputZero = false;
                 inOptional = true;
                 firstOptionalNonLiteral = false;
               } else {
                 //leaving optional block
                 inOptional = false;
               }
             }
             if (isLiteral) {
                 if (!inOptional || !lastOutputZero) {
                     buffer.append(value.toString());
                 }
             } else if (value.equals(y)) {
                 lastOutputSeconds = false;
                 lastOutputZero = years == 0;
                 if (!inOptional || !lastOutputZero) {
                     buffer.append(paddedValue(years, padWithZeros, count));
                 }
             } else if (value.equals(M)) {
                 lastOutputSeconds = false;
                 lastOutputZero = months == 0;
                 if (!inOptional || !lastOutputZero) {
                     buffer.append(paddedValue(months, padWithZeros, count));
                 }
             } else if (value.equals(d)) {
                 lastOutputSeconds = false;
                 lastOutputZero = days == 0;
                 if (!inOptional || !lastOutputZero) {
                     buffer.append(paddedValue(days, padWithZeros, count));
                 }
             } else if (value.equals(H)) {
                 lastOutputSeconds = false;
                 lastOutputZero = hours == 0;
                 if (!inOptional || !lastOutputZero) {
                     buffer.append(paddedValue(hours, padWithZeros, count));
                 }
             } else if (value.equals(m)) {
                 lastOutputSeconds = false;
                 lastOutputZero = minutes == 0;
                 if (!inOptional || !lastOutputZero) {
                     buffer.append(paddedValue(minutes, padWithZeros, count));
                 }
             } else if (value.equals(s)) {
                 lastOutputSeconds = true;
                 lastOutputZero = seconds == 0;
                 if (!inOptional || !lastOutputZero) {
                     buffer.append(paddedValue(seconds, padWithZeros, count));
                 }
             } else if (value.equals(S)) {
                 lastOutputZero = milliseconds == 0;
                 if (!inOptional || !lastOutputZero) {
                     if (lastOutputSeconds) {
                         // ensure at least 3 digits are displayed even if padding is not selected
                         final int width = padWithZeros ? Math.max(3, count) : 3;
                         buffer.append(paddedValue(milliseconds, true, width));
                     } else {
                         buffer.append(paddedValue(milliseconds, padWithZeros, count));
                     }
                 }
                 lastOutputSeconds = false;
             }
             //as soon as we hit first nonliteral in optional, check for literal prefix
             if (inOptional && !isLiteral && !firstOptionalNonLiteral) {
                 firstOptionalNonLiteral = true;
                 if (lastOutputZero) {
                     buffer.delete(optionalStart, buffer.length());
                 }
             }
         }
         return buffer.toString();
     }
 
     /**
      * Formats the time gap as a string, using the specified format, and padding with zeros.
      *
      * <p>This method formats durations using the days and lower fields of the
      * format pattern. Months and larger are not used.</p>
      *
      * @param durationMillis  the duration to format
      * @param format  the way in which to format the duration, not null
      * @return the formatted duration, not null
      * @throws IllegalArgumentException if durationMillis is negative
      */
     public static String formatDuration(final long durationMillis, final String format) {
         return formatDuration(durationMillis, format, true);
     }
 
     /**
      * Formats the time gap as a string, using the specified format.
      * Padding the left-hand side side of numbers with zeroes is optional.
      *
      * <p>This method formats durations using the days and lower fields of the
      * format pattern. Months and larger are not used.</p>
      *
      * @param durationMillis  the duration to format
      * @param format  the way in which to format the duration, not null
      * @param padWithZeros  whether to pad the left-hand side side of numbers with 0's
      * @return the formatted duration, not null
      * @throws IllegalArgumentException if durationMillis is negative
      */
     public static String formatDuration(final long durationMillis, final String format, final boolean padWithZeros) {
         Validate.inclusiveBetween(0, Long.MAX_VALUE, durationMillis, "durationMillis must not be negative");
 
         final Token[] tokens = lexx(format);
 
         long days = 0;
         long hours = 0;
         long minutes = 0;
         long seconds = 0;
         long milliseconds = durationMillis;
 
         if (Token.containsTokenWithValue(tokens, d)) {
             days = milliseconds / DateUtils.MILLIS_PER_DAY;
             milliseconds -= days * DateUtils.MILLIS_PER_DAY;
         }
         if (Token.containsTokenWithValue(tokens, H)) {
             hours = milliseconds / DateUtils.MILLIS_PER_HOUR;
             milliseconds -= hours * DateUtils.MILLIS_PER_HOUR;
         }
         if (Token.containsTokenWithValue(tokens, m)) {
             minutes = milliseconds / DateUtils.MILLIS_PER_MINUTE;
             milliseconds -= minutes * DateUtils.MILLIS_PER_MINUTE;
         }
         if (Token.containsTokenWithValue(tokens, s)) {
             seconds = milliseconds / DateUtils.MILLIS_PER_SECOND;
             milliseconds -= seconds * DateUtils.MILLIS_PER_SECOND;
         }
 
         return format(tokens, 0, 0, days, hours, minutes, seconds, milliseconds, padWithZeros);
     }
 
     /**
      * Formats the time gap as a string.
      *
      * <p>The format used is ISO 8601-like: {@code HH:mm:ss.SSS}.</p>
      *
      * @param durationMillis  the duration to format
      * @return the formatted duration, not null
      * @throws IllegalArgumentException if durationMillis is negative
      */
     public static String formatDurationHMS(final long durationMillis) {
         return formatDuration(durationMillis, "HH:mm:ss.SSS");
     }
 
     /**
      * Formats the time gap as a string.
      *
      * <p>The format used is the ISO 8601 period format.</p>
      *
      * <p>This method formats durations using the days and lower fields of the
      * ISO format pattern, such as P7D6TH5M4.321S.</p>
      *
      * @param durationMillis  the duration to format
      * @return the formatted duration, not null
      * @throws IllegalArgumentException if durationMillis is negative
      */
     public static String formatDurationISO(final long durationMillis) {
         return formatDuration(durationMillis, ISO_EXTENDED_FORMAT_PATTERN, false);
     }
 
     /**
      * Formats an elapsed time into a pluralization correct string.
      *
      * <p>This method formats durations using the days and lower fields of the
      * format pattern. Months and larger are not used.</p>
      *
      * @param durationMillis  the elapsed time to report in milliseconds
      * @param suppressLeadingZeroElements  suppresses leading 0 elements
      * @param suppressTrailingZeroElements  suppresses trailing 0 elements
      * @return the formatted text in days/hours/minutes/seconds, not null
      * @throws IllegalArgumentException if durationMillis is negative
      */
     public static String formatDurationWords(
         final long durationMillis,
         final boolean suppressLeadingZeroElements,
         final boolean suppressTrailingZeroElements) {
 
         // This method is generally replaceable by the format method, but
         // there are a series of tweaks and special cases that require
         // trickery to replicate.
         String duration = formatDuration(durationMillis, "d' days 'H' hours 'm' minutes 's' seconds'");
         if (suppressLeadingZeroElements) {
             // this is a temporary marker on the front. Like ^ in regexp.
             duration = " " + duration;
             final String text = duration;
             String tmp = Strings.CS.replaceOnce(text, " 0 days", StringUtils.EMPTY);
             if (tmp.length() != duration.length()) {
                 duration = tmp;
                 final String text1 = duration;
                 tmp = Strings.CS.replaceOnce(text1, " 0 hours", StringUtils.EMPTY);
                 if (tmp.length() != duration.length()) {
                     duration = tmp;
                     final String text2 = duration;
                     tmp = Strings.CS.replaceOnce(text2, " 0 minutes", StringUtils.EMPTY);
                     duration = tmp;
                 }
             }
             if (!duration.isEmpty()) {
                 // strip the space off again
                 duration = duration.substring(1);
             }
         }
         if (suppressTrailingZeroElements) {
             final String text = duration;
             String tmp = Strings.CS.replaceOnce(text, " 0 seconds", StringUtils.EMPTY);
             if (tmp.length() != duration.length()) {
                 duration = tmp;
                 final String text1 = duration;
                 tmp = Strings.CS.replaceOnce(text1, " 0 minutes", StringUtils.EMPTY);
                 if (tmp.length() != duration.length()) {
                     duration = tmp;
                     final String text2 = duration;
                     tmp = Strings.CS.replaceOnce(text2, " 0 hours", StringUtils.EMPTY);
                     if (tmp.length() != duration.length()) {
                         final String text3 = tmp;
                         duration = Strings.CS.replaceOnce(text3, " 0 days", StringUtils.EMPTY);
                     }
                 }
             }
         }
         // handle plurals
         duration = " " + duration;
         final String text = duration;
         duration = Strings.CS.replaceOnce(text, " 1 seconds", " 1 second");
         final String text1 = duration;
         duration = Strings.CS.replaceOnce(text1, " 1 minutes", " 1 minute");
         final String text2 = duration;
         duration = Strings.CS.replaceOnce(text2, " 1 hours", " 1 hour");
         final String text3 = duration;
         duration = Strings.CS.replaceOnce(text3, " 1 days", " 1 day");
         return duration.trim();
     }
 
     /**
      * Formats the time gap as a string, using the specified format.
      * Padding the left-hand side side of numbers with zeroes is optional.
      *
      * @param startMillis  the start of the duration
      * @param endMillis  the end of the duration
      * @param format  the way in which to format the duration, not null
      * @return the formatted duration, not null
      * @throws IllegalArgumentException if startMillis is greater than endMillis
      */
     public static String formatPeriod(final long startMillis, final long endMillis, final String format) {
         return formatPeriod(startMillis, endMillis, format, true, TimeZone.getDefault());
     }
 
     /**
      * <p>Formats the time gap as a string, using the specified format.
      * Padding the left-hand side side of numbers with zeroes is optional and
      * the time zone may be specified.
      *
      * <p>When calculating the difference between months/days, it chooses to
      * calculate months first. So when working out the number of months and
      * days between January 15th and March 10th, it choose 1 month and
      * 23 days gained by choosing January-&gt;February = 1 month and then
      * calculating days forwards, and not the 1 month and 26 days gained by
      * choosing March -&gt; February = 1 month and then calculating days
      * backwards.</p>
      *
      * <p>For more control, the <a href="https://www.joda.org/joda-time/">Joda-Time</a>
      * library is recommended.</p>
      *
      * @param startMillis  the start of the duration
      * @param endMillis  the end of the duration
      * @param format  the way in which to format the duration, not null
      * @param padWithZeros  whether to pad the left-hand side side of numbers with 0's
      * @param timezone  the millis are defined in
      * @return the formatted duration, not null
      * @throws IllegalArgumentException if startMillis is greater than endMillis
      */
     public static String formatPeriod(final long startMillis, final long endMillis, final String format, final boolean padWithZeros,
             final TimeZone timezone) {
         Validate.isTrue(startMillis <= endMillis, "startMillis must not be greater than endMillis");
 
         // Used to optimize for differences under 28 days and
         // called formatDuration(millis, format); however this did not work
         // over leap years.
         // TODO: Compare performance to see if anything was lost by
         // losing this optimization.
 
         final Token[] tokens = lexx(format);
 
         // time zones get funky around 0, so normalizing everything to GMT
         // stops the hours being off
         final Calendar start = Calendar.getInstance(timezone);
         start.setTime(new Date(startMillis));
         final Calendar end = Calendar.getInstance(timezone);
         end.setTime(new Date(endMillis));
 
         // initial estimates
         long milliseconds = end.get(Calendar.MILLISECOND) - start.get(Calendar.MILLISECOND);
         int seconds = end.get(Calendar.SECOND) - start.get(Calendar.SECOND);
         int minutes = end.get(Calendar.MINUTE) - start.get(Calendar.MINUTE);
         int hours = end.get(Calendar.HOUR_OF_DAY) - start.get(Calendar.HOUR_OF_DAY);
         int days = end.get(Calendar.DAY_OF_MONTH) - start.get(Calendar.DAY_OF_MONTH);
         int months = end.get(Calendar.MONTH) - start.get(Calendar.MONTH);
         int years = end.get(Calendar.YEAR) - start.get(Calendar.YEAR);
 
         // each initial estimate is adjusted in case it is under 0
         while (milliseconds < 0) {
             milliseconds += DateUtils.MILLIS_PER_SECOND;
             seconds -= 1;
         }
         while (seconds < 0) {
             seconds += SECONDS_PER_MINUTES;
             minutes -= 1;
         }
         while (minutes < 0) {
             minutes += MINUTES_PER_HOUR;
             hours -= 1;
         }
         while (hours < 0) {
             hours += HOURS_PER_DAY;
             days -= 1;
         }
 
         if (Token.containsTokenWithValue(tokens, M)) {
             while (days < 0) {
                 days += start.getActualMaximum(Calendar.DAY_OF_MONTH);
                 months -= 1;
                 start.add(Calendar.MONTH, 1);
             }
 
             while (months < 0) {
                 months += 12;
                 years -= 1;
             }
 
             if (!Token.containsTokenWithValue(tokens, y) && years != 0) {
                 while (years != 0) {
                     months += 12 * years;
                     years = 0;
                 }
             }
         } else {
             // there are no M's in the format string
 
             if (!Token.containsTokenWithValue(tokens, y)) {
                 int target = end.get(Calendar.YEAR);
                 if (months < 0) {
                     // target is end-year -1
                     target -= 1;
                 }
 
                 while (start.get(Calendar.YEAR) != target) {
                     days += start.getActualMaximum(Calendar.DAY_OF_YEAR) - start.get(Calendar.DAY_OF_YEAR);
 
                     // Not sure I grok why this is needed, but the brutal tests show it is
                     if (start instanceof GregorianCalendar &&
                             start.get(Calendar.MONTH) == Calendar.FEBRUARY &&
                             start.get(Calendar.DAY_OF_MONTH) == 29) {
                         days += 1;
                     }
 
                     start.add(Calendar.YEAR, 1);
 
                     days += start.get(Calendar.DAY_OF_YEAR);
                 }
 
                 years = 0;
             }
 
             while (start.get(Calendar.MONTH) != end.get(Calendar.MONTH)) {
                 days += start.getActualMaximum(Calendar.DAY_OF_MONTH);
                 start.add(Calendar.MONTH, 1);
             }
 
             months = 0;
 
             while (days < 0) {
                 days += start.getActualMaximum(Calendar.DAY_OF_MONTH);
                 months -= 1;
                 start.add(Calendar.MONTH, 1);
             }
 
         }
 
         // The rest of this code adds in values that
         // aren't requested. This allows the user to ask for the
         // number of months and get the real count and not just 0->11.
 
         if (!Token.containsTokenWithValue(tokens, d)) {
             hours += HOURS_PER_DAY * days;
             days = 0;
         }
         if (!Token.containsTokenWithValue(tokens, H)) {
             minutes += MINUTES_PER_HOUR * hours;
             hours = 0;
         }
         if (!Token.containsTokenWithValue(tokens, m)) {
             seconds += SECONDS_PER_MINUTES * minutes;
             minutes = 0;
         }
         if (!Token.containsTokenWithValue(tokens, s)) {
             milliseconds += DateUtils.MILLIS_PER_SECOND * seconds;
             seconds = 0;
         }
 
         return format(tokens, years, months, days, hours, minutes, seconds, milliseconds, padWithZeros);
     }
 
     /**
      * Formats the time gap as a string.
      *
      * <p>The format used is the ISO 8601 period format.</p>
      *
      * @param startMillis  the start of the duration to format
      * @param endMillis  the end of the duration to format
      * @return the formatted duration, not null
      * @throws IllegalArgumentException if startMillis is greater than endMillis
      */
     public static String formatPeriodISO(final long startMillis, final long endMillis) {
         return formatPeriod(startMillis, endMillis, ISO_EXTENDED_FORMAT_PATTERN, false, TimeZone.getDefault());
     }
 
     /**
      * Parses a classic date format string into Tokens
      *
      * @param format  the format to parse, not null
      * @return array of Token[]
      */
     static Token[] lexx(final String format) {
         final ArrayList<Token> list = new ArrayList<>(format.length());
 
         boolean inLiteral = false;
         // Although the buffer is stored in a Token, the Tokens are only
         // used internally, so cannot be accessed by other threads
         StringBuilder buffer = null;
         Token previous = null;
         boolean inOptional = false;
         int optionalIndex = -1;
         for (int i = 0; i < format.length(); i++) {
             final char ch = format.charAt(i);
             if (inLiteral && ch != '\'') {
                 buffer.append(ch); // buffer can't be null if inLiteral is true
                 continue;
             }
             String value = null;
             switch (ch) {
             // TODO: Need to handle escaping of '
             case '[':
                 if (inOptional) {
                     throw new IllegalArgumentException("Nested optional block at index: " + i);
                 }
                 optionalIndex++;
                 inOptional = true;
                 break;
             case ']':
                 if (!inOptional) {
                     throw new IllegalArgumentException("Attempting to close unopened optional block at index: " + i);
                 }
                 inOptional = false;
                 break;
             case '\'':
                 if (inLiteral) {
                     buffer = null;
                     inLiteral = false;
                 } else {
                     buffer = new StringBuilder();
                     list.add(new Token(buffer, inOptional, optionalIndex));
                     inLiteral = true;
                 }
                 break;
             case 'y':
                 value = y;
                 break;
             case 'M':
                 value = M;
                 break;
             case 'd':
                 value = d;
                 break;
             case 'H':
                 value = H;
                 break;
             case 'm':
                 value = m;
                 break;
             case 's':
                 value = s;
                 break;
             case 'S':
                 value = S;
                 break;
             default:
                 if (buffer == null) {
                     buffer = new StringBuilder();
                     list.add(new Token(buffer, inOptional, optionalIndex));
                 }
                 buffer.append(ch);
             }
 
             if (value != null) {
                 if (previous != null && previous.getValue().equals(value)) {
                     previous.increment();
                 } else {
                     final Token token = new Token(value, inOptional, optionalIndex);
                     list.add(token);
                     previous = token;
                 }
                 buffer = null;
             }
         }
         if (inLiteral) { // i.e. we have not found the end of the literal
             throw new IllegalArgumentException("Unmatched quote in format: " + format);
         }
         if (inOptional) { // i.e. we have not found the end of the literal
             throw new IllegalArgumentException("Unmatched optional in format: " + format);
         }
         return list.toArray(Token.EMPTY_ARRAY);
     }
 
     /**
      * Converts a {@code long} to a {@link String} with optional
      * zero padding.
      *
      * @param value the value to convert
      * @param padWithZeros whether to pad with zeroes
      * @param count the size to pad to (ignored if {@code padWithZeros} is false)
      * @return the string result
      */
     private static String paddedValue(final long value, final boolean padWithZeros, final int count) {
         final String longString = Long.toString(value);
         return padWithZeros ? StringUtils.leftPad(longString, count, '0') : longString;
     }
 
     /**
      * DurationFormatUtils instances should NOT be constructed in standard programming.
      *
      * <p>This constructor is public to permit tools that require a JavaBean instance
      * to operate.</p>
      *
      * @deprecated TODO Make private in 4.0.
      */
     @Deprecated
     public DurationFormatUtils() {
         // empty
     }
 
 }