/*
    * 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.io.IOException;
  import java.io.ObjectInputStream;
  import java.io.Serializable;
  import java.text.DateFormat;
  import java.text.DateFormatSymbols;
  import java.text.FieldPosition;
  import java.text.SimpleDateFormat;
  import java.util.ArrayList;
  import java.util.Calendar;
  import java.util.Date;
  import java.util.List;
  import java.util.Locale;
  import java.util.TimeZone;
  import java.util.concurrent.ConcurrentHashMap;
  import java.util.concurrent.ConcurrentMap;
  
  import org.apache.commons.lang3.CharUtils;
  import org.apache.commons.lang3.ClassUtils;
  import org.apache.commons.lang3.LocaleUtils;
  import org.apache.commons.lang3.exception.ExceptionUtils;
  
  /**
   * FastDatePrinter is a fast and thread-safe version of
   * {@link java.text.SimpleDateFormat}.
   *
   * <p>
   * To obtain a FastDatePrinter, use {@link FastDateFormat#getInstance(String, TimeZone, Locale)}
   * or another variation of the factory methods of {@link FastDateFormat}.
   * </p>
   *
   * <p>
   * Since FastDatePrinter is thread safe, you can use a static member instance:
   * </p>
   * {@code
   *     private static final DatePrinter DATE_PRINTER = FastDateFormat.getInstance("yyyy-MM-dd");
   * }
   *
   * <p>
   * This class can be used as a direct replacement to
   * {@link SimpleDateFormat} in most formatting situations.
   * This class is especially useful in multi-threaded server environments.
   * {@link SimpleDateFormat} is not thread-safe in any JDK version,
   * nor will it be as Sun have closed the bug/RFE.
   * </p>
   *
   * <p>
   * Only formatting is supported by this class, but all patterns are compatible with
   * SimpleDateFormat (except time zones and some year patterns - see below).
   * </p>
   *
   * <p>
   * Java 1.4 introduced a new pattern letter, {@code 'Z'}, to represent
   * time zones in RFC822 format (for example, {@code +0800} or {@code -1100}).
   * This pattern letter can be used here (on all JDK versions).
   * </p>
   *
   * <p>
   * In addition, the pattern {@code 'ZZ'} has been made to represent
   * ISO 8601 extended format time zones (for example, {@code +08:00} or {@code -11:00}).
   * This introduces a minor incompatibility with Java 1.4, but at a gain of
   * useful functionality.
   * </p>
   *
   * <p>
   * Starting with JDK7, ISO 8601 support was added using the pattern {@code 'X'}.
   * To maintain compatibility, {@code 'ZZ'} will continue to be supported, but using
   * one of the {@code 'X'} formats is recommended.
   *
   * <p>
   * Javadoc cites for the year pattern: <i>For formatting, if the number of
   * pattern letters is 2, the year is truncated to 2 digits; otherwise it is
   * interpreted as a number.</i> Starting with Java 1.7 a pattern of 'Y' or
   * 'YYY' will be formatted as '2003', while it was '03' in former Java
   * versions. FastDatePrinter implements the behavior of Java 7.
   * </p>
   *
   * @since 3.2
   * @see FastDateParser
   */
  public class FastDatePrinter implements DatePrinter, Serializable {
      // A lot of the speed in this class comes from caching, but some comes
     // from the special int to StringBuffer conversion.
     //
     // The following produces a padded 2-digit number:
     //   buffer.append((char)(value / 10 + '0'));
     //   buffer.append((char)(value % 10 + '0'));
     //
     // Note that the fastest append to StringBuffer is a single char (used here).
     // Note that Integer.toString() is not called, the conversion is simply
     // taking the value and adding (mathematically) the ASCII value for '0'.
     // So, don't change this code! It works and is very fast.
 
     /**
      * Inner class to output a constant single character.
      */
     private static final class CharacterLiteral implements Rule {
         private final char value;
 
         /**
          * Constructs a new instance of {@link CharacterLiteral}
          * to hold the specified value.
          *
          * @param value The character literal
          */
         CharacterLiteral(final char value) {
             this.value = value;
         }
 
         /**
          * {@inheritDoc}
          */
         @Override
         public void appendTo(final Appendable buffer, final Calendar calendar) throws IOException {
             buffer.append(value);
         }
 
         /**
          * {@inheritDoc}
          */
         @Override
         public int estimateLength() {
             return 1;
         }
     }
 
     /**
      * Inner class to output the numeric day in week.
      */
     private static final class DayInWeekField implements NumberRule {
         private final NumberRule rule;
 
         DayInWeekField(final NumberRule rule) {
             this.rule = rule;
         }
 
         @Override
         public void appendTo(final Appendable buffer, final Calendar calendar) throws IOException {
             final int value = calendar.get(Calendar.DAY_OF_WEEK);
             rule.appendTo(buffer, value == Calendar.SUNDAY ? 7 : value - 1);
         }
 
         @Override
         public void appendTo(final Appendable buffer, final int value) throws IOException {
             rule.appendTo(buffer, value);
         }
 
         @Override
         public int estimateLength() {
             return rule.estimateLength();
         }
     }
 
     /**
      * Inner class to output a time zone as a number {@code +/-HHMM}
      * or {@code +/-HH:MM}.
      */
     private static final class Iso8601_Rule implements Rule {
 
         // Sign TwoDigitHours or Z
         static final Iso8601_Rule ISO8601_HOURS = new Iso8601_Rule(3);
         // Sign TwoDigitHours Minutes or Z
         static final Iso8601_Rule ISO8601_HOURS_MINUTES = new Iso8601_Rule(5);
         // Sign TwoDigitHours : Minutes or Z
         static final Iso8601_Rule ISO8601_HOURS_COLON_MINUTES = new Iso8601_Rule(6);
 
         /**
          * Gets the ISO 8601 formatting rule.
          *
          * @param tokenLen A token indicating the length of the TimeZone String to be formatted.
          * @return An Iso8601_Rule that can format TimeZone String of length {@code tokenLen}. If no such
          *          rule exists, an IllegalArgumentException will be thrown.
          */
         static Iso8601_Rule getRule(final int tokenLen) {
             switch (tokenLen) {
             case 1:
                 return ISO8601_HOURS;
             case 2:
                 return ISO8601_HOURS_MINUTES;
             case 3:
                 return ISO8601_HOURS_COLON_MINUTES;
             default:
                 throw new IllegalArgumentException("invalid number of X");
             }
         }
 
         private final int length;
 
         /**
          * Constructs an instance of {@code Iso8601_Rule} with the specified properties.
          *
          * @param length The number of characters in output (unless Z is output).
          */
         Iso8601_Rule(final int length) {
             this.length = length;
         }
 
         /**
          * {@inheritDoc}
          */
         @Override
         public void appendTo(final Appendable buffer, final Calendar calendar) throws IOException {
             int offset = calendar.get(Calendar.ZONE_OFFSET) + calendar.get(Calendar.DST_OFFSET);
             if (offset == 0) {
                 buffer.append("Z");
                 return;
             }
 
             if (offset < 0) {
                 buffer.append('-');
                 offset = -offset;
             } else {
                 buffer.append('+');
             }
 
             final int hours = offset / (60 * 60 * 1000);
             appendDigits(buffer, hours);
 
             if (length < 5) {
                 return;
             }
 
             if (length == 6) {
                 buffer.append(':');
             }
 
             final int minutes = offset / (60 * 1000) - 60 * hours;
             appendDigits(buffer, minutes);
         }
 
         /**
          * {@inheritDoc}
          */
         @Override
         public int estimateLength() {
             return length;
         }
     }
 
     /**
      * Inner class defining a numeric rule.
      */
     private interface NumberRule extends Rule {
 
         /**
          * Appends the specified value to the output buffer based on the rule implementation.
          *
          * @param buffer The output buffer.
          * @param value The value to be appended.
          * @throws IOException Thrown if an I/O error occurs.
          */
         void appendTo(Appendable buffer, int value) throws IOException;
     }
 
     /**
      * Inner class to output a padded number.
      */
     private static final class PaddedNumberField implements NumberRule {
         // Note: This is final to avoid Spotbugs CT_CONSTRUCTOR_THROW
         private final int field;
         private final int size;
 
         /**
          * Constructs an instance of {@link PaddedNumberField}.
          *
          * @param field The field.
          * @param size size of the output field.
          */
         PaddedNumberField(final int field, final int size) {
             if (size < 3) {
                 // Should use UnpaddedNumberField or TwoDigitNumberField.
                 throw new IllegalArgumentException();
             }
             this.field = field;
             this.size = size;
         }
 
         /**
          * {@inheritDoc}
          */
         @Override
         public void appendTo(final Appendable buffer, final Calendar calendar) throws IOException {
             appendTo(buffer, calendar.get(field));
         }
 
         /**
          * {@inheritDoc}
          */
         @Override
         public /* final */ void appendTo(final Appendable buffer, final int value) throws IOException {
             // Checkstyle complains about redundant qualifier
             appendFullDigits(buffer, value, size);
         }
 
         /**
          * {@inheritDoc}
          */
         @Override
         public int estimateLength() {
             return size;
         }
     }
 
     /**
      * Inner class defining a rule.
      */
     private interface Rule {
 
         /**
          * Appends the value of the specified calendar to the output buffer based on the rule implementation.
          *
          * @param buf The output buffer.
          * @param calendar calendar to be appended.
          * @throws IOException Thrown if an I/O error occurs.
          */
         void appendTo(Appendable buf, Calendar calendar) throws IOException;
 
         /**
          * Returns the estimated length of the result.
          *
          * @return The estimated length of the result.
          */
         int estimateLength();
     }
 
     /**
      * Inner class to output a constant string.
      */
     private static final class StringLiteral implements Rule {
         private final String value;
 
         /**
          * Constructs a new instance of {@link StringLiteral}
          * to hold the specified value.
          *
          * @param value The string literal.
          */
         StringLiteral(final String value) {
             this.value = value;
         }
 
         /**
          * {@inheritDoc}
          */
         @Override
         public void appendTo(final Appendable buffer, final Calendar calendar) throws IOException {
             buffer.append(value);
         }
 
         /**
          * {@inheritDoc}
          */
         @Override
         public int estimateLength() {
             return value.length();
         }
     }
 
     /**
      * Inner class to output one of a set of values.
      */
     private static final class TextField implements Rule {
         private final int field;
         private final String[] values;
 
         /**
          * Constructs an instance of {@link TextField}
          * with the specified field and values.
          *
          * @param field The field.
          * @param values The field values.
          */
         TextField(final int field, final String[] values) {
             this.field = field;
             this.values = values;
         }
 
         /**
          * {@inheritDoc}
          */
         @Override
         public void appendTo(final Appendable buffer, final Calendar calendar) throws IOException {
             buffer.append(values[calendar.get(field)]);
         }
 
         /**
          * {@inheritDoc}
          */
         @Override
         public int estimateLength() {
             int max = 0;
             for (int i = values.length; --i >= 0;) {
                 final int len = values[i].length();
                 if (len > max) {
                     max = len;
                 }
             }
             return max;
         }
     }
 
     /**
      * Inner class that acts as a compound key for time zone names.
      */
     private static final class TimeZoneDisplayKey {
         private final TimeZone timeZone;
         private final int style;
         private final Locale locale;
 
         /**
          * Constructs an instance of {@link TimeZoneDisplayKey} with the specified properties.
          *
          * @param timeZone The time zone.
          * @param daylight adjust the style for daylight saving time if {@code true}.
          * @param style The time zone style.
          * @param locale The time zone locale.
          */
         TimeZoneDisplayKey(final TimeZone timeZone,
                            final boolean daylight, final int style, final Locale locale) {
             this.timeZone = timeZone;
             if (daylight) {
                 this.style = style | 0x80000000;
             } else {
                 this.style = style;
             }
             this.locale = LocaleUtils.toLocale(locale);
         }
 
         /**
          * {@inheritDoc}
          */
         @Override
         public boolean equals(final Object obj) {
             if (this == obj) {
                 return true;
             }
             if (obj instanceof TimeZoneDisplayKey) {
                 final TimeZoneDisplayKey other = (TimeZoneDisplayKey) obj;
                 return
                     timeZone.equals(other.timeZone) &&
                     style == other.style &&
                     locale.equals(other.locale);
             }
             return false;
         }
 
         /**
          * {@inheritDoc}
          */
         @Override
         public int hashCode() {
             return (style * 31 + locale.hashCode()) * 31 + timeZone.hashCode();
         }
     }
 
     /**
      * Inner class to output a time zone name.
      */
     private static final class TimeZoneNameRule implements Rule {
         private final Locale locale;
         private final int style;
         private final String standard;
         private final String daylight;
 
         /**
          * Constructs an instance of {@link TimeZoneNameRule} with the specified properties.
          *
          * @param timeZone The time zone.
          * @param locale The locale.
          * @param style The style.
          */
         TimeZoneNameRule(final TimeZone timeZone, final Locale locale, final int style) {
             this.locale = LocaleUtils.toLocale(locale);
             this.style = style;
             this.standard = getTimeZoneDisplay(timeZone, false, style, locale);
             this.daylight = getTimeZoneDisplay(timeZone, true, style, locale);
         }
 
         /**
          * {@inheritDoc}
          */
         @Override
         public void appendTo(final Appendable buffer, final Calendar calendar) throws IOException {
             final TimeZone zone = calendar.getTimeZone();
             final boolean daylight = calendar.get(Calendar.DST_OFFSET) != 0;
             buffer.append(getTimeZoneDisplay(zone, daylight, style, locale));
         }
 
         /**
          * {@inheritDoc}
          */
         @Override
         public int estimateLength() {
             // We have no access to the Calendar object that will be passed to
             // appendTo so base estimate on the TimeZone passed to the
             // constructor
             return Math.max(standard.length(), daylight.length());
         }
     }
 
     /**
      * Inner class to output a time zone as a number {@code +/-HHMM}
      * or {@code +/-HH:MM}.
      */
     private static final class TimeZoneNumberRule implements Rule {
         static final TimeZoneNumberRule INSTANCE_COLON = new TimeZoneNumberRule(true);
         static final TimeZoneNumberRule INSTANCE_NO_COLON = new TimeZoneNumberRule(false);
 
         private final boolean colon;
 
         /**
          * Constructs an instance of {@link TimeZoneNumberRule} with the specified properties.
          *
          * @param colon add colon between HH and MM in the output if {@code true}.
          */
         TimeZoneNumberRule(final boolean colon) {
             this.colon = colon;
         }
 
         /**
          * {@inheritDoc}
          */
         @Override
         public void appendTo(final Appendable buffer, final Calendar calendar) throws IOException {
 
             int offset = calendar.get(Calendar.ZONE_OFFSET) + calendar.get(Calendar.DST_OFFSET);
 
             if (offset < 0) {
                 buffer.append('-');
                 offset = -offset;
             } else {
                 buffer.append('+');
             }
 
             final int hours = offset / (60 * 60 * 1000);
             appendDigits(buffer, hours);
 
             if (colon) {
                 buffer.append(':');
             }
 
             final int minutes = offset / (60 * 1000) - 60 * hours;
             appendDigits(buffer, minutes);
         }
 
         /**
          * {@inheritDoc}
          */
         @Override
         public int estimateLength() {
             return 5;
         }
     }
 
     /**
      * Inner class to output the twelve hour field.
      */
     private static final class TwelveHourField implements NumberRule {
         private final NumberRule rule;
 
         /**
          * Constructs an instance of {@link TwelveHourField} with the specified
          * {@link NumberRule}.
          *
          * @param rule The rule.
          */
         TwelveHourField(final NumberRule rule) {
             this.rule = rule;
         }
 
         /**
          * {@inheritDoc}
          */
         @Override
         public void appendTo(final Appendable buffer, final Calendar calendar) throws IOException {
             int value = calendar.get(Calendar.HOUR);
             if (value == 0) {
                 value = calendar.getLeastMaximum(Calendar.HOUR) + 1;
             }
             rule.appendTo(buffer, value);
         }
 
         /**
          * {@inheritDoc}
          */
         @Override
         public void appendTo(final Appendable buffer, final int value) throws IOException {
             rule.appendTo(buffer, value);
         }
 
         /**
          * {@inheritDoc}
          */
         @Override
         public int estimateLength() {
             return rule.estimateLength();
         }
     }
 
     /**
      * Inner class to output the twenty four hour field.
      */
     private static final class TwentyFourHourField implements NumberRule {
         private final NumberRule rule;
 
         /**
          * Constructs an instance of {@link TwentyFourHourField} with the specified
          * {@link NumberRule}.
          *
          * @param rule The rule.
          */
         TwentyFourHourField(final NumberRule rule) {
             this.rule = rule;
         }
 
         /**
          * {@inheritDoc}
          */
         @Override
         public void appendTo(final Appendable buffer, final Calendar calendar) throws IOException {
             int value = calendar.get(Calendar.HOUR_OF_DAY);
             if (value == 0) {
                 value = calendar.getMaximum(Calendar.HOUR_OF_DAY) + 1;
             }
             rule.appendTo(buffer, value);
         }
 
         /**
          * {@inheritDoc}
          */
         @Override
         public void appendTo(final Appendable buffer, final int value) throws IOException {
             rule.appendTo(buffer, value);
         }
 
         /**
          * {@inheritDoc}
          */
         @Override
         public int estimateLength() {
             return rule.estimateLength();
         }
     }
 
     /**
      * Inner class to output a two digit month.
      */
     private static final class TwoDigitMonthField implements NumberRule {
         static final TwoDigitMonthField INSTANCE = new TwoDigitMonthField();
 
         /**
          * Constructs an instance of {@link TwoDigitMonthField}.
          */
         TwoDigitMonthField() {
         }
 
         /**
          * {@inheritDoc}
          */
         @Override
         public void appendTo(final Appendable buffer, final Calendar calendar) throws IOException {
             appendTo(buffer, calendar.get(Calendar.MONTH) + 1);
         }
 
         /**
          * {@inheritDoc}
          */
         @Override
         public void appendTo(final Appendable buffer, final int value) throws IOException {
             appendDigits(buffer, value);
         }
 
         /**
          * {@inheritDoc}
          */
         @Override
         public int estimateLength() {
             return 2;
         }
     }
 
     /**
      * Inner class to output a two digit number.
      */
     private static final class TwoDigitNumberField implements NumberRule {
         private final int field;
 
         /**
          * Constructs an instance of {@link TwoDigitNumberField} with the specified field.
          *
          * @param field The field
          */
         TwoDigitNumberField(final int field) {
             this.field = field;
         }
 
         /**
          * {@inheritDoc}
          */
         @Override
         public void appendTo(final Appendable buffer, final Calendar calendar) throws IOException {
             appendTo(buffer, calendar.get(field));
         }
 
         /**
          * {@inheritDoc}
          */
         @Override
         public void appendTo(final Appendable buffer, final int value) throws IOException {
             if (value < 100) {
                 appendDigits(buffer, value);
             } else {
                 appendFullDigits(buffer, value, 2);
             }
         }
 
         /**
          * {@inheritDoc}
          */
         @Override
         public int estimateLength() {
             return 2;
         }
     }
 
     /**
      * Inner class to output a two digit year.
      */
     private static final class TwoDigitYearField implements NumberRule {
         static final TwoDigitYearField INSTANCE = new TwoDigitYearField();
 
         /**
          * Constructs an instance of {@link TwoDigitYearField}.
          */
         TwoDigitYearField() {
         }
 
         /**
          * {@inheritDoc}
          */
         @Override
         public void appendTo(final Appendable buffer, final Calendar calendar) throws IOException {
             appendTo(buffer, calendar.get(Calendar.YEAR) % 100);
         }
 
         /**
          * {@inheritDoc}
          */
         @Override
         public void appendTo(final Appendable buffer, final int value) throws IOException {
             appendDigits(buffer, value % 100);
         }
 
         /**
          * {@inheritDoc}
          */
         @Override
         public int estimateLength() {
             return 2;
         }
     }
 
     /**
      * Inner class to output an unpadded month.
      */
     private static final class UnpaddedMonthField implements NumberRule {
         static final UnpaddedMonthField INSTANCE = new UnpaddedMonthField();
 
         /**
          * Constructs an instance of {@link UnpaddedMonthField}.
          */
         UnpaddedMonthField() {
         }
 
         /**
          * {@inheritDoc}
          */
         @Override
         public void appendTo(final Appendable buffer, final Calendar calendar) throws IOException {
             appendTo(buffer, calendar.get(Calendar.MONTH) + 1);
         }
 
         /**
          * {@inheritDoc}
          */
         @Override
         public void appendTo(final Appendable buffer, final int value) throws IOException {
             if (value < 10) {
                 buffer.append((char) (value + '0'));
             } else {
                 appendDigits(buffer, value);
             }
         }
 
         /**
          * {@inheritDoc}
          */
         @Override
         public int estimateLength() {
             return 2;
         }
     }
 
     /**
      * Inner class to output an unpadded number.
      */
     private static final class UnpaddedNumberField implements NumberRule {
         private final int field;
 
         /**
          * Constructs an instance of {@link UnpaddedNumberField} with the specified field.
          *
          * @param field The field.
          */
         UnpaddedNumberField(final int field) {
             this.field = field;
         }
 
         /**
          * {@inheritDoc}
          */
         @Override
         public void appendTo(final Appendable buffer, final Calendar calendar) throws IOException {
             appendTo(buffer, calendar.get(field));
         }
 
         /**
          * {@inheritDoc}
          */
         @Override
         public void appendTo(final Appendable buffer, final int value) throws IOException {
             if (value < 10) {
                 buffer.append((char) (value + '0'));
             } else if (value < 100) {
                 appendDigits(buffer, value);
             } else {
                appendFullDigits(buffer, value, 1);
             }
         }
 
         /**
          * {@inheritDoc}
          */
         @Override
         public int estimateLength() {
             return 4;
         }
     }
 
     /**
      * Inner class to output the numeric day in week.
      */
     private static final class WeekYear implements NumberRule {
         private final NumberRule rule;
 
         WeekYear(final NumberRule rule) {
             this.rule = rule;
         }
 
         @Override
         public void appendTo(final Appendable buffer, final Calendar calendar) throws IOException {
             // Some Calendar implementations (JapaneseImperialCalendar) do not support week-dates.
             // Fall back to Calendar.YEAR in that case.
             appendTo(buffer, calendar.isWeekDateSupported() ? calendar.getWeekYear() : calendar.get(Calendar.YEAR));
         }
 
         @Override
         public void appendTo(final Appendable buffer, int value) throws IOException {
             // A week year is proleptic, so a BC date gives a negative value the digit rules cannot render.
             if (value < 0) {
                 buffer.append('-');
                 value = -value;
             }
             rule.appendTo(buffer, value);
         }
 
         @Override
         public int estimateLength() {
             return rule.estimateLength();
         }
     }
 
     /** Empty array. */
     private static final Rule[] EMPTY_RULE_ARRAY = {};
 
     /**
      * Required for serialization support.
      *
      * @see java.io.Serializable
      */
     private static final long serialVersionUID = 1L;
 
     /**
      * FULL locale dependent date or time style.
      */
     public static final int FULL = DateFormat.FULL;
 
     /**
      * LONG locale dependent date or time style.
      */
     public static final int LONG = DateFormat.LONG;
 
     /**
      * MEDIUM locale dependent date or time style.
      */
     public static final int MEDIUM = DateFormat.MEDIUM;
 
     /**
      * SHORT locale dependent date or time style.
      */
     public static final int SHORT = DateFormat.SHORT;
 
     private static final int MAX_DIGITS = 10; // log10(Integer.MAX_VALUE) ~= 9.3
 
     private static final ConcurrentMap<TimeZoneDisplayKey, String> timeZoneDisplayCache = new ConcurrentHashMap<>(7);
 
     /**
      * Appends two digits to the given buffer.
      *
      * @param buffer The buffer to append to.
      * @param value The value to append digits from.
      * @throws IOException Thrown if an I/O error occurs.
      */
     private static void appendDigits(final Appendable buffer, final int value) throws IOException {
         buffer.append((char) (value / 10 + '0'));
         buffer.append((char) (value % 10 + '0'));
     }
 
     /**
      * Appends all digits to the given buffer.
      *
      * @param buffer The buffer to append to.
      * @param value The value to append digits from.
      * @param minFieldWidth Minimum field width.
      * @throws IOException Thrown if an I/O error occurs.
      */
     private static void appendFullDigits(final Appendable buffer, int value, int minFieldWidth) throws IOException {
         // specialized paths for 1 to 4 digits -> avoid the memory allocation from the temporary work array
         // see LANG-1248
         if (value < 10000) {
             // less memory allocation path works for four digits or less
 
             int nDigits = 4;
             if (value < 1000) {
                 --nDigits;
                 if (value < 100) {
                     --nDigits;
                     if (value < 10) {
                         --nDigits;
                     }
                 }
             }
             // left zero pad
             for (int i = minFieldWidth - nDigits; i > 0; --i) {
                 buffer.append('0');
             }
 
             switch (nDigits) {
             case 4:
                 buffer.append((char) (value / 1000 + '0'));
                 value %= 1000;
                 // falls-through
             case 3:
                 if (value >= 100) {
                     buffer.append((char) (value / 100 + '0'));
                     value %= 100;
                 } else {
                     buffer.append('0');
                 }
                 // falls-through
             case 2:
                 if (value >= 10) {
                     buffer.append((char) (value / 10 + '0'));
                     value %= 10;
                 } else {
                     buffer.append('0');
                 }
                 // falls-through
             case 1:
                 buffer.append((char) (value + '0'));
             }
         } else {
             // more memory allocation path works for any digits
 
             // build up decimal representation in reverse
             final char[] work = new char[MAX_DIGITS];
             int digit = 0;
             while (value != 0) {
                 work[digit++] = (char) (value % 10 + '0');
                 value /= 10;
             }
 
             // pad with zeros
             while (digit < minFieldWidth) {
                 buffer.append('0');
                 --minFieldWidth;
             }
 
             // reverse
             while (--digit >= 0) {
                 buffer.append(work[digit]);
             }
         }
     }
 
     static void clear() {
         timeZoneDisplayCache.clear();
     }
 
     /**
      * Gets the time zone display name, using a cache for performance.
      *
      * @param tz  The zone to query.
      * @param daylight  true if daylight savings.
      * @param style  The style to use {@link TimeZone#LONG} or {@link TimeZone#SHORT}.
      * @param locale  The locale to use.
      * @return The textual name of the time zone.
      */
     static String getTimeZoneDisplay(final TimeZone tz, final boolean daylight, final int style, final Locale locale) {
         final TimeZoneDisplayKey key = new TimeZoneDisplayKey(tz, daylight, style, locale);
         // Bound the cache: it is static and process-lifetime, and custom time zone IDs give the
         // key unbounded cardinality, which would otherwise pin memory forever.
         if (timeZoneDisplayCache.size() >= AbstractFormatCache.MAX_CACHE_SIZE && !timeZoneDisplayCache.containsKey(key)) {
             timeZoneDisplayCache.clear();
         }
         // This is a very slow call, so cache the results.
         return timeZoneDisplayCache.computeIfAbsent(key, k -> tz.getDisplayName(daylight, style, locale));
     }
 
     /**
      * The pattern.
      */
     private final String pattern;
 
     /**
      * The time zone.
      */
     private final TimeZone timeZone;
 
     /**
      * The locale.
      */
     private final Locale locale;
 
     /**
      * The parsed rules.
      */
     private transient Rule[] rules;
 
     /**
      * The estimated maximum length.
      */
     private transient int maxLengthEstimate;
 
     /**
      * Constructs a new FastDatePrinter.
      * Use {@link FastDateFormat#getInstance(String, TimeZone, Locale)}  or another variation of the
      * factory methods of {@link FastDateFormat} to get a cached FastDatePrinter instance.
      *
      * @param pattern  {@link java.text.SimpleDateFormat} compatible pattern.
      * @param timeZone  non-null time zone to use.
      * @param locale  non-null locale to use.
      * @throws NullPointerException Thrown if pattern, timeZone, or locale is null.
      */
     protected FastDatePrinter(final String pattern, final TimeZone timeZone, final Locale locale) {
         this.pattern = pattern;
         // TimeZone is mutable and instances are shared through the FastDateFormat cache.
         this.timeZone = (TimeZone) timeZone.clone();
         this.locale = LocaleUtils.toLocale(locale);
         init();
     }
 
     /**
      * Performs the formatting by applying the rules to the
      * specified calendar.
      *
      * @param calendar  The calendar to format.
      * @param buf  The buffer to format into.
      * @param <B> The Appendable class type, usually StringBuilder or StringBuffer.
      * @return The specified string buffer.
      */
     private <B extends Appendable> B applyRules(final Calendar calendar, final B buf) {
         try {
             for (final Rule rule : rules) {
                 rule.appendTo(buf, calendar);
             }
         } catch (final IOException ioe) {
             ExceptionUtils.asRuntimeException(ioe);
         }
         return buf;
     }
 
     /**
      * Performs the formatting by applying the rules to the
      * specified calendar.
      *
      * @param calendar The calendar to format.
      * @param buf The buffer to format into.
      * @return The specified string buffer.
      * @deprecated Use {@link #format(Calendar)} or {@link #format(Calendar, Appendable)}
      */
     @Deprecated
     protected StringBuffer applyRules(final Calendar calendar, final StringBuffer buf) {
         return (StringBuffer) applyRules(calendar, (Appendable) buf);
     }
 
     /**
      * Creates a String representation of the given Calendar by applying the rules of this printer to it.
      *
      * @param c The Calendar to apply the rules to.
      * @return A String representation of the given Calendar.
      */
     private String applyRulesToString(final Calendar c) {
         return applyRules(c, new StringBuilder(maxLengthEstimate)).toString();
     }
 
     /**
      * Compares two objects for equality.
      *
      * @param obj  The object to compare to.
      * @return {@code true} if equal.
      */
     @Override
     public boolean equals(final Object obj) {
         if (!(obj instanceof FastDatePrinter)) {
             return false;
         }
         final FastDatePrinter other = (FastDatePrinter) obj;
         return pattern.equals(other.pattern)
             && timeZone.equals(other.timeZone)
             && locale.equals(other.locale);
     }
 
     /* (non-Javadoc)
      * @see org.apache.commons.lang3.time.DatePrinter#format(java.util.Calendar)
      */
     @Override
     public String format(final Calendar calendar) {
         return format(calendar, new StringBuilder(maxLengthEstimate)).toString();
     }
 
     /* (non-Javadoc)
      * @see org.apache.commons.lang3.time.DatePrinter#format(java.util.Calendar, Appendable)
      */
     @Override
     public <B extends Appendable> B format(final Calendar calendar, final B buf) {
         // Don't edit the given Calendar, clone it only if needed.
         Calendar actual = calendar;
         if (!calendar.getTimeZone().equals(timeZone)) {
             actual = (Calendar) calendar.clone();
             actual.setTimeZone(timeZone);
         }
         return applyRules(actual, buf);
     }
 
     /* (non-Javadoc)
      * @see org.apache.commons.lang3.time.DatePrinter#format(java.util.Calendar, StringBuffer)
      */
     @Override
     public StringBuffer format(final Calendar calendar, final StringBuffer buf) {
         // do not pass in calendar directly, this will cause TimeZone of FastDatePrinter to be ignored
         return format(calendar.getTime(), buf);
     }
 
     /* (non-Javadoc)
      * @see org.apache.commons.lang3.time.DatePrinter#format(java.util.Date)
      */
     @Override
     public String format(final Date date) {
         final Calendar c = newCalendar();
         c.setTime(date);
         return applyRulesToString(c);
     }
 
     /* (non-Javadoc)
      * @see org.apache.commons.lang3.time.DatePrinter#format(java.util.Date, Appendable)
      */
     @Override
     public <B extends Appendable> B format(final Date date, final B buf) {
         final Calendar c = newCalendar();
         c.setTime(date);
         return applyRules(c, buf);
     }
 
     /* (non-Javadoc)
      * @see org.apache.commons.lang3.time.DatePrinter#format(java.util.Date, StringBuffer)
      */
     @Override
     public StringBuffer format(final Date date, final StringBuffer buf) {
         final Calendar c = newCalendar();
         c.setTime(date);
         return (StringBuffer) applyRules(c, (Appendable) buf);
     }
 
     /* (non-Javadoc)
      * @see org.apache.commons.lang3.time.DatePrinter#format(long)
      */
     @Override
     public String format(final long millis) {
         final Calendar c = newCalendar();
         c.setTimeInMillis(millis);
         return applyRulesToString(c);
     }
 
     /* (non-Javadoc)
      * @see org.apache.commons.lang3.time.DatePrinter#format(long, Appendable)
      */
     @Override
     public <B extends Appendable> B format(final long millis, final B buf) {
         final Calendar c = newCalendar();
         c.setTimeInMillis(millis);
         return applyRules(c, buf);
     }
 
     /* (non-Javadoc)
      * @see org.apache.commons.lang3.time.DatePrinter#format(long, StringBuffer)
      */
     @Override
     public StringBuffer format(final long millis, final StringBuffer buf) {
         final Calendar c = newCalendar();
         c.setTimeInMillis(millis);
         return (StringBuffer) applyRules(c, (Appendable) buf);
     }
 
     /**
      * Formats a {@link Date}, {@link Calendar} or
      * {@link Long} (milliseconds) object.
      *
      * @param obj  The object to format.
      * @return The formatted value.
      * @since 3.5
      */
     String format(final Object obj) {
         if (obj instanceof Date) {
             return format((Date) obj);
         }
         if (obj instanceof Calendar) {
             return format((Calendar) obj);
         }
         if (obj instanceof Long) {
             return format(((Long) obj).longValue());
         }
         throw new IllegalArgumentException("Unknown class: " + ClassUtils.getName(obj, "<null>"));
     }
 
     /**
      * Formats a {@link Date}, {@link Calendar} or
      * {@link Long} (milliseconds) object.
      *
      * @param obj  The object to format.
      * @param toAppendTo  The buffer to append to.
      * @param pos  The position; ignored.
      * @return The buffer passed in.
      * @deprecated Use {{@link #format(Date)}, {{@link #format(Calendar)}, {{@link #format(long)}.
      */
     @Deprecated
     @Override
     public StringBuffer format(final Object obj, final StringBuffer toAppendTo, final FieldPosition pos) {
         if (obj instanceof Date) {
             return format((Date) obj, toAppendTo);
         }
         if (obj instanceof Calendar) {
             return format((Calendar) obj, toAppendTo);
         }
         if (obj instanceof Long) {
             return format(((Long) obj).longValue(), toAppendTo);
         }
         throw new IllegalArgumentException("Unknown class: " + ClassUtils.getName(obj, "<null>"));
     }
 
     /* (non-Javadoc)
      * @see org.apache.commons.lang3.time.DatePrinter#getLocale()
      */
     @Override
     public Locale getLocale() {
         return locale;
     }
 
     /**
      * Gets an estimate for the maximum string length that the
      * formatter will produce.
      *
      * <p>
      * The actual formatted length will almost always be less than or
      * equal to this amount.
      * </p>
      *
      * @return The maximum formatted length.
      */
     public int getMaxLengthEstimate() {
         return maxLengthEstimate;
     }
 
     /* (non-Javadoc)
      * @see org.apache.commons.lang3.time.DatePrinter#getPattern()
      */
     @Override
     public String getPattern() {
         return pattern;
     }
 
     /* (non-Javadoc)
      * @see org.apache.commons.lang3.time.DatePrinter#getTimeZone()
      */
     @Override
     public TimeZone getTimeZone() {
         return (TimeZone) timeZone.clone();
     }
 
     /**
      * Returns a hash code compatible with equals.
      *
      * @return A hash code compatible with equals.
      */
     @Override
     public int hashCode() {
         return pattern.hashCode() + 13 * (timeZone.hashCode() + 13 * locale.hashCode());
     }
 
     /**
      * Initializes the instance for first use.
      */
     private void init() {
         final List<Rule> rulesList = parsePattern();
         rules = rulesList.toArray(EMPTY_RULE_ARRAY);
 
         int len = 0;
         for (int i = rules.length; --i >= 0;) {
             len += rules[i].estimateLength();
         }
 
         maxLengthEstimate = len;
     }
 
     /**
      * Creates a new Calendar instance.
      *
      * @return A new Calendar instance.
      */
     private Calendar newCalendar() {
         return Calendar.getInstance(timeZone, locale);
     }
 
     /**
      * Returns a list of Rules given a pattern.
      *
      * @return A {@link List} of Rule objects.
      * @throws IllegalArgumentException Thrown if pattern is invalid.
      */
     protected List<Rule> parsePattern() {
         final DateFormatSymbols symbols = new DateFormatSymbols(locale);
         final List<Rule> rules = new ArrayList<>();
 
         final String[] ERAs = symbols.getEras();
         final String[] months = symbols.getMonths();
         final String[] shortMonths = symbols.getShortMonths();
         final String[] weekdays = symbols.getWeekdays();
         final String[] shortWeekdays = symbols.getShortWeekdays();
         final String[] AmPmStrings = symbols.getAmPmStrings();
 
         final int length = pattern.length();
         final int[] indexRef = new int[1];
 
         for (int i = 0; i < length; i++) {
             indexRef[0] = i;
             final String token = parseToken(pattern, indexRef);
             i = indexRef[0];
 
             final int tokenLen = token.length();
             if (tokenLen == 0) {
                 break;
             }
 
             Rule rule;
             final char c = token.charAt(0);
 
             switch (c) {
             case 'G': // era designator (text)
                 rule = new TextField(Calendar.ERA, ERAs);
                 break;
             case 'y': // year (number)
             case 'Y': // week year
                 if (tokenLen == 2) {
                     rule = TwoDigitYearField.INSTANCE;
                 } else {
                     rule = selectNumberRule(Calendar.YEAR, Math.max(tokenLen, 4));
                 }
                 if (c == 'Y') {
                     rule = new WeekYear((NumberRule) rule);
                 }
                 break;
             case 'M': // month in year (text and number)
                 if (tokenLen >= 4) {
                     rule = new TextField(Calendar.MONTH, months);
                 } else if (tokenLen == 3) {
                     rule = new TextField(Calendar.MONTH, shortMonths);
                 } else if (tokenLen == 2) {
                     rule = TwoDigitMonthField.INSTANCE;
                 } else {
                     rule = UnpaddedMonthField.INSTANCE;
                 }
                 break;
             case 'L': // month in year (text and number)
                 if (tokenLen >= 4) {
                     rule = new TextField(Calendar.MONTH, CalendarUtils.getInstance(locale).getStandaloneLongMonthNames());
                 } else if (tokenLen == 3) {
                     rule = new TextField(Calendar.MONTH, CalendarUtils.getInstance(locale).getStandaloneShortMonthNames());
                 } else if (tokenLen == 2) {
                     rule = TwoDigitMonthField.INSTANCE;
                 } else {
                     rule = UnpaddedMonthField.INSTANCE;
                 }
                 break;
             case 'd': // day in month (number)
                 rule = selectNumberRule(Calendar.DAY_OF_MONTH, tokenLen);
                 break;
             case 'h': // hour in am/pm (number, 1..12)
                 rule = new TwelveHourField(selectNumberRule(Calendar.HOUR, tokenLen));
                 break;
             case 'H': // hour in day (number, 0..23)
                 rule = selectNumberRule(Calendar.HOUR_OF_DAY, tokenLen);
                 break;
             case 'm': // minute in hour (number)
                 rule = selectNumberRule(Calendar.MINUTE, tokenLen);
                 break;
             case 's': // second in minute (number)
                 rule = selectNumberRule(Calendar.SECOND, tokenLen);
                 break;
             case 'S': // millisecond (number)
                 rule = selectNumberRule(Calendar.MILLISECOND, tokenLen);
                 break;
             case 'E': // day in week (text)
                 rule = new TextField(Calendar.DAY_OF_WEEK, tokenLen < 4 ? shortWeekdays : weekdays);
                 break;
             case 'u': // day in week (number)
                 rule = new DayInWeekField(selectNumberRule(Calendar.DAY_OF_WEEK, tokenLen));
                 break;
             case 'D': // day in year (number)
                 rule = selectNumberRule(Calendar.DAY_OF_YEAR, tokenLen);
                 break;
             case 'F': // day of week in month (number)
                 rule = selectNumberRule(Calendar.DAY_OF_WEEK_IN_MONTH, tokenLen);
                 break;
             case 'w': // week in year (number)
                 rule = selectNumberRule(Calendar.WEEK_OF_YEAR, tokenLen);
                 break;
             case 'W': // week in month (number)
                 rule = selectNumberRule(Calendar.WEEK_OF_MONTH, tokenLen);
                 break;
             case 'a': // am/pm marker (text)
                 rule = new TextField(Calendar.AM_PM, AmPmStrings);
                 break;
             case 'k': // hour in day (1..24)
                 rule = new TwentyFourHourField(selectNumberRule(Calendar.HOUR_OF_DAY, tokenLen));
                 break;
             case 'K': // hour in am/pm (0..11)
                 rule = selectNumberRule(Calendar.HOUR, tokenLen);
                 break;
             case 'X': // ISO 8601
                 rule = Iso8601_Rule.getRule(tokenLen);
                 break;
             case 'z': // time zone (text)
                 rule = new TimeZoneNameRule(timeZone, locale, tokenLen >= 4 ? TimeZone.LONG : TimeZone.SHORT);
                 break;
             case 'Z': // time zone (value)
                 if (tokenLen == 1) {
                     rule = TimeZoneNumberRule.INSTANCE_NO_COLON;
                 } else if (tokenLen == 2) {
                     rule = Iso8601_Rule.ISO8601_HOURS_COLON_MINUTES;
                 } else {
                     rule = TimeZoneNumberRule.INSTANCE_COLON;
                 }
                 break;
             case '\'': // literal text
                 final String sub = token.substring(1);
                 if (sub.length() == 1) {
                     rule = new CharacterLiteral(sub.charAt(0));
                 } else {
                     rule = new StringLiteral(sub);
                 }
                 break;
             default:
                 throw new IllegalArgumentException("Illegal pattern component: " + token);
             }
 
             rules.add(rule);
         }
 
         return rules;
     }
 
     /**
      * Performs the parsing of tokens.
      *
      * @param pattern  The pattern.
      * @param indexRef  index references.
      * @return parsed token.
      */
     protected String parseToken(final String pattern, final int[] indexRef) {
         final StringBuilder buf = new StringBuilder();
         int i = indexRef[0];
         final int length = pattern.length();
         char c = pattern.charAt(i);
         final char c1 = c;
         if (CharUtils.isAsciiAlpha(c1)) {
             // Scan a run of the same character, which indicates a time
             // pattern.
             buf.append(c);
             while (i + 1 < length) {
                 final char peek = pattern.charAt(i + 1);
                 if (peek != c) {
                     break;
                 }
                 buf.append(c);
                 i++;
             }
         } else {
             // This will identify token as text.
             buf.append('\'');
             boolean inLiteral = false;
             for (; i < length; i++) {
                 c = pattern.charAt(i);
                 if (c == '\'') {
                     if (i + 1 < length && pattern.charAt(i + 1) == '\'') {
                         // '' is treated as escaped '
                         i++;
                         buf.append(c);
                     } else {
                         inLiteral = !inLiteral;
                     }
                 } else {
                     final char c2 = c;
                     if (!inLiteral && CharUtils.isAsciiAlpha(c2)) {
                         i--;
                         break;
                     }
                     buf.append(c);
                 }
             }
         }
         indexRef[0] = i;
         return buf.toString();
     }
 
     /**
      * Create the object after serialization. This implementation reinitializes the
      * transient properties.
      *
      * @param in ObjectInputStream from which the object is being deserialized.
      * @throws IOException Thrown if there is an IO issue.
      * @throws ClassNotFoundException Thrown if a class cannot be found.
      */
     private void readObject(final ObjectInputStream in) throws IOException, ClassNotFoundException {
         in.defaultReadObject();
         init();
     }
 
     /**
      * Gets an appropriate rule for the padding required.
      *
      * @param field  The field to get a rule for.
      * @param padding  The padding required.
      * @return A new rule with the correct padding.
      */
     protected NumberRule selectNumberRule(final int field, final int padding) {
         switch (padding) {
         case 1:
             return new UnpaddedNumberField(field);
         case 2:
             return new TwoDigitNumberField(field);
         default:
             return new PaddedNumberField(field, padding);
         }
     }
 
     /**
      * Gets a debugging string version of this formatter.
      *
      * @return A debugging string.
      */
     @Override
     public String toString() {
         return "FastDatePrinter[" + pattern + "," + locale + "," + timeZone.getID() + "]";
     }
 }