/*
 * Licensed to the Apache Software Foundation (ASF) under one or more
 * contributor license agreements.  See the NOTICE file distributed with
 * this work for additional information regarding copyright ownership.
 * The ASF licenses this file to You under the Apache License, Version 2.0
 * (the "License"); you may not use this file except in compliance with
 * the License.  You may obtain a copy of the License at
 * 
 *      http://www.apache.org/licenses/LICENSE-2.0
 * 
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */
package org.apache.commons.lang.time;

import java.io.IOException;
import java.io.ObjectInputStream;
import java.text.DateFormat;
import java.text.DateFormatSymbols;
import java.text.FieldPosition;
import java.text.Format;
import java.text.ParsePosition;
import java.text.SimpleDateFormat;
import java.util.ArrayList;
import java.util.Calendar;
import java.util.Date;
import java.util.GregorianCalendar;
import java.util.HashMap;
import java.util.List;
import java.util.Locale;
import java.util.Map;
import java.util.TimeZone;

import org.apache.commons.lang.Validate;

/**
 * <p>FastDateFormat is a fast and thread-safe version of
 * {@link java.text.SimpleDateFormat}.</p>
 * 
 * <p>This class can be used as a direct replacement to
 * <code>SimpleDateFormat</code> in most formatting situations.
 * This class is especially useful in multi-threaded server environments.
 * <code>SimpleDateFormat</code> 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, but all patterns are compatible with
 * SimpleDateFormat (except time zones - see below).</p>
 *
 * <p>Java 1.4 introduced a new pattern letter, <code>'Z'</code>, to represent
 * time zones in RFC822 format (eg. <code>+0800</code> or <code>-1100</code>).
 * This pattern letter can be used here (on all JDK versions).</p>
 *
 * <p>In addition, the pattern <code>'ZZ'</code> has been made to represent
 * ISO8601 full format time zones (eg. <code>+08:00</code> or <code>-11:00</code>).
 * This introduces a minor incompatibility with Java 1.4, but at a gain of
 * useful functionality.</p>
 *
 * @author TeaTrove project
 * @author Brian S O'Neill
 * @author Sean Schofield
 * @author Gary Gregory
 * @author Stephen Colebourne
 * @author Nikolay Metchev
 * @since 2.0
 * @version $Id$
 */
public class FastDateFormat extends Format {
    // 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.
    
    /**
     * 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 String cDefaultPattern;

    private static final Map cInstanceCache = new HashMap(7);
    private static final Map cDateInstanceCache = new HashMap(7);
    private static final Map cTimeInstanceCache = new HashMap(7);
    private static final Map cDateTimeInstanceCache = new HashMap(7);
    private static final Map cTimeZoneDisplayCache = new HashMap(7);

    /**
     * The pattern.
     */
    private final String mPattern;
    /**
     * The time zone.
     */
    private final TimeZone mTimeZone;
    /**
     * Whether the time zone overrides any on Calendars.
     */
    private final boolean mTimeZoneForced;
    /**
     * The locale.
     */
    private final Locale mLocale;
    /**
     * Whether the locale overrides the default.
     */
    private final boolean mLocaleForced;
    /**
     * The parsed rules.
     */
    private transient Rule[] mRules;
    /**
     * The estimated maximum length.
     */
    private transient int mMaxLengthEstimate;

    //-----------------------------------------------------------------------
    /**
     * <p>Gets a formatter instance using the default pattern in the
     * default locale.</p>
     * 
     * @return a date/time formatter
     */
    public static FastDateFormat getInstance() {
        return getInstance(getDefaultPattern(), null, null);
    }

    /**
     * <p>Gets a formatter instance using the specified pattern in the
     * default locale.</p>
     * 
     * @param pattern  {@link java.text.SimpleDateFormat} compatible
     *  pattern
     * @return a pattern based date/time formatter
     * @throws IllegalArgumentException if pattern is invalid
     */
    public static FastDateFormat getInstance(String pattern) {
        return getInstance(pattern, null, null);
    }

    /**
     * <p>Gets a formatter instance using the specified pattern and
     * time zone.</p>
     * 
     * @param pattern  {@link java.text.SimpleDateFormat} compatible
     *  pattern
     * @param timeZone  optional time zone, overrides time zone of
     *  formatted date
     * @return a pattern based date/time formatter
     * @throws IllegalArgumentException if pattern is invalid
     */
    public static FastDateFormat getInstance(String pattern, TimeZone timeZone) {
        return getInstance(pattern, timeZone, null);
    }

    /**
     * <p>Gets a formatter instance using the specified pattern and
     * locale.</p>
     * 
     * @param pattern  {@link java.text.SimpleDateFormat} compatible
     *  pattern
     * @param locale  optional locale, overrides system locale
     * @return a pattern based date/time formatter
     * @throws IllegalArgumentException if pattern is invalid
     */
    public static FastDateFormat getInstance(String pattern, Locale locale) {
        return getInstance(pattern, null, locale);
    }

    /**
     * <p>Gets a formatter instance using the specified pattern, time zone
     * and locale.</p>
     * 
     * @param pattern  {@link java.text.SimpleDateFormat} compatible
     *  pattern
     * @param timeZone  optional time zone, overrides time zone of
     *  formatted date
     * @param locale  optional locale, overrides system locale
     * @return a pattern based date/time formatter
     * @throws IllegalArgumentException if pattern is invalid
     *  or <code>null</code>
     */
    public static synchronized FastDateFormat getInstance(String pattern, TimeZone timeZone, Locale locale) {
        FastDateFormat emptyFormat = new FastDateFormat(pattern, timeZone, locale);
        FastDateFormat format = (FastDateFormat) cInstanceCache.get(emptyFormat);
        if (format == null) {
            format = emptyFormat;
            format.init();  // convert shell format into usable one
            cInstanceCache.put(format, format);  // this is OK!
        }
        return format;
    }

    //-----------------------------------------------------------------------
    /**
     * <p>Gets a date formatter instance using the specified style in the
     * default time zone and locale.</p>
     * 
     * @param style  date style: FULL, LONG, MEDIUM, or SHORT
     * @return a localized standard date formatter
     * @throws IllegalArgumentException if the Locale has no date
     *  pattern defined
     * @since 2.1
     */
    public static FastDateFormat getDateInstance(int style) {
        return getDateInstance(style, null, null);
    }

    /**
     * <p>Gets a date formatter instance using the specified style and
     * locale in the default time zone.</p>
     * 
     * @param style  date style: FULL, LONG, MEDIUM, or SHORT
     * @param locale  optional locale, overrides system locale
     * @return a localized standard date formatter
     * @throws IllegalArgumentException if the Locale has no date
     *  pattern defined
     * @since 2.1
     */
    public static FastDateFormat getDateInstance(int style, Locale locale) {
        return getDateInstance(style, null, locale);
    }

    /**
     * <p>Gets a date formatter instance using the specified style and
     * time zone in the default locale.</p>
     * 
     * @param style  date style: FULL, LONG, MEDIUM, or SHORT
     * @param timeZone  optional time zone, overrides time zone of
     *  formatted date
     * @return a localized standard date formatter
     * @throws IllegalArgumentException if the Locale has no date
     *  pattern defined
     * @since 2.1
     */
    public static FastDateFormat getDateInstance(int style, TimeZone timeZone) {
        return getDateInstance(style, timeZone, null);
    }
    /**
     * <p>Gets a date formatter instance using the specified style, time
     * zone and locale.</p>
     * 
     * @param style  date style: FULL, LONG, MEDIUM, or SHORT
     * @param timeZone  optional time zone, overrides time zone of
     *  formatted date
     * @param locale  optional locale, overrides system locale
     * @return a localized standard date formatter
     * @throws IllegalArgumentException if the Locale has no date
     *  pattern defined
     */
    public static synchronized FastDateFormat getDateInstance(int style, TimeZone timeZone, Locale locale) {
        Object key = new Integer(style);
        if (timeZone != null) {
            key = new Pair(key, timeZone);
        }

        if (locale == null) {
            locale = Locale.getDefault();
        }

        key = new Pair(key, locale);

        FastDateFormat format = (FastDateFormat) cDateInstanceCache.get(key);
        if (format == null) {
            try {
                SimpleDateFormat formatter = (SimpleDateFormat) DateFormat.getDateInstance(style, locale);
                String pattern = formatter.toPattern();
                format = getInstance(pattern, timeZone, locale);
                cDateInstanceCache.put(key, format);
                
            } catch (ClassCastException ex) {
                throw new IllegalArgumentException("No date pattern for locale: " + locale);
            }
        }
        return format;
    }

    //-----------------------------------------------------------------------
    /**
     * <p>Gets a time formatter instance using the specified style in the
     * default time zone and locale.</p>
     * 
     * @param style  time style: FULL, LONG, MEDIUM, or SHORT
     * @return a localized standard time formatter
     * @throws IllegalArgumentException if the Locale has no time
     *  pattern defined
     * @since 2.1
     */
    public static FastDateFormat getTimeInstance(int style) {
        return getTimeInstance(style, null, null);
    }

    /**
     * <p>Gets a time formatter instance using the specified style and
     * locale in the default time zone.</p>
     * 
     * @param style  time style: FULL, LONG, MEDIUM, or SHORT
     * @param locale  optional locale, overrides system locale
     * @return a localized standard time formatter
     * @throws IllegalArgumentException if the Locale has no time
     *  pattern defined
     * @since 2.1
     */
    public static FastDateFormat getTimeInstance(int style, Locale locale) {
        return getTimeInstance(style, null, locale);
    }
    
    /**
     * <p>Gets a time formatter instance using the specified style and
     * time zone in the default locale.</p>
     * 
     * @param style  time style: FULL, LONG, MEDIUM, or SHORT
     * @param timeZone  optional time zone, overrides time zone of
     *  formatted time
     * @return a localized standard time formatter
     * @throws IllegalArgumentException if the Locale has no time
     *  pattern defined
     * @since 2.1
     */
    public static FastDateFormat getTimeInstance(int style, TimeZone timeZone) {
        return getTimeInstance(style, timeZone, null);
    }
    
    /**
     * <p>Gets a time formatter instance using the specified style, time
     * zone and locale.</p>
     * 
     * @param style  time style: FULL, LONG, MEDIUM, or SHORT
     * @param timeZone  optional time zone, overrides time zone of
     *  formatted time
     * @param locale  optional locale, overrides system locale
     * @return a localized standard time formatter
     * @throws IllegalArgumentException if the Locale has no time
     *  pattern defined
     */
    public static synchronized FastDateFormat getTimeInstance(int style, TimeZone timeZone, Locale locale) {
        Object key = new Integer(style);
        if (timeZone != null) {
            key = new Pair(key, timeZone);
        }
        if (locale != null) {
            key = new Pair(key, locale);
        }

        FastDateFormat format = (FastDateFormat) cTimeInstanceCache.get(key);
        if (format == null) {
            if (locale == null) {
                locale = Locale.getDefault();
            }

            try {
                SimpleDateFormat formatter = (SimpleDateFormat) DateFormat.getTimeInstance(style, locale);
                String pattern = formatter.toPattern();
                format = getInstance(pattern, timeZone, locale);
                cTimeInstanceCache.put(key, format);
            
            } catch (ClassCastException ex) {
                throw new IllegalArgumentException("No date pattern for locale: " + locale);
            }
        }
        return format;
    }

    //-----------------------------------------------------------------------
    /**
     * <p>Gets a date/time formatter instance using the specified style
     * in the default time zone and locale.</p>
     * 
     * @param dateStyle  date style: FULL, LONG, MEDIUM, or SHORT
     * @param timeStyle  time style: FULL, LONG, MEDIUM, or SHORT
     * @return a localized standard date/time formatter
     * @throws IllegalArgumentException if the Locale has no date/time
     *  pattern defined
     * @since 2.1
     */
    public static FastDateFormat getDateTimeInstance(
            int dateStyle, int timeStyle) {
        return getDateTimeInstance(dateStyle, timeStyle, null, null);
    }
    
    /**
     * <p>Gets a date/time formatter instance using the specified style and
     * locale in the default time zone.</p>
     * 
     * @param dateStyle  date style: FULL, LONG, MEDIUM, or SHORT
     * @param timeStyle  time style: FULL, LONG, MEDIUM, or SHORT
     * @param locale  optional locale, overrides system locale
     * @return a localized standard date/time formatter
     * @throws IllegalArgumentException if the Locale has no date/time
     *  pattern defined
     * @since 2.1
     */
    public static FastDateFormat getDateTimeInstance(
            int dateStyle, int timeStyle, Locale locale) {
        return getDateTimeInstance(dateStyle, timeStyle, null, locale);
    }
    
    /**
     * <p>Gets a date/time formatter instance using the specified style and
     * time zone in the default locale.</p>
     * 
     * @param dateStyle  date style: FULL, LONG, MEDIUM, or SHORT
     * @param timeStyle  time style: FULL, LONG, MEDIUM, or SHORT
     * @param timeZone  optional time zone, overrides time zone of
     *  formatted date
     * @return a localized standard date/time formatter
     * @throws IllegalArgumentException if the Locale has no date/time
     *  pattern defined
     * @since 2.1
     */
    public static FastDateFormat getDateTimeInstance(
            int dateStyle, int timeStyle, TimeZone timeZone) {
        return getDateTimeInstance(dateStyle, timeStyle, timeZone, null);
    }    
    /**
     * <p>Gets a date/time formatter instance using the specified style,
     * time zone and locale.</p>
     * 
     * @param dateStyle  date style: FULL, LONG, MEDIUM, or SHORT
     * @param timeStyle  time style: FULL, LONG, MEDIUM, or SHORT
     * @param timeZone  optional time zone, overrides time zone of
     *  formatted date
     * @param locale  optional locale, overrides system locale
     * @return a localized standard date/time formatter
     * @throws IllegalArgumentException if the Locale has no date/time
     *  pattern defined
     */
    public static synchronized FastDateFormat getDateTimeInstance(int dateStyle, int timeStyle, TimeZone timeZone,
            Locale locale) {

        Object key = new Pair(new Integer(dateStyle), new Integer(timeStyle));
        if (timeZone != null) {
            key = new Pair(key, timeZone);
        }
        if (locale == null) {
            locale = Locale.getDefault();
        }
        key = new Pair(key, locale);

        FastDateFormat format = (FastDateFormat) cDateTimeInstanceCache.get(key);
        if (format == null) {
            try {
                SimpleDateFormat formatter = (SimpleDateFormat) DateFormat.getDateTimeInstance(dateStyle, timeStyle,
                        locale);
                String pattern = formatter.toPattern();
                format = getInstance(pattern, timeZone, locale);
                cDateTimeInstanceCache.put(key, format);

            } catch (ClassCastException ex) {
                throw new IllegalArgumentException("No date time pattern for locale: " + locale);
            }
        }
        return format;
    }

    //-----------------------------------------------------------------------
    /**
     * <p>Gets the time zone display name, using a cache for performance.</p>
     * 
     * @param tz  the zone to query
     * @param daylight  true if daylight savings
     * @param style  the style to use <code>TimeZone.LONG</code>
     *  or <code>TimeZone.SHORT</code>
     * @param locale  the locale to use
     * @return the textual name of the time zone
     */
    static synchronized String getTimeZoneDisplay(TimeZone tz, boolean daylight, int style, Locale locale) {
        Object key = new TimeZoneDisplayKey(tz, daylight, style, locale);
        String value = (String) cTimeZoneDisplayCache.get(key);
        if (value == null) {
            // This is a very slow call, so cache the results.
            value = tz.getDisplayName(daylight, style, locale);
            cTimeZoneDisplayCache.put(key, value);
        }
        return value;
    }

    /**
     * <p>Gets the default pattern.</p>
     * 
     * @return the default pattern
     */
    private static synchronized String getDefaultPattern() {
        if (cDefaultPattern == null) {
            cDefaultPattern = new SimpleDateFormat().toPattern();
        }
        return cDefaultPattern;
    }

    // Constructor
    //-----------------------------------------------------------------------
    /**
     * <p>Constructs a new FastDateFormat.</p>
     * 
     * @param pattern  {@link java.text.SimpleDateFormat} compatible
     *  pattern
     * @param timeZone  time zone to use, <code>null</code> means use
     *  default for <code>Date</code> and value within for
     *  <code>Calendar</code>
     * @param locale  locale, <code>null</code> means use system
     *  default
     * @throws IllegalArgumentException if pattern is invalid or
     *  <code>null</code>
     */
    protected FastDateFormat(String pattern, TimeZone timeZone, Locale locale) {
        super();
        if (pattern == null) {
            throw new IllegalArgumentException("The pattern must not be null");
        }
        mPattern = pattern;
        
        mTimeZoneForced = (timeZone != null);
        if (timeZone == null) {
            timeZone = TimeZone.getDefault();
        }
        mTimeZone = timeZone;
        
        mLocaleForced = (locale != null);
        if (locale == null) {
            locale = Locale.getDefault();
        }
        mLocale = locale;
    }

    /**
     * <p>Initializes the instance for first use.</p>
     */
    protected void init() {
        List rulesList = parsePattern();
        mRules = (Rule[]) rulesList.toArray(new Rule[rulesList.size()]);

        int len = 0;
        for (int i=mRules.length; --i >= 0; ) {
            len += mRules[i].estimateLength();
        }

        mMaxLengthEstimate = len;
    }

    // Parse the pattern
    //-----------------------------------------------------------------------
    /**
     * <p>Returns a list of Rules given a pattern.</p>
     * 
     * @return a <code>List</code> of Rule objects
     * @throws IllegalArgumentException if pattern is invalid
     */
    protected List parsePattern() {
        DateFormatSymbols symbols = new DateFormatSymbols(mLocale);
        List rules = new ArrayList();

        String[] ERAs = symbols.getEras();
        String[] months = symbols.getMonths();
        String[] shortMonths = symbols.getShortMonths();
        String[] weekdays = symbols.getWeekdays();
        String[] shortWeekdays = symbols.getShortWeekdays();
        String[] AmPmStrings = symbols.getAmPmStrings();

        int length = mPattern.length();
        int[] indexRef = new int[1];

        for (int i = 0; i < length; i++) {
            indexRef[0] = i;
            String token = parseToken(mPattern, indexRef);
            i = indexRef[0];

            int tokenLen = token.length();
            if (tokenLen == 0) {
                break;
            }

            Rule rule;
            char c = token.charAt(0);

            switch (c) {
            case 'G': // era designator (text)
                rule = new TextField(Calendar.ERA, ERAs);
                break;
            case 'y': // year (number)
                if (tokenLen >= 4) {
                    rule = selectNumberRule(Calendar.YEAR, tokenLen);
                } else {
                    rule = TwoDigitYearField.INSTANCE;
                }
                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 '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 '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 'z': // time zone (text)
                if (tokenLen >= 4) {
                    rule = new TimeZoneNameRule(mTimeZone, mTimeZoneForced, mLocale, TimeZone.LONG);
                } else {
                    rule = new TimeZoneNameRule(mTimeZone, mTimeZoneForced, mLocale, TimeZone.SHORT);
                }
                break;
            case 'Z': // time zone (value)
                if (tokenLen == 1) {
                    rule = TimeZoneNumberRule.INSTANCE_NO_COLON;
                } else {
                    rule = TimeZoneNumberRule.INSTANCE_COLON;
                }
                break;
            case '\'': // literal text
                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;
    }

    /**
     * <p>Performs the parsing of tokens.</p>
     * 
     * @param pattern  the pattern
     * @param indexRef  index references
     * @return parsed token
     */
    protected String parseToken(String pattern, int[] indexRef) {
        StringBuffer buf = new StringBuffer();

        int i = indexRef[0];
        int length = pattern.length();

        char c = pattern.charAt(i);
        if (c >= 'A' && c <= 'Z' || c >= 'a' && c <= 'z') {
            // Scan a run of the same character, which indicates a time
            // pattern.
            buf.append(c);

            while (i + 1 < length) {
                char peek = pattern.charAt(i + 1);
                if (peek == c) {
                    buf.append(c);
                    i++;
                } else {
                    break;
                }
            }
        } 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 if (!inLiteral &&
                         (c >= 'A' && c <= 'Z' || c >= 'a' && c <= 'z')) {
                    i--;
                    break;
                } else {
                    buf.append(c);
                }
            }
        }

        indexRef[0] = i;
        return buf.toString();
    }

    /**
     * <p>Gets an appropriate rule for the padding required.</p>
     * 
     * @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(int field, int padding) {
        switch (padding) {
        case 1:
            return new UnpaddedNumberField(field);
        case 2:
            return new TwoDigitNumberField(field);
        default:
            return new PaddedNumberField(field, padding);
        }
    }

    // Format methods
    //-----------------------------------------------------------------------
    /**
     * <p>Formats a <code>Date</code>, <code>Calendar</code> or
     * <code>Long</code> (milliseconds) object.</p>
     * 
     * @param obj  the object to format
     * @param toAppendTo  the buffer to append to
     * @param pos  the position - ignored
     * @return the buffer passed in
     */
    public StringBuffer format(Object obj, StringBuffer toAppendTo, FieldPosition pos) {
        if (obj instanceof Date) {
            return format((Date) obj, toAppendTo);
        } else if (obj instanceof Calendar) {
            return format((Calendar) obj, toAppendTo);
        } else if (obj instanceof Long) {
            return format(((Long) obj).longValue(), toAppendTo);
        } else {
            throw new IllegalArgumentException("Unknown class: " +
                (obj == null ? "<null>" : obj.getClass().getName()));
        }
    }

    /**
     * <p>Formats a millisecond <code>long</code> value.</p>
     * 
     * @param millis  the millisecond value to format
     * @return the formatted string
     * @since 2.1
     */
    public String format(long millis) {
        return format(new Date(millis));
    }

    /**
     * <p>Formats a <code>Date</code> object.</p>
     * 
     * @param date  the date to format
     * @return the formatted string
     */
    public String format(Date date) {
        Calendar c = new GregorianCalendar(mTimeZone);
        c.setTime(date);
        return applyRules(c, new StringBuffer(mMaxLengthEstimate)).toString();
    }

    /**
     * <p>Formats a <code>Calendar</code> object.</p>
     * 
     * @param calendar  the calendar to format
     * @return the formatted string
     */
    public String format(Calendar calendar) {
        return format(calendar, new StringBuffer(mMaxLengthEstimate)).toString();
    }

    /**
     * <p>Formats a milliseond <code>long</code> value into the
     * supplied <code>StringBuffer</code>.</p>
     * 
     * @param millis  the millisecond value to format
     * @param buf  the buffer to format into
     * @return the specified string buffer
     * @since 2.1
     */
    public StringBuffer format(long millis, StringBuffer buf) {
        return format(new Date(millis), buf);
    }

    /**
     * <p>Formats a <code>Date</code> object into the
     * supplied <code>StringBuffer</code>.</p>
     * 
     * @param date  the date to format
     * @param buf  the buffer to format into
     * @return the specified string buffer
     */
    public StringBuffer format(Date date, StringBuffer buf) {
        Calendar c = new GregorianCalendar(mTimeZone);
        c.setTime(date);
        return applyRules(c, buf);
    }

    /**
     * <p>Formats a <code>Calendar</code> object into the
     * supplied <code>StringBuffer</code>.</p>
     * 
     * @param calendar  the calendar to format
     * @param buf  the buffer to format into
     * @return the specified string buffer
     */
    public StringBuffer format(Calendar calendar, StringBuffer buf) {
        if (mTimeZoneForced) {
            calendar = (Calendar) calendar.clone();
            calendar.setTimeZone(mTimeZone);
        }
        return applyRules(calendar, buf);
    }

    /**
     * <p>Performs the formatting by applying the rules to the
     * specified calendar.</p>
     * 
     * @param calendar  the calendar to format
     * @param buf  the buffer to format into
     * @return the specified string buffer
     */
    protected StringBuffer applyRules(Calendar calendar, StringBuffer buf) {
        Rule[] rules = mRules;
        int len = mRules.length;
        for (int i = 0; i < len; i++) {
            rules[i].appendTo(buf, calendar);
        }
        return buf;
    }

    // Parsing
    //-----------------------------------------------------------------------
    /**
     * <p>Parsing is not supported.</p>
     * 
     * @param source  the string to parse
     * @param pos  the parsing position
     * @return <code>null</code> as not supported
     */
    public Object parseObject(String source, ParsePosition pos) {
        pos.setIndex(0);
        pos.setErrorIndex(0);
        return null;
    }
    
    // Accessors
    //-----------------------------------------------------------------------
    /**
     * <p>Gets the pattern used by this formatter.</p>
     * 
     * @return the pattern, {@link java.text.SimpleDateFormat} compatible
     */
    public String getPattern() {
        return mPattern;
    }

    /**
     * <p>Gets the time zone used by this formatter.</p>
     *
     * <p>This zone is always used for <code>Date</code> formatting.
     * If a <code>Calendar</code> is passed in to be formatted, the
     * time zone on that may be used depending on
     * {@link #getTimeZoneOverridesCalendar()}.</p>
     * 
     * @return the time zone
     */
    public TimeZone getTimeZone() {
        return mTimeZone;
    }

    /**
     * <p>Returns <code>true</code> if the time zone of the
     * calendar overrides the time zone of the formatter.</p>
     * 
     * @return <code>true</code> if time zone of formatter
     *  overridden for calendars
     */
    public boolean getTimeZoneOverridesCalendar() {
        return mTimeZoneForced;
    }

    /**
     * <p>Gets the locale used by this formatter.</p>
     * 
     * @return the locale
     */
    public Locale getLocale() {
        return mLocale;
    }

    /**
     * <p>Gets an estimate for the maximum string length that the
     * formatter will produce.</p>
     *
     * <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 mMaxLengthEstimate;
    }

    // Basics
    //-----------------------------------------------------------------------
    /**
     * <p>Compares two objects for equality.</p>
     * 
     * @param obj  the object to compare to
     * @return <code>true</code> if equal
     */
    public boolean equals(Object obj) {
        if (obj instanceof FastDateFormat == false) {
            return false;
        }
        FastDateFormat other = (FastDateFormat) obj;
        if (
            (mPattern == other.mPattern || mPattern.equals(other.mPattern)) &&
            (mTimeZone == other.mTimeZone || mTimeZone.equals(other.mTimeZone)) &&
            (mLocale == other.mLocale || mLocale.equals(other.mLocale)) &&
            (mTimeZoneForced == other.mTimeZoneForced) &&
            (mLocaleForced == other.mLocaleForced)
            ) {
            return true;
        }
        return false;
    }

    /**
     * <p>Returns a hashcode compatible with equals.</p>
     * 
     * @return a hashcode compatible with equals
     */
    public int hashCode() {
        int total = 0;
        total += mPattern.hashCode();
        total += mTimeZone.hashCode();
        total += (mTimeZoneForced ? 1 : 0);
        total += mLocale.hashCode();
        total += (mLocaleForced ? 1 : 0);
        return total;
    }

    /**
     * <p>Gets a debugging string version of this formatter.</p>
     * 
     * @return a debugging string
     */
    public String toString() {
        return "FastDateFormat[" + mPattern + "]";
    }

    // Serializing
    //-----------------------------------------------------------------------
    /**
     * Create the object after serialization. This implementation reinitializes the 
     * transient properties.
     *
     * @param in ObjectInputStream from which the object is being deserialized.
     * @throws IOException if there is an IO issue.
     * @throws ClassNotFoundException if a class cannot be found.
     */
    private void readObject(ObjectInputStream in) throws IOException, ClassNotFoundException {
        in.defaultReadObject();
        init();
    }
    
    // Rules
    //-----------------------------------------------------------------------
    /**
     * <p>Inner class defining a rule.</p>
     */
    private interface Rule {
        /**
         * Returns the estimated lentgh of the result.
         * 
         * @return the estimated length
         */
        int estimateLength();
        
        /**
         * Appends the value of the specified calendar to the output buffer based on the rule implementation.
         * 
         * @param buffer the output buffer
         * @param calendar calendar to be appended
         */
        void appendTo(StringBuffer buffer, Calendar calendar);
    }

    /**
     * <p>Inner class defining a numeric rule.</p>
     */
    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
         */
        void appendTo(StringBuffer buffer, int value);
    }

    /**
     * <p>Inner class to output a constant single character.</p>
     */
    private static class CharacterLiteral implements Rule {
        private final char mValue;

        /**
         * Constructs a new instance of <code>CharacterLiteral</code>
         * to hold the specified value.
         * 
         * @param value the character literal
         */
        CharacterLiteral(char value) {
            mValue = value;
        }

        /**
         * {@inheritDoc}
         */
        public int estimateLength() {
            return 1;
        }

        /**
         * {@inheritDoc}
         */
        public void appendTo(StringBuffer buffer, Calendar calendar) {
            buffer.append(mValue);
        }
    }

    /**
     * <p>Inner class to output a constant string.</p>
     */
    private static class StringLiteral implements Rule {
        private final String mValue;

        /**
         * Constructs a new instance of <code>StringLiteral</code>
         * to hold the specified value.
         * 
         * @param value the string literal
         */
        StringLiteral(String value) {
            mValue = value;
        }

        /**
         * {@inheritDoc}
         */
        public int estimateLength() {
            return mValue.length();
        }

        /**
         * {@inheritDoc}
         */
        public void appendTo(StringBuffer buffer, Calendar calendar) {
            buffer.append(mValue);
        }
    }

    /**
     * <p>Inner class to output one of a set of values.</p>
     */
    private static class TextField implements Rule {
        private final int mField;
        private final String[] mValues;

        /**
         * Constructs an instance of <code>TextField</code>
         * with the specified field and values.
         * 
         * @param field the field
         * @param values the field values
         */
        TextField(int field, String[] values) {
            mField = field;
            mValues = values;
        }

        /**
         * {@inheritDoc}
         */
        public int estimateLength() {
            int max = 0;
            for (int i=mValues.length; --i >= 0; ) {
                int len = mValues[i].length();
                if (len > max) {
                    max = len;
                }
            }
            return max;
        }

        /**
         * {@inheritDoc}
         */
        public void appendTo(StringBuffer buffer, Calendar calendar) {
            buffer.append(mValues[calendar.get(mField)]);
        }
    }

    /**
     * <p>Inner class to output an unpadded number.</p>
     */
    private static class UnpaddedNumberField implements NumberRule {
        static final UnpaddedNumberField INSTANCE_YEAR = new UnpaddedNumberField(Calendar.YEAR);
        
        private final int mField;

        /**
         * Constructs an instance of <code>UnpadedNumberField</code> with the specified field.
         * 
         * @param field the field
         */
        UnpaddedNumberField(int field) {
            mField = field;
        }

        /**
         * {@inheritDoc}
         */
        public int estimateLength() {
            return 4;
        }

        /**
         * {@inheritDoc}
         */
        public void appendTo(StringBuffer buffer, Calendar calendar) {
            appendTo(buffer, calendar.get(mField));
        }

        /**
         * {@inheritDoc}
         */
        public final void appendTo(StringBuffer buffer, int value) {
            if (value < 10) {
                buffer.append((char)(value + '0'));
            } else if (value < 100) {
                buffer.append((char)(value / 10 + '0'));
                buffer.append((char)(value % 10 + '0'));
            } else {
                buffer.append(Integer.toString(value));
            }
        }
    }

    /**
     * <p>Inner class to output an unpadded month.</p>
     */
    private static class UnpaddedMonthField implements NumberRule {
        static final UnpaddedMonthField INSTANCE = new UnpaddedMonthField();

        /**
         * Constructs an instance of <code>UnpaddedMonthField</code>.
         *
         */
        UnpaddedMonthField() {
            super();
        }

        /**
         * {@inheritDoc}
         */
        public int estimateLength() {
            return 2;
        }

        /**
         * {@inheritDoc}
         */
        public void appendTo(StringBuffer buffer, Calendar calendar) {
            appendTo(buffer, calendar.get(Calendar.MONTH) + 1);
        }

        /**
         * {@inheritDoc}
         */
        public final void appendTo(StringBuffer buffer, int value) {
            if (value < 10) {
                buffer.append((char)(value + '0'));
            } else {
                buffer.append((char)(value / 10 + '0'));
                buffer.append((char)(value % 10 + '0'));
            }
        }
    }

    /**
     * <p>Inner class to output a padded number.</p>
     */
    private static class PaddedNumberField implements NumberRule {
        private final int mField;
        private final int mSize;

        /**
         * Constructs an instance of <code>PaddedNumberField</code>.
         * 
         * @param field the field
         * @param size size of the output field
         */
        PaddedNumberField(int field, int size) {
            if (size < 3) {
                // Should use UnpaddedNumberField or TwoDigitNumberField.
                throw new IllegalArgumentException();
            }
            mField = field;
            mSize = size;
        }

        /**
         * {@inheritDoc}
         */
        public int estimateLength() {
            return 4;
        }

        /**
         * {@inheritDoc}
         */
        public void appendTo(StringBuffer buffer, Calendar calendar) {
            appendTo(buffer, calendar.get(mField));
        }

        /**
         * {@inheritDoc}
         */
        public final void appendTo(StringBuffer buffer, int value) {
            if (value < 100) {
                for (int i = mSize; --i >= 2; ) {
                    buffer.append('0');
                }
                buffer.append((char)(value / 10 + '0'));
                buffer.append((char)(value % 10 + '0'));
            } else {
                int digits;
                if (value < 1000) {
                    digits = 3;
                } else {
                    Validate.isTrue(value > -1, "Negative values should not be possible", value);
                    digits = Integer.toString(value).length();
                }
                for (int i = mSize; --i >= digits; ) {
                    buffer.append('0');
                }
                buffer.append(Integer.toString(value));
            }
        }
    }

    /**
     * <p>Inner class to output a two digit number.</p>
     */
    private static class TwoDigitNumberField implements NumberRule {
        private final int mField;

        /**
         * Constructs an instance of <code>TwoDigitNumberField</code> with the specified field.
         * 
         * @param field the field
         */
        TwoDigitNumberField(int field) {
            mField = field;
        }

        /**
         * {@inheritDoc}
         */
        public int estimateLength() {
            return 2;
        }

        /**
         * {@inheritDoc}
         */
        public void appendTo(StringBuffer buffer, Calendar calendar) {
            appendTo(buffer, calendar.get(mField));
        }

        /**
         * {@inheritDoc}
         */
        public final void appendTo(StringBuffer buffer, int value) {
            if (value < 100) {
                buffer.append((char)(value / 10 + '0'));
                buffer.append((char)(value % 10 + '0'));
            } else {
                buffer.append(Integer.toString(value));
            }
        }
    }

    /**
     * <p>Inner class to output a two digit year.</p>
     */
    private static class TwoDigitYearField implements NumberRule {
        static final TwoDigitYearField INSTANCE = new TwoDigitYearField();

        /**
         * Constructs an instance of <code>TwoDigitYearField</code>.
         */
        TwoDigitYearField() {
            super();
        }

        /**
         * {@inheritDoc}
         */
        public int estimateLength() {
            return 2;
        }

        /**
         * {@inheritDoc}
         */
        public void appendTo(StringBuffer buffer, Calendar calendar) {
            appendTo(buffer, calendar.get(Calendar.YEAR) % 100);
        }

        /**
         * {@inheritDoc}
         */
        public final void appendTo(StringBuffer buffer, int value) {
            buffer.append((char)(value / 10 + '0'));
            buffer.append((char)(value % 10 + '0'));
        }
    }

    /**
     * <p>Inner class to output a two digit month.</p>
     */
    private static class TwoDigitMonthField implements NumberRule {
        static final TwoDigitMonthField INSTANCE = new TwoDigitMonthField();

        /**
         * Constructs an instance of <code>TwoDigitMonthField</code>.
         */
        TwoDigitMonthField() {
            super();
        }

        /**
         * {@inheritDoc}
         */
        public int estimateLength() {
            return 2;
        }

        /**
         * {@inheritDoc}
         */
        public void appendTo(StringBuffer buffer, Calendar calendar) {
            appendTo(buffer, calendar.get(Calendar.MONTH) + 1);
        }

        /**
         * {@inheritDoc}
         */
        public final void appendTo(StringBuffer buffer, int value) {
            buffer.append((char)(value / 10 + '0'));
            buffer.append((char)(value % 10 + '0'));
        }
    }

    /**
     * <p>Inner class to output the twelve hour field.</p>
     */
    private static class TwelveHourField implements NumberRule {
        private final NumberRule mRule;

        /**
         * Constructs an instance of <code>TwelveHourField</code> with the specified
         * <code>NumberRule</code>.
         * 
         * @param rule the rule
         */
        TwelveHourField(NumberRule rule) {
            mRule = rule;
        }

        /**
         * {@inheritDoc}
         */
        public int estimateLength() {
            return mRule.estimateLength();
        }

        /**
         * {@inheritDoc}
         */
        public void appendTo(StringBuffer buffer, Calendar calendar) {
            int value = calendar.get(Calendar.HOUR);
            if (value == 0) {
                value = calendar.getLeastMaximum(Calendar.HOUR) + 1;
            }
            mRule.appendTo(buffer, value);
        }

        /**
         * {@inheritDoc}
         */
        public void appendTo(StringBuffer buffer, int value) {
            mRule.appendTo(buffer, value);
        }
    }

    /**
     * <p>Inner class to output the twenty four hour field.</p>
     */
    private static class TwentyFourHourField implements NumberRule {
        private final NumberRule mRule;

        /**
         * Constructs an instance of <code>TwentyFourHourField</code> with the specified
         * <code>NumberRule</code>.
         * 
         * @param rule the rule
         */
        TwentyFourHourField(NumberRule rule) {
            mRule = rule;
        }

        /**
         * {@inheritDoc}
         */
        public int estimateLength() {
            return mRule.estimateLength();
        }

        /**
         * {@inheritDoc}
         */
        public void appendTo(StringBuffer buffer, Calendar calendar) {
            int value = calendar.get(Calendar.HOUR_OF_DAY);
            if (value == 0) {
                value = calendar.getMaximum(Calendar.HOUR_OF_DAY) + 1;
            }
            mRule.appendTo(buffer, value);
        }

        /**
         * {@inheritDoc}
         */
        public void appendTo(StringBuffer buffer, int value) {
            mRule.appendTo(buffer, value);
        }
    }

    /**
     * <p>Inner class to output a time zone name.</p>
     */
    private static class TimeZoneNameRule implements Rule {
        private final TimeZone mTimeZone;
        private final boolean mTimeZoneForced;
        private final Locale mLocale;
        private final int mStyle;
        private final String mStandard;
        private final String mDaylight;

        /**
         * Constructs an instance of <code>TimeZoneNameRule</code> with the specified properties.
         * 
         * @param timeZone the time zone
         * @param timeZoneForced if <code>true</code> the time zone is forced into standard and daylight
         * @param locale the locale
         * @param style the style
         */
        TimeZoneNameRule(TimeZone timeZone, boolean timeZoneForced, Locale locale, int style) {
            mTimeZone = timeZone;
            mTimeZoneForced = timeZoneForced;
            mLocale = locale;
            mStyle = style;

            if (timeZoneForced) {
                mStandard = getTimeZoneDisplay(timeZone, false, style, locale);
                mDaylight = getTimeZoneDisplay(timeZone, true, style, locale);
            } else {
                mStandard = null;
                mDaylight = null;
            }
        }

        /**
         * {@inheritDoc}
         */
        public int estimateLength() {
            if (mTimeZoneForced) {
                return Math.max(mStandard.length(), mDaylight.length());
            } else if (mStyle == TimeZone.SHORT) {
                return 4;
            } else {
                return 40;
            }
        }

        /**
         * {@inheritDoc}
         */
        public void appendTo(StringBuffer buffer, Calendar calendar) {
            if (mTimeZoneForced) {
                if (mTimeZone.useDaylightTime() && calendar.get(Calendar.DST_OFFSET) != 0) {
                    buffer.append(mDaylight);
                } else {
                    buffer.append(mStandard);
                }
            } else {
                TimeZone timeZone = calendar.getTimeZone();
                if (timeZone.useDaylightTime() && calendar.get(Calendar.DST_OFFSET) != 0) {
                    buffer.append(getTimeZoneDisplay(timeZone, true, mStyle, mLocale));
                } else {
                    buffer.append(getTimeZoneDisplay(timeZone, false, mStyle, mLocale));
                }
            }
        }
    }

    /**
     * <p>Inner class to output a time zone as a number <code>+/-HHMM</code>
     * or <code>+/-HH:MM</code>.</p>
     */
    private static class TimeZoneNumberRule implements Rule {
        static final TimeZoneNumberRule INSTANCE_COLON = new TimeZoneNumberRule(true);
        static final TimeZoneNumberRule INSTANCE_NO_COLON = new TimeZoneNumberRule(false);
        
        final boolean mColon;
        
        /**
         * Constructs an instance of <code>TimeZoneNumberRule</code> with the specified properties.
         * 
         * @param colon add colon between HH and MM in the output if <code>true</code>
         */
        TimeZoneNumberRule(boolean colon) {
            mColon = colon;
        }

        /**
         * {@inheritDoc}
         */
        public int estimateLength() {
            return 5;
        }

        /**
         * {@inheritDoc}
         */
        public void appendTo(StringBuffer buffer, Calendar calendar) {
            int offset = calendar.get(Calendar.ZONE_OFFSET) + calendar.get(Calendar.DST_OFFSET);
            
            if (offset < 0) {
                buffer.append('-');
                offset = -offset;
            } else {
                buffer.append('+');
            }
            
            int hours = offset / (60 * 60 * 1000);
            buffer.append((char)(hours / 10 + '0'));
            buffer.append((char)(hours % 10 + '0'));
            
            if (mColon) {
                buffer.append(':');
            }
            
            int minutes = offset / (60 * 1000) - 60 * hours;
            buffer.append((char)(minutes / 10 + '0'));
            buffer.append((char)(minutes % 10 + '0'));
        }            
    }

    // ----------------------------------------------------------------------
    /**
     * <p>Inner class that acts as a compound key for time zone names.</p>
     */
    private static class TimeZoneDisplayKey {
        private final TimeZone mTimeZone;
        private final int mStyle;
        private final Locale mLocale;

        /**
         * Constructs an instance of <code>TimeZoneDisplayKey</code> with the specified properties.
         *  
         * @param timeZone the time zone
         * @param daylight adjust the style for daylight saving time if <code>true</code>
         * @param style the timezone style
         * @param locale the timezone locale
         */
        TimeZoneDisplayKey(TimeZone timeZone,
                           boolean daylight, int style, Locale locale) {
            mTimeZone = timeZone;
            if (daylight) {
                style |= 0x80000000;
            }
            mStyle = style;
            mLocale = locale;
        }

        /**
         * {@inheritDoc}
         */
        public int hashCode() {
            return mStyle * 31 + mLocale.hashCode();
        }

        /**
         * {@inheritDoc}
         */
        public boolean equals(Object obj) {
            if (this == obj) {
                return true;
            }
            if (obj instanceof TimeZoneDisplayKey) {
                TimeZoneDisplayKey other = (TimeZoneDisplayKey)obj;
                return
                    mTimeZone.equals(other.mTimeZone) &&
                    mStyle == other.mStyle &&
                    mLocale.equals(other.mLocale);
            }
            return false;
        }
    }

    // ----------------------------------------------------------------------
    /**
     * <p>Helper class for creating compound objects.</p>
     *
     * <p>One use for this class is to create a hashtable key
     * out of multiple objects.</p>
     */
    private static class Pair {
        private final Object mObj1;
        private final Object mObj2;

        /**
         * Constructs an instance of <code>Pair</code> to hold the specified objects.
         * @param obj1 one object in the pair
         * @param obj2 second object in the pair
         */
        public Pair(Object obj1, Object obj2) {
            mObj1 = obj1;
            mObj2 = obj2;
        }

        /**
         * {@inheritDoc}
         */
        public boolean equals(Object obj) {
            if (this == obj) {
                return true;
            }

            if (!(obj instanceof Pair)) {
                return false;
            }

            Pair key = (Pair)obj;

            return
                (mObj1 == null ?
                 key.mObj1 == null : mObj1.equals(key.mObj1)) &&
                (mObj2 == null ?
                 key.mObj2 == null : mObj2.equals(key.mObj2));
        }

        /**
         * {@inheritDoc}
         */
        public int hashCode() {
            return
                (mObj1 == null ? 0 : mObj1.hashCode()) +
                (mObj2 == null ? 0 : mObj2.hashCode());
        }

        /**
         * {@inheritDoc}
         */
        public String toString() {
            return "[" + mObj1 + ':' + mObj2 + ']';
        }
    }

}