lib/src/intl/date_format_field.dart - intl - Git at Google

 // Copyright (c) 2012, the Dart project authors.  Please see the AUTHORS file
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.

 part of intl;

 /**
  * This is a private class internal to DateFormat which is used for formatting
  * particular fields in a template. e.g. if the format is hh:mm:ss then the
  * fields would be "hh", ":", "mm", ":", and "ss". Each type of field knows
  * how to format that portion of a date.
  */
 abstract class _DateFormatField {
   /** The format string that defines us, e.g. "hh" */
   String pattern;

   /** The DateFormat that we are part of.*/
   DateFormat parent;

   _DateFormatField(this.pattern, this.parent);

   /**
    * Return the width of [pattern]. Different widths represent different
    * formatting options. See the comment for DateFormat for details.
    */
   int get width => pattern.length;

   String fullPattern() => pattern;

   String toString() => pattern;

   /** Format date according to our specification and return the result. */
   String format(DateTime date) {
     // Default implementation in the superclass, works for both types of
     // literal patterns, and is overridden by _DateFormatPatternField.
     return pattern;
   }

   /** Abstract method for subclasses to implementing parsing for their format.*/
   void parse(_Stream input, _DateBuilder dateFields);

   /**
    * Abstract method for subclasses to implementing 'loose' parsing for
    * their format, accepting input case-insensitively, and allowing some
    * delimiters to be skipped.
    */
   void parseLoose(_Stream input, _DateBuilder dateFields);

   /** Parse a literal field. We just look for the exact input. */
   void parseLiteral(_Stream input) {
     var found = input.read(width);
     if (found != pattern) {
       throwFormatException(input);
     }
   }

   /**
    * Parse a literal field. We accept either an exact match, or an arbitrary
    * amount of whitespace.
    */
   void parseLiteralLoose(_Stream input) {
     var found = input.peek(width);
     if (found == pattern) {
       input.read(width);
     }
     while (!input.atEnd() && input.peek().trim().isEmpty) {
       input.read();
     }
   }

   /** Throw a format exception with an error message indicating the position.*/
   void throwFormatException(_Stream stream) {
     throw new FormatException("Trying to read $this from ${stream.contents} "
         "at position ${stream.index}");
   }
 }

 /**
  * Represents a literal field - a sequence of characters that doesn't
  * change according to the date's data. As such, the implementation
  * is extremely simple.
  */
 class _DateFormatLiteralField extends _DateFormatField {
   _DateFormatLiteralField(pattern, parent) : super(pattern, parent);

   parse(_Stream input, _DateBuilder dateFields) {
     parseLiteral(input);
   }

   parseLoose(_Stream input, _DateBuilder dateFields) =>
       parseLiteralLoose(input);
 }

 /**
  * Represents a literal field with quoted characters in it. This is
  * only slightly more complex than a _DateFormatLiteralField.
  */
 class _DateFormatQuotedField extends _DateFormatField {
   String _fullPattern;

   String fullPattern() => _fullPattern;

   _DateFormatQuotedField(pattern, parent) : super(pattern, parent) {
     _fullPattern = pattern;
     patchQuotes();
   }

   parse(_Stream input, _DateBuilder dateFields) {
     parseLiteral(input);
   }

   parseLoose(_Stream input, _DateBuilder dateFields) =>
       parseLiteralLoose(input);

   void patchQuotes() {
     if (pattern == "''") {
       pattern = "'";
     } else {
       pattern = pattern.substring(1, pattern.length - 1);
       var twoEscapedQuotes = new RegExp(r"''");
       pattern = pattern.replaceAll(twoEscapedQuotes, "'");
     }
   }
 }

 /**
  * A field that parses "loosely", meaning that we'll accept input that is
  * missing delimiters, has upper/lower case mixed up, and might not strictly
  * conform to the pattern, e.g. the pattern calls for Sep we might accept
  * sep, september, sEPTember. Doesn't affect numeric fields.
  */
 class _LoosePatternField extends _DateFormatPatternField {
   _LoosePatternField(String pattern, parent) : super(pattern, parent);

   /**
     * Parse from a list of possibilities, but case-insensitively.
     * Assumes that input is lower case.
     */
   int parseEnumeratedString(_Stream input, List possibilities) {
     var lowercasePossibilities =
         possibilities.map((x) => x.toLowerCase()).toList();
     try {
       return super.parseEnumeratedString(input, lowercasePossibilities);
     } on FormatException {
       return -1;
     }
   }

   /**
    * Parse a month name, case-insensitively, and set it in [dateFields].
    * Assumes that [input] is lower case.
    */
   void parseMonth(input, dateFields) {
     if (width <= 2) {
       handleNumericField(input, dateFields.setMonth);
       return;
     }
     var possibilities = [symbols.MONTHS, symbols.SHORTMONTHS];
     for (var monthNames in possibilities) {
       var month = parseEnumeratedString(input, monthNames);
       if (month != -1) {
         dateFields.month = month + 1;
         return;
       }
     }
   }

   /**
    * Parse a standalone day name, case-insensitively.
    * Assumes that input is lower case. Doesn't do anything
    */
   void parseStandaloneDay(input) {
     // This is ignored, but we still have to skip over it the correct amount.
     if (width <= 2) {
       handleNumericField(input, (x) => x);
       return;
     }
     var possibilities = [
       symbols.STANDALONEWEEKDAYS,
       symbols.STANDALONESHORTWEEKDAYS
     ];
     for (var dayNames in possibilities) {
       var day = parseEnumeratedString(input, dayNames);
       if (day != -1) {
         return;
       }
     }
   }

   /**
    * Parse a standalone month name, case-insensitively.
    * Assumes that input is lower case. Doesn't do anything
    */
   void parseStandaloneMonth(input, dateFields) {
     if (width <= 2) {
       handleNumericField(input, (x) => x);
       return;
     }
     var possibilities = [
       symbols.STANDALONEMONTHS,
       symbols.STANDALONESHORTMONTHS
     ];
     for (var monthNames in possibilities) {
       var month = parseEnumeratedString(input, monthNames);
       if (month != -1) {
         dateFields.month = month + 1;
         return;
       }
     }
   }

   /**
    * Parse a day of the week name, case-insensitively.
    * Assumes that input is lower case. Doesn't do anything
    */
   void parseDayOfWeek(_Stream input) {
     // This is IGNORED, but we still have to skip over it the correct amount.
     if (width <= 2) {
       handleNumericField(input, (x) => x);
       return;
     }
     var possibilities = [symbols.WEEKDAYS, symbols.SHORTWEEKDAYS];
     for (var dayNames in possibilities) {
       var day = parseEnumeratedString(input, dayNames);
       if (day != -1) {
         return;
       }
     }
   }
 }

 /*
  * Represents a field in the pattern that formats some aspect of the
  * date. Consists primarily of a switch on the particular pattern characters
  * to determine what to do.
  */
 class _DateFormatPatternField extends _DateFormatField {
   _DateFormatPatternField(pattern, parent) : super(pattern, parent);

   /** Format date according to our specification and return the result. */
   String format(DateTime date) {
     return formatField(date);
   }

   /**
    * Parse the date according to our specification and put the result
    * into the correct place in dateFields.
    */
   void parse(_Stream input, _DateBuilder dateFields) {
     parseField(input, dateFields);
   }

   /**
    * Parse the date according to our specification and put the result
    * into the correct place in dateFields. Allow looser parsing, accepting
    * case-insensitive input and skipped delimiters.
    */
   void parseLoose(_Stream input, _DateBuilder dateFields) {
     new _LoosePatternField(pattern, parent).parse(input, dateFields);
   }

   /**
    * Parse a field representing part of a date pattern. Note that we do not
    * return a value, but rather build up the result in [builder].
    */
   void parseField(_Stream input, _DateBuilder builder) {
     try {
       switch (pattern[0]) {
         case 'a':
           parseAmPm(input, builder);
           break;
         case 'c':
           parseStandaloneDay(input);
           break;
         case 'd':
           handleNumericField(input, builder.setDay);
           break; // day
         // Day of year. Setting month=January with any day of the year works
         case 'D':
           handleNumericField(input, builder.setDay);
           break; // dayofyear
         case 'E':
           parseDayOfWeek(input);
           break;
         case 'G':
           break; // era
         case 'h':
           parse1To12Hours(input, builder);
           break;
         case 'H':
           handleNumericField(input, builder.setHour);
           break; // hour 0-23
         case 'K':
           handleNumericField(input, builder.setHour);
           break; //hour 0-11
         case 'k':
           handleNumericField(input, builder.setHour, -1);
           break; //hr 1-24
         case 'L':
           parseStandaloneMonth(input, builder);
           break;
         case 'M':
           parseMonth(input, builder);
           break;
         case 'm':
           handleNumericField(input, builder.setMinute);
           break; // minutes
         case 'Q':
           break; // quarter
         case 'S':
           handleNumericField(input, builder.setFractionalSecond);
           break;
         case 's':
           handleNumericField(input, builder.setSecond);
           break;
         case 'v':
           break; // time zone id
         case 'y':
           handleNumericField(input, builder.setYear);
           break;
         case 'z':
           break; // time zone
         case 'Z':
           break; // time zone RFC
         default:
           return;
       }
     } catch (e) {
       throwFormatException(input);
     }
   }

   /** Formatting logic if we are of type FIELD */
   String formatField(DateTime date) {
     switch (pattern[0]) {
       case 'a':
         return formatAmPm(date);
       case 'c':
         return formatStandaloneDay(date);
       case 'd':
         return formatDayOfMonth(date);
       case 'D':
         return formatDayOfYear(date);
       case 'E':
         return formatDayOfWeek(date);
       case 'G':
         return formatEra(date);
       case 'h':
         return format1To12Hours(date);
       case 'H':
         return format0To23Hours(date);
       case 'K':
         return format0To11Hours(date);
       case 'k':
         return format24Hours(date);
       case 'L':
         return formatStandaloneMonth(date);
       case 'M':
         return formatMonth(date);
       case 'm':
         return formatMinutes(date);
       case 'Q':
         return formatQuarter(date);
       case 'S':
         return formatFractionalSeconds(date);
       case 's':
         return formatSeconds(date);
       case 'v':
         return formatTimeZoneId(date);
       case 'y':
         return formatYear(date);
       case 'z':
         return formatTimeZone(date);
       case 'Z':
         return formatTimeZoneRFC(date);
       default:
         return '';
     }
   }

   /** Return the symbols for our current locale. */
   DateSymbols get symbols => dateTimeSymbols[parent.locale];

   formatEra(DateTime date) {
     var era = date.year > 0 ? 1 : 0;
     return width >= 4 ? symbols.ERANAMES[era] : symbols.ERAS[era];
   }

   formatYear(DateTime date) {
     // TODO(alanknight): Proper handling of years <= 0
     var year = date.year;
     if (year < 0) {
       year = -year;
     }
     return width == 2 ? padTo(2, year % 100) : padTo(width, year);
   }

   /**
    * We are given [input] as a stream from which we want to read a date. We
    * can't dynamically build up a date, so we are given a list [dateFields] of
    * the constructor arguments and an [position] at which to set it
    * (year,month,day,hour,minute,second,fractionalSecond)
    * then after all parsing is done we construct a date from the arguments.
    * This method handles reading any of the numeric fields. The [offset]
    * argument allows us to compensate for zero-based versus one-based values.
    */
   void handleNumericField(_Stream input, Function setter, [int offset = 0]) {
     var result = input.nextInteger();
     if (result == null) throwFormatException(input);
     setter(result + offset);
   }

   /**
    * We are given [input] as a stream from which we want to read a date. We
    * can't dynamically build up a date, so we are given a list [dateFields] of
    * the constructor arguments and an [position] at which to set it
    * (year,month,day,hour,minute,second,fractionalSecond)
    * then after all parsing is done we construct a date from the arguments.
    * This method handles reading any of string fields from an enumerated set.
    */
   int parseEnumeratedString(_Stream input, List possibilities) {
     var results = new _Stream(possibilities)
         .findIndexes((each) => input.peek(each.length) == each);
     if (results.isEmpty) throwFormatException(input);
     results.sort(
         (a, b) => possibilities[a].length.compareTo(possibilities[b].length));
     var longestResult = results.last;
     input.read(possibilities[longestResult].length);
     return longestResult;
   }

   String formatMonth(DateTime date) {
     switch (width) {
       case 5:
         return symbols.NARROWMONTHS[date.month - 1];
       case 4:
         return symbols.MONTHS[date.month - 1];
       case 3:
         return symbols.SHORTMONTHS[date.month - 1];
       default:
         return padTo(width, date.month);
     }
   }

   void parseMonth(input, dateFields) {
     var possibilities;
     switch (width) {
       case 5:
         possibilities = symbols.NARROWMONTHS;
         break;
       case 4:
         possibilities = symbols.MONTHS;
         break;
       case 3:
         possibilities = symbols.SHORTMONTHS;
         break;
       default:
         return handleNumericField(input, dateFields.setMonth);
     }
     dateFields.month = parseEnumeratedString(input, possibilities) + 1;
   }

   String format24Hours(DateTime date) {
     return padTo(width, date.hour);
   }

   String formatFractionalSeconds(DateTime date) {
     // Always print at least 3 digits. If the width is greater, append 0s
     var basic = padTo(3, date.millisecond);
     if (width - 3 > 0) {
       var extra = padTo(width - 3, 0);
       return basic + extra;
     } else {
       return basic;
     }
   }

   String formatAmPm(DateTime date) {
     var hours = date.hour;
     var index = (date.hour >= 12) && (date.hour < 24) ? 1 : 0;
     var ampm = symbols.AMPMS;
     return ampm[index];
   }

   void parseAmPm(input, dateFields) {
     // If we see a "PM" note it in an extra field.
     var ampm = parseEnumeratedString(input, symbols.AMPMS);
     if (ampm == 1) dateFields.pm = true;
   }

   String format1To12Hours(DateTime date) {
     var hours = date.hour;
     if (date.hour > 12) hours = hours - 12;
     if (hours == 0) hours = 12;
     return padTo(width, hours);
   }

   void parse1To12Hours(_Stream input, _DateBuilder dateFields) {
     handleNumericField(input, dateFields.setHour);
     if (dateFields.hour == 12) dateFields.hour = 0;
   }

   String format0To11Hours(DateTime date) {
     return padTo(width, date.hour % 12);
   }

   String format0To23Hours(DateTime date) {
     return padTo(width, date.hour);
   }

   String formatStandaloneDay(DateTime date) {
     switch (width) {
       case 5:
         return symbols.STANDALONENARROWWEEKDAYS[date.weekday % 7];
       case 4:
         return symbols.STANDALONEWEEKDAYS[date.weekday % 7];
       case 3:
         return symbols.STANDALONESHORTWEEKDAYS[date.weekday % 7];
       default:
         return padTo(1, date.day);
     }
   }

   void parseStandaloneDay(_Stream input) {
     // This is ignored, but we still have to skip over it the correct amount.
     var possibilities;
     switch (width) {
       case 5:
         possibilities = symbols.STANDALONENARROWWEEKDAYS;
         break;
       case 4:
         possibilities = symbols.STANDALONEWEEKDAYS;
         break;
       case 3:
         possibilities = symbols.STANDALONESHORTWEEKDAYS;
         break;
       default:
         return handleNumericField(input, (x) => x);
     }
     parseEnumeratedString(input, possibilities);
   }

   String formatStandaloneMonth(DateTime date) {
     switch (width) {
       case 5:
         return symbols.STANDALONENARROWMONTHS[date.month - 1];
       case 4:
         return symbols.STANDALONEMONTHS[date.month - 1];
       case 3:
         return symbols.STANDALONESHORTMONTHS[date.month - 1];
       default:
         return padTo(width, date.month);
     }
   }

   void parseStandaloneMonth(input, dateFields) {
     var possibilities;
     switch (width) {
       case 5:
         possibilities = symbols.STANDALONENARROWMONTHS;
         break;
       case 4:
         possibilities = symbols.STANDALONEMONTHS;
         break;
       case 3:
         possibilities = symbols.STANDALONESHORTMONTHS;
         break;
       default:
         return handleNumericField(input, dateFields.setMonth);
     }
     dateFields.month = parseEnumeratedString(input, possibilities) + 1;
   }

   String formatQuarter(DateTime date) {
     var quarter = ((date.month - 1) / 3).truncate();
     if (width < 4) {
       return symbols.SHORTQUARTERS[quarter];
     } else {
       return symbols.QUARTERS[quarter];
     }
   }
   String formatDayOfMonth(DateTime date) {
     return padTo(width, date.day);
   }

   String formatDayOfYear(DateTime date) => padTo(width, dayNumberInYear(date));

   /** Return the ordinal day, i.e. the day number in the year. */
   int dayNumberInYear(DateTime date) {
     if (date.month == 1) return date.day;
     if (date.month == 2) return date.day + 31;
     return ordinalDayFromMarchFirst(date) + 59 + (isLeapYear(date) ? 1 : 0);
   }

   /**
    * Return the day of the year counting March 1st as 1, after which the
    * number of days per month is constant, so it's easier to calculate.
    * Formula from http://en.wikipedia.org/wiki/Ordinal_date
    */
   int ordinalDayFromMarchFirst(DateTime date) =>
       ((30.6 * date.month) - 91.4).floor() + date.day;

   /**
    * Return true if this is a leap year. Rely on [DateTime] to do the
    * underlying calculation, even though it doesn't expose the test to us.
    */
   bool isLeapYear(DateTime date) {
     var feb29 = new DateTime(date.year, 2, 29);
     return feb29.month == 2;
   }

   String formatDayOfWeek(DateTime date) {
     // Note that Dart's weekday returns 1 for Monday and 7 for Sunday.
     return (width >= 4
         ? symbols.WEEKDAYS
         : symbols.SHORTWEEKDAYS)[(date.weekday) % 7];
   }

   void parseDayOfWeek(_Stream input) {
     // This is IGNORED, but we still have to skip over it the correct amount.
     var possibilities = width >= 4 ? symbols.WEEKDAYS : symbols.SHORTWEEKDAYS;
     parseEnumeratedString(input, possibilities);
   }

   String formatMinutes(DateTime date) {
     return padTo(width, date.minute);
   }

   String formatSeconds(DateTime date) {
     return padTo(width, date.second);
   }

   String formatTimeZoneId(DateTime date) {
     // TODO(alanknight): implement time zone support
     throw new UnimplementedError();
   }

   String formatTimeZone(DateTime date) {
     throw new UnimplementedError();
   }

   String formatTimeZoneRFC(DateTime date) {
     throw new UnimplementedError();
   }

   /**
   * Return a string representation of the object padded to the left with
   * zeros. Primarily useful for numbers.
   */
   String padTo(int width, Object toBePrinted) {
     var basicString = toBePrinted.toString();
     if (basicString.length >= width) return basicString;
     var buffer = new StringBuffer();
     for (var i = 0; i < width - basicString.length; i++) {
       buffer.write('0');
     }
     buffer.write(basicString);
     return buffer.toString();
   }
 }
	// Copyright (c) 2012, the Dart project authors. Please see the AUTHORS file
	// for details. All rights reserved. Use of this source code is governed by a
	// BSD-style license that can be found in the LICENSE file.

	part of intl;

	/**
	* This is a private class internal to DateFormat which is used for formatting
	* particular fields in a template. e.g. if the format is hh:mm:ss then the
	* fields would be "hh", ":", "mm", ":", and "ss". Each type of field knows
	* how to format that portion of a date.
	*/
	abstract class _DateFormatField {
	/** The format string that defines us, e.g. "hh" */
	String pattern;

	/** The DateFormat that we are part of.*/
	DateFormat parent;

	_DateFormatField(this.pattern, this.parent);

	/**
	* Return the width of [pattern]. Different widths represent different
	* formatting options. See the comment for DateFormat for details.
	*/
	int get width => pattern.length;

	String fullPattern() => pattern;

	String toString() => pattern;

	/** Format date according to our specification and return the result. */
	String format(DateTime date) {
	// Default implementation in the superclass, works for both types of
	// literal patterns, and is overridden by _DateFormatPatternField.
	return pattern;
	}

	/** Abstract method for subclasses to implementing parsing for their format.*/
	void parse(_Stream input, _DateBuilder dateFields);

	/**
	* Abstract method for subclasses to implementing 'loose' parsing for
	* their format, accepting input case-insensitively, and allowing some
	* delimiters to be skipped.
	*/
	void parseLoose(_Stream input, _DateBuilder dateFields);

	/** Parse a literal field. We just look for the exact input. */
	void parseLiteral(_Stream input) {
	var found = input.read(width);
	if (found != pattern) {
	throwFormatException(input);
	}
	}

	/**
	* Parse a literal field. We accept either an exact match, or an arbitrary
	* amount of whitespace.
	*/
	void parseLiteralLoose(_Stream input) {
	var found = input.peek(width);
	if (found == pattern) {
	input.read(width);
	}
	while (!input.atEnd() && input.peek().trim().isEmpty) {
	input.read();
	}
	}

	/** Throw a format exception with an error message indicating the position.*/
	void throwFormatException(_Stream stream) {
	throw new FormatException("Trying to read $this from ${stream.contents} "
	"at position ${stream.index}");
	}
	}

	/**
	* Represents a literal field - a sequence of characters that doesn't
	* change according to the date's data. As such, the implementation
	* is extremely simple.
	*/
	class _DateFormatLiteralField extends _DateFormatField {
	_DateFormatLiteralField(pattern, parent) : super(pattern, parent);

	parse(_Stream input, _DateBuilder dateFields) {
	parseLiteral(input);
	}

	parseLoose(_Stream input, _DateBuilder dateFields) =>
	parseLiteralLoose(input);
	}

	/**
	* Represents a literal field with quoted characters in it. This is
	* only slightly more complex than a _DateFormatLiteralField.
	*/
	class _DateFormatQuotedField extends _DateFormatField {
	String _fullPattern;

	String fullPattern() => _fullPattern;

	_DateFormatQuotedField(pattern, parent) : super(pattern, parent) {
	_fullPattern = pattern;
	patchQuotes();
	}

	parse(_Stream input, _DateBuilder dateFields) {
	parseLiteral(input);
	}

	parseLoose(_Stream input, _DateBuilder dateFields) =>
	parseLiteralLoose(input);

	void patchQuotes() {
	if (pattern == "''") {
	pattern = "'";
	} else {
	pattern = pattern.substring(1, pattern.length - 1);
	var twoEscapedQuotes = new RegExp(r"''");
	pattern = pattern.replaceAll(twoEscapedQuotes, "'");
	}
	}
	}

	/**
	* A field that parses "loosely", meaning that we'll accept input that is
	* missing delimiters, has upper/lower case mixed up, and might not strictly
	* conform to the pattern, e.g. the pattern calls for Sep we might accept
	* sep, september, sEPTember. Doesn't affect numeric fields.
	*/
	class _LoosePatternField extends _DateFormatPatternField {
	_LoosePatternField(String pattern, parent) : super(pattern, parent);

	/**
	* Parse from a list of possibilities, but case-insensitively.
	* Assumes that input is lower case.
	*/
	int parseEnumeratedString(_Stream input, List possibilities) {
	var lowercasePossibilities =
	possibilities.map((x) => x.toLowerCase()).toList();
	try {
	return super.parseEnumeratedString(input, lowercasePossibilities);
	} on FormatException {
	return -1;
	}
	}

	/**
	* Parse a month name, case-insensitively, and set it in [dateFields].
	* Assumes that [input] is lower case.
	*/
	void parseMonth(input, dateFields) {
	if (width <= 2) {
	handleNumericField(input, dateFields.setMonth);
	return;
	}
	var possibilities = [symbols.MONTHS, symbols.SHORTMONTHS];
	for (var monthNames in possibilities) {
	var month = parseEnumeratedString(input, monthNames);
	if (month != -1) {
	dateFields.month = month + 1;
	return;
	}
	}
	}

	/**
	* Parse a standalone day name, case-insensitively.
	* Assumes that input is lower case. Doesn't do anything
	*/
	void parseStandaloneDay(input) {
	// This is ignored, but we still have to skip over it the correct amount.
	if (width <= 2) {
	handleNumericField(input, (x) => x);
	return;
	}
	var possibilities = [
	symbols.STANDALONEWEEKDAYS,
	symbols.STANDALONESHORTWEEKDAYS
	];
	for (var dayNames in possibilities) {
	var day = parseEnumeratedString(input, dayNames);
	if (day != -1) {
	return;
	}
	}
	}

	/**
	* Parse a standalone month name, case-insensitively.
	* Assumes that input is lower case. Doesn't do anything
	*/
	void parseStandaloneMonth(input, dateFields) {
	if (width <= 2) {
	handleNumericField(input, (x) => x);
	return;
	}
	var possibilities = [
	symbols.STANDALONEMONTHS,
	symbols.STANDALONESHORTMONTHS
	];
	for (var monthNames in possibilities) {
	var month = parseEnumeratedString(input, monthNames);
	if (month != -1) {
	dateFields.month = month + 1;
	return;
	}
	}
	}

	/**
	* Parse a day of the week name, case-insensitively.
	* Assumes that input is lower case. Doesn't do anything
	*/
	void parseDayOfWeek(_Stream input) {
	// This is IGNORED, but we still have to skip over it the correct amount.
	if (width <= 2) {
	handleNumericField(input, (x) => x);
	return;
	}
	var possibilities = [symbols.WEEKDAYS, symbols.SHORTWEEKDAYS];
	for (var dayNames in possibilities) {
	var day = parseEnumeratedString(input, dayNames);
	if (day != -1) {
	return;
	}
	}
	}
	}

	/*
	* Represents a field in the pattern that formats some aspect of the
	* date. Consists primarily of a switch on the particular pattern characters
	* to determine what to do.
	*/
	class _DateFormatPatternField extends _DateFormatField {
	_DateFormatPatternField(pattern, parent) : super(pattern, parent);

	/** Format date according to our specification and return the result. */
	String format(DateTime date) {
	return formatField(date);
	}

	/**
	* Parse the date according to our specification and put the result
	* into the correct place in dateFields.
	*/
	void parse(_Stream input, _DateBuilder dateFields) {
	parseField(input, dateFields);
	}

	/**
	* Parse the date according to our specification and put the result
	* into the correct place in dateFields. Allow looser parsing, accepting
	* case-insensitive input and skipped delimiters.
	*/
	void parseLoose(_Stream input, _DateBuilder dateFields) {
	new _LoosePatternField(pattern, parent).parse(input, dateFields);
	}

	/**
	* Parse a field representing part of a date pattern. Note that we do not
	* return a value, but rather build up the result in [builder].
	*/
	void parseField(_Stream input, _DateBuilder builder) {
	try {
	switch (pattern[0]) {
	case 'a':
	parseAmPm(input, builder);
	break;
	case 'c':
	parseStandaloneDay(input);
	break;
	case 'd':
	handleNumericField(input, builder.setDay);
	break; // day
	// Day of year. Setting month=January with any day of the year works
	case 'D':
	handleNumericField(input, builder.setDay);
	break; // dayofyear
	case 'E':
	parseDayOfWeek(input);
	break;
	case 'G':
	break; // era
	case 'h':
	parse1To12Hours(input, builder);
	break;
	case 'H':
	handleNumericField(input, builder.setHour);
	break; // hour 0-23
	case 'K':
	handleNumericField(input, builder.setHour);
	break; //hour 0-11
	case 'k':
	handleNumericField(input, builder.setHour, -1);
	break; //hr 1-24
	case 'L':
	parseStandaloneMonth(input, builder);
	break;
	case 'M':
	parseMonth(input, builder);
	break;
	case 'm':
	handleNumericField(input, builder.setMinute);
	break; // minutes
	case 'Q':
	break; // quarter
	case 'S':
	handleNumericField(input, builder.setFractionalSecond);
	break;
	case 's':
	handleNumericField(input, builder.setSecond);
	break;
	case 'v':
	break; // time zone id
	case 'y':
	handleNumericField(input, builder.setYear);
	break;
	case 'z':
	break; // time zone
	case 'Z':
	break; // time zone RFC
	default:
	return;
	}
	} catch (e) {
	throwFormatException(input);
	}
	}

	/** Formatting logic if we are of type FIELD */
	String formatField(DateTime date) {
	switch (pattern[0]) {
	case 'a':
	return formatAmPm(date);
	case 'c':
	return formatStandaloneDay(date);
	case 'd':
	return formatDayOfMonth(date);
	case 'D':
	return formatDayOfYear(date);
	case 'E':
	return formatDayOfWeek(date);
	case 'G':
	return formatEra(date);
	case 'h':
	return format1To12Hours(date);
	case 'H':
	return format0To23Hours(date);
	case 'K':
	return format0To11Hours(date);
	case 'k':
	return format24Hours(date);
	case 'L':
	return formatStandaloneMonth(date);
	case 'M':
	return formatMonth(date);
	case 'm':
	return formatMinutes(date);
	case 'Q':
	return formatQuarter(date);
	case 'S':
	return formatFractionalSeconds(date);
	case 's':
	return formatSeconds(date);
	case 'v':
	return formatTimeZoneId(date);
	case 'y':
	return formatYear(date);
	case 'z':
	return formatTimeZone(date);
	case 'Z':
	return formatTimeZoneRFC(date);
	default:
	return '';
	}
	}

	/** Return the symbols for our current locale. */
	DateSymbols get symbols => dateTimeSymbols[parent.locale];

	formatEra(DateTime date) {
	var era = date.year > 0 ? 1 : 0;
	return width >= 4 ? symbols.ERANAMES[era] : symbols.ERAS[era];
	}

	formatYear(DateTime date) {
	// TODO(alanknight): Proper handling of years <= 0
	var year = date.year;
	if (year < 0) {
	year = -year;
	}
	return width == 2 ? padTo(2, year % 100) : padTo(width, year);
	}

	/**
	* We are given [input] as a stream from which we want to read a date. We
	* can't dynamically build up a date, so we are given a list [dateFields] of
	* the constructor arguments and an [position] at which to set it
	* (year,month,day,hour,minute,second,fractionalSecond)
	* then after all parsing is done we construct a date from the arguments.
	* This method handles reading any of the numeric fields. The [offset]
	* argument allows us to compensate for zero-based versus one-based values.
	*/
	void handleNumericField(_Stream input, Function setter, [int offset = 0]) {
	var result = input.nextInteger();
	if (result == null) throwFormatException(input);
	setter(result + offset);
	}

	/**
	* We are given [input] as a stream from which we want to read a date. We
	* can't dynamically build up a date, so we are given a list [dateFields] of
	* the constructor arguments and an [position] at which to set it
	* (year,month,day,hour,minute,second,fractionalSecond)
	* then after all parsing is done we construct a date from the arguments.
	* This method handles reading any of string fields from an enumerated set.
	*/
	int parseEnumeratedString(_Stream input, List possibilities) {
	var results = new _Stream(possibilities)
	.findIndexes((each) => input.peek(each.length) == each);
	if (results.isEmpty) throwFormatException(input);
	results.sort(
	(a, b) => possibilities[a].length.compareTo(possibilities[b].length));
	var longestResult = results.last;
	input.read(possibilities[longestResult].length);
	return longestResult;
	}

	String formatMonth(DateTime date) {
	switch (width) {
	case 5:
	return symbols.NARROWMONTHS[date.month - 1];
	case 4:
	return symbols.MONTHS[date.month - 1];
	case 3:
	return symbols.SHORTMONTHS[date.month - 1];
	default:
	return padTo(width, date.month);
	}
	}

	void parseMonth(input, dateFields) {
	var possibilities;
	switch (width) {
	case 5:
	possibilities = symbols.NARROWMONTHS;
	break;
	case 4:
	possibilities = symbols.MONTHS;
	break;
	case 3:
	possibilities = symbols.SHORTMONTHS;
	break;
	default:
	return handleNumericField(input, dateFields.setMonth);
	}
	dateFields.month = parseEnumeratedString(input, possibilities) + 1;
	}

	String format24Hours(DateTime date) {
	return padTo(width, date.hour);
	}

	String formatFractionalSeconds(DateTime date) {
	// Always print at least 3 digits. If the width is greater, append 0s
	var basic = padTo(3, date.millisecond);
	if (width - 3 > 0) {
	var extra = padTo(width - 3, 0);
	return basic + extra;
	} else {
	return basic;
	}
	}

	String formatAmPm(DateTime date) {
	var hours = date.hour;
	var index = (date.hour >= 12) && (date.hour < 24) ? 1 : 0;
	var ampm = symbols.AMPMS;
	return ampm[index];
	}

	void parseAmPm(input, dateFields) {
	// If we see a "PM" note it in an extra field.
	var ampm = parseEnumeratedString(input, symbols.AMPMS);
	if (ampm == 1) dateFields.pm = true;
	}

	String format1To12Hours(DateTime date) {
	var hours = date.hour;
	if (date.hour > 12) hours = hours - 12;
	if (hours == 0) hours = 12;
	return padTo(width, hours);
	}

	void parse1To12Hours(_Stream input, _DateBuilder dateFields) {
	handleNumericField(input, dateFields.setHour);
	if (dateFields.hour == 12) dateFields.hour = 0;
	}

	String format0To11Hours(DateTime date) {
	return padTo(width, date.hour % 12);
	}

	String format0To23Hours(DateTime date) {
	return padTo(width, date.hour);
	}

	String formatStandaloneDay(DateTime date) {
	switch (width) {
	case 5:
	return symbols.STANDALONENARROWWEEKDAYS[date.weekday % 7];
	case 4:
	return symbols.STANDALONEWEEKDAYS[date.weekday % 7];
	case 3:
	return symbols.STANDALONESHORTWEEKDAYS[date.weekday % 7];
	default:
	return padTo(1, date.day);
	}
	}

	void parseStandaloneDay(_Stream input) {
	// This is ignored, but we still have to skip over it the correct amount.
	var possibilities;
	switch (width) {
	case 5:
	possibilities = symbols.STANDALONENARROWWEEKDAYS;
	break;
	case 4:
	possibilities = symbols.STANDALONEWEEKDAYS;
	break;
	case 3:
	possibilities = symbols.STANDALONESHORTWEEKDAYS;
	break;
	default:
	return handleNumericField(input, (x) => x);
	}
	parseEnumeratedString(input, possibilities);
	}

	String formatStandaloneMonth(DateTime date) {
	switch (width) {
	case 5:
	return symbols.STANDALONENARROWMONTHS[date.month - 1];
	case 4:
	return symbols.STANDALONEMONTHS[date.month - 1];
	case 3:
	return symbols.STANDALONESHORTMONTHS[date.month - 1];
	default:
	return padTo(width, date.month);
	}
	}

	void parseStandaloneMonth(input, dateFields) {
	var possibilities;
	switch (width) {
	case 5:
	possibilities = symbols.STANDALONENARROWMONTHS;
	break;
	case 4:
	possibilities = symbols.STANDALONEMONTHS;
	break;
	case 3:
	possibilities = symbols.STANDALONESHORTMONTHS;
	break;
	default:
	return handleNumericField(input, dateFields.setMonth);
	}
	dateFields.month = parseEnumeratedString(input, possibilities) + 1;
	}

	String formatQuarter(DateTime date) {
	var quarter = ((date.month - 1) / 3).truncate();
	if (width < 4) {
	return symbols.SHORTQUARTERS[quarter];
	} else {
	return symbols.QUARTERS[quarter];
	}
	}
	String formatDayOfMonth(DateTime date) {
	return padTo(width, date.day);
	}

	String formatDayOfYear(DateTime date) => padTo(width, dayNumberInYear(date));

	/** Return the ordinal day, i.e. the day number in the year. */
	int dayNumberInYear(DateTime date) {
	if (date.month == 1) return date.day;
	if (date.month == 2) return date.day + 31;
	return ordinalDayFromMarchFirst(date) + 59 + (isLeapYear(date) ? 1 : 0);
	}

	/**
	* Return the day of the year counting March 1st as 1, after which the
	* number of days per month is constant, so it's easier to calculate.
	* Formula from http://en.wikipedia.org/wiki/Ordinal_date
	*/
	int ordinalDayFromMarchFirst(DateTime date) =>
	((30.6 * date.month) - 91.4).floor() + date.day;

	/**
	* Return true if this is a leap year. Rely on [DateTime] to do the
	* underlying calculation, even though it doesn't expose the test to us.
	*/
	bool isLeapYear(DateTime date) {
	var feb29 = new DateTime(date.year, 2, 29);
	return feb29.month == 2;
	}

	String formatDayOfWeek(DateTime date) {
	// Note that Dart's weekday returns 1 for Monday and 7 for Sunday.
	return (width >= 4
	? symbols.WEEKDAYS
	: symbols.SHORTWEEKDAYS)[(date.weekday) % 7];
	}

	void parseDayOfWeek(_Stream input) {
	// This is IGNORED, but we still have to skip over it the correct amount.
	var possibilities = width >= 4 ? symbols.WEEKDAYS : symbols.SHORTWEEKDAYS;
	parseEnumeratedString(input, possibilities);
	}

	String formatMinutes(DateTime date) {
	return padTo(width, date.minute);
	}

	String formatSeconds(DateTime date) {
	return padTo(width, date.second);
	}

	String formatTimeZoneId(DateTime date) {
	// TODO(alanknight): implement time zone support
	throw new UnimplementedError();
	}

	String formatTimeZone(DateTime date) {
	throw new UnimplementedError();
	}

	String formatTimeZoneRFC(DateTime date) {
	throw new UnimplementedError();
	}

	/**
	* Return a string representation of the object padded to the left with
	* zeros. Primarily useful for numbers.
	*/
	String padTo(int width, Object toBePrinted) {
	var basicString = toBePrinted.toString();
	if (basicString.length >= width) return basicString;
	var buffer = new StringBuffer();
	for (var i = 0; i < width - basicString.length; i++) {
	buffer.write('0');
	}
	buffer.write(basicString);
	return buffer.toString();
	}
	}