Added i18n skeleton API for message_formatting

lib/i18n/date_format.dart

Index: lib/i18n/date_format.dart
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+/**
+ * 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.
+ *
+ * DateFormat is for formatting and parsing dates in a locale-sensitive 
+ * manner. 
+ * It allows the user to use any customized pattern to parse or format 
+ * date-time strings under certain locales. Date elements that vary across 
+ * locales include month name, weekname, field, order, etc.
+ *
+ * This library uses the ICU/JDK date/time pattern specification as described
+ * below.
+ *
+ * Time Format Syntax: To specify the time format use a time pattern string.
+ * In this pattern, following letters are reserved as pattern letters, which
+ * are defined in the following manner:
+ *
+ *     Symbol   Meaning                Presentation        Example
+ *     ------   -------                ------------        -------
+ *     G        era designator         (Text)              AD
+ *     y#       year                   (Number)            1996
+ *     M        month in year          (Text & Number)     July & 07
+ *     d        day in month           (Number)            10
+ *     h        hour in am/pm (1~12)   (Number)            12
+ *     H        hour in day (0~23)     (Number)            0
+ *     m        minute in hour         (Number)            30
+ *     s        second in minute       (Number)            55
+ *     S        fractional second      (Number)            978
+ *     E        day of week            (Text)              Tuesday
+ *     D        day in year            (Number)            189
+ *     a        am/pm marker           (Text)              PM
+ *     k        hour in day (1~24)     (Number)            24
+ *     K        hour in am/pm (0~11)   (Number)            0
+ *     z        time zone              (Text)              Pacific Standard Time
+ *     Z        time zone (RFC 822)    (Number)            -0800
+ *     v        time zone (generic)    (Text)              Pacific Time
+ *     '        escape for text        (Delimiter)         'Date='
+ *     ''       single quote           (Literal)           'o''clock'
+ *
+ * Items marked with '#' work differently than in Java.
+ *
+ * The count of pattern letters determine the format.
+ * (Text): 4 or more pattern letters--use full form,
+ *         less than 4--use short or abbreviated form if one exists.
+ *         In parsing, we will always try long format, then short.
+ *         (e.g., "EEEE" produces "Monday", "EEE" produces "Mon")
+ *
+ * (Number): the minimum number of digits. Shorter numbers are zero-padded to
+ * this amount (e.g. if "m" produces "6", "mm" produces "06"). Year is handled
+ * specially; that is, if the count of 'y' is 2, the Year will be truncated to
+ * 2 digits. (e.g., if "yyyy" produces "1997", "yy" produces "97".) Unlike other
+ * fields, fractional seconds are padded on the right with zero.
+ *
+ * (Text & Number): 3 or over, use text, otherwise use number.
+ *
+ * Any characters that not in the pattern will be treated as quoted text. For
+ * instance, characters like ':', '.', ' ', '#' and '@' will appear in the
+ * resulting time text even they are not embraced within single quotes. In our
+ * current pattern usage, we didn't use up all letters. But those unused
+ * letters are strongly discouraged to be used as quoted text without quote.
+ * That's because we may use other letter for pattern in future.
+ *
+ * Examples Using the US Locale:
+ *
+ *     Format Pattern                         Result
+ *     --------------                         -------
+ *     "yyyy.MM.dd G 'at' HH:mm:ss vvvv"->> 1996.07.10 AD at 15:08:56 Pacific Time
+ *     "EEE, MMM d, ''yy"               ->> Wed, July 10, '96
+ *     "h:mm a"                         ->> 12:08 PM
+ *     "hh 'o''clock' a, zzzz"          ->> 12 o'clock PM, Pacific Daylight Time
+ *     "K:mm a, vvv"                    ->> 0:00 PM, PT
+ *     "yyyyy.MMMMM.dd GGG hh:mm aaa"   ->> 01996.July.10 AD 12:08 PM
+ *
+ * When parsing a date string using the abbreviated year pattern ("yy"),
+ * DateTimeParse must interpret the abbreviated year relative to some
+ * century. It does this by adjusting dates to be within 80 years before and 20
+ * years after the time the parse function is called. For example, using a
+ * pattern of "MM/dd/yy" and a DateTimeParse instance created on Jan 1, 1997,
+ * the string "01/11/12" would be interpreted as Jan 11, 2012 while the string
+ * "05/04/64" would be interpreted as May 4, 1964. During parsing, only
+ * strings consisting of exactly two digits, as defined by {@link
+ * java.lang.Character#isDigit(char)}, will be parsed into the default
+ * century. Any other numeric string, such as a one digit string, a three or
+ * more digit string will be interpreted as its face value.
+ *
+ * If the year pattern does not have exactly two 'y' characters, the year is
+ * interpreted literally, regardless of the number of digits. So using the
+ * pattern "MM/dd/yyyy", "01/11/12" parses to Jan 11, 12 A.D.
+ *
+ * When numeric fields abut one another directly, with no intervening
+ * delimiter characters, they constitute a run of abutting numeric fields. Such
+ * runs are parsed specially. For example, the format "HHmmss" parses the input
+ * text "123456" to 12:34:56, parses the input text "12345" to 1:23:45, and
+ * fails to parse "1234". In other words, the leftmost field of the run is
+ * flexible, while the others keep a fixed width. If the parse fails anywhere in
+ * the run, then the leftmost field is shortened by one character, and the
+ * entire run is parsed again. This is repeated until either the parse succeeds
+ * or the leftmost field is one character in length. If the parse still fails at
+ * that point, the parse of the run fails.
+ */
+
+#library('DateFormat');
+
+class DateFormat {
+
+  /** Definition of this object formats dates. */
+  var formatDefinition;
+
+   /** Date/Time format patterns. */
+   // TODO(alanknight): There's a style question of whether to use fullDate or 
+   // FULL_DATE naming conventions.
+   static final int _fullDate = 0;
+   static final int _longDate = 1;
+   static final int _mediumDate = 2;
+   static final int _shortDate = 3;
+   static final int _fullTime = 4;
+   static final int _longTime = 5;
+   static final int _mediumTime = 6;
+   static final int _shortTime = 7;
+   static final int _fullDateTime = 8;
+   static final int _longDateTime = 9;
+   static final int _mediumDateTime = 10;
+   static final int _shortDateTime = 11;
+    
+  /**
+   * Named constructors for each of the above values.
+   * These could probably be made shorter if we just set the format to the 
+   * constant and the parsing was lazy.
+   */
+  DateFormat.fullDate() : this.formatDefinition = _fullDate;
+  DateFormat.longDate() : this.formatDefinition = _longDate;
+  DateFormat.mediumDate() : this.formatDefinition = _mediumDate;
+  DateFormat.shortDate() : this.formatDefinition = _shortDate;
+  DateFormat.fullTime() : this.formatDefinition = _fullTime;
+  DateFormat.longTime() : this.formatDefinition = _longTime;
+  DateFormat.mediumTime() : this.formatDefinition = _mediumTime;
+  DateFormat.shortTime() : this.formatDefinition = _shortTime;
+  DateFormat.fullDateTime() : this.formatDefinition = _fullDateTime;
+  DateFormat.longDateTime() : this.formatDefinition = _longDateTime;
+  DateFormat.mediumDateTime() : this.formatDefinition = _mediumDateTime;
+  DateFormat.shortDateTime() : this.formatDefinition = _shortDateTime;
+  
+  DateFormat(this.formatDefinition);
+
+  /**
+   * 
+   */
+  String parse(String inputString) {
+    return inputString;
+  }
+
+ /**
+  * Format the given [date] object according to preset pattern and current 
+  * locale and return a formated string for the given date.
+  */
+  String format(Date date, [TimeZone timeZone]) {

[Alan Knight, 2012/05/30 21:45:30]

I don't love the name format for this method, as the obvious thing to name an
object of this type is something like "format" and you end up with
format.format(thing). I'd originally called it print, but that may have
connotations of side effects. Closure does use "format"

[Emily Fortuna, 2012/05/30 22:18:07]

I understand your concern, but I'm inclined to go with it as it seems to be the
"standard practice": Java and Python and GWT all use "format"

+    // TODO(efortuna): optional TimeZone argument? TimeZone is deprecated...
+    return date.toString();
+  }
+}