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Issue 10829442: Rename i18n to intl (Closed) Base URL: http://dart.googlecode.com/svn/branches/bleeding_edge/dart/
Patch Set: Created 8 years, 4 months ago
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1 // Copyright (c) 2012, the Dart project authors. Please see the AUTHORS file
2 // for details. All rights reserved. Use of this source code is governed by a
3 // BSD-style license that can be found in the LICENSE file.
4
5 /**
6 * DateFormat is for formatting and parsing dates in a locale-sensitive
7 * manner.
8 * It allows the user to choose from a set of standard date time formats as well
9 * as specify a customized pattern under certain locales. Date elements that
10 * vary across locales include month name, week name, field order, etc.
11 * <!-- TODO(efortuna): Customized pattern system -- suggested by i18n needs
12 * feedback on appropriateness. -->
13 * We also allow the user to use any customized pattern to parse or format
14 * date-time strings under certain locales. Date elements that vary across
15 * locales include month name, weekname, field, order, etc.
16 *
17 * This library uses the ICU/JDK date/time pattern specification both for
18 * complete format specifications and also the abbreviated "skeleton" form
19 * which can also adapt to different locales and is preferred where available.
20 *
21 * Skeletons: These can be specified either as the ICU constant name or as the
22 * skeleton to which it resolves. The supported set of skeletons is as follows
23 * ICU Name Skeleton
24 * -------- --------
25 * DAY d
26 * ABBR_WEEKDAY E
27 * WEEKDAY EEEE
28 * ABBR_STANDALONE_MONTH LLL
29 * STANDALONE_MONTH LLLL
30 * NUM_MONTH M
31 * NUM_MONTH_DAY Md
32 * NUM_MONTH_WEEKDAY_DAY MEd
33 * ABBR_MONTH MMM
34 * ABBR_MONTH_DAY MMMd
35 * ABBR_MONTH_WEEKDAY_DAY MMMEd
36 * MONTH MMMM
37 * MONTH_DAY MMMMd
38 * MONTH_WEEKDAY_DAY MMMMEEEEd
39 * ABBR_QUARTER QQQ
40 * QUARTER QQQQ
41 * YEAR y
42 * YEAR_NUM_MONTH yM
43 * YEAR_NUM_MONTH_DAY yMd
44 * YEAR_NUM_MONTH_WEEKDAY_DAY yMEd
45 * YEAR_ABBR_MONTH yMMM
46 * YEAR_ABBR_MONTH_DAY yMMMd
47 * YEAR_ABBR_MONTH_WEEKDAY_DAY yMMMEd
48 * YEAR_MONTH yMMMM
49 * YEAR_MONTH_DAY yMMMMd
50 * YEAR_MONTH_WEEKDAY_DAY yMMMMEEEEd
51 * YEAR_ABBR_QUARTER yQQQ
52 * YEAR_QUARTER yQQQQ
53 * HOUR24 H
54 * HOUR24_MINUTE Hm
55 * HOUR24_MINUTE_SECOND Hms
56 * HOUR j
57 * HOUR_MINUTE jm
58 * HOUR_MINUTE_SECOND jms
59 * HOUR_MINUTE_GENERIC_TZ jmv
60 * HOUR_MINUTE_TZ jmz
61 * HOUR_GENERIC_TZ jv
62 * HOUR_TZ jz
63 * MINUTE m
64 * MINUTE_SECOND ms
65 * SECOND s
66 *
67 * Examples Using the US Locale:
68 *
69 * Pattern Result
70 * ---------------- -------
71 * "yMd" -> 07/10/1996
72 * "yMMMMd" -> July 10, 1996
73 * "Hm" -> 12:08 PM
74 *
75 * Explicit Pattern Syntax: Formats can also be specified with a pattern string.
76 * The skeleton forms will resolve to explicit patterns of this form, but will
77 * also adapt to different patterns in different locales.
78 * The following characters are reserved:
79 *
80 * Symbol Meaning Presentation Example
81 * ------ ------- ------------ -------
82 * G era designator (Text) AD
83 * y year (Number) 1996
84 * M month in year (Text & Number) July & 07
85 * L standalone month (Text & Number) July & 07
86 * d day in month (Number) 10
87 * c standalone day (Number) 10
88 * h hour in am/pm (1~12) (Number) 12
89 * H hour in day (0~23) (Number) 0
90 * m minute in hour (Number) 30
91 * s second in minute (Number) 55
92 * S fractional second (Number) 978
93 * E day of week (Text) Tuesday
94 * D day in year (Number) 189
95 * a am/pm marker (Text) PM
96 * k hour in day (1~24) (Number) 24
97 * K hour in am/pm (0~11) (Number) 0
98 * z time zone (Text) Pacific Standard Time
99 * Z time zone (RFC 822) (Number) -0800
100 * v time zone (generic) (Text) Pacific Time
101 * Q quarter (Text) Q3
102 * ' escape for text (Delimiter) 'Date='
103 * '' single quote (Literal) 'o''clock'
104 *
105 * The count of pattern letters determine the format.
106 * **Text**:
107 * * 5 pattern letters--use narrow form for standalone. Otherwise does not apply
108 * * 4 or more pattern letters--use full form,
109 * * 3 pattern letters--use short or abbreviated form if one exists
110 * * less than 3--use numeric form if one exists
111 *
112 * **Number**: the minimum number of digits. Shorter numbers are zero-padded to
113 * this amount (e.g. if "m" produces "6", "mm" produces "06"). Year is handled
114 * specially; that is, if the count of 'y' is 2, the Year will be truncated to
115 * 2 digits. (e.g., if "yyyy" produces "1997", "yy" produces "97".) Unlike other
116 * fields, fractional seconds are padded on the right with zero.
117 *
118 * (Text & Number): 3 or over, use text, otherwise use number.
119 *
120 * Any characters that not in the pattern will be treated as quoted text. For
121 * instance, characters like ':', '.', ' ', '#' and '@' will appear in the
122 * resulting time text even they are not embraced within single quotes. In our
123 * current pattern usage, we didn't use up all letters. But those unused
124 * letters are strongly discouraged to be used as quoted text without quote.
125 * That's because we may use other letter for pattern in future.
126 *
127 * Examples Using the US Locale:
128 *
129 * Format Pattern Result
130 * -------------- -------
131 * "yyyy.MM.dd G 'at' HH:mm:ss vvvv"->1996.07.10 AD at 15:08:56 Pacific Time
132 * "EEE, MMM d, ''yy" ->Wed, July 10, '96
133 * "h:mm a" ->12:08 PM
134 * "hh 'o''clock' a, zzzz" ->12 o'clock PM, Pacific Daylight Time
135 * "K:mm a, vvv" ->0:00 PM, PT
136 * "yyyyy.MMMMM.dd GGG hh:mm aaa" ->01996.July.10 AD 12:08 PM
137 *
138 * When parsing a date string using the abbreviated year pattern ("yy"),
139 * DateFormat must interpret the abbreviated year relative to some
140 * century. It does this by adjusting dates to be within 80 years before and 20
141 * years after the time the parse function is called. For example, using a
142 * pattern of "MM/dd/yy" and a DateTimeParse instance created on Jan 1, 1997,
143 * the string "01/11/12" would be interpreted as Jan 11, 2012 while the string
144 * "05/04/64" would be interpreted as May 4, 1964. During parsing, only
145 * strings consisting of exactly two digits, as defined by {@link
146 * java.lang.Character#isDigit(char)}, will be parsed into the default
147 * century. Any other numeric string, such as a one digit string, a three or
148 * more digit string will be interpreted as its face value.
149 *
150 * If the year pattern does not have exactly two 'y' characters, the year is
151 * interpreted literally, regardless of the number of digits. So using the
152 * pattern "MM/dd/yyyy", "01/11/12" parses to Jan 11, 12 A.D.
153 *
154 * When numeric fields abut one another directly, with no intervening
155 * delimiter characters, they constitute a run of abutting numeric fields. Such
156 * runs are parsed specially. For example, the format "HHmmss" parses the input
157 * text "123456" to 12:34:56, parses the input text "12345" to 1:23:45, and
158 * fails to parse "1234". In other words, the leftmost field of the run is
159 * flexible, while the others keep a fixed width. If the parse fails anywhere in
160 * the run, then the leftmost field is shortened by one character, and the
161 * entire run is parsed again. This is repeated until either the parse succeeds
162 * or the leftmost field is one character in length. If the parse still fails at
163 * that point, the parse of the run fails.
164 */
165
166 #library('date_format');
167
168 #import('intl.dart');
169 #import('date_time_patterns.dart');
170 #import('date_symbols.dart');
171 #import('date_symbol_data.dart');
172
173 #source('lib/date_format_field.dart');
174 #source('lib/date_format_helpers.dart');
175
176 class DateFormat {
177
178 /**
179 * If [newPattern] matches one of the skeleton forms, it is looked up
180 * in [locale] or in the default if none is specified, and the corresponding
181 * full format string is used. If [newPattern] does not match one
182 * of the supported skeleton forms then it is used as a format directly.
183 *
184 * For example, in an en_US locale, specifying the skeleton
185 * `new DateFormat('yMEd');`
186 * or the explicit
187 * `new DateFormat('EEE, M/d/y');`
188 * would produce the same result, a date of the form
189 * `Wed, 6/27/2012`
190 * However, the skeleton version would also adapt to other locales.
191 *
192 * If [locale] does not exist in our set of supported locales then an
193 * [IllegalArgumentException] is thrown.
194 */
195 DateFormat([String newPattern, String locale]) {
196 // TODO(alanknight): It should be possible to specify multiple skeletons eg
197 // date, time, timezone all separately. Adding many or named parameters to
198 // the constructor seems awkward, especially with the possibility of
199 // confusion with the locale. A "fluent" interface with cascading on an
200 // instance might work better? A list of patterns is also possible.
201 // TODO(alanknight): There will need to be at least setup type async
202 // operations to avoid the need to bring along every locale in every program
203 _locale = Intl.verifiedLocale(locale);
204 _setPattern(newPattern);
205 }
206
207 /**
208 * Return a string representing [date] formatted according to our locale
209 * and internal format.
210 */
211 String format(Date date) {
212 // TODO(efortuna): read optional TimeZone argument (or similar)?
213 var result = new StringBuffer();
214 _formatFields.forEach((field) => result.add(field.format(date)));
215 return result.toString();
216 }
217
218 /**
219 * Returns a date string indicating how long ago (3 hours, 2 minutes)
220 * something has happened or how long in the future something will happen
221 * given a [reference] Date relative to the current time.
222 */
223 String formatDuration(Date reference) {
224 return '';
225 }
226
227 /**
228 * Formats a string indicating how long ago (negative [duration]) or how far
229 * in the future (positive [duration]) some time is with respect to a
230 * reference [date].
231 */
232 String formatDurationFrom(Duration duration, Date date) {
233 return '';
234 }
235
236 /**
237 * Given user input, attempt to parse the [inputString] into the anticipated
238 * format, treating it as being in the local timezone.
239 */
240 Date parse(String inputString, [utc = false]) {
241 var dateFields = new _DateBuilder();
242 if (utc) dateFields.utc=true;
243 var stream = new _Stream(inputString);
244 _formatFields.forEach(
245 (each) => each.parse(stream, dateFields));
246 return dateFields.asDate();
247 }
248
249 /**
250 * Given user input, attempt to parse the [inputString] into the anticipated
251 * format, treating it as being in UTC.
252 */
253 Date parseUTC(String inputString) {
254 return parse(inputString, true);
255 }
256
257 /**
258 * Return the locale code in which we operate, e.g. 'en_US' or 'pt'.
259 */
260 String get locale() => _locale;
261
262 /**
263 * Constructors for a set of predefined formats for which
264 * internationalized forms are known. These can be specified
265 * either as ICU constants, or as skeletons.
266 */
267 DateFormat.DAY([locale]) : this(DAY, locale);
268 DateFormat.ABBR_WEEKDAY([locale]) : this(ABBR_WEEKDAY, locale);
269 DateFormat.WEEKDAY([locale]) : this(WEEKDAY, locale);
270 DateFormat.ABBR_STANDALONE_MONTH([locale]) :
271 this(ABBR_STANDALONE_MONTH, locale);
272 DateFormat.STANDALONE_MONTH([locale]) : this(STANDALONE_MONTH, locale);
273 DateFormat.NUM_MONTH([locale]) : this(NUM_MONTH, locale);
274 DateFormat.NUM_MONTH_DAY([locale]) : this(NUM_MONTH_DAY, locale);
275 DateFormat.NUM_MONTH_WEEKDAY_DAY([locale]) :
276 this(NUM_MONTH_WEEKDAY_DAY, locale);
277 DateFormat.ABBR_MONTH([locale]) : this(ABBR_MONTH, locale);
278 DateFormat.ABBR_MONTH_DAY([locale]) : this(ABBR_MONTH_DAY, locale);
279 DateFormat.ABBR_MONTH_WEEKDAY_DAY([locale]) :
280 this(ABBR_MONTH_WEEKDAY_DAY, locale);
281 DateFormat.MONTH([locale]) : this(MONTH, locale);
282 DateFormat.MONTH_DAY([locale]) : this(MONTH_DAY, locale);
283 DateFormat.MONTH_WEEKDAY_DAY([locale]) : this(MONTH_WEEKDAY_DAY, locale);
284 DateFormat.ABBR_QUARTER([locale]) : this(ABBR_QUARTER, locale);
285 DateFormat.QUARTER([locale]) : this(QUARTER, locale);
286 DateFormat.YEAR([locale]) : this(YEAR, locale);
287 DateFormat.YEAR_NUM_MONTH([locale]) : this(YEAR_NUM_MONTH, locale);
288 DateFormat.YEAR_NUM_MONTH_DAY([locale]) : this(YEAR_NUM_MONTH_DAY, locale);
289 DateFormat.YEAR_NUM_MONTH_WEEKDAY_DAY([locale]) :
290 this(YEAR_NUM_MONTH_WEEKDAY_DAY, locale);
291 DateFormat.YEAR_ABBR_MONTH([locale]) : this(YEAR_ABBR_MONTH, locale);
292 DateFormat.YEAR_ABBR_MONTH_DAY([locale]) : this(YEAR_ABBR_MONTH_DAY, locale);
293 DateFormat.YEAR_ABBR_MONTH_WEEKDAY_DAY([locale]) :
294 this(YEAR_ABBR_MONTH_WEEKDAY_DAY, locale);
295 DateFormat.YEAR_MONTH([locale]) : this(YEAR_MONTH, locale);
296 DateFormat.YEAR_MONTH_DAY([locale]) : this(YEAR_MONTH_DAY, locale);
297 DateFormat.YEAR_MONTH_WEEKDAY_DAY([locale]) :
298 this(YEAR_MONTH_WEEKDAY_DAY, locale);
299 DateFormat.YEAR_ABBR_QUARTER([locale]) : this(YEAR_ABBR_QUARTER, locale);
300 DateFormat.YEAR_QUARTER([locale]) : this(YEAR_QUARTER, locale);
301 DateFormat.HOUR24([locale]) : this(HOUR24, locale);
302 DateFormat.HOUR24_MINUTE([locale]) : this(HOUR24_MINUTE, locale);
303 DateFormat.HOUR24_MINUTE_SECOND([locale]) :
304 this(HOUR24_MINUTE_SECOND, locale);
305 DateFormat.HOUR([locale]) : this(HOUR, locale);
306 DateFormat.HOUR_MINUTE([locale]) : this(HOUR_MINUTE, locale);
307 DateFormat.HOUR_MINUTE_SECOND([locale]) : this(HOUR_MINUTE_SECOND, locale);
308 DateFormat.HOUR_MINUTE_GENERIC_TZ([locale]) :
309 this(HOUR_MINUTE_GENERIC_TZ, locale);
310 DateFormat.HOUR_MINUTE_TZ([locale]) : this(HOUR_MINUTE_TZ, locale);
311 DateFormat.HOUR_GENERIC_TZ([locale]) : this(HOUR_GENERIC_TZ, locale);
312 DateFormat.HOUR_TZ([locale]) : this(HOUR_TZ, locale);
313 DateFormat.MINUTE([locale]) : this(MINUTE, locale);
314 DateFormat.MINUTE_SECOND([locale]) : this(MINUTE_SECOND, locale);
315 DateFormat.SECOND([locale]) : this(SECOND, locale);
316
317 DateFormat.d([locale]) : this("d", locale);
318 DateFormat.E([locale]) : this("E", locale);
319 DateFormat.EEEE([locale]) : this("EEEE", locale);
320 DateFormat.LLL([locale]) : this("LLL", locale);
321 DateFormat.LLLL([locale]) : this("LLLL", locale);
322 DateFormat.M([locale]) : this("M", locale);
323 DateFormat.Md([locale]) : this("Md", locale);
324 DateFormat.MEd([locale]) : this("MEd", locale);
325 DateFormat.MMM([locale]) : this("MMM", locale);
326 DateFormat.MMMd([locale]) : this("MMMd", locale);
327 DateFormat.MMMEd([locale]) : this("MMMEd", locale);
328 DateFormat.MMMM([locale]) : this("MMMM", locale);
329 DateFormat.MMMMd([locale]) : this("MMMMd", locale);
330 DateFormat.MMMMEEEEd([locale]) : this("MMMMEEEEd", locale);
331 DateFormat.QQQ([locale]) : this("QQQ", locale);
332 DateFormat.QQQQ([locale]) : this("QQQQ", locale);
333 DateFormat.y([locale]) : this("y", locale);
334 DateFormat.yM([locale]) : this("yM", locale);
335 DateFormat.yMd([locale]) : this("yMd", locale);
336 DateFormat.yMEd([locale]) : this("yMEd", locale);
337 DateFormat.yMMM([locale]) : this("yMMM", locale);
338 DateFormat.yMMMd([locale]) : this("yMMMd", locale);
339 DateFormat.yMMMEd([locale]) : this("yMMMEd", locale);
340 DateFormat.yMMMM([locale]) : this("yMMMM", locale);
341 DateFormat.yMMMMd([locale]) : this("yMMMMd", locale);
342 DateFormat.yMMMMEEEEd([locale]) : this("yMMMMEEEEd", locale);
343 DateFormat.yQQQ([locale]) : this("yQQQ", locale);
344 DateFormat.yQQQQ([locale]) : this("yQQQQ", locale);
345 DateFormat.H([locale]) : this("H", locale);
346 DateFormat.Hm([locale]) : this("Hm", locale);
347 DateFormat.Hms([locale]) : this("Hms", locale);
348 DateFormat.j([locale]) : this("j", locale);
349 DateFormat.jm([locale]) : this("jm", locale);
350 DateFormat.jms([locale]) : this("jms", locale);
351 DateFormat.jmv([locale]) : this("jmv", locale);
352 DateFormat.jmz([locale]) : this("jmz", locale);
353 DateFormat.jv([locale]) : this("jv", locale);
354 DateFormat.jz([locale]) : this("jz", locale);
355 DateFormat.m([locale]) : this("m", locale);
356 DateFormat.ms([locale]) : this("ms", locale);
357 DateFormat.s([locale]) : this("s", locale);
358
359 /**
360 * ICU constants for format names, resolving to the corresponding skeletons.
361 */
362 static final String DAY = 'd';
363 static final String ABBR_WEEKDAY = 'E';
364 static final String WEEKDAY = 'EEEE';
365 static final String ABBR_STANDALONE_MONTH = 'LLL';
366 static final String STANDALONE_MONTH = 'LLLL';
367 static final String NUM_MONTH = 'M';
368 static final String NUM_MONTH_DAY = 'Md';
369 static final String NUM_MONTH_WEEKDAY_DAY = 'MEd';
370 static final String ABBR_MONTH = 'MMM';
371 static final String ABBR_MONTH_DAY = 'MMMd';
372 static final String ABBR_MONTH_WEEKDAY_DAY = 'MMMEd';
373 static final String MONTH = 'MMMM';
374 static final String MONTH_DAY = 'MMMMd';
375 static final String MONTH_WEEKDAY_DAY = 'MMMMEEEEd';
376 static final String ABBR_QUARTER = 'QQQ';
377 static final String QUARTER = 'QQQQ';
378 static final String YEAR = 'y';
379 static final String YEAR_NUM_MONTH = 'yM';
380 static final String YEAR_NUM_MONTH_DAY = 'yMd';
381 static final String YEAR_NUM_MONTH_WEEKDAY_DAY = 'yMEd';
382 static final String YEAR_ABBR_MONTH = 'yMMM';
383 static final String YEAR_ABBR_MONTH_DAY = 'yMMMd';
384 static final String YEAR_ABBR_MONTH_WEEKDAY_DAY = 'yMMMEd';
385 static final String YEAR_MONTH = 'yMMMM';
386 static final String YEAR_MONTH_DAY = 'yMMMMd';
387 static final String YEAR_MONTH_WEEKDAY_DAY = 'yMMMMEEEEd';
388 static final String YEAR_ABBR_QUARTER = 'yQQQ';
389 static final String YEAR_QUARTER = 'yQQQQ';
390 static final String HOUR24 = 'H';
391 static final String HOUR24_MINUTE = 'Hm';
392 static final String HOUR24_MINUTE_SECOND = 'Hms';
393 static final String HOUR = 'j';
394 static final String HOUR_MINUTE = 'jm';
395 static final String HOUR_MINUTE_SECOND = 'jms';
396 static final String HOUR_MINUTE_GENERIC_TZ = 'jmv';
397 static final String HOUR_MINUTE_TZ = 'jmz';
398 static final String HOUR_GENERIC_TZ = 'jv';
399 static final String HOUR_TZ = 'jz';
400 static final String MINUTE = 'm';
401 static final String MINUTE_SECOND = 'ms';
402 static final String SECOND = 's';
403
404 /** The locale in which we operate, e.g. 'en_US', or 'pt'. */
405 String _locale;
406
407 /**
408 * The full template string. This may have been specified directly, or
409 * it may have been derived from a skeleton and the locale information
410 * on how to interpret that skeleton.
411 */
412 String _pattern;
413
414 /**
415 * We parse the format string into individual fields and store them here.
416 * This is what is actually used to do the formatting.
417 */
418 List<_DateFormatField> _formatFields;
419
420 /**
421 * A series of regular expressions used to parse a format string into its
422 * component fields.
423 */
424 static var _matchers = const [
425 // Quoted String - anything between single quotes, with escaping
426 // of single quotes by doubling them.
427 // e.g. in the pattern "hh 'o''clock'" will match 'o''clock'
428 const RegExp("^\'(?:[^\']|\'\')*\'"),
429 // Fields - any sequence of 1 or more of the same field characters.
430 // e.g. in "hh:mm:ss" will match hh, mm, and ss. But in "hms" would
431 // match each letter individually.
432 const RegExp(
433 "^(?:G+|y+|M+|k+|S+|E+|a+|h+|K+|H+|c+|L+|Q+|d+|m+|s+|v+|z+|Z+)"),
434 // Everything else - A sequence that is not quotes or field characters.
435 // e.g. in "hh:mm:ss" will match the colons.
436 const RegExp("^[^\'GyMkSEahKHcLQdmsvzZ]+")
437 ];
438
439 /**
440 * Given a format from the user look it up in our list of known skeletons.
441 * If it's there, then use the corresponding pattern for this locale.
442 * If it's not, then treat it as an explicit pattern.
443 */
444 _setPattern(String inputPattern) {
445 // TODO(alanknight): This is an expensive operation. Caching recently used
446 // formats, or possibly introducing an entire "locale" object that would
447 // cache patterns for that locale could be a good optimization.
448 if (!_availableSkeletons.containsKey(inputPattern)) {
449 _pattern = inputPattern;
450 } else {
451 _pattern = _availableSkeletons[inputPattern];
452 }
453 _formatFields = parsePattern(_pattern);
454 }
455
456 /** Return the pattern that we use to format dates.*/
457 get pattern() => _pattern;
458
459 /** Return the skeletons for our current locale. */
460 Map get _availableSkeletons() {
461 return dateTimePatterns[locale];
462 }
463
464 /**
465 * Set the locale. If the locale can't be found, we also look up
466 * based on alternative versions, e.g. if we have no 'en_CA' we will
467 * look for 'en' as a fallback. It will also translate en-ca into en_CA.
468 * Null is also considered a valid value for [newLocale], indicating
469 * to use the default.
470 */
471 _setLocale(String newLocale) {
472 _locale = Intl.verifiedLocale(newLocale);
473 }
474
475 /**
476 * Return true if the locale exists, or if it is null. The null case
477 * is interpreted to mean that we use the default locale.
478 */
479 static bool localeExists(localeName) {
480 if (localeName == null) return false;
481 return dateTimeSymbols.containsKey(localeName);
482 }
483
484 // TODO(alanknight): This can be a variable once that's permitted.
485 static List get _fieldConstructors() => [
486 (pattern, parent) => new _DateFormatQuotedField(pattern, parent),
487 (pattern, parent) => new _DateFormatPatternField(pattern, parent),
488 (pattern, parent) => new _DateFormatLiteralField(pattern, parent)];
489
490 /** Parse the template pattern and return a list of field objects.*/
491 List parsePattern(String pattern) {
492 if (pattern == null) return null;
493 return _reverse(_parsePatternHelper(pattern));
494 }
495
496 /** Recursive helper for parsing the template pattern. */
497 List _parsePatternHelper(String pattern) {
498 if (pattern.isEmpty()) return [];
499
500 var matched = _match(pattern);
501 if (matched == null) return [];
502
503 var parsed = _parsePatternHelper(
504 pattern.substring(matched.fullPattern().length));
505 parsed.add(matched);
506 return parsed;
507 }
508
509 /** Find elements in a string that are patterns for specific fields.*/
510 _DateFormatField _match(String pattern) {
511 for (var i = 0; i < _matchers.length; i++) {
512 var regex = _matchers[i];
513 var match = regex.firstMatch(pattern);
514 if (match != null) {
515 return _fieldConstructors[i](match.group(0), this);
516 }
517 }
518 }
519
520 /** Polyfill for missing library function. */
521 List _reverse(List list) {
522 // TODO(alanknight): Use standardized list reverse when implemented.
523 // See Issue 2804.
524 var result = new List();
525 for (var i = list.length-1; i >= 0; i--) {
526 result.addLast(list[i]);
527 }
528 return result;
529 }
530 }
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