Change timezone API (#1022)

* add js timezone parsing

* Switch icu4x and ecma to use timezones

* fix timezone calculation time

* fixes

* extract

* add changelog

* Fixes

* fixes

* Fixes as per review

* rev version to major

* support all timezones

* Fixes as per review?

---------

Co-authored-by: Robert Bastian <[email protected]>

Author: mosuem

pkgs/intl4x/CHANGELOG.md

@@ -1,3 +1,7 @@
+## 0.14.0
+
+- Change timezone API, adding a dependency on package:timezone.
+
 ## 0.13.2
 
 - Add `withEra`.

pkgs/intl4x/example/bin/example.dart

@@ -6,8 +6,8 @@ import 'package:intl4x/datetime_format.dart';
 import 'package:intl4x/intl4x.dart';
 
 void main(List<String> arguments) {
-  const timeZone = TimeZone(name: 'Europe/Paris', offset: Duration(hours: 2));
-  final dateTime = DateTime.parse('2024-07-01T08:50:07Z');
+  final timeZone = 'Europe/Paris';
+  final dateTime = DateTime.parse('2024-07-01T08:50:07');
 
   print(Intl().locale.toString());
 

pkgs/intl4x/lib/src/datetime_format/datetime_format_ecma.dart

@@ -4,6 +4,8 @@
 
 import 'dart:js_interop';
 
+import 'package:collection/collection.dart' show IterableExtension;
+
 import '../locale/locale.dart';
 import '../options.dart';
 import 'datetime_format_impl.dart';
@@ -21,7 +23,7 @@ class DateTimeJSOptions {
   final TimeStyle? hour;
   final TimeStyle? minute;
   final TimeStyle? second;
-  final TimeZone? timeZone;
+  final String? timeZone;
   final TimeZoneType? timeZoneType;
   final Style? weekday;
 
@@ -44,7 +46,7 @@ class DateTimeJSOptions {
     TimeStyle? hour,
     TimeStyle? minute,
     TimeStyle? second,
-    TimeZone? timeZone,
+    String? timeZone,
     TimeZoneType? timeZoneType,
     Style? weekday,
   }) => DateTimeJSOptions(
@@ -122,7 +124,7 @@ class FormatterZonedECMA extends FormatterZonedImpl {
   static DateTimeFormat createDateTimeFormat(
     FormatterECMA formatter,
     TimeZoneType timeZoneType,
-    TimeZone timeZone,
+    String timeZone,
   ) {
     final localeJS = [formatter.locale.toLanguageTag().toJS].toJS;
     return DateTimeFormat(
@@ -140,12 +142,36 @@ class FormatterZonedECMA extends FormatterZonedImpl {
   }
 
   @override
-  String formatInternal(DateTime datetime, TimeZone timeZone) =>
-      createDateTimeFormat(
+  String formatInternal(DateTime datetime, String timeZone) {
+    try {
+      // ECMA will interpret this as UTC time and convert it
+      // into the time zone, we need to invert that change.
+      final adjustedDateTime = datetime.subtract(
+        offsetForTimeZone(datetime, timeZone),
+      );
+      return createDateTimeFormat(
         formatter,
         timeZoneType,
         timeZone,
-      ).format(datetime.subtract(timeZone.offset).jsUtc);
+      ).format(adjustedDateTime.jsUtc);
+    } catch (e) {
+      // Unknown timezone. Format with UTC and append '+?'
+      // to construct a localized 'UTC+?'
+      final parts = createDateTimeFormat(
+        formatter,
+        TimeZoneType.shortOffset,
+        'UTC',
+      ).formatToParts(datetime.jsUtc).toDart;
+      return parts
+          .map(Part._)
+          .map(
+            (part) => part.isTimezoneName
+                ? '${part.value.split('+')[0]}+?'
+                : part.value,
+          )
+          .join();
+    }
+  }
 }
 
 class _DateTimeFormatECMA extends DateTimeFormatImpl {
@@ -365,15 +391,63 @@ extension type Date._(JSObject _) implements JSObject {
   );
 }
 
+Duration offsetForTimeZone(DateTime datetime, String iana) {
+  final timeZoneName = DateTimeFormat(
+    ['en'.toJS].toJS,
+    {'timeZoneName': TimeZoneType.longOffset.name, 'timeZone': iana}.jsify()!,
+  ).timeZoneName(datetime.js);
+  return parseTimeZoneOffset(timeZoneName);
+}
+
 @JS('Intl.DateTimeFormat')
 extension type DateTimeFormat._(JSObject _) implements JSObject {
   external factory DateTimeFormat([JSArray<JSString> locale, JSAny options]);
-  external String format(JSAny num);
+  external String format(Date num);
 
   external static JSArray<JSString> supportedLocalesOf(
     JSArray listOfLocales, [
     JSAny options,
   ]);
+
+  external JSArray<JSObject> formatToParts(JSAny num);
+
+  String? timeZoneName(Date date) {
+    final timezoneNameObject = formatToParts(
+      date,
+    ).toDart.map(Part._).firstWhereOrNull((part) => part.isTimezoneName);
+    return timezoneNameObject?.value;
+  }
+}
+
+@JS()
+extension type Part._(JSObject _) implements JSObject {
+  external String get type;
+  external String get value;
+
+  bool get isTimezoneName => type == 'timeZoneName';
+}
+
+final _offsetRegex = RegExp(
+  r'([+\-\u2212])(\d{2}):?(\d{2})(?:(?::?)(\d{2}))?$',
+);
+
+Duration parseTimeZoneOffset(String? offsetString) {
+  if (offsetString == null || offsetString == 'UTC' || offsetString == 'GMT') {
+    return Duration.zero;
+  }
+
+  final Match? match = _offsetRegex.firstMatch(offsetString);
+
+  if (match == null) {
+    throw ArgumentError('Invalid time zone offset format: "$offsetString"');
+  }
+
+  final sign = (match.group(1)! == '-' || match.group(1)! == '\u2212') ? -1 : 1;
+  final hours = int.parse(match.group(2)!);
+  final minutes = int.parse(match.group(3)!);
+  final seconds = int.parse(match.group(4) ?? '0');
+
+  return Duration(hours: hours, minutes: minutes, seconds: seconds) * sign;
 }
 
 extension on DateTime {
@@ -397,7 +471,7 @@ extension on DateTimeFormatOptions {
     if (dayPeriod != null) 'dayPeriod': dayPeriod!.name,
     if (numberingSystem != null) 'numberingSystem': numberingSystem!.name,
     if (options.timeZone != null) ...{
-      'timeZone': options.timeZone!.name,
+      'timeZone': options.timeZone,
       'timeZoneName': options.timeZoneType!.name,
     },
     if (clockstyle != null) ...{

pkgs/intl4x/lib/src/datetime_format/datetime_format_impl.dart

@@ -70,12 +70,12 @@ abstract class FormatterZonedImpl extends ZonedDateTimeFormatter {
   final DateTimeFormatImpl _impl;
   final TimeZoneType timeZoneType;
 
-  String formatInternal(DateTime datetime, TimeZone timeZone);
+  String formatInternal(DateTime datetime, String timeZone);
 
   FormatterZonedImpl(this._impl, this.timeZoneType);
 
   @override
-  String format(DateTime datetime, TimeZone timeZone) {
+  String format(DateTime datetime, String timeZone) {
     if (isInTest) {
       return '$datetime//${_impl.locale}';
     } else {
@@ -96,8 +96,8 @@ sealed class DateTimeFormatter {
   ZonedDateTimeFormatter withTimeZoneLongGeneric();
 }
 
-/// A base class for formatters that can format a [DateTime] and [TimeZone] into
-/// a string.
+/// A base class for formatters that can format a [DateTime] and time zone
+/// string into a string.
 sealed class ZonedDateTimeFormatter {
-  String format(DateTime datetime, TimeZone timeZone);
+  String format(DateTime datetime, String timeZone);
 }

pkgs/intl4x/lib/src/datetime_format/datetime_format_options.dart

@@ -125,13 +125,6 @@ enum TimeStyle {
   const TimeStyle([this._jsName]);
 }
 
-final class TimeZone {
-  final String name;
-  final Duration offset;
-
-  const TimeZone({required this.name, required this.offset});
-}
-
 enum TimeZoneType {
   /// Example: `Pacific Standard Time`
   long,

pkgs/intl4x/lib/src/datetime_format/icu4x/date_formatter.dart

@@ -166,13 +166,9 @@ class DateFormatterZonedX extends FormatterZonedImpl {
       super(dateFormatter.impl, TimeZoneType.longGeneric);
 
   @override
-  String formatInternal(DateTime datetime, TimeZone timeZone) {
-    final utcOffset = icu.UtcOffset.fromSeconds(timeZone.offset.inSeconds);
+  String formatInternal(DateTime datetime, String timeZone) {
+    final timeZoneX = timeZoneToX(timeZone, datetime);
     final (isoDate, time) = datetime.toX;
-    final timeZoneX = icu.IanaParser()
-        .parse(timeZone.name)
-        .withOffset(utcOffset)
-        .atDateTimeIso(isoDate, time);
 
     return formatter.formatIso(isoDate, timeZoneX);
   }

pkgs/intl4x/lib/src/datetime_format/icu4x/date_time_formatter.dart

@@ -137,13 +137,9 @@ class DateTimeFormatterZonedX extends FormatterZonedImpl {
       super(dateFormatter.impl, TimeZoneType.longGeneric);
 
   @override
-  String formatInternal(DateTime datetime, TimeZone timeZone) {
-    final utcOffset = icu.UtcOffset.fromSeconds(timeZone.offset.inSeconds);
+  String formatInternal(DateTime datetime, String timeZone) {
+    final timeZoneX = timeZoneToX(timeZone, datetime);
     final (isoDate, time) = datetime.toX;
-    final timeZoneX = icu.IanaParser()
-        .parse(timeZone.name)
-        .withOffset(utcOffset)
-        .atDateTimeIso(isoDate, time);
 
     return formatter.formatIso(isoDate, time, timeZoneX);
   }

pkgs/intl4x/lib/src/datetime_format/icu4x/datetime_format_4x.dart

@@ -3,6 +3,8 @@
 // BSD-style license that can be found in the LICENSE file.
 
 import 'package:icu4x/icu4x.dart' as icu;
+import 'package:timezone/data/latest_all.dart' show initializeTimeZones;
+import 'package:timezone/timezone.dart' show TZDateTime, timeZoneDatabase;
 
 import '../../../datetime_format.dart';
 import '../../locale/locale.dart';
@@ -211,6 +213,33 @@ extension on DateTimeFormatOptions {
   }
 }
 
+icu.TimeZoneInfo timeZoneToX(String timeZone, DateTime datetime) {
+  if (!timeZoneDatabase.isInitialized) {
+    initializeTimeZones();
+  }
+  final location = timeZoneDatabase.locations[timeZone];
+  final timeZoneX = location != null
+      ? icu.IanaParser()
+            .parse(timeZone)
+            .withOffset(
+              icu.UtcOffset.fromSeconds(
+                TZDateTime(
+                  location,
+                  datetime.year,
+                  datetime.month,
+                  datetime.day,
+                  datetime.hour,
+                  datetime.minute,
+                  datetime.second,
+                  datetime.millisecond,
+                  datetime.microsecond,
+                ).timeZoneOffset.inSeconds,
+              ),
+            )
+      : icu.TimeZone.unknown().withoutOffset();
+  return timeZoneX;
+}
+
 icu.Locale setLocaleExtensions(
   icu.Locale locale,
   DateTimeFormatOptions options,

pkgs/intl4x/lib/src/datetime_format/icu4x/time_formatter.dart

@@ -119,13 +119,9 @@ class TimeFormatterZonedX extends FormatterZonedImpl {
       super(timeFormatter.impl, TimeZoneType.longGeneric);
 
   @override
-  String formatInternal(DateTime datetime, TimeZone timeZone) {
-    final utcOffset = icu.UtcOffset.fromSeconds(timeZone.offset.inSeconds);
+  String formatInternal(DateTime datetime, String timeZone) {
+    final timeZoneX = timeZoneToX(timeZone, datetime);
     final (isoDate, time) = datetime.toX;
-    final timeZoneX = icu.IanaParser()
-        .parse(timeZone.name)
-        .withOffset(utcOffset)
-        .atDateTimeIso(isoDate, time);
     return formatter.format(time, timeZoneX);
   }
 }

pkgs/intl4x/pubspec.yaml

@@ -1,7 +1,7 @@
 name: intl4x
 description: >-
   A lightweight modular library for internationalization (i18n) functionality.
-version: 0.13.2
+version: 0.14.0
 repository: https://github.com/dart-lang/i18n/tree/main/pkgs/intl4x
 issue_tracker: https://github.com/dart-lang/i18n/issues?q=is%3Aissue+is%3Aopen+label%3Apackage%3Aintl4x
 
@@ -20,13 +20,14 @@ environment:
   sdk: ^3.9.3
 
 dependencies:
+  collection: ^1.19.1
   hooks: ^0.20.4
   icu4x: ^2.1.0-dev.0
   meta: ^1.17.0
   record_use: ^0.4.2
+  timezone: ^0.10.1
 
 dev_dependencies:
   args: ^2.7.0
-  collection: ^1.19.1
   dart_flutter_team_lints: ^3.5.2
   test: ^1.26.3