feat: add xsd:gMonthDay codec and data type

CHANGELOG.md

@@ -24,3 +24,4 @@
 - Implement `xsd:nonPositiveInteger` data type codec
 - Implement `xsd:unsignedLong` data type codec
 - Implement `xsd:gDay` codec and data type
+- Implement `xsd:gMonthDay` codec and data type

README.md

@@ -59,8 +59,8 @@ This library aims to support the following XSD 1.1 built-in datatypes that are c
 | `xsd:time` |      ✅      |        ❌        |    ???    |     ???    |
 | `xsd:gYearMonth` |      ✅      |        ✅        |    `YearMonth`    |     `package:xsd`    |
 | `xsd:gYear` |      ✅      |        ✅        |    `GregorianYear`    |     `package:xsd`    |
-| `xsd:gMonthDay` |      ✅      |        ❌        |    ???    |     ???    |
-| `xsd:gDay` |      ✅      |        ✅        |    GregorianDay    |     `package:xsd`    |
+| `xsd:gMonthDay` |      ✅      |        ✅        |    `GregorianMonthDay`    |     `package:xsd`    |
+| `xsd:gDay` |      ✅      |        ✅        |    `GregorianDay`    |     `package:xsd`    |
 | `xsd:gMonth` |      ✅      |        ✅        |    `GregorianMonth`    |     `package:xsd`    |
 | `xsd:QName` |      ❌      |        ❌        |    ❌    |     ❌    |
 | `xsd:NOTATION` |      ❌      |        ❌        |    ❌    |     ❌    |

lib/src/codecs/codecs.dart

@@ -21,3 +21,4 @@ export 'positive_integer/positive_integer_codec.dart';
 export 'non_positive_integer/non_positive_integer_codec.dart';
 export 'unsigned_long/unsigned_long_codec.dart';
 export 'g_day/g_day_codec.dart';
+export 'g_month_day/gregorian_month_day_codec.dart';

lib/src/codecs/g_month_day/gregorian_month_day_codec.dart

@@ -0,0 +1,18 @@
+import 'dart:convert';
+
+import '../../types/gregorian_month_day.dart';
+import 'gregorian_month_day_decoder.dart';
+import 'gregorian_month_day_encoder.dart';
+
+/// A codec for converting between [GregorianMonthDay] objects and their XSD gMonthDay string representations.
+class GregorianMonthDayCodec extends Codec<GregorianMonthDay, String> {
+  const GregorianMonthDayCodec();
+
+  @override
+  Converter<String, GregorianMonthDay> get decoder =>
+      const GregorianMonthDayDecoder();
+
+  @override
+  Converter<GregorianMonthDay, String> get encoder =>
+      const GregorianMonthDayEncoder();
+}

lib/src/codecs/g_month_day/gregorian_month_day_decoder.dart

@@ -0,0 +1,13 @@
+import 'dart:convert';
+
+import '../../types/gregorian_month_day.dart';
+
+/// A converter that parses XSD gMonthDay strings into [GregorianMonthDay] objects.
+class GregorianMonthDayDecoder extends Converter<String, GregorianMonthDay> {
+  const GregorianMonthDayDecoder();
+
+  @override
+  GregorianMonthDay convert(String input) {
+    return GregorianMonthDay.parse(input);
+  }
+}

lib/src/codecs/g_month_day/gregorian_month_day_encoder.dart

@@ -0,0 +1,13 @@
+import 'dart:convert';
+
+import '../../types/gregorian_month_day.dart';
+
+/// A converter that converts [GregorianMonthDay] objects to their XSD gMonthDay string representation.
+class GregorianMonthDayEncoder extends Converter<GregorianMonthDay, String> {
+  const GregorianMonthDayEncoder();
+
+  @override
+  String convert(GregorianMonthDay input) {
+    return input.toString();
+  }
+}

lib/src/types/gregorian_month_day.dart

@@ -0,0 +1,213 @@
+import 'package:meta/meta.dart';
+
+import '../helpers/whitespace.dart';
+
+/// Represents an xsd:gMonthDay value.
+///
+/// A gMonthDay is a specific day of a specific month, independent of the year.
+/// It has a month, a day, and an optional timezone.
+///
+/// See [XSD gMonthDay](https://www.w3.org/TR/xmlschema11-2/#gMonthDay).
+@immutable
+class GregorianMonthDay {
+  /// The month component of this gMonthDay, from 1 (January) to 12 (December).
+  final int month;
+
+  /// The day component of this gMonthDay, from 1 to 31.
+  final int day;
+
+  /// Optional timezone offset in minutes from UTC.
+  ///
+  /// A positive value indicates a timezone east of UTC, negative for west.
+  /// `null` means no timezone is specified.
+  final int? timezoneOffsetInMinutes;
+
+  /// Constructs a [GregorianMonthDay] instance.
+  ///
+  /// The [month] must be between 1 and 12.
+  /// The [day] must be valid for the given [month] (e.g., 30 for April, 31 for January).
+  /// February 29 is allowed.
+  /// The [timezoneOffsetInMinutes], if provided, must be between -840 and 840.
+  GregorianMonthDay(this.month, this.day, {this.timezoneOffsetInMinutes}) {
+    if (month < 1 || month > 12) {
+      throw ArgumentError.value(
+        month,
+        'month',
+        'Month must be between 1 and 12',
+      );
+    }
+    if (day < 1 || day > 31) {
+      throw ArgumentError.value(day, 'day', 'Day must be between 1 and 31');
+    }
+    // Validate day against month
+    final maxDays = _daysInMonth(month);
+    if (day > maxDays) {
+      throw ArgumentError.value(
+        day,
+        'day',
+        'Day must be between 1 and $maxDays for month $month',
+      );
+    }
+
+    const minOffset = -14 * 60;
+    const maxOffset = 14 * 60;
+    if (timezoneOffsetInMinutes != null) {
+      if (timezoneOffsetInMinutes! < minOffset ||
+          timezoneOffsetInMinutes! > maxOffset) {
+        throw ArgumentError.value(
+          timezoneOffsetInMinutes,
+          'timezoneOffsetInMinutes',
+          'Timezone offset must be between -PT14H and PT14H ($minOffset and $maxOffset minutes)',
+        );
+      }
+    }
+  }
+
+  static int _daysInMonth(int month) {
+    switch (month) {
+      case 2:
+        return 29; // gMonthDay allows Feb 29
+      case 4:
+      case 6:
+      case 9:
+      case 11:
+        return 30;
+      default:
+        return 31;
+    }
+  }
+
+  /// Parses a string in XSD gMonthDay format into a [GregorianMonthDay] object.
+  ///
+  /// The expected format is `--MM-DD` with an optional timezone suffix
+  /// (e.g., "--10-25", "--02-29Z", "--12-31+05:30").
+  ///
+  /// Throws a [FormatException] if the input string is not a valid gMonthDay.
+  static GregorianMonthDay parse(String lexicalForm) {
+    final String collapsedInput = processWhiteSpace(
+      lexicalForm,
+      Whitespace.collapse,
+    );
+
+    // Regular expression for gMonthDay: --MM-DD(Z|(+|-)HH:MM)?
+    // Month part: (0[1-9]|1[0-2])
+    // Day part: (0[1-9]|[12][0-9]|3[01])
+    // Timezone part: (Z|(\+|-)((0[0-9]|1[0-3]):[0-5][0-9]|14:00))?
+    final RegExp gMonthDayPattern = RegExp(
+      r'^--(0[1-9]|1[0-2])-(0[1-9]|[12][0-9]|3[01])(Z|(?:\+|-)(?:(?:0[0-9]|1[0-3]):[0-5][0-9]|14:00))?$',
+    );
+
+    final Match? match = gMonthDayPattern.firstMatch(collapsedInput);
+
+    if (match == null) {
+      throw FormatException(
+        "Invalid gMonthDay format: '$lexicalForm' (collapsed to '$collapsedInput')",
+      );
+    }
+
+    final String monthStr = match.group(1)!;
+    final String dayStr = match.group(2)!;
+    final String? timezoneStr = match.group(3); // This group is optional
+
+    final int month;
+    try {
+      month = int.parse(monthStr);
+    } catch (e) {
+      throw FormatException(
+        "Invalid month component in gMonthDay: '$monthStr'",
+        collapsedInput,
+      );
+    }
+
+    final int day;
+    try {
+      day = int.parse(dayStr);
+    } catch (e) {
+      throw FormatException(
+        "Invalid day component in gMonthDay: '$dayStr'",
+        collapsedInput,
+      );
+    }
+
+    // Validate day against month logic (regex is loose on 30/31 days for some months)
+    final maxDays = _daysInMonth(month);
+    if (day > maxDays) {
+      throw FormatException(
+        "Day value '$dayStr' is invalid for month '$monthStr' (max $maxDays).",
+        collapsedInput,
+      );
+    }
+
+    int? timezoneOffsetMinutes;
+    if (timezoneStr != null) {
+      if (timezoneStr == 'Z') {
+        timezoneOffsetMinutes = 0;
+      } else {
+        final int sign = timezoneStr.startsWith('+') ? 1 : -1;
+        final parts = timezoneStr.substring(1).split(':');
+        final int hours = int.parse(parts[0]);
+        final int minutes = int.parse(parts[1]);
+        timezoneOffsetMinutes = sign * (hours * 60 + minutes);
+      }
+    }
+
+    return GregorianMonthDay(
+      month,
+      day,
+      timezoneOffsetInMinutes: timezoneOffsetMinutes,
+    );
+  }
+
+  /// Returns the canonical lexical representation of this [GregorianMonthDay].
+  ///
+  /// Format is "--MM-DD" e.g., "--10-25".
+  /// If a timezone is present, it's appended (e.g., "--05-20Z", "--12-01+05:30").
+  @override
+  String toString() {
+    final monthString = month.toString().padLeft(2, '0');
+    final dayString = day.toString().padLeft(2, '0');
+    final buffer = StringBuffer('--$monthString-$dayString');
+
+    if (timezoneOffsetInMinutes != null) {
+      if (timezoneOffsetInMinutes == 0) {
+        buffer.write('Z');
+      } else {
+        final int offset = timezoneOffsetInMinutes!;
+        final String sign = offset.isNegative ? '-' : '+';
+        final int absOffset = offset.abs();
+        final String hours = (absOffset ~/ 60).toString().padLeft(2, '0');
+        final String minutes = (absOffset % 60).toString().padLeft(2, '0');
+        buffer.write('$sign$hours:$minutes');
+      }
+    }
+    return buffer.toString();
+  }
+
+  /// Creates a new [GregorianMonthDay] instance with the given fields updated.
+  GregorianMonthDay copyWith({
+    int? month,
+    int? day,
+    int? timezoneOffsetInMinutes,
+    bool setToNoTimezone = false, // Special flag to remove timezone
+  }) {
+    return GregorianMonthDay(
+      month ?? this.month,
+      day ?? this.day,
+      timezoneOffsetInMinutes:
+          timezoneOffsetInMinutes ??
+          (setToNoTimezone ? null : this.timezoneOffsetInMinutes),
+    );
+  }
+
+  @override
+  bool operator ==(Object other) {
+    if (identical(this, other)) return true;
+    return other is GregorianMonthDay &&
+        other.month == month &&
+        other.day == day &&
+        other.timezoneOffsetInMinutes == timezoneOffsetInMinutes;
+  }
+
+  @override
+  int get hashCode => Object.hash(month, day, timezoneOffsetInMinutes);
+}

lib/src/types/types.dart

@@ -2,3 +2,4 @@ export 'year_month.dart';
 export 'gregorian_year.dart';
 export 'gregorian_month.dart';
 export 'gregorian_day.dart';
+export 'gregorian_month_day.dart';