feat: add xsd:decimal codec

CHANGELOG.md

@@ -27,4 +27,5 @@
 - Implement `xsd:gMonthDay` codec and data type
 - Implement `xsd:duration` codec and data type
 - Implement `xsd:datetime` codec and data type
-- Implement `xsd:anyUri` codec
+- Implement `xsd:anyUri` codec
+- Implement `xsd:decimal` codec

README.md

@@ -31,7 +31,7 @@ This library aims to support the following XSD 1.1 built-in datatypes that are c
 |             `xsd:Name` |      ✅      |        ✅        |    `String`    |     `dart:core`    |
 |         `xsd:language` |      ✅      |        ✅        |    `Locale`    |     `package:intl`    |
 |           `xsd:NCName` |      ✅      |        ✅        |    `String`    |     `dart:core`    |
-|          `xsd:decimal` |      ✅      |        ❌        |    `Decimal`    |     `package:decimal`    |
+|          `xsd:decimal` |      ✅      |        ✅        |    `Decimal`    |     `package:decimal`    |
 |           `xsd:double` |      ✅      |        ❌        |    `double`    |     `dart:core`    |
 |            `xsd:float` |      ✅      |        ❌        |    `double`    |     `dart:core`    |
 |          `xsd:integer` |      ✅      |        ❌        |    `BigInt`    |     `dart:core`    |

lib/src/codecs/codecs.dart

@@ -25,3 +25,4 @@ export 'g_month_day/gregorian_month_day_codec.dart';
 export 'duration/xsd_duration_codec.dart';
 export 'datetime/xsd_datetime_codec.dart';
 export 'any_uri/any_uri_codec.dart';
+export 'decimal/decimal_codec.dart';

lib/src/codecs/decimal/decimal_codec.dart

@@ -0,0 +1,41 @@
+import 'dart:convert';
+
+import 'package:decimal/decimal.dart';
+import 'package:xsd/src/helpers/whitespace.dart';
+
+/// A [Codec] that converts between XSD `decimal` strings and [Decimal] objects.
+class XsdDecimalCodec extends Codec<Decimal, String> {
+  const XsdDecimalCodec();
+
+  @override
+  Converter<Decimal, String> get encoder => const XsdDecimalEncoder();
+
+  @override
+  Converter<String, Decimal> get decoder => const XsdDecimalDecoder();
+}
+
+class XsdDecimalEncoder extends Converter<Decimal, String> {
+  const XsdDecimalEncoder();
+
+  @override
+  String convert(Decimal input) => input.toString();
+}
+
+class XsdDecimalDecoder extends Converter<String, Decimal> {
+  const XsdDecimalDecoder();
+
+  static final _validationRegex = RegExp(
+    r'^(\+|-)?([0-9]+(\.[0-9]*)?|\.[0-9]+)$',
+  );
+
+  @override
+  Decimal convert(String input) {
+    final trimmed = processWhiteSpace(input, Whitespace.collapse);
+
+    if (!_validationRegex.hasMatch(trimmed)) {
+      throw FormatException('Invalid XSD decimal format', input);
+    }
+
+    return Decimal.parse(trimmed);
+  }
+}

test/codecs/decimal_codec_test.dart

@@ -0,0 +1,34 @@
+import 'package:decimal/decimal.dart';
+import 'package:test/test.dart';
+import 'package:xsd/xsd.dart';
+
+void main() {
+  group('XsdDecimalCodec', () {
+    const codec = XsdDecimalCodec();
+
+    test('should encode valid decimal', () {
+      expect(codec.encode(Decimal.parse('123.45')), '123.45');
+      expect(codec.encode(Decimal.parse('-123.45')), '-123.45');
+    });
+
+    test('should decode valid decimal', () {
+      expect(codec.decode('123.45'), Decimal.parse('123.45'));
+      expect(codec.decode('-123.45'), Decimal.parse('-123.45'));
+      expect(codec.decode('  +123.45  '), Decimal.parse('123.45'));
+      expect(codec.decode('.45'), Decimal.parse('0.45'));
+      expect(codec.decode('123'), Decimal.parse('123'));
+      expect(codec.decode('+123'), Decimal.parse('123'));
+      expect(codec.decode('-123'), Decimal.parse('-123'));
+      expect(codec.decode('123.'), Decimal.parse('123'));
+    });
+
+    test('should throw on invalid decimal', () {
+      expect(() => codec.decode('12.3.4'), throwsFormatException);
+      expect(() => codec.decode('abc'), throwsFormatException);
+      expect(
+        () => codec.decode('1E4'),
+        throwsFormatException,
+      ); // Scientific notation not allowed in decimal
+    });
+  });
+}