RDART-866: kn/decimal128 web support (#1713)

* Implement Decimal128 for web

* fromDouble

* ==, hashCode

* Add deps on decimal and rational

* Match IEEE 754 Decimal128 precision (+/- 10^6144)

* Comment on compliancy

* Fix compile for web regression

* Update CHANGELOG

.vscode/settings.json

@@ -24,6 +24,7 @@
     "fnum",
     "geospatial",
     "HRESULT",
+    "intf",
     "keepalive",
     "keypaths",
     "loggable",

CHANGELOG.md

@@ -10,7 +10,8 @@
 ### Enhancements
 * Report the originating error that caused a client reset to occur. (Core 14.9.0)
 * Allow the realm package, and code generated by realm_generator to be included when building 
-  for web without breaking compilation. (Issue [#1374](https://github.com/realm/realm-dart/issues/1374))
+  for web without breaking compilation. (Issue [#1374](https://github.com/realm/realm-dart/issues/1374),
+  PR [#1713](https://github.com/realm/realm-dart/pull/1713))
 
 ### Fixed
 * `Realm.writeAsync` did not handle async callbacks (`Future<T> Function()`) correctly. (Issue [#1667](https://github.com/realm/realm-dart/issues/1667)) 

packages/realm_dart/lib/src/handles/web/decimal128.dart

@@ -1,9 +1,27 @@
 // Copyright 2024 MongoDB, Inc.
 // SPDX-License-Identifier: Apache-2.0
 
-import '../decimal128.dart' as intf;
+import 'package:decimal/decimal.dart';
+
+import 'package:realm_dart/src/convert.dart';
+
 import 'web_not_supported.dart';
 
+import '../decimal128.dart' as intf;
+
+/// This is not a compliant IEEE 754-2008 Decimal128 implementation, as it is
+/// just based on the [decimal](https://pub.dev/packages/decimal) package.
+/// Which is based on the [rational](https://pub.dev/packages/rational) package,
+/// which is again based on the [BigInt] class.
+///
+/// The issues are mostly in some of the odd corner cases of IEEE 754-2008
+/// Decimal128, such as:
+/// * -0 < 0,
+/// * NaN != NaN,
+/// * 1 / 0 = Inf, etc.
+///
+/// Also, be warned that this class is incredible slow compared to the native
+/// implementation.
 class Decimal128 implements intf.Decimal128 {
   static final zero = Decimal128.fromInt(0);
 
@@ -23,17 +41,75 @@ class Decimal128 implements intf.Decimal128 {
   static final negativeInfinity = -infinity;
 
   /// Parses a string into a [Decimal128]. Returns `null` if the string is not a valid [Decimal128].
-  static Decimal128? tryParse(String source) => webNotSupported();
+  static Decimal128? tryParse(String source) => Decimal.tryParse(source).convert(Decimal128._);
 
   /// Parses a string into a [Decimal128]. Throws a [FormatException] if the string is not a valid [Decimal128].
-  factory Decimal128.parse(String source) => webNotSupported();
+  factory Decimal128.parse(String source) => Decimal128._(Decimal.parse(source));
 
   /// Converts a `int` into a [Decimal128].
-  factory Decimal128.fromInt(int value) => webNotSupported();
+  factory Decimal128.fromInt(int value) => Decimal128._(Decimal.fromInt(value));
 
   /// Converts a `double` into a [Decimal128].
-  factory Decimal128.fromDouble(double value) => webNotSupported();
+  factory Decimal128.fromDouble(double value) {
+    if (value.isNaN) return nan;
+    if (value.isInfinite) return value.isNegative ? negativeInfinity : infinity;
+    return Decimal128._(Decimal.parse(value.toString()));
+  }
+
+  final Decimal _value;
+  Decimal128._(Decimal value) : _value = value.truncate(scale: 6144);
+
+  @override
+  Decimal128 operator *(covariant Decimal128 other) => Decimal128._(_value * other._value);
+
+  @override
+  Decimal128 operator +(covariant Decimal128 other) => Decimal128._(_value + other._value);
+
+  @override
+  Decimal128 operator -() => Decimal128._(-_value);
+
+  @override
+  Decimal128 operator -(covariant Decimal128 other) => Decimal128._(_value - other._value);
+
+  // Note IEEE 754 Decimal128 defines division with zero as infinity, similar to double
+  @override
+  Decimal128 operator /(covariant Decimal128 other) => Decimal128._((_value / other._value).toDecimal(scaleOnInfinitePrecision: 6144));
+
+  @override
+  bool operator <(covariant Decimal128 other) => _value < other._value;
+
+  @override
+  bool operator <=(covariant Decimal128 other) => _value <= other._value;
+
+  @override
+  bool operator >(covariant Decimal128 other) => _value > other._value;
+
+  @override
+  bool operator >=(covariant Decimal128 other) => _value >= other._value;
+
+  @override
+  Decimal128 abs() => Decimal128._(_value.abs());
+
+  @override
+  int compareTo(covariant Decimal128 other) {
+    final sign = _value.compareTo(other._value);
+    if (sign < 0) return -1;
+    if (sign > 0) return 1;
+    return 0;
+  }
+
+  @override
+  bool get isNaN => this == nan;
+
+  @override
+  int toInt() => _value.toBigInt().toInt();
+
+  @override
+  String toString() => _value.toStringAsExponential(27);
+
+  @override
+  operator ==(Object other) => other is Decimal128 && _value == other._value;
 
   @override
-  noSuchMethod(Invocation invocation) => webNotSupported();
+  int get hashCode => _value.hashCode;
 }

packages/realm_dart/pubspec.yaml

@@ -29,6 +29,8 @@ dependencies:
   build_runner: ^2.1.0
   http: ^1.0.0
   cancellation_token: ^2.0.0
+  decimal: ^3.0.1
+  rational: ^2.2.3
 
 dev_dependencies:
   build_cli: ^2.2.2