WIP amount class

lib/utilities/amount.dart

@@ -0,0 +1,43 @@
+import 'package:decimal/decimal.dart';
+
+final _ten = BigInt.from(10);
+
+class Amount {
+  Amount({
+    required BigInt rawValue,
+    required this.fractionDigits,
+  })  : assert(fractionDigits >= 0),
+        _value = rawValue;
+
+  /// truncate double value to [fractionDigits] places
+  Amount.fromDouble(double amount, {required this.fractionDigits})
+      : assert(fractionDigits >= 0),
+        _value =
+            Decimal.parse(amount.toString()).shift(fractionDigits).toBigInt();
+
+  /// truncate decimal value to [fractionDigits] places
+  Amount.fromDecimal(Decimal amount, {required this.fractionDigits})
+      : assert(fractionDigits >= 0),
+        _value = amount.shift(fractionDigits).toBigInt();
+
+  // ===========================================================================
+  // ======= Instance properties ===============================================
+
+  final int fractionDigits;
+  final BigInt _value;
+
+  // ===========================================================================
+  // ======= Getters ===========================================================
+
+  /// raw base value
+  BigInt get raw => _value;
+
+  /// actual decimal vale represented
+  Decimal get decimal =>
+      (Decimal.fromBigInt(_value) / _ten.pow(fractionDigits).toDecimal())
+          .toDecimal(scaleOnInfinitePrecision: fractionDigits);
+
+  /// convenience getter
+  @Deprecated("provided for convenience only. Use fractionDigits instead.")
+  int get decimals => fractionDigits;
+}

pubspec.lock

@@ -1358,7 +1358,7 @@ packages:
     source: hosted
     version: "4.0.0"
   rational:
-    dependency: transitive
+    dependency: "direct main"
     description:
       name: rational
       sha256: ba58e9e18df9abde280e8b10051e4bce85091e41e8e7e411b6cde2e738d357cf

pubspec.yaml

@@ -150,6 +150,7 @@ dependencies:
   dart_bs58: ^1.0.1
   dart_bs58check: ^3.0.2
   hex: ^0.2.0
+  rational: ^2.2.2
 
 dev_dependencies:
   flutter_test:

test/utilities/amount_test.dart

@@ -0,0 +1,81 @@
+import 'package:decimal/decimal.dart';
+import 'package:flutter_test/flutter_test.dart';
+import 'package:stackwallet/utilities/amount.dart';
+
+void main() {
+  test("Basic Amount Constructor tests", () {
+    Amount amount = Amount(rawValue: BigInt.two, fractionDigits: 0);
+    expect(amount.fractionDigits, 0);
+    expect(amount.raw, BigInt.two);
+    expect(amount.decimal, Decimal.fromInt(2));
+
+    amount = Amount(rawValue: BigInt.two, fractionDigits: 2);
+    expect(amount.fractionDigits, 2);
+    expect(amount.raw, BigInt.two);
+    expect(amount.decimal, Decimal.parse("0.02"));
+
+    amount = Amount(rawValue: BigInt.from(123456789), fractionDigits: 7);
+    expect(amount.fractionDigits, 7);
+    expect(amount.raw, BigInt.from(123456789));
+    expect(amount.decimal, Decimal.parse("12.3456789"));
+
+    bool didThrow = false;
+    try {
+      amount = Amount(rawValue: BigInt.one, fractionDigits: -1);
+    } catch (_) {
+      didThrow = true;
+    }
+    expect(didThrow, true);
+  });
+
+  test("Named fromDouble Amount Constructor tests", () {
+    Amount amount = Amount.fromDouble(2.0, fractionDigits: 0);
+    expect(amount.fractionDigits, 0);
+    expect(amount.raw, BigInt.two);
+    expect(amount.decimal, Decimal.fromInt(2));
+
+    amount = Amount.fromDouble(2.0, fractionDigits: 2);
+    expect(amount.fractionDigits, 2);
+    expect(amount.raw, BigInt.from(200));
+    expect(amount.decimal, Decimal.fromInt(2));
+
+    amount = Amount.fromDouble(0.0123456789, fractionDigits: 7);
+    expect(amount.fractionDigits, 7);
+    expect(amount.raw, BigInt.from(123456));
+    expect(amount.decimal, Decimal.parse("0.0123456"));
+
+    bool didThrow = false;
+    try {
+      amount = Amount.fromDouble(2.0, fractionDigits: -1);
+    } catch (_) {
+      didThrow = true;
+    }
+    expect(didThrow, true);
+  });
+
+  test("Named fromDecimal Amount Constructor tests", () {
+    Amount amount = Amount.fromDecimal(Decimal.fromInt(2), fractionDigits: 0);
+    expect(amount.fractionDigits, 0);
+    expect(amount.raw, BigInt.two);
+    expect(amount.decimal, Decimal.fromInt(2));
+
+    amount = Amount.fromDecimal(Decimal.fromInt(2), fractionDigits: 2);
+    expect(amount.fractionDigits, 2);
+    expect(amount.raw, BigInt.from(200));
+    expect(amount.decimal, Decimal.fromInt(2));
+
+    amount =
+        Amount.fromDecimal(Decimal.parse("0.0123456789"), fractionDigits: 7);
+    expect(amount.fractionDigits, 7);
+    expect(amount.raw, BigInt.from(123456));
+    expect(amount.decimal, Decimal.parse("0.0123456"));
+
+    bool didThrow = false;
+    try {
+      amount = Amount.fromDecimal(Decimal.fromInt(2), fractionDigits: -1);
+    } catch (_) {
+      didThrow = true;
+    }
+    expect(didThrow, true);
+  });
+}