amount unit + tests

lib/utilities/amount/amount_unit.dart

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+import 'dart:math' as math;
+
+import 'package:decimal/decimal.dart';
+import 'package:intl/number_symbols.dart';
+import 'package:intl/number_symbols_data.dart';
+import 'package:stackwallet/utilities/amount/amount.dart';
+import 'package:stackwallet/utilities/enums/coin_enum.dart';
+
+enum AmountUnit {
+  normal(0),
+  milli(3),
+  micro(6),
+  nano(9),
+  pico(12),
+  femto(15),
+  atto(18),
+  ;
+
+  const AmountUnit(this.shift);
+  final int shift;
+}
+
+extension AmountUnitExt on AmountUnit {
+  String unitForCoin(Coin coin) {
+    switch (this) {
+      case AmountUnit.normal:
+        return coin.ticker;
+      case AmountUnit.milli:
+        return "m${coin.ticker}";
+      case AmountUnit.micro:
+        return "µ${coin.ticker}";
+      case AmountUnit.nano:
+        if (coin == Coin.ethereum) {
+          return "gwei";
+        } else if (coin == Coin.wownero || coin == Coin.monero) {
+          return "n${coin.ticker}";
+        } else {
+          return "sats";
+        }
+      case AmountUnit.pico:
+        if (coin == Coin.ethereum) {
+          return "mwei";
+        } else if (coin == Coin.wownero || coin == Coin.monero) {
+          return "p${coin.ticker}";
+        } else {
+          return "invalid";
+        }
+      case AmountUnit.femto:
+        if (coin == Coin.ethereum) {
+          return "kwei";
+        } else {
+          return "invalid";
+        }
+      case AmountUnit.atto:
+        if (coin == Coin.ethereum) {
+          return "wei";
+        } else {
+          return "invalid";
+        }
+    }
+  }
+
+  String displayAmount({
+    required Amount amount,
+    required String locale,
+    required Coin coin,
+    required int maxDecimalPlaces,
+  }) {
+    assert(maxDecimalPlaces >= 0);
+    // ensure we don't shift past minimum atomic value
+    final realShift = math.min(shift, amount.fractionDigits);
+
+    // shifted to unit
+    final Decimal shifted = amount.decimal.shift(realShift);
+
+    // get shift int value without fractional value
+    final BigInt wholeNumber = shifted.toBigInt();
+
+    // get decimal places to display
+    final int places = math.max(0, amount.fractionDigits - realShift);
+
+    // start building the return value with just the whole value
+    String returnValue = wholeNumber.toString();
+
+    // if any decimal places should be shown continue building the return value
+    if (places > 0) {
+      // get the fractional value
+      final Decimal fraction = shifted - shifted.truncate();
+
+      // get final decimal based on max precision wanted
+      final int actualDecimalPlaces = math.min(places, maxDecimalPlaces);
+
+      // get remainder string without the prepending "0."
+      String remainder = fraction.toString().substring(2);
+
+      if (remainder.length > actualDecimalPlaces) {
+        // trim unwanted trailing digits
+        remainder = remainder.substring(0, actualDecimalPlaces);
+      } else if (remainder.length < actualDecimalPlaces) {
+        // pad with zeros to achieve requested precision
+        for (int i = remainder.length; i < actualDecimalPlaces; i++) {
+          remainder += "0";
+        }
+      }
+
+      // get decimal separator based on locale
+      final String separator =
+          (numberFormatSymbols[locale] as NumberSymbols?)?.DECIMAL_SEP ??
+              (numberFormatSymbols[locale.substring(0, 2)] as NumberSymbols?)
+                  ?.DECIMAL_SEP ??
+              ".";
+
+      // append separator and fractional amount
+      returnValue += "$separator$remainder";
+    }
+
+    // return the value with the proper unit symbol
+    return "$returnValue ${unitForCoin(coin)}";
+  }
+}

test/utilities/amount/amount_unit_test.dart

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+import 'package:decimal/decimal.dart';
+import 'package:flutter_test/flutter_test.dart';
+import 'package:stackwallet/utilities/amount/amount.dart';
+import 'package:stackwallet/utilities/amount/amount_unit.dart';
+import 'package:stackwallet/utilities/enums/coin_enum.dart';
+
+void main() {
+  test("displayAmount BTC", () {
+    final Amount amount = Amount(
+      rawValue: BigInt.from(1012345678),
+      fractionDigits: 8,
+    );
+
+    expect(
+      AmountUnit.normal.displayAmount(
+        amount: amount,
+        locale: "en_US",
+        coin: Coin.bitcoin,
+        maxDecimalPlaces: 8,
+      ),
+      "10.12345678 BTC",
+    );
+
+    expect(
+      AmountUnit.milli.displayAmount(
+        amount: amount,
+        locale: "en_US",
+        coin: Coin.bitcoin,
+        maxDecimalPlaces: 8,
+      ),
+      "10123.45678 mBTC",
+    );
+
+    expect(
+      AmountUnit.micro.displayAmount(
+        amount: amount,
+        locale: "en_US",
+        coin: Coin.bitcoin,
+        maxDecimalPlaces: 8,
+      ),
+      "10123456.78 µBTC",
+    );
+
+    expect(
+      AmountUnit.nano.displayAmount(
+        amount: amount,
+        locale: "en_US",
+        coin: Coin.bitcoin,
+        maxDecimalPlaces: 8,
+      ),
+      "1012345678 sats",
+    );
+    final dec = Decimal.parse("10.123456789123456789");
+
+    expect(dec.toString(), "10.123456789123456789");
+  });
+
+  test("displayAmount ETH", () {
+    final Amount amount = Amount.fromDecimal(
+      Decimal.parse("10.123456789123456789"),
+      fractionDigits: Coin.ethereum.decimals,
+    );
+
+    expect(
+      AmountUnit.normal.displayAmount(
+        amount: amount,
+        locale: "en_US",
+        coin: Coin.ethereum,
+        maxDecimalPlaces: 8,
+      ),
+      "10.12345678 ETH",
+    );
+
+    expect(
+      AmountUnit.normal.displayAmount(
+        amount: amount,
+        locale: "en_US",
+        coin: Coin.ethereum,
+        maxDecimalPlaces: 18,
+      ),
+      "10.123456789123456789 ETH",
+    );
+
+    expect(
+      AmountUnit.milli.displayAmount(
+        amount: amount,
+        locale: "en_US",
+        coin: Coin.ethereum,
+        maxDecimalPlaces: 9,
+      ),
+      "10123.456789123 mETH",
+    );
+
+    expect(
+      AmountUnit.micro.displayAmount(
+        amount: amount,
+        locale: "en_US",
+        coin: Coin.ethereum,
+        maxDecimalPlaces: 8,
+      ),
+      "10123456.78912345 µETH",
+    );
+
+    expect(
+      AmountUnit.nano.displayAmount(
+        amount: amount,
+        locale: "en_US",
+        coin: Coin.ethereum,
+        maxDecimalPlaces: 1,
+      ),
+      "10123456789.1 gwei",
+    );
+
+    expect(
+      AmountUnit.pico.displayAmount(
+        amount: amount,
+        locale: "en_US",
+        coin: Coin.ethereum,
+        maxDecimalPlaces: 18,
+      ),
+      "10123456789123.456789 mwei",
+    );
+
+    expect(
+      AmountUnit.femto.displayAmount(
+        amount: amount,
+        locale: "en_US",
+        coin: Coin.ethereum,
+        maxDecimalPlaces: 4,
+      ),
+      "10123456789123456.789 kwei",
+    );
+
+    expect(
+      AmountUnit.atto.displayAmount(
+        amount: amount,
+        locale: "en_US",
+        coin: Coin.ethereum,
+        maxDecimalPlaces: 1,
+      ),
+      "10123456789123456789 wei",
+    );
+  });
+}