feat(wallet): Add formatting with subscripts to amounts with long decimals

apps/core/src/hooks/__tests__/useFormatCoin.test.ts

@@ -24,6 +24,21 @@ describe('formatBalance', () => {
         expect(formatBalance('0.000', IOTA_DECIMALS)).toEqual('0');
     });
 
+    it('formats decimal amounts with less than 4 leading zeroes, truncated with up to 4 decimals', () => {
+        expect(formatBalance('512345678', IOTA_DECIMALS)).toEqual('0.5');
+        expect(formatBalance('51234567', IOTA_DECIMALS)).toEqual('0.05');
+        expect(formatBalance('5123456', IOTA_DECIMALS)).toEqual('0.005');
+        expect(formatBalance('523456', IOTA_DECIMALS)).toEqual('0.0005');
+    });
+
+    it('formats decimal amounts with 4 or more leading zeroes (after decimal point) with subscripts', () => {
+        expect(formatBalance('19723', IOTA_DECIMALS)).toEqual('0.0₄19723');
+        expect(formatBalance('1234', IOTA_DECIMALS)).toEqual('0.0₅1234');
+        expect(formatBalance('123', IOTA_DECIMALS)).toEqual('0.0₆123');
+        expect(formatBalance('12', IOTA_DECIMALS)).toEqual('0.0₇12');
+        expect(formatBalance('1', IOTA_DECIMALS)).toEqual('0.0₈1');
+    });
+
     it('formats integer amounts correctly', () => {
         expect(formatBalance(toNano('1'), IOTA_DECIMALS)).toEqual('1');
         expect(formatBalance(toNano('1.0001'), IOTA_DECIMALS)).toEqual('1');

apps/core/src/utils/formatAmount.ts

@@ -4,7 +4,7 @@
 
 import BigNumber from 'bignumber.js';
 
-export function formatAmountParts(amount?: BigNumber | bigint | number | string | null) {
+export function formatAmountParts(amount?: BigNumber | bigint | number | string | null): string[] {
     if (typeof amount === 'undefined' || amount === null) {
         return ['--'];
     }
@@ -29,6 +29,16 @@ export function formatAmountParts(amount?: BigNumber | bigint | number | string
         bn = bn.decimalPlaces(2, BigNumber.ROUND_DOWN);
     }
 
+    if (bnAbs.gt(0) && bnAbs.lt(1)) {
+        const leadingZeros = countDecimalLeadingZeros(bn.toFormat());
+
+        if (leadingZeros >= 4) {
+            return [formatWithSubscript(bn.toFormat(), leadingZeros), postfix];
+        } else {
+            return [bn.toFormat(leadingZeros + 1), postfix];
+        }
+    }
+
     return [bn.toFormat(), postfix];
 }
 
@@ -37,3 +47,45 @@ export function formatAmount(...args: Parameters<typeof formatAmountParts>) {
         .filter(Boolean)
         .join(' ');
 }
+
+export const countDecimalLeadingZeros = (
+    input: BigNumber | bigint | number | string | null,
+): number => {
+    if (input === null) {
+        return 0;
+    }
+
+    const [, decimals] = input.toString().split('.');
+
+    if (!decimals) {
+        return 0;
+    }
+
+    let count = 0;
+
+    for (const digit of decimals) {
+        if (digit === '0') {
+            count++;
+        } else {
+            break;
+        }
+    }
+
+    return count;
+};
+
+const SUBSCRIPTS = ['₀', '₁', '₂', '₃', '₄', '₅', '₆', '₇', '₈', '₉'];
+
+export const formatWithSubscript = (
+    input: BigNumber | bigint | number | string | null,
+    zeroCount: number,
+): string => {
+    if (input === null) {
+        return '0';
+    }
+
+    const [, decimals] = input.toString().split('.');
+    const remainder = decimals.slice(zeroCount);
+
+    return `0.0${SUBSCRIPTS[zeroCount]}${remainder}`;
+};

apps/wallet/src/ui/app/pages/home/tokens/coin-balance/index.tsx

@@ -2,10 +2,12 @@
 // Modifications Copyright (c) 2024 IOTA Stiftung
 // SPDX-License-Identifier: Apache-2.0
 import { useAppSelector } from '_hooks';
-import { useBalanceInUSD, useFormatCoin } from '@iota/core';
+import { CoinFormat, formatBalance, useBalanceInUSD, useFormatCoin } from '@iota/core';
 import { Network } from '@iota/iota-sdk/client';
 import { IOTA_TYPE_ARG } from '@iota/iota-sdk/utils';
 import { useMemo } from 'react';
+import { Tooltip, TooltipPosition } from '@iota/apps-ui-kit';
+import BigNumber from 'bignumber.js';
 
 export interface CoinProps {
     type: string;
@@ -37,17 +39,39 @@ function WalletBalanceUsd({ amount: walletBalance }: WalletBalanceUsdProps) {
 
 export function CoinBalance({ amount: walletBalance, type }: CoinProps) {
     const network = useAppSelector((state) => state.app.network);
-    const [formatted, symbol] = useFormatCoin(walletBalance, type);
+    const [formatted, symbol, { data: coinMetadata }] = useFormatCoin(walletBalance, type);
+
+    const iotaDecimals = coinMetadata?.decimals ?? 9;
+    const bnBalance = new BigNumber(walletBalance.toString()).shiftedBy(-1 * iotaDecimals);
+    const shouldShowTooltip = bnBalance.gt(0) && bnBalance.lt(1);
 
     return (
         <>
             <div className="flex items-baseline gap-0.5">
-                <div
-                    className="text-headline-lg text-neutral-10 dark:text-neutral-92"
-                    data-testid="coin-balance"
-                >
-                    {formatted}
-                </div>
+                {shouldShowTooltip ? (
+                    <Tooltip
+                        text={formatBalance(
+                            walletBalance,
+                            coinMetadata?.decimals ?? 9,
+                            CoinFormat.FULL,
+                        )}
+                        position={TooltipPosition.Bottom}
+                    >
+                        <div
+                            className="text-headline-lg text-neutral-10 dark:text-neutral-92"
+                            data-testid="coin-balance"
+                        >
+                            {formatted}
+                        </div>
+                    </Tooltip>
+                ) : (
+                    <div
+                        className="text-headline-lg text-neutral-10 dark:text-neutral-92"
+                        data-testid="coin-balance"
+                    >
+                        {formatted}
+                    </div>
+                )}
                 <div className="text-label-md text-neutral-40">{symbol}</div>
             </div>
             {network === Network.Mainnet ? <WalletBalanceUsd amount={walletBalance} /> : null}