refactor: improve balance sufficiency calculations and update currency handling

- Refactored the calculateBalanceSufficiency function to consistently use BigNumber for USD amounts, enhancing precision in financial calculations.
- Updated the MessagesRefillModal to display insufficient funds in USDT, improving user clarity on payment requirements.
- Introduced UsdCurrencyAmount for better currency formatting and handling, ensuring accurate representation of amounts in the UI.

These changes collectively enhance the accuracy and usability of financial interactions within the application.

Author: mois-ilya

src/features/app-messages/ui/MessagesRefillModal.tsx

@@ -1,4 +1,5 @@
 import { FC, useEffect, useState } from 'react';
+import BigNumber from 'bignumber.js';
 import {
     Box,
     Button,
@@ -18,7 +19,7 @@ import {
     UseRadioProps,
     VStack
 } from '@chakra-ui/react';
-import { FilledWarnIcon16, formatWithSuffix, H4 } from 'src/shared';
+import { FilledWarnIcon16, formatWithSuffix, H4, UsdCurrencyAmount } from 'src/shared';
 import { RadioCard } from 'src/shared/ui/checkbox';
 import { AppMessagesPackage } from '../model';
 import { RefillModalContent } from 'src/entities';
@@ -39,12 +40,9 @@ const MessagesRefillModal: FC<{
         onChange: name => setSelectedPlan(options.find(pkg => pkg.name === name) || null)
     });
     const group = getRootProps();
-    const sufficiencyCheck = useBalanceSufficiencyCheck(selectedPlan?.price.amount || null);
+    const sufficiencyCheck = useBalanceSufficiencyCheck(selectedPlan?.price.amount ?? null);
     const notEnoughAmount = sufficiencyCheck ? getPaymentDeficit(sufficiencyCheck) : BigInt(0);
-
-    useEffect(() => {
-        setSelectedPlan(options[0]);
-    }, [options]);
+    const notEnoughAmountUsdt = new UsdCurrencyAmount(new BigNumber(notEnoughAmount).div(1e6));
 
     const tonRefillModal = useDisclosure();
     const confirmPaymentModal = useDisclosure();
@@ -104,8 +102,8 @@ const MessagesRefillModal: FC<{
                 {!!notEnoughAmount && (
                     <Text textStyle="body2" mt="3" color="text.secondary">
                         <FilledWarnIcon16 />
-                        &nbsp;Not enough ${notEnoughAmount.toString()} to buy the plan, fund your
-                        account
+                        &nbsp;Not enough {notEnoughAmountUsdt.stringCurrencyAmount} USDT to buy the
+                        plan, fund your account
                     </Text>
                 )}
             </ModalBody>

src/features/balance/model/queries.ts

@@ -56,22 +56,20 @@ function mapDTOBalanceToBalance(
  */
 export function calculateBalanceSufficiency(
     balance: Balance,
-    amountInUsd: BigNumber | number,
+    amountInUsd: BigNumber,
     tonRate: number,
     includePromo = true
 ): SufficiencyCheckResult {
-    const amountBn = amountInUsd instanceof BigNumber ? amountInUsd : new BigNumber(amountInUsd);
-
     // Convert USD amount to cents (since USDT is in 6 decimals, but we work in cents for simplicity)
-    const amountInCents = amountBn.multipliedBy(100);
+    const amountInMicroUsdt = amountInUsd.multipliedBy(1e6);
 
     // Check USDT sufficiency
     const usdtBalance = includePromo
         ? balance.usdt.amount + balance.usdt.promo_amount
         : balance.usdt.amount;
 
-    const usdtSufficient = usdtBalance >= BigInt(amountInCents.toFixed(0));
-    const usdtDeficit = usdtSufficient ? BigInt(0) : BigInt(amountInCents.toFixed(0)) - usdtBalance;
+    const usdtSufficient = usdtBalance >= BigInt(amountInMicroUsdt.toFixed(0));
+    const usdtDeficit = usdtSufficient ? BigInt(0) : BigInt(amountInMicroUsdt.toFixed(0)) - usdtBalance;
 
     // Check TON sufficiency (if TON balance exists)
     let tonSufficient = false;
@@ -85,10 +83,10 @@ export function calculateBalanceSufficiency(
         // Convert TON to USD equivalent
         // tonBalance is in nanoTON (10^9), so convert to TON first
         const tonInUsd = Number(tonBalance) / Math.pow(10, TON_DECIMALS) * tonRate;
-        const tonInUsdCents = new BigNumber(tonInUsd).multipliedBy(100);
+        const tonInUsdMicroUsd = new BigNumber(tonInUsd).multipliedBy(1e6);
 
-        tonSufficient = tonInUsdCents.gte(amountInCents);
-        tonDeficit = tonSufficient ? BigInt(0) : BigInt(amountInCents.minus(tonInUsdCents).toFixed(0));
+        tonSufficient = tonInUsdMicroUsd.gte(amountInMicroUsdt);
+        tonDeficit = tonSufficient ? BigInt(0) : BigInt(amountInMicroUsdt.minus(tonInUsdMicroUsd).toFixed(0));
     }
 
     return {
@@ -211,7 +209,7 @@ export function useTonRateQuery() {
  * @returns SufficiencyCheckResult or undefined if loading/error
  */
 export function useBalanceSufficiencyCheck(
-    amountInUsd: BigNumber | number | null | undefined,
+    amountInUsd: BigNumber | null,
     options?: { includePromo?: boolean }
 ): SufficiencyCheckResult | undefined {
     const { data: balance } = useBalanceQuery();