Fix 562 dynamic currency rate precision

docs/CURRENCY_CONVERSIONS.md

@@ -14,6 +14,7 @@ SplitPro can convert expenses and balances between currencies using cached excha
 - Rates are fetched from the configured provider and cached in the database.
 - Conversions can be created for an expense and later edited if needed.
 - Group balances can be converted on demand without changing the original expense currency.
+- Currency rate precisions are set to the number of digits obtained from the provider.
 
 ## Providers and limitations
 
@@ -22,22 +23,24 @@ Exchange rate APIs are typically rate limited or paywalled. SplitPro supports th
 - Frankfurter (https://frankfurter.dev/)
   - Free, but limited currency set.
   - Check availability at https://api.frankfurter.dev/v1/currencies.
+  - Responses truncate trailing zeros in rate values, which may limit the precision input.
 - Open Exchange Rates (https://openexchangerates.org/)
   - Free tier includes 1000 requests/day and wide currency coverage.
   - Free tier uses USD as the base currency; SplitPro joins rates internally.
   - Requires an API key.
+  - Responses truncate trailing zeros in rate values, which may limit the precision input.
 - NBP (https://api.nbp.pl/en.html)
   - Polish National Bank.
   - No API key required, base currency PLN.
-  - Table A updates daily, table B (less common currencies) updates weekly.
+  - Table A updates daily, table B (currencies less common for Poland) updates weekly.
 
 ## Provider comparison
 
-| Provider            | Base currency | Coverage | API key | Notes                      |
-| ------------------- | ------------- | -------- | ------- | -------------------------- |
-| Frankfurter         | EUR           | Limited  | No      | Free, limited currency set |
-| Open Exchange Rates | USD           | Broad    | Yes     | Free tier 1000 req/day     |
-| NBP                 | PLN           | Medium   | No      | Table B updates weekly     |
+| Provider            | Base currency | Coverage | API key | Trailing zeros | Notes                      |
+| ------------------- | ------------- | -------- | ------- | -------------- | -------------------------- |
+| Frankfurter         | EUR           | Limited  | No      | Truncated      | Free, limited currency set |
+| Open Exchange Rates | USD           | Broad    | Yes     | Truncated      | Free tier 1000 req/day     |
+| NBP                 | PLN           | Medium   | No      | Preserved      | Table B updates weekly     |
 
 ## Configuration
 
@@ -47,6 +50,7 @@ Set your provider in `CURRENCY_RATE_PROVIDER` and supply `OPEN_EXCHANGE_RATES_AP
 
 - Rates are cached in the database to minimize calls and stay within provider limits.
 - Provider coverage and rate freshness depend on the selected provider.
+- Frankfurter and Open Exchange Rates truncate trailing zeros in rate values, which limits the reported precision for those responses.
 
 ## Common use cases
 

prisma/migrations/20260209204650_add_cached_currency_rate_precision/migration.sql

@@ -0,0 +1,6 @@
+-- Clear cached currency rates to repopulate with precision
+TRUNCATE TABLE "CachedCurrencyRate";
+
+-- Add precision to cached currency rates
+ALTER TABLE "CachedCurrencyRate"
+ADD COLUMN "precision" INTEGER NOT NULL;

prisma/schema.prisma

@@ -210,6 +210,7 @@ model CachedCurrencyRate {
   to          String
   date        DateTime
   rate        Float
+  precision   Int
   lastFetched DateTime
   createdAt   DateTime @default(now())
   updatedAt   DateTime @updatedAt

src/components/AddExpense/AddExpensePage.tsx

@@ -223,7 +223,7 @@ export const AddOrEditExpensePage: React.FC<{
   const previousCurrencyRef = React.useRef<CurrencyCode | null>(null);
 
   const onConvertAmount: React.ComponentProps<typeof CurrencyConversion>['onSubmit'] = useCallback(
-    ({ amount: absAmount, rate }) => {
+    ({ amount: absAmount, rate, ratePrecision }) => {
       if (!previousCurrencyRef.current) {
         return;
       }
@@ -233,6 +233,7 @@ export const AddOrEditExpensePage: React.FC<{
         currencyConversion({
           amount: absAmount,
           rate,
+          ratePrecision,
           from: previousCurrencyRef.current,
           to: currency,
         });

src/components/Expense/ConvertibleBalance.tsx

@@ -113,7 +113,8 @@ export const ConvertibleBalance: React.FC<ConvertibleBalanceProps> = ({
           from: balance.currency,
           to: selectedCurrency,
           amount: balance.amount,
-          rate,
+          rate: rate.rate,
+          ratePrecision: rate.precision,
         });
         total += convertedValue;
       }

src/components/Friend/CurrencyConversion.tsx

@@ -1,7 +1,7 @@
 import React, { type ReactNode, useCallback, useEffect, useMemo, useState } from 'react';
 import { useTranslationWithUtils } from '~/hooks/useTranslationWithUtils';
 import { api } from '~/utils/api';
-import { currencyConversion } from '~/utils/numbers';
+import { currencyConversion, getRatePrecision } from '~/utils/numbers';
 
 import { toast } from 'sonner';
 import { env } from '~/env';
@@ -26,6 +26,7 @@ export const CurrencyConversion: React.FC<{
     to: CurrencyCode;
     amount: bigint;
     rate: number;
+    ratePrecision: number;
   }) => Promise<void> | void;
 }> = ({ amount, editingRate, editingTargetCurrency, currency, children, onSubmit }) => {
   const { t, getCurrencyHelpersCached } = useTranslationWithUtils();
@@ -34,6 +35,7 @@ export const CurrencyConversion: React.FC<{
 
   const [amountStr, setAmountStr] = useState('');
   const [rate, setRate] = useState('');
+  const [ratePrecision, setRatePrecision] = useState(0);
   const [targetAmountStr, setTargetAmountStr] = useState('');
   const preferredCurrency = useAddExpenseStore((state) => state.currency);
   const { setCurrency } = useAddExpenseStore((state) => state.actions);
@@ -49,21 +51,30 @@ export const CurrencyConversion: React.FC<{
   useEffect(() => {
     if (getCurrencyRate.isPending) {
       setRate('');
+      setRatePrecision(0);
       setTargetAmountStr('');
     }
   }, [getCurrencyRate.isPending]);
 
   useEffect(() => {
     setAmountStr(toUIString(amount, false, true));
-    setRate(editingRate ? editingRate.toFixed(4) : '');
+    if (editingRate) {
+      const precision = Number.isFinite(editingRate) ? getRatePrecision(editingRate.toString()) : 0;
+      setRate(editingRate.toFixed(precision));
+      setRatePrecision(precision);
+    } else {
+      setRate('');
+      setRatePrecision(0);
+    }
     if (editingTargetCurrency && isCurrencyCode(editingTargetCurrency)) {
       setTargetCurrency(editingTargetCurrency);
     }
   }, [amount, editingRate, editingTargetCurrency, toUIString]);
 
   useEffect(() => {
     if (getCurrencyRate.data?.rate) {
-      setRate(getCurrencyRate.data.rate.toFixed(4));
+      setRate(getCurrencyRate.data.rate.toFixed(getCurrencyRate.data.precision));
+      setRatePrecision(getCurrencyRate.data.precision);
     }
   }, [getCurrencyRate.data]);
 
@@ -79,9 +90,10 @@ export const CurrencyConversion: React.FC<{
       to: targetCurrency,
       amount: toSafeBigInt(amountStr),
       rate: Number(rate),
+      ratePrecision,
     });
     setTargetAmountStr(toUITargetString(targetAmount, false, true));
-  }, [amountStr, rate, toSafeBigInt, toUITargetString, currency, targetCurrency]);
+  }, [amountStr, rate, ratePrecision, toSafeBigInt, toUITargetString, currency, targetCurrency]);
 
   const onUpdateAmount = useCallback(
     ({ strValue }: { strValue?: string; bigIntValue?: bigint }) => {
@@ -97,21 +109,24 @@ export const CurrencyConversion: React.FC<{
     // Allow empty while typing
     if (raw === '') {
       setRate('');
+      setRatePrecision(0);
       return;
     }
     // Only digits and optional dot
     if (!/^[0-9]*\.?[0-9]*$/.test(raw)) {
       return;
     }
     const [int = '', dec = ''] = raw.split('.');
-    const trimmedDec = dec.slice(0, 4);
-    const normalized = raw.includes('.') ? `${int}.${trimmedDec}` : int;
+    const precision = raw.includes('.') ? dec.length : 0;
+    const normalized = raw.includes('.') ? `${int}.${dec}` : int;
     setRate(normalized);
+    setRatePrecision(precision);
   }, []);
 
   const onChangeTargetCurrency = useCallback(
     (currency: CurrencyCode) => {
       setRate('');
+      setRatePrecision(0);
       setTargetCurrency(currency);
       setCurrency(currency);
     },
@@ -124,13 +139,14 @@ export const CurrencyConversion: React.FC<{
         const amount = currencyConversion({
           amount: bigIntValue ?? 0n,
           rate: 1 / Number(rate),
+          ratePrecision,
           from: targetCurrency,
           to: currency,
         });
         setAmountStr(toUIString(amount, false, true));
       }
     },
-    [rate, toUIString, targetCurrency, currency],
+    [rate, ratePrecision, toUIString, targetCurrency, currency],
   );
 
   const onSave = useCallback(async () => {
@@ -143,6 +159,7 @@ export const CurrencyConversion: React.FC<{
       await onSubmit({
         amount: getCurrencyHelpersCached(currency).toSafeBigInt(amountStr),
         rate: Number(rate),
+        ratePrecision,
         from: currency,
         to: targetCurrency,
       });
@@ -151,7 +168,16 @@ export const CurrencyConversion: React.FC<{
       console.error(error);
       toast.error(t('errors.currency_conversion_error'));
     }
-  }, [onSubmit, targetCurrency, amountStr, rate, currency, getCurrencyHelpersCached, t]);
+  }, [
+    onSubmit,
+    targetCurrency,
+    amountStr,
+    rate,
+    ratePrecision,
+    currency,
+    getCurrencyHelpersCached,
+    t,
+  ]);
 
   return (
     <AppDrawer
@@ -226,7 +252,7 @@ export const CurrencyConversion: React.FC<{
                   <Input
                     aria-label="Rate"
                     type="number"
-                    step="0.0001"
+                    step={0 === ratePrecision ? '1' : `0.${'0'.repeat(ratePrecision - 1)}1`}
                     min={0}
                     value={rate}
                     inputMode="numeric"
@@ -238,13 +264,13 @@ export const CurrencyConversion: React.FC<{
                       {t('currency_conversion.fetching_rate')}
                     </span>
                   )}
-                  {!!rate && (
+                  {Boolean(rate) && (
                     <>
                       <span className="pointer-events-none text-xs text-gray-500">
-                        1 {currency} = {Number(rate).toFixed(4)} {targetCurrency}
+                        1 {currency} = {Number(rate).toFixed(ratePrecision)} {targetCurrency}
                       </span>
                       <span className="pointer-events-none text-xs text-gray-500">
-                        1 {targetCurrency} = {(1 / Number(rate)).toFixed(4)} {currency}
+                        1 {targetCurrency} = {(1 / Number(rate)).toFixed(ratePrecision)} {currency}
                       </span>
                     </>
                   )}

src/server/api/routers/expense.ts

@@ -14,7 +14,7 @@ import {
   getCurrencyRateSchema,
 } from '~/types/expense.types';
 import { createExpense, deleteExpense, editExpense } from '../services/splitService';
-import { currencyRateProvider } from '../services/currencyRateService';
+import { type ParsedRate, currencyRateProvider } from '../services/currencyRateService';
 import { type CurrencyCode, isCurrencyCode } from '~/lib/currency';
 import { SplitType } from '@prisma/client';
 import { DEFAULT_CATEGORY } from '~/lib/category';
@@ -103,7 +103,7 @@ export const expenseRouter = createTRPCRouter({
       if (!acc[friendId]) {
         acc[friendId] = [];
       }
-      acc[friendId]!.push({ currency, amount });
+      acc[friendId].push({ currency, amount });
       return acc;
     }, {});
 
@@ -168,13 +168,14 @@ export const expenseRouter = createTRPCRouter({
   addOrEditCurrencyConversion: protectedProcedure
     .input(createCurrencyConversionSchema)
     .mutation(async ({ input, ctx }) => {
-      const { amount, rate, from, to, senderId, receiverId, groupId, expenseId } = input;
+      const { amount, rate, ratePrecision, from, to, senderId, receiverId, groupId, expenseId } =
+        input;
 
       if (!isCurrencyCode(from) || !isCurrencyCode(to)) {
         throw new TRPCError({ code: 'BAD_REQUEST', message: 'Invalid currency code' });
       }
 
-      const amountTo = currencyConversion({ from, to, amount, rate });
+      const amountTo = currencyConversion({ from, to, amount, rate, ratePrecision });
       const name = `${from} → ${to} @ ${rate}`;
 
       const conversionFrom = {
@@ -583,7 +584,7 @@ export const expenseRouter = createTRPCRouter({
 
     const rate = await currencyRateProvider.getCurrencyRate(from, to, date);
 
-    return { rate };
+    return rate;
   }),
 
   getBatchCurrencyRates: protectedProcedure
@@ -599,7 +600,7 @@ export const expenseRouter = createTRPCRouter({
         throw new TRPCError({ code: 'BAD_REQUEST', message: 'Invalid currency code' });
       }
 
-      const rates = new Map<string, number>();
+      const rates = new Map<string, ParsedRate>();
 
       // Get the first rate to precache rates for the target currency
       const rate = await currencyRateProvider.getCurrencyRate(from[0] as CurrencyCode, to, date);
@@ -609,11 +610,7 @@ export const expenseRouter = createTRPCRouter({
         // Fetch rates for remaining currencies and return as map
         await Promise.all(
           from.slice(1).map(async (currency) => {
-            const r = await currencyRateProvider.getCurrencyRate(
-              currency as CurrencyCode,
-              to,
-              date,
-            );
+            const r = await currencyRateProvider.getCurrencyRate(currency, to, date);
             rates.set(currency, r);
           }),
         );