fix(amount-input): allow negative amounts via a sign toggle on iOS (#674)

## Problem

On the create/edit transaction form, the amount field uses
`inputMode="decimal"`. On iOS the numeric keypad that this triggers has
**no minus key**, so users cannot type the leading `-` the input relies
on to record a negative amount (e.g. an outgoing transfer).

## Fix

Add an opt-in `allowNegative` prop to `AmountInput` that renders a small
`+`/`−` sign-toggle button at the **start** of the field. It works with
any keyboard, so it does not depend on the OS keypad. It is enabled only
on the create-transaction amount input; budgets, balances and loan
fields keep their current UI.

- The button turns red with a `−` when the amount is negative, and shows
`+` otherwise (`aria-pressed` reflects the state).
- Toggle fires on `click` (works for both pointer and keyboard);
`onPointerDown` `preventDefault` keeps the input focused to avoid a
blur/reformat race.
- A leading `-` set via the toggle **before** typing is preserved on
focus, so the sign is not silently dropped.
- The currency symbol shifts right when the toggle is present so the two
never overlap; layout is unchanged when `allowNegative` is off.

## Refactor

Extracted the repeated `evaluateMathExpression(x) ?? parseInputValue(x)`
string→cents resolution (previously duplicated across blur, Enter, and
the new toggle) into a single `resolveCents()` helper.

## Tests

`resources/js/components/ui/amount-input.test.tsx` — the toggle is
hidden unless `allowNegative`, flips positive↔negative, and preserves
the sign when focusing after toggling an empty field.

## QA

Manually verified in the running app (create-transaction dialog): typing
an amount and toggling the sign both ways updates the value and the
button state correctly, on both prefix (USD `$`) and suffix (EUR `€`)
currency layouts.

lang/es.json

@@ -1038,6 +1038,8 @@
     "Main Checking": "Cuenta Corriente Principal",
     "Maintain and promptly update your account information": "Mantén y actualiza prontamente tu información de cuenta",
     "Maintain and promptly update your account\\n                                    information": "Mantén y actualiza puntualmente la información de tu cuenta",
+    "Make amount negative": "Hacer el importe negativo",
+    "Make amount positive": "Hacer el importe positivo",
     "Make child categories top level": "Convertir las categorías hijas en categorías principales",
     "mail support": "escribir a soporte",
     "Making your money talk...": "Haciendo que tu dinero hable...",

resources/js/components/transactions/edit-transaction-dialog.tsx

@@ -753,9 +753,10 @@ export function EditTransactionDialog({
                                             selectedAccount?.currency_code ||
                                             'USD'
                                         }
-                                        placeholder="-25.00"
+                                        placeholder="25.00"
                                         disabled={isSubmitting}
                                         required
+                                        allowNegative
                                     />
 
                                     {!selectedAccount?.banking_connection_id && (

resources/js/components/ui/amount-input.test.tsx

@@ -0,0 +1,63 @@
+import { fireEvent, render, screen } from '@testing-library/react';
+import { describe, expect, it, vi } from 'vitest';
+import { AmountInput } from './amount-input';
+
+vi.mock('@inertiajs/react', () => ({
+    usePage: () => ({ props: { locale: 'en-US' } }),
+}));
+
+describe('AmountInput sign toggle', () => {
+    it('is hidden unless allowNegative is set', () => {
+        const { rerender } = render(
+            <AmountInput value={0} onChange={vi.fn()} currencyCode="USD" />,
+        );
+        expect(screen.queryByRole('button')).toBeNull();
+
+        rerender(
+            <AmountInput value={0} onChange={vi.fn()} currencyCode="USD" allowNegative />,
+        );
+        expect(screen.getByRole('button')).toBeInTheDocument();
+    });
+
+    it('flips a typed positive amount to negative', () => {
+        const onChange = vi.fn();
+        render(
+            <AmountInput value={0} onChange={onChange} currencyCode="USD" allowNegative />,
+        );
+
+        const input = screen.getByRole('textbox');
+        fireEvent.focus(input);
+        fireEvent.change(input, { target: { value: '25' } });
+
+        fireEvent.click(screen.getByRole('button'));
+
+        expect(onChange).toHaveBeenCalledWith(-2500);
+    });
+
+    it('flips a negative amount back to positive', () => {
+        const onChange = vi.fn();
+        render(
+            <AmountInput value={0} onChange={onChange} currencyCode="USD" allowNegative />,
+        );
+
+        const input = screen.getByRole('textbox');
+        fireEvent.focus(input);
+        fireEvent.change(input, { target: { value: '-25' } });
+
+        fireEvent.click(screen.getByRole('button'));
+
+        expect(onChange).toHaveBeenLastCalledWith(2500);
+    });
+
+    it('keeps the negative sign when focusing after toggling an empty field', () => {
+        render(
+            <AmountInput value={0} onChange={vi.fn()} currencyCode="USD" allowNegative />,
+        );
+
+        const input = screen.getByRole('textbox');
+        fireEvent.click(screen.getByRole('button'));
+        fireEvent.focus(input);
+
+        expect(input).toHaveValue('-');
+    });
+});

resources/js/components/ui/amount-input.tsx

@@ -3,6 +3,7 @@ import * as React from 'react';
 import { Input } from '@/components/ui/input';
 import { useLocale } from '@/hooks/use-locale';
 import { cn } from '@/lib/utils';
+import { __ } from '@/utils/i18n';
 
 interface AmountInputProps {
     value: number;
@@ -13,6 +14,7 @@ interface AmountInputProps {
     placeholder?: string;
     id?: string;
     className?: string;
+    allowNegative?: boolean;
 }
 
 const getCurrencyInfo = (
@@ -153,6 +155,9 @@ const evaluateMathExpression = (input: string): number | null => {
     }
 };
 
+const resolveCents = (input: string): number =>
+    evaluateMathExpression(input) ?? parseInputValue(input);
+
 export const AmountInput = React.forwardRef<HTMLInputElement, AmountInputProps>(
     (
         {
@@ -164,6 +169,7 @@ export const AmountInput = React.forwardRef<HTMLInputElement, AmountInputProps>(
             placeholder = '0.00',
             id,
             className = '',
+            allowNegative = false,
         },
         ref,
     ) => {
@@ -186,19 +192,15 @@ export const AmountInput = React.forwardRef<HTMLInputElement, AmountInputProps>(
             if (value !== 0) {
                 const amount = (value / 100).toFixed(2);
                 setDisplayValue(amount);
-            } else {
+            } else if (!displayValue.startsWith('-')) {
+                // Keep a lone '-' the user set via the toggle before typing.
                 setDisplayValue('');
             }
         };
 
         const handleBlur = () => {
             setIsFocused(false);
-
-            // Try to evaluate as math expression first
-            const mathResult = evaluateMathExpression(displayValue);
-            const valueInCents = mathResult !== null ? mathResult : parseInputValue(displayValue);
-
-            onChange(valueInCents);
+            onChange(resolveCents(displayValue));
         };
 
         const handleChange = (e: React.ChangeEvent<HTMLInputElement>) => {
@@ -207,20 +209,35 @@ export const AmountInput = React.forwardRef<HTMLInputElement, AmountInputProps>(
 
         const handleKeyDown = (e: React.KeyboardEvent<HTMLInputElement>) => {
             if (e.key === 'Enter') {
-                // Try to evaluate as math expression first
-                const mathResult = evaluateMathExpression(displayValue);
-                const valueInCents = mathResult !== null ? mathResult : parseInputValue(displayValue);
-
-                onChange(valueInCents);
+                onChange(resolveCents(displayValue));
             }
         };
 
+        // iOS numeric keypads (inputMode="decimal") have no minus key, so
+        // negative amounts need an explicit toggle. onClick handles both pointer
+        // and keyboard; onPointerDown preventDefault keeps the input focused,
+        // avoiding the blur/reformat race with the effect above.
+        const toggleSign = () => {
+            const next = displayValue.trim().startsWith('-')
+                ? displayValue.replace('-', '')
+                : `-${displayValue}`;
+            setDisplayValue(next);
+            onChange(resolveCents(next));
+        };
+
+        const isNegative = displayValue.trim().startsWith('-');
+
         const { symbol: currencySymbol, position: symbolPosition } = getCurrencyInfo(currencyCode, locale);
 
         return (
             <div className="relative">
                 {symbolPosition === 'prefix' && (
-                    <span className="-translate-y-1/2 absolute top-1/2 left-3 text-muted-foreground text-sm">
+                    <span
+                        className={cn([
+                            '-translate-y-1/2 absolute top-1/2 text-muted-foreground text-sm',
+                            allowNegative ? 'left-10' : 'left-3',
+                        ])}
+                    >
                         {currencySymbol}
                     </span>
                 )}
@@ -239,7 +256,12 @@ export const AmountInput = React.forwardRef<HTMLInputElement, AmountInputProps>(
                     required={required}
                     className={cn([
                         'bg-background',
-                        symbolPosition === 'prefix' ? 'pl-9' : 'pr-9',
+                        symbolPosition === 'suffix' && 'pr-9',
+                        allowNegative
+                            ? symbolPosition === 'prefix'
+                                ? 'pl-14'
+                                : 'pl-11'
+                            : symbolPosition === 'prefix' && 'pl-9',
                         className,
                     ])}
                 />
@@ -248,6 +270,24 @@ export const AmountInput = React.forwardRef<HTMLInputElement, AmountInputProps>(
                         {currencySymbol}
                     </span>
                 )}
+                {allowNegative && (
+                    <button
+                        type="button"
+                        onPointerDown={(e) => e.preventDefault()}
+                        onClick={toggleSign}
+                        disabled={disabled}
+                        aria-label={isNegative ? __('Make amount positive') : __('Make amount negative')}
+                        aria-pressed={isNegative}
+                        className={cn([
+                            '-translate-y-1/2 absolute top-1/2 left-[0.35rem] flex h-7 w-7 items-center justify-center rounded-sm border font-semibold text-lg leading-none transition-colors focus-visible:outline-none focus-visible:ring-2 focus-visible:ring-ring disabled:cursor-not-allowed disabled:opacity-50',
+                            isNegative
+                                ? 'border-destructive/40 bg-destructive/10 text-destructive'
+                                : 'border-input bg-muted text-foreground hover:bg-accent',
+                        ])}
+                    >
+                        {isNegative ? '−' : '+'}
+                    </button>
+                )}
             </div>
         );
     },