Lucas WintherandClaude Opus 5
cdece63c68
Two requests. The second is small; the first changed the money layer.
TYPING THE CURRENCY. The purchase total field now reads "30$" as thirty
dollars, "€25,50" as EUR 25.50, "250 kr" as DKK, "1.234,56 usd" as USD
1234.56, and sets the currency selector from what was typed. Entry speed is a
stated product feature and a second control per amount works against it.
The field is type="text", not type="number": a number input silently discards
anything non-numeric, so "30$" would never reach the parser. It keeps its own
text so a half-typed "30." stays as typed and only commits when it parses.
Separator handling is where parseMoneyInput earns its 26 tests. With both "."
and "," present the LAST is the decimal point, which covers "1.234,56" and
"1,234.56" without knowing a locale. With one, it groups thousands if exactly
three digits follow and is a decimal point otherwise — so "1,500" is fifteen
hundred and "1,5" is one and a half. Spaces group thousands only in
three-digit groups, because "30 40" is two amounts typed by mistake and
committing it as 3040 would be worse than rejecting it. An unrecognised
currency returns null rather than falling back: reading "30 GBP" as 30 DKK
would book money at the wrong currency.
USER-DEFINED CURRENCIES. `Currency` was a closed union and decimal places were
a module constant, so "add a currency" was a code change. Both now live in the
dataset: `Dataset.currencies` is the authority on which codes are valid, what
they are called, their symbol, and how many decimals they round to. Settings
grows a table to add, edit and remove them.
That forced the money layer open. `roundMoney` takes a DIGIT COUNT, not a
currency code, and every one of its ~29 call sites resolves digits from the
dataset via `digitsFor`. Making digits a required number rather than an
optional one with a default of 2 is the whole safety argument: every site
became a compile error the type checker enumerated for me, where a default
would have left each one silently correct for DKK/USD/EUR and silently wrong
for the first zero-decimal currency the owner adds.
Because every existing currency uses two decimals, a broken version of this
refactor would still pass all 356 previous tests. src/domain/currencyDigits.test.ts
is the oracle that cannot lie: a JPY-style zero-decimal currency driven through
roundMoney, both FX directions, both split modes, finance-plan division, the
fold, and the month view, asserting no figure has a fractional yen in it.
Guards that come with it, all tested:
- Codes are identity — they key the FX table and every stored Money — so they
are normalised (" jpy " -> "JPY") and cannot be edited, only added/removed.
- A currency in use cannot be removed, and the refusal names what refers to
it. The same reasoning as posts being archived rather than deleted: stored
Money carries the code, and dangling references would make the import
validator refuse the owner's own exported file. Removing an unused one takes
its exchange rate with it, leaving no orphan row.
- The import validator now checks the currency table itself — codes, duplicate
codes, integer decimals 0-4 — and validates every Money against it. That
boundary check replaces the compile-time safety the closed union provided.
- parseFxResponse takes the accepted codes instead of a global constant, so a
rate service returning dozens cannot put unreachable rows in the table.
Migration v2 -> v3 seeds the currency table. Behaviour-preserving by
construction: every currency that existed had two decimal places and the
seeded table records two, so not one stored amount can round differently than
it did before. An existing `currencies` field is kept rather than overwritten,
since a hand-edited file could already carry currencies the owner added.
Verified in the browser, not just in tests: JPY added through the real Settings
form with 0 decimals, and the five inputs above typed into the real purchase
field, each setting the right currency.
Two obsolete test helpers went away. plans.test.ts and actions.test.ts used to
monkey-patch the CURRENCY_DIGITS constant to prove the table was consulted;
digits are an argument now, so those tests just ask for zero decimals.
types.test.ts no longer asserts "the supported currencies are exactly DKK,
USD, EUR" — that stopped being a property of the code.
Co-Authored-By: Claude Opus 5 (1M context) <[email protected]>
Budget 2.0
A personal budgeting PWA. Envelope-style monthly budgets with rollover, split purchases, finance plans, multi-currency, and JSON/ODS export. All data lives in your browser — there is no server and no account.
Development
bun install
bun --hot src/index.ts # dev server with hot reload
bun test # run the test suite
bun run build # production build into dist/
Self-hosting with Docker
docker build -t budget2 .
docker run --rm -p 3000:3000 budget2
To serve from a subpath, build and run with BUN_PUBLIC_BASE_PATH:
docker build -t budget2 --build-arg BUN_PUBLIC_BASE_PATH=/budget/ .
docker run --rm -p 3000:3000 -e BUN_PUBLIC_BASE_PATH=/budget/ budget2
GitHub Pages
Pushing to main builds and deploys to Pages automatically, using
/<repository-name>/ as the base path. Enable Pages with "GitHub Actions" as
the source in the repository settings.
Your data
Everything is stored in this browser's IndexedDB. Export regularly from Settings → Your data: the JSON export is both your backup and how you move your budget to another device. Import replaces everything and downloads a backup of your current data first.
Known limitations
- Data is per-browser. There is no account and no sync. If you clear this browser's site data, or move to a different browser or device, your budget is gone unless you exported it first. The JSON export is not just a nice-to-have backup — it is the only way to move a budget between devices.
- The install prompt is incomplete.
manifest.webmanifestcurrently only ships an SVG icon. Chrome requires PNG icons at 192×192 and 512×512 to offer the "Install app" prompt; until those are added, the app works fine as a regular tab but won't be installable on Chrome/Chromium.
Documentation
- Design:
docs/superpowers/specs/2026-09-01-budget-app-design.md - Implementation plan:
docs/superpowers/plans/2026-09-01-budget-app.md