BarCalc

A small, native Android app for splitting a bar tab item by item — including individual units of a shared round — down to the exact cent. Built with Jetpack Compose.

What it does

A three-step wizard:

1. Items — add each item on the tab (name, price, quantity), editable inline.
2. People — add who's splitting, then tap a person to open their claim sheet. Each item has one slot per unit; tapping a unit claims it. When two people claim the same unit, its price splits between them. Add an optional tip.
3. Results — a per-person total, expandable into a breakdown of each item, their subtotal, and their share of the tip.

Finishing a tab files it in history, where it can be renamed, deleted, or reopened as the starting point for a new tab. A tab you'd rather not keep can be cleared outright from the Items or People header instead.

Highlights:

• Exact-cent math. All money is integer cents; uneven splits hand out the leftover pennies by largest remainder, so the shares always sum exactly to the total (no $9.99-from-$10.00 drift).
• Per-unit claiming. Share one beer out of a round of three without splitting the whole line — or claim the entire round in a single tap.
• Proportional tip. Each person's tip is based on their own share of the tab, not an even split — someone who only had a $10 item tips on $10.
• POS-style money entry. Prices accumulate from the right as you type — key 1 0 5 0 and the field reads 10.50 — so amounts are always two decimals.
• Persists across restarts. An in-progress tab is saved and restored.
• Tab history. Finished tabs are archived on-device, so a regular Friday round can be reopened and reused instead of retyped.
• Nothing leaves the device. No accounts, no ads, no analytics — the app declares zero Android permissions and contains no networking code. See PRIVACY.md.
• Localized in English and Brazilian Portuguese (pt-BR), including the currency symbol.

Tech stack

• UI: Jetpack Compose + Material 3, custom theme ported from a design system built in Claude Design
• Architecture: MVVM with unidirectional data flow — a single TabViewModel exposes immutable TabUiState via StateFlow; the UI sends sealed TabAction events through one onAction entry point, so screens are pure and previewable
• Domain: a dependency-free SplitCalculator (pure Kotlin, fully unit-tested)
• Persistence: Jetpack DataStore + kotlinx.serialization (JSON) for the in-progress tab; Room (via KSP, schemas exported) for the finished-tab history, behind a HistoryStore interface so the view model stays testable without Android
• Build: Android Gradle Plugin 9.1 (built-in Kotlin 2.2.10), Gradle version catalog

Project structure

app/src/main/java/com/pedrotlf/barcalc/
├── MainActivity.kt
├── domain/                   # pure, Android-free
│   ├── TabItem.kt · Person.kt · HistoryEntry.kt
│   └── SplitCalculator.kt     # the split engine (integer cents)
├── data/
│   ├── SessionRepository.kt   # DataStore-backed in-progress tab
│   └── history/               # Room entity · DAO · database
│       └── HistoryStore.kt    # the seam the view model is tested against
└── ui/
    ├── BarTabApp.kt           # root: screen switching + overlay stack
    ├── TabViewModel.kt · TabUiState.kt · TabAction.kt
    ├── theme/                 # Color · Type · Dimens · Theme
    ├── components/            # reusable composables · AppIcons · Modifiers
    └── screens/               # Items · People · ClaimSheet · Results · History
                               #   + drawer, About, confirmation dialogs

app/schemas/                   # exported Room schemas (checked in)
app/src/test/…                 # JUnit: split engine, view model, persistence

Building & running

Requirements: a recent Android Studio (AGP 9.1) and an Android 9+ device or emulator (minSdk 28).

# Debug build
./gradlew :app:assembleDebug

# Install on a connected device/emulator
./gradlew :app:installDebug

# Unit tests (split engine, view model, persistence)
./gradlew :app:testDebugUnitTest

Or just open the project in Android Studio and hit Run.

Trying the Portuguese translation

Without changing your whole device, set a per-app locale (Android 13+):

adb shell cmd locale set-app-locales com.pedrotlf.barcalc --user 0 --locales pt-BR
# reset with: --locales ""

Credits & licenses

• Fonts (bundled in app/src/main/res/font/) are used under the SIL Open Font License 1.1; full texts in licenses/:
  • Caprasimo — © 2023 The Caprasimo Project Authors
  • Figtree — © 2022 The Figtree Project Authors
• Design & build. BarCalc's visual design — layouts, the "Organic" design-system tokens (colors, spacing, radii, type scale), and the launcher icon — was elaborated in Claude Design, and the app was built with Claude Code, Anthropic's AI coding agent. The design tokens are ported into ui/theme/.

The application code is all rights reserved. It's published here to read and learn from, not to reuse — no open-source license is granted for it (the bundled fonts keep their own licenses, noted above).