Flouze, an app to keep track of expenses among friends

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Flouze is an open source group expense tracker. Whenever you're traveling with other people, keeping track of who paid what and who owes whom quickly gets complicated. Flouze helps keeping a log of all expenses, which can be synchronized across several devices.

Another popular group expense tracking service supporting synchronization is Tricount which works really well but lacks the following features:

• History view of all changes to an expense log (for auditing/fixing mistakes)
• Monthly statistics (useful with long running accounts)
• Open protocol (although they do seem to have an API)
• Open Source (what is their app doing with my data?)

Another good open source alternative is Tricky Tripper, but it lacks proper support for synchronization.

Flouze is also an exercise in mixing Rust (for the logic) and Flutter (for the UI) in a mobile application.

Status

Flouze is currently at an early stage of development, and supports the following features:

• Support several accounts (expense logs)
• Adding/editing/deleting Transactions
• Balance view showing who owes whom
• Synchronization (needs more testing)

The features currently being developed include:

• Statistics per day/week/month for long running accounts (eg. shared flat)

Compatibility

Rust and Flutter theoretically allow targeting both Android and iOS as mobile platforms. I currently only develop for Android. There's also a very basic CLI tool for interacting with Flouze accounts, that one should work on all desktop platforms.

Development

The main parts of this repository are:

• lib/ the main Rust library holding all the shared logic
• flouze_flutter/ a Flutter package exposing the Rust API to Flutter via Platform Channels
• mobile/ the (pure Dart/Flutter) sources of the mobile app
• cli/ a simple CLI tool to interact with Flouze account files

The OpenSSL development headers are required for compilation to succeed, the package is named openssl-devel on Fedora and libssl-dev on Debian derivatives. Installing this package is only needed if you want to build the flouze CLI for the host architecture, for cross compilation the build scripts will take care of downloading and building OpenSSL for Android.

The Rust library needs to be cross-compiled for all supported Android targets before building the mobile app. The generate-toolchains.sh script in flouze_flutter/ needs to be run once to create standalone versions of the toolchains contained in the Android NDK (which needs to be installed beforehand). Once this is in place, the build-openssl.sh compiles OpenSSL for various Android architectures, and the build-jni-libs.sh script in the same directory builds the library for all targets.

After the native libraries are built, the following commands can be used from the mobile/ folder to run/develop/debug the application:

# Get the dependencies
flutter packages get

# Generate the Dart files with language translations
./l10n-merge-translations.sh

# Run the code generation
flutter packages pub run build_runner build

Synchronization server

The synchronization server URL is configured by the mobile/assets/sync_server_uri.txt file. The file should contain a URL in the form http://my.sync.server.tld:8080/.

Flouze ships with a basic built-in server, accessible via the serve command of flouze-cli.

Sharing accounts between devices

Sharing is accomplished by registering a URL prefix with the application, and interpreting the URLs under that prefix in the app. The URL used for sharing needs not match the actual address of the synchronization server, in other words it is a "vanity" URL, which however needs to validate certain criteria described in the Android Developer Documentation, notably the hosting of a /.well-known/assetlinks.json file.

The URL of the sharing server is configured by the mobile/assets/share_server_uri.txt file. The file should contain a URL of the form https://myapp.com/app.

With the example above, any link starting with https://myapp.com/app will activate the mobile application. As of now, the only action using such links is the cloning of a remote account. Clicking a link of the form https://myapp.com/app/clone?accountId=[ACCOUNT_ID], where [ACCOUNT_ID] is the UUID of the account, will activate the "Clone remote account" page of the app. Remember, the server that will be contacted for the cloning is the synchronization server, not the sharing server.

Sentry

The mobile application can be configured to report crashes to Sentry (for now in the Dart part only, the Rust part needs to be done). To do so, place your Sentry DSN in mobile/assets/sentry_dsn.txt, and rebuild the application.

Internationalization (i18n)

Flouze is using Dart's intl package for internationalization. The translations are stored in ARB files in mobile/lib/l10n, those ARB files are edited using CrowdIn and (at the moment) imported manually into Git when changes happen. Contact me to get added to the project if you want to add new languages.

Signing releases

Follow the official Flutter documentation and add a key.properties file in mobile/android/.