# Halkyon Learn Halkyon Learn is for creating, sharing and collaborating on study material. It schedules flashcards with [FSRS](https://github.com/open-spaced-repetition) to strengthen retention, and organises study material together with the external references it draws on. It is offline-first: everything works on the device, without a connection. And the whole stack is transparent: the app, the server and everything needed to host an instance are published, so anyone can see how an instance works and run their own. - **Offline first.** Each device keeps its own database and syncs in the background (`serverpod_offline_sync`). Edits made on two devices while offline are never lost: card content is stored as append-only revisions, and a side changed differently on two devices is shown as a conflict until the person picks a version ([ADR 0001](../../docs/adr/0001-offline-sync.md), [ADR 0003](../../docs/adr/0003-card-revisions.md)). - **Every account has a way in**: SimpleLogin, whose ID alone the instance keeps, or an email address with a password and an authenticator, the password never leaving the device ([ADR 0020](../../docs/adr/0020-sign-in-with-simplelogin.md), [ADR 0017](../../docs/adr/0017-password-totp-and-keys.md)). GitHub still signs in those who have it, until the instance ends it. - **No end-to-end encryption.** Content is readable by the operator of the instance, as on Mastodon; whoever trusts no operator can run their own ([ADR 0002](../../docs/adr/0002-no-end-to-end-encryption.md)). Targets: Linux, Windows, macOS, Android and iOS. There is no web build. ## Packages Learn lives in `apps/learn/` of the Halkyon repository, one workspace with Halkyon's other apps and the packages they share ([the repository's README](../../README.md)). | Package | What it is | Licence | |---|---|---| | `halkyon_learn_server` | The [Serverpod](https://serverpod.dev) server: endpoints, models, migrations | SSPL-1.0 | | `halkyon_learn_client` | The client, generated from the server's models | AGPL-3.0-or-later | | `halkyon_learn_flutter` | The app (`app.halkyon.learn`) | AGPL-3.0-or-later | | `halkyon_learn_curator` | Turns dictionary sources into the files the server loads | AGPL-3.0-or-later | It builds on the shared packages in `packages/`: `halkyon_base` (sign-in, accounts, the instance's basics; a Serverpod module), `halkyon_app` (instances, sign-in, sync) and `halkyon_ui` (the look). ## Setting up - **Flutter v3.47.5**, the version CI uses (`FLUTTER_VERSION` in `.forgejo/workflows/ci.yaml`). Set up each platform you build for with Flutter's own guides: [Linux](https://docs.flutter.dev/platform-integration/linux/setup), [Windows](https://docs.flutter.dev/platform-integration/windows/setup), [Android](https://docs.flutter.dev/platform-integration/android/setup), [macOS](https://docs.flutter.dev/platform-integration/macos/setup), [iOS](https://docs.flutter.dev/platform-integration/ios/setup). - **The Serverpod CLI v4.0.4**: `dart install serverpod_cli@4.0.4`. Pass `--no-analytics` to every call; otherwise it reports the commands run to Serverpod. - **Linux**, on top of Flutter's packages, the libraries of four plugins: WebKitGTK (pulled in by the sign-in package), libsecret (keeps the session), GStreamer (plays sounds) and libmpv (plays videos from Jellyfin; the app doesn't start without it). On Debian or Ubuntu, Flutter's and these together: ```sh sudo apt-get install clang cmake ninja-build pkg-config libgtk-3-dev libstdc++-12-dev \ libwebkit2gtk-4.1-dev libsecret-1-dev libgstreamer1.0-dev libgstreamer-plugins-base1.0-dev \ libmpv-dev ``` - **Windows** needs Developer Mode (Settings › System › For developers): building makes symbolic links, as Flutter links each plugin's native code into the build and the PDF engine's build does too, and Windows lets ordinary users make them only in Developer Mode. - **No Docker** for development: `serverpod start` and the server's tests run an embedded PostgreSQL. Docker Compose is only for running an instance (below). - **For Learn's scripts in `apps/learn/tool/`**, run from `apps/learn`: Python 3 (`tool/app_icons.py` also needs Pillow, `python3-pil`); for releases what [Releases](#releases) lists. The rich-text editor comes from our fork of AppFlowy Editor ([project-halkyon/appflowy-editor](https://code.halkyon.app/project-halkyon/appflowy-editor)), which `flutter pub get` fetches by itself. ## Running it locally The server's secrets live in `apps/learn/halkyon_learn_server/config/passwords.yaml`, which is never committed. In a fresh clone, create it with a `development` and a `test` section, each holding `database`, `serverSideSessionKeyHashPepper` and `serviceSecret` (for example from `openssl rand -base64 32`). GitHub sign-in is optional: add `githubClientId` and `githubClientSecret` of your own GitHub OAuth app to `development`, registered with the callback URLs `app.halkyon.learn://github-callback` and `http://127.0.0.1/github-callback`. Then start the server, its embedded database and the app: ```sh cd apps/learn/halkyon_learn_server serverpod --no-analytics start ``` `serverpod start` applies pending migrations and reloads on changes. The app talks to the server named by `--dart-define=SERVER_URL=…`, or else to the one in `apps/learn/halkyon_learn_flutter/assets/config.json` (`http://localhost:8080`). Without `--no-analytics`, the Serverpod CLI reports usage to Serverpod. ## Tests From the repository's root, ```sh dart run tool/check.dart ``` runs the format check, the analyzer with the strict lints of `leancode_lint` and every package's tests, Learn's server's (against an embedded PostgreSQL, no Docker needed), its curator's and its app's among them; `dart run melos run test:flutter --scope=halkyon_learn_flutter` runs the app's alone. To run the checks before every push: `ln -s ../../tool/pre-push .git/hooks/pre-push`. CI runs them on every push too (`.forgejo/workflows/ci.yaml`). The sync tests need a running server (`serverpod start`); run them in `apps/learn/halkyon_learn_flutter` with `flutter test -t requires-server`. ## Running an instance `deploy/`, at the repository's root, holds a Docker Compose setup: Caddy (HTTPS), the server and PostgreSQL. Copy `deploy/.env.example` to `deploy/.env` and fill it in; it explains every value. The licences require offering the source of what the instance runs to the people who use it. learn.halkyon.eu itself deploys from `main` once CI is green: `deploy/redeploy.sh`, run by the CI runner described in `deploy/runner/`, deploys only commits signed by a key in `deploy/allowed-signers`. It backs up its database every hour, off-site and encrypted; [`deploy/backups.md`](../../deploy/backups.md) says how to set that up and how to restore. ## Releases Releases are published on [code.halkyon.app](https://code.halkyon.app/project-halkyon/halkyon/releases), with the APK and the snap, and the APK also in the project's F-Droid repository (`https://halkyon.app/fdroid/repo?fingerprint=E8082788756F6B7E682AA22FCEAD24B53E2A8B0912AD66D65E8C2D4F07BB94B0`, added in the F-Droid app as a repository). The Snap Store (`halkyon-learn`) follows. Their builds offer learn.halkyon.eu, the project's instance, at first start; people may choose another there, and keep accounts on several. - **Checking a download:** `SHA256SUMS` lists the checksum of every file, signed with the maintainer's GPG key (`SHA256SUMS.asc`). The APK is signed with the app's key, whose certificate has the SHA-256 `27:E2:43:FC:BD:C8:26:FF:98:AB:7D:BB:10:43:6C:98:C3:BE:A2:4B:2A:01:5E:94:E4:CF:C7:D1:FC:2A:00:6C` (`apksigner verify --print-certs` shows it). - **Versions** follow [semantic versioning](https://semver.org): `version` in `apps/learn/halkyon_learn_flutter/pubspec.yaml`, `..+`. Since the last release, a commit typed `feat` raises the minor number, `fix` or `perf` the patch number, and a breaking one (`feat!:` or a `BREAKING CHANGE:` line) the major number from 1.0 on, the minor one before; other commits release nothing by themselves. Every release raises the build number: Android only installs a higher one over an older, and the server tells apps below the build it supports to update. - **Making one** is for maintainers, on their own machine and never in CI, from the repository's root: `dart run tool/release.dart learn`, or with `minor` (or `major`, `patch`) after `learn` to choose; `--dry-run` shows what it would do and changes nothing. It is the apps' shared release tool ([ADR 0015](../../docs/adr/0015-one-repository.md)), configured in `apps/learn/release.dart`. It needs `main` clean, pushed and green in CI, the app's key, the F-Droid repository's key and a Forgejo token; its header says more. Tags are `learn-vX.Y.Z`, and only commits touching Learn count for its version. It shows the version and its commits and asks first, then writes the version into the pubspec in a signed release commit with a signed tag, builds the APK and the snap (`snap/snapcraft.yaml`, built in LXD; its icon comes from `apps/learn/tool/app_icons.py`), checks both, signs the checksums, pushes, and publishes on code.halkyon.app, in the F-Droid repository and in the Snap Store's edge channel (`snapcraft login` first). Besides Flutter and the Android SDK, it uses snapcraft with LXD, a JDK (keytool), GnuPG, curl, jq, unzip, squashfs-tools, rsync and fdroidserver. Release builds made without the app's key are signed with the debug key and can't update a released app. - **The F-Droid repository** is kept by `tool/fdroid_repo.sh` (fdroidserver v2.4.5, e.g. `pipx install fdroidserver==2.4.5`); its settings and the app's listing are in `tool/release/fdroid/`. ## More - [`AGENTS.md`](AGENTS.md): how Learn's code is organised and the rules it follows; the [repository's](../../AGENTS.md) for what holds for every app. - [`docs/adr/`](../../docs/adr/): the architecture decisions and their reasons. - [`CONTRIBUTING.md`](../../CONTRIBUTING.md): licences of contributions and the sign-off. - [`LICENSE.md`](../../LICENSE.md): which licence covers what.