halkyon/packages/halkyon_app/README.md

# halkyon_app

What every Halkyon app (Learn, Todo, Train) is built around, on an instance's
`halkyon_base` module: the instances a device keeps an account on, signing in,
each person's data opened and closed, and syncing it. Taken from Halkyon Learn,
which it was written for, so it behaves as Learn's own did; the texts are in
British English, American English and German, and where they name the app,
they name yours.

Written as the apps are: Dart 3.13's primary constructors, Material from
`package:material_ui`, Lucide icons, blocs (`flutter_bloc`), LeanCode's lints.

## What it holds

- **Instances** (`lib/src/instance/`): `Instance` (an address as people type
  it), `InstanceChoice` (those the device keeps an account on, one in use;
  `FileInstanceStore`), `InstanceStorage` (each instance's people's folders and
  session key), `InstanceChecker` (does an address answer, where does it keep
  people's data; `ServerpodInstanceChecker` asks its `instance.basics()`),
  `InstanceScope`. The screens: `FirstStartScreen` (the build's instance and
  another, as tiles, `InstanceTile`), `InstanceStep` (an address, checked),
  `showAccountSwitcher` and `AddAccountScreen`, and where an instance keeps
  people's data, as a flag and words (`InstanceLocationBuilder`,
  `InstanceFlag`, `instanceLocationWords`): `EU`, a country or a subdivision
  (ISO 3166-2, `US-CA`) as its operator says, "Germany (EU)" for a member of
  the European Union (`europeanUnionMembers`) and "California, United States"
  for a subdivision, with the most specific flag there is (a few subdivisions
  have their own, such as Scotland; else the country's). Countries are named
  by the app's `CountryNames`, subdivisions by Unicode CLDR's names in English
  and German, which come with the package (`AssetSubdivisionNames`; the
  workspace's `tool/subdivision_names.py` writes them).
- **Gates** (`lib/src/app/`): `InstanceGate` opens the app's dependencies on
  the instance in use (`AppDependencies`, handed down by `AppScope`), anew on
  a switch, the previous ones closed first; `SessionGate` keeps a person
  signed in, signing in anonymously at a first start and asking how to start
  once signed out (`StartScreen`); `PersonScope` opens each person's own
  dependencies and closes them when the person goes.
- **Signing in** (`lib/src/auth/`): `AuthRepository` on an `AuthGateway`;
  `ServerpodAuthGateway` signs in anonymously, with GitHub (the system
  browser and a loopback address on Linux and Windows, `LoopbackWebAuth`) and
  with a code by mail, through the instance's `halkyon_base`; `SessionBloc`,
  `GitHubSignInBloc`, `EmailSignInBloc` (with `showEmailSignInSheet`) and
  `SignInWaysCubit`; `SignedOutMark`, `SignInAddresses`, `PersonFolders`.
- **Sync** (`lib/src/sync/`): `SyncService` (once at start, shortly after
  local changes, on resume and every few minutes, one sync at a time, counting
  the changes not on the server yet, `PendingChangesStore`), `AppCompatibility`
  and `compatibleSync` (the instance's minimum app build, the engine's table
  check), `SyncStatusBloc`, `syncAndWait`, and the widgets: `SyncStatusCard`,
  `AppMismatchBanner`, `SyncTroubleBadge`.
- **A client of `halkyon_base` alone** (`BaseClient`): to ask an instance
  about itself, and to sign in as another person than the app's client holds.
- **Testing** (`package:halkyon_app/testing.dart`): fakes of every boundary
  (`FakeAuthGateway`, `FakeInstanceChecker`, the stores in memory), a frame
  (`testFrame`), `testApp`, and `TestAppDependencies`.

## Using it in an app

1. **The server** includes `halkyon_base` with the nickname `base` (its
   README), so the app's generated client has `client.modules.base`.
2. **Depend on it** by git, pinned to a signed commit of halkyon_shared's
   main, as `halkyon_ui` (whose README shows the `pubspec_overrides.yaml` for
   working on both at once):

   ```yaml
   dependencies:
     halkyon_app:
       git:
         url: https://code.halkyon.app/project-halkyon/halkyon_shared.git
         path: packages/halkyon_app
         ref: <signed commit>
   ```

3. **Texts**: add `HalkyonAppLocalizations.delegate` to every `MaterialApp`'s
   delegates, beside `HalkyonUiLocalizations.delegate` and material_ui's
   `GlobalMaterialLocalizations.delegates`.
4. **The frame** (`AppFrame`): the app's name and wordmark word, its icon, an
   example address, its theme, delegates, languages and launch screen, and the
   two sentences only it can say: what the first start's instance keeps of
   the person's, and what a switch to another account leaves behind.
5. **The dependencies**: the app's composition root implements
   `AppDependencies<P>` (`serverName`, `auth`, `signedOut`, `openPerson`,
   `dispose`), its person's dependencies `Disposable`. Its `auth` is an
   `AuthRepository` on `ServerpodAuthGateway(client, base:
   client.modules.base, callbackScheme: …, appName: …)`; the scheme is the
   app's own (`app.halkyon.learn`), registered with each platform and in the
   instance's GitHub OAuth app, whose loopback address on Linux and Windows is
   `http://127.0.0.1/github-callback` (port 43823 unless given).
6. **The tree**:

   ```dart
   InstanceGate(
     frame: frame,
     choice: choice,
     checker: ServerpodInstanceChecker(app: 'todo'),
     countryNames: …,
     readLook: …,           // the device's theme mode and language
     open: Dependencies.create,
     app: SessionGate(
       look: (context) => …,
       app: (person) => PersonApp(person: person), // with PersonScope inside
     ),
   )
   ```

   A person's widgets find their dependencies with
   `PersonScope.of<PersonDependencies>(context)` and the app's with
   `AppScope.of<Dependencies>(context)`.
7. **Licences**: call `registerHalkyonAppLicenses()` once at startup (the
   flags' and Unicode CLDR's notices), beside halkyon_ui's
   `registerFontLicenses()`.

## Licence

GNU Affero General Public License 3.0 or later (`LICENSE`). The flags are
lipis' flag-icons, drawn by the `flag` package, under the MIT licence
(`assets/flags/LICENSE-flag-icons.txt`). The subdivisions' names are Unicode
CLDR's (release 48.2), under the Unicode License v3
(`assets/subdivisions/LICENSE-CLDR.txt`, `assets/subdivisions/ATTRIBUTION.md`).