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 and
  subdivisions are named by Unicode CLDR's names in English and German, which
  come with the package (`AssetCountryNames`, `AssetSubdivisionNames`; the
  package's `tool/country_names.py` and `tool/subdivision_names.py` write
  them, from one release); tests give names of their own (`CountryNames`,
  `SubdivisionNames`).
- **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. `resolveAppLocale`
  picks the app's language as every Halkyon app does: the first preferred
  language it speaks, never by country alone, British English otherwise.
- **About** (`showAppAbout`): the app's name (its frame's), its version,
  icon and legalese where it gives them, where the source of what the
  instance runs is (`InstanceSourceCode`, from `AppDependencies.sourceCodeUrl`;
  both licences require offering it), the app's own parts (its credits), and
  the licence list.
- **The account** (`AccountTiles`): whose account on which instance,
  switching to the account on another, signing out (which of an anonymous
  account deletes it, so asks first) and deleting it (after asking), for an
  app's settings, in the app's words where only it can say them.
- **Signing in** (`lib/src/auth/`): `AuthRepository` on an `AuthGateway`;
  `ServerpodAuthGateway` signs in anonymously and with GitHub (the system
  browser and a loopback address on Linux and Windows, `LoopbackWebAuth`),
  through the instance's `halkyon_base`, and puts a session granted elsewhere
  in place (`useSession`); `SessionBloc`, `GitHubSignInBloc` and
  `SignInWaysCubit`; `SignedOutMark`, `SignInAddresses`, `PersonFolders`.
- **A password and TOTP** (`lib/src/password/`, ADR 0017): `PasswordRepository`
  on a `PasswordGateway` (`ServerpodPasswordGateway`), an `AccountCrypto`
  (`SodiumAccountCrypto`: halkyon_keys and SRP's client half, each step on an
  isolate of its own, whose results are copied before they cross back:
  sodium's are views of memory freed with the isolate that made them) and an
  `AccountKeyStore` (`SecureAccountKeyStore`: the account's unlocked keys in
  the system's keyring, per instance and person, gone once another person
  signs in or nobody). Signing in (SRP's M2 checked and the keys opened before
  anything is trusted), signing up (the recovery phrase shown once and three of
  its words typed back before anything reaches the instance), a setup never
  finished, the authenticators (QR codes drawn with pub.dev's `qr`), recovery
  codes, changing the password, a new phrase, and getting back in. The
  screens: the start screen's Sign in and Create an account,
  `showPasswordSignInSheet`, `showAccountSetupSheet`,
  `showAccountRecoverySheet`, and `AccountSecuritySection` for an app's
  account part. Every change of how the account is secured asks for the
  password with the code, one answer per sheet (`OwnerAnswer`, the owner's
  proof: a session alone gets no code checked), each answer bound to the
  instance's base URL and to the change it approves (its purpose and the
  digest of what it sets, `proof_digests.dart`), so nobody between the device
  and the instance swaps anything in; deleting by a code by mail
  follows `secondFactorWorks`, as the instance tells it, and asks for the
  address only where the device doesn't know it. Anonymous people get no keys until something is encrypted
  (step 4). Every build of an app needs a C compiler and make: sodium's build
  hook compiles libsodium.
- **Files** (`FileSaver`, `PlatformFileSaver`): keeping a file the app made
  where the person chooses (a recovery phrase, recovery codes, an app's
  exports).
- **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`, `FakePasswordGateway`, `FakeAccountCrypto`,
  `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 path, within the repository's workspace, as on
   `halkyon_ui`:

   ```yaml
   dependencies:
     halkyon_app:
       path: ../../../packages/halkyon_app
   ```

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 (`resolveAppLocale` as
   its resolution) and launch screen, and the three sentences only it can
   say: what the first start's instance keeps of the person's, what a switch
   to another account leaves behind, and where GitHub is added later.
5. **The dependencies**: the app's composition root implements
   `AppDependencies<P>` (`serverName`, `auth`, `signedOut`, `passwords`,
   `fileSaver`, `sourceCodeUrl`, `openPerson`, `dispose`), its person's
   dependencies `Disposable`. Its `passwords` is a `PasswordRepository` on
   `ServerpodPasswordGateway(client, base: client.modules.base)`,
   `SodiumAccountCrypto()`, `SecureAccountKeyStore(storage.keysOf(instance))`,
   the auth gateway and the app's `SignInAddresses`. 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'),
     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`).