Wholphin/DEVELOPMENT.md

# Wholphin developer's guide

See also the [Contributing](CONTRIBUTING.md) guide for general information on contributing to the project.

##  Overview

This project is an Android TV client for Jellyfin. It is written in Kotlin and uses the official [Jellyfin Kotlin SDK](https://github.com/jellyfin/jellyfin-sdk-kotlin) to interact with the server.

The app is a single Activity (`MainActivity`) with MVVM architecture.

The app uses:
* [Compose](https://developer.android.com/jetpack/compose) for the UI
* [Navigation 3](https://developer.android.com/guide/navigation/navigation-3) for navigating app screen
* [Room](https://developer.android.com/training/data-storage/room) & [DataStore](https://developer.android.com/topic/libraries/architecture/datastore) for local data storage
* [Hilt](https://developer.android.com/training/dependency-injection/hilt-android) for dependency injection
* [Media3/ExoPlayer](https://developer.android.com/media/media3/exoplayer) for media playback
* [MPV/libmpv](https://github.com/mpv-player/mpv) for media playback
* [Coil](https://coil-kt.github.io/coil/) for image loading
* [OkHttp](https://square.github.io/okhttp/) for HTTP requests

## Getting started

We follow GitHub's fork & pull request model for contributions.

After forking and cloning your fork, you can import the project into Android Studio.

### Development environment

It is recommended to use a recent version of [Android Studio](https://developer.android.com/studio). Make sure the [version is compatible](https://developer.android.com/build/releases/gradle-plugin#android_gradle_plugin_and_android_studio_compatibility) with Wholphin's AGP version.

Code formatting should follow [ktlint's](https://github.com/pinterest/ktlint) rules. Find the `ktlint` version in [`.pre-commit-config.yaml`](./.pre-commit-config.yaml). Optionally, install the [ktlint plugin](https://plugins.jetbrains.com/plugin/15057-ktlint) in Android Studio to run automatically. Configure the version in `Settings->Tools->KtLint->Ruleset Version`.

Also, it's recommend to add an extra ruleset jar for Compose-specific KtLint: https://mrmans0n.github.io/compose-rules/ktlint/#using-with-ktlint-cli-or-the-ktlint-intellij-plugin

Also setup [pre-commit](https://github.com/pre-commit/pre-commit) which will run `ktlint` as well on each commit, plus check for other common issues.

#### Extensions

Wholphin uses several native components for extra playback compatibility. This includes Media3 ffmpeg/av1 decoders and `libmpv`. These extensions are not required to build the app, but without them some functionality will not work.

If you want to include these in a local build, see the [instructions here](https://github.com/damontecres/wholphin-extensions?tab=readme-ov-file#usage) for configuring the repository.

You can also build the extensions locally from https://github.com/damontecres/wholphin-extensions and include them in `app/libs`. The gradle build dependency resolution prefers these local files over fetching from the remote maven registry.

Finally, if no `wholphin-mpv` implementation is found, `wholphin-mpv-stub` will be used. This allows the app to compile, but any runtime usage of MPV will throw an exception.

## Code organization

Code is split into several packages:
- `data` - app-specific data models and services
- `preferences` - Non-UI related code for user settings and preferences
- `services` - hilt injectable services often used by ViewModels for API calls
- `ui` - User interface code and ViewModels
- `util` - Utility classes and functions

### Settings

There are a few different ways user settings are stored:
1. `AppPreferences` via DataStore
2. Room database
3. Key-Value DataStore

#### App preferences

These are generally settings that apply across the whole app regardless of the currently active user.

The `AppPreferences` object can be retrieved from the `UserPreferencesService` or directly via injecting `DataStore<AppPreferences>`.

The `AppPreference` (note the `s` differences) objects are used to create the UI for configuring settings using the composable functions in `com.github.damontecres.wholphin.ui.preferences`.

##### How to add a new app setting

1. Add entry in `WholphinDataStore.proto` & build to generate classes
2. Add new `AppPreference` object in `AppPreference.kt`
3. Add new object to a `PreferenceGroup` (listed in `AppPreference.kt`)
4. Update `AppPreferencesSerializer` to set the default value for new installs
5. If needed, update `AppUpgradeHandler` to set the default value for app upgrades
    - Since preferences use proto3, the [default values](https://protobuf.dev/programming-guides/proto3/#default) are zero, false, or the first enum, so only need this step if the default value is different

#### Room settings

These are settings were generally are applied per user. They are stored in several different tables. The entities are defined in `com.github.damontecres.wholphin.data.model`.

Additionally, all server and user info for both Jellyfin and Seerr are stored in Room tables.

Some examples are:
- `JellyfinServer`
- `JellyfinUser`
- `SeerrServer`
- `LibraryDisplayInfo`
- `ItemPlayback`

Some of the models, such as `GetItemsFilter` or `ViewOptions`, are stored as JSON in a column instead of defined entities. This should be used sparingly.

#### Key-value settings

These settings are similar to Room ones and are usually stored per user. These can be accessed via `KeyValueService`. The values are `@Serializable` objects saved as JSON.

This should be used sparingly.

#### Experimental

Some settings are considered "experimental". These may cause instabilities or may need further testing. They may be changed or removed any time.

These are stored in the `ExperimentalPreferences` object in `AppPreferences`. Accessing them should always be gated with `ExperimentalPreferences.enabled`. There are a few helper functions for this purpose.