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kryz-go-flutter/PROJECT_STRUCTURE.md
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robot f3393348f7 docs: add project structure and architecture analysis report 
- Map out complete folder structure with descriptions
- Identify Flutter+Dart as primary stack (no Go backend)
- Document all Dart source modules and their responsibilities
- Document native platform code (Android Cast, iOS CarPlay)
- Describe whitelabel build system (build_whitelabel.py + theme.json)
- Document data flow between modules
- List dependencies, dev environment, and test coverage
2026-07-31 23:59:33 +00:00

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# KRYZ Go! — Project Structure & Architecture
> Analysis of `kryz-go-flutter` on the `setup/project-onboarding` branch.
## 1. Overview
**KRYZ Go!** is a multi-platform **Flutter** mobile application for the KRYZ LP-FM 98.5 Mariposa community radio station. It streams live audio from the station, displays real-time metadata (now playing, upcoming show), and supports casting to external displays (Chromecast, Android Auto, iOS CarPlay/AirPlay).
**Primary stack:** Flutter + Dart (frontend only). There is no Go backend in this repository — the project name "kryz-go-flutter" refers to the app name "KRYZ Go!", not a Go language backend.
**Target platforms:** Android (including Android Auto), iOS (including CarPlay), macOS, Windows, Linux, and Web.
## 2. Folder Structure
```
kryz-go-flutter/
├── lib/ # Dart application source
│ ├── main.dart # App entry point + MaterialApp + MainPage UI
│ ├── kryz_audio_handler.dart # Background audio handler (audio_service)
│ ├── streaming_audio_business_object.dart # Audio playback controller
│ ├── casting_business_object.dart # Cast/AirPlay state machine (platform channels)
│ ├── live_info_business_object.dart # Live metadata poller + data models
│ ├── live_info_panel.dart # "Live Studio Feed" widget (now/next cards)
│ ├── track_card.dart # Individual track display widget
│ ├── show_card.dart # Show schedule display widget
│ ├── recently_played_list.dart # Recently-played list widget (unused in current UI)
│ ├── app_theme_business_object.dart # Theme colors + light/dark ThemeData
│ ├── time_formatter.dart # Timestamp parsing + timezone conversion
│ └── generated/ # Auto-generated by build_whitelabel.py (not committed)
│ ├── app_config.dart # Compile-time constants (station name, stream URL, etc.)
│ └── theme_colors.dart # Generated AppThemeColors (light + dark)
├── android/ # Android native project
│ └── app/src/main/
│ ├── kotlin/.../MainActivity.kt # Cast framework + MethodChannel bridge
│ ├── kotlin/.../KryzAutoMediaBrowserService.kt # Android Auto media browser
│ ├── kotlin/.../CastOptionsProvider.kt # Cast receiver config
│ ├── AndroidManifest.xml # App manifest + permissions
│ └── res/values/automotive_colors.xml # Android Auto theming
├── ios/ # iOS native project
│ └── Runner/
│ ├── AppDelegate.swift # Flutter engine + CarPlay setup
│ ├── SceneDelegate.swift # Scene lifecycle
│ └── CarPlaySceneDelegate.swift # CarPlay template
├── macos/ # macOS native project (Swift)
├── linux/ # Linux native project (C++)
├── windows/ # Windows native project (C++)
├── web/ # Web entry point (index.html, manifest.json)
├── assets/icon/ # App icon source
│ └── app_icon.png
├── test/ # Dart tests
│ ├── widget_test.dart # Basic widget smoke test
│ └── time_formatter_test.dart # Timezone + formatting unit tests
├── build_whitelabel.py # Whitelabel build script (Python)
├── requirements.txt # Python deps for whitelabel script (Pillow, cairosvg)
├── pubspec.yaml # Flutter package manifest + Dart deps
├── analysis_options.yaml # Dart linter config (flutter_lints)
├── README.md # Brief project docs
├── .devcontainer/ # VS Code Dev Container (Dockerfile + JSON)
└── theme.json # Station theme config (colors, images, stream URLs)
```
## 3. Key Configuration Files
### pubspec.yaml
- **Package:** `kryz_go_flutter`
- **SDK:** Dart ^3.11.5
- **Version:** 1.0.0+1
- **Core dependencies:**
- `just_audio` (^0.10.5) — audio playback engine
- `just_audio_background` (^0.0.1-beta.17) — background audio support
- `audio_service` (^0.18.18) — media session integration (notifications, lock screen)
- `audio_session` (^0.2.2) — audio focus/Duck configuration
- `webview_flutter` (^4.13.0) — embedded WebView (unused in current code path)
- `http` (^1.5.0) — HTTP client for live-info API
- `intl` (^0.20.2) — date/time formatting
- `timezone` (^0.10.1) — timezone-aware datetime handling
- **Dev dependencies:**
- `flutter_name_manager` — rename app across platforms
- `flutter_launcher_icons` — generate platform-specific icons
- `flutter_lints` (^6.0.0) — recommended lint rules
### Android build.gradle.kts
- **Namespace:** `com.example.kryz_go_flutter`
- **Java/Kotlin target:** Java 17
- **Cast dependency:** `play-services-cast-framework:22.1.0`
- **Media router:** `androidx.mediarouter:1.7.0`
- **Media:** `androidx.media:1.7.0`
## 4. Architecture
### Entry Point
`lib/main.dart` initializes timezone data, then runs `MyApp` which creates two top-level business objects: `StreamingAudioBusinessObject` and `CastingBusinessObject`. The `MainPage` widget composes the full UI (header card + live info panel + playback controls).
### Core Modules
#### Audio Playback (`kryz_audio_handler.dart`, `streaming_audio_business_object.dart`)
- `KryzAudioHandler` extends `BaseAudioHandler` (from `audio_service`). It manages a `just_audio.AudioPlayer` instance that streams from a hard-coded `streamUrl` (loaded from `AppConfig`).
- Supports play/stop only (no seek — live stream). Keeps a persistent metadata refresh timer that polls the live-info API every 20 seconds.
- `StreamingAudioBusinessObject` wraps the handler, exposing a simplified `StreamingPlaybackStatus` enum and current track title/artist to the UI.
#### Casting / Remote Playback (`casting_business_object.dart`)
- Communicates with native Android/iOS code through Flutter platform channels (`MethodChannel` + `EventChannel`).
- On Android: integrates with the Google Cast framework (Chromecast) and Android Auto.
- On iOS: integrates with AirPlay.
- Supports showing a device picker, starting a cast stream, stopping playback, and disconnecting.
- Handles the handoff from local playback to remote playback (stops `audio_service` when cast loads).
#### Live Metadata (`live_info_business_object.dart`)
- Polls a metadata endpoint (configurable via `theme.json` or `KRYZ_LIVE_INFO_URL` env var) every 20 seconds.
- Parses the JSON response into `LiveInfoSnapshot` containing:
- `current`, `next`, `previous` track info (title, artist, album, timestamps)
- `currentShow`, `nextShow` (name, description, start/end times)
- `timezone`, `schedulerTime`, `sourceEnabled`
- Maintains a deduplicated "recently played" list (max 40 items) built at runtime.
#### Theme / Whitelabeling (`build_whitelabel.py`, `app_theme_business_object.dart`)
- `theme.json` (not committed) defines station name, callsign, frequency, stream URL, metadata URL, color palette, and embedded images (logo, hero icon).
- `build_whitelabel.py` reads `theme.json` and generates:
- `lib/generated/app_config.dart` — compile-time constants
- `lib/generated/theme_colors.dart` — light + dark `AppThemeColors`
- `assets/icon/app_icon.png` — from embedded logo
- Patches `AndroidManifest.xml`, `Info.plist`, `automotive_colors.xml`, and Kotlin source files
- This design enables re-branding the entire app for different stations by changing a single JSON file.
#### Native Platform Code
- **Android** (`MainActivity.kt`): Full Google Cast framework integration with session management, retry logic, media browser service for Android Auto, and platform channel bridging to Flutter.
- **iOS** (`AppDelegate.swift`, `CarPlaySceneDelegate.swift`): Flutter engine setup and CarPlay template scene delegate.
- **macOS/Linux/Windows**: Standard Flutter shell templates.
### Data Flow
```
[Radio Station API] ──HTTP──> [LiveInfoBusinessObject] ──poll──> [UI: LiveInfoPanel]
└─> [KryzAudioHandler: updateMetadata]
└─> [RecentlyPlayedList (runtime)]
[Station Stream URL] ──stream──> [just_audio Player] ──state──> [StreamingAudioBusinessObject] ──> [UI: Play/Stop buttons]
[Cast/AirPlay] ◄──platform channels──> [CastingBusinessObject] ──> [UI: Cast button]
│ │
└──native──> MainActivity.kt / iOS native └──> [stops local audio on handoff]
```
## 5. Business Object Pattern
The codebase uses a "Business Object" naming convention for stateful singletons:
- `StreamingAudioBusinessObject` — audio playback state
- `CastingBusinessObject` — cast/AirPlay connection state
- `LiveInfoBusinessObject` — live metadata + recently-played history
- `AppThemeBusinessObject` — theme color definitions
All extend `ChangeNotifier`, providing reactive state updates to Flutter widgets via `addListener`/`notifyListeners`.
## 6. Development Environment
- **Dev Container:** VS Code remote container with Flutter + Python venv. Extensions: Flutter, TypeScript.
- **Post-create:** `flutter pub get`, Python venv + deps install, Claude CLI install.
- **Build:** `flutter build <platform>` or `flutter run <platform>` for debug.
- **Whitelabel build:** `python3 build_whitelabel.py [--theme theme.json] [--dry-run] [--no-tools]`
## 7. Test Coverage
- `test/widget_test.dart` — basic smoke test verifying app title and playback buttons render.
- `test/time_formatter_test.dart` — comprehensive tests for timezone conversion, naive vs. explicit UTC timestamps, and time-window formatting.
No integration tests, mock API tests, or casting-specific tests currently exist.
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