# 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.