# JellyTau Software Architecture

This document describes the current architecture of JellyTau, a cross-platform Jellyfin client built with Tauri, SvelteKit, and Rust.

**Last Updated:** 2026-06-20

## Architecture Overview

JellyTau uses a client-server architecture: business logic lives in a comprehensive Rust backend, while a UI-rich Svelte frontend handles presentation and interaction.

### Architecture Principles

- **Business Logic in Rust**: Core logic — playback, repository, sync, downloads, connectivity — lives in Rust for performance, reliability, and type safety.
- **Presentation in Svelte**: The frontend (~20.5k non-test lines) owns UI, layout, navigation, and interaction state and invokes Rust commands. It is intentionally UI-heavy, **not** a thin wrapper. Largest pieces: components + routes (~14.6k lines), stores (~3.4k), api/services/utils (~2.4k); `VideoPlayer.svelte` alone is ~1.6k lines.
- **Events + Polling hybrid**: Rust emits events the frontend listens to, and the UI also polls status on short intervals in a few hot spots (e.g. queue status in `library/+layout.svelte`, playback progress in `VideoPlayer.svelte`).
- **Unified player boundary**: UI components control playback only through the frontend facade `src/lib/player/index.ts` (`playerController`), never by calling `commands.player*` directly. Webview-rendered HTML5 video reports its state back into Rust via `src/lib/player/html5Adapter.ts` and the `player_report_*` commands, so the `PlayerController` stays the single source of truth in both native (MPV/ExoPlayer) and HTML5 modes (see [05-platform-backends.md](05-platform-backends.md)).
- **Handle-Based Resources**: UUID handles for stateful Rust objects.
- **Cache-First**: Parallel queries with intelligent fallback.
- **Single source of truth for reachability**: Server reachability is derived from the outcome of *real repository traffic*, not a side-channel poller. The `OnlineRepository` reports each server result to the `ConnectivityMonitor` (classified via `RepoError`), which applies a time-window debounce before declaring the server offline and recovers instantly on the first success. The standalone `/System/Info/Public` probe runs *only while offline*, as a recovery detector for idle sessions.
- **Poison-tolerant locking**: Shared `std::sync` state is accessed via the `MutexSafe`/`RwLockSafe` helpers in `utils/lock.rs`, which recover a poisoned lock instead of cascading a panic across the player.
- **Graceful backend init**: If a native player backend (MPV/ExoPlayer) fails to initialize, the app falls back to a no-op backend and emits a `backend-init-failed` event rather than crashing.

```mermaid
flowchart TB
    subgraph Frontend["Svelte Frontend"]
        subgraph Stores["Stores (Thin Wrappers)"]
            auth["auth"]
            player["player"]
            queue["queue"]
            library["library"]
            connectivity["connectivity"]
            playbackMode["playbackMode"]
        end
        subgraph Components
            playerComp["player/"]
            libraryComp["library/"]
            Search["Search"]
        end
        subgraph Routes
            routeLibrary["/library"]
            routePlayer["/player"]
            routeRoot["/"]
        end
        subgraph API["API Layer (Thin Client)"]
            RepositoryClient["RepositoryClient<br/>(Handle-based)"]
            JellyfinClient["JellyfinClient<br/>(Helper)"]
        end
    end

    Frontend -->|"Tauri IPC (invoke)"| Backend

    subgraph Backend["Rust Backend (Business Logic)"]
        subgraph Commands["Tauri Commands (90+)"]
            PlayerCmds["player.rs"]
            RepoCmds["repository.rs (27)"]
            PlaybackModeCmds["playback_mode.rs (5)"]
            StorageCmds["storage.rs"]
            ConnectivityCmds["connectivity.rs (7)"]
        end

        subgraph Core["Core Modules"]
            MediaSessionManager["MediaSessionManager<br/>(Audio/Movie/TvShow/Idle)"]

            PlayerController["PlayerController<br/>+ PlayerBackend<br/>+ QueueManager"]

            Repository["Repository Layer<br/>HybridRepository (cache-first)<br/>OnlineRepository (HTTP)<br/>OfflineRepository (SQLite)"]

            PlaybackModeManager["PlaybackModeManager<br/>(Local/Remote/Idle)"]

            ConnectivityMonitor["ConnectivityMonitor<br/>(Adaptive polling)"]

            HttpClient["HttpClient<br/>(Exponential backoff retry)"]
        end

        subgraph Storage["Storage Layer"]
            DatabaseService["DatabaseService<br/>(Async trait)"]
            SQLite["SQLite Database<br/>(13 tables)"]
        end

        Commands --> Core
        Core --> Storage
        Repository --> HttpClient
        Repository --> DatabaseService
        Repository -->|"reports server outcome<br/>(success / RepoError)"| ConnectivityMonitor
    end
```

> The `Repository --> ConnectivityMonitor` edge is the source of truth for the offline/online banner: every server request the user actually makes updates reachability. The monitor's own polling is now an offline-only recovery probe (see [07-connectivity.md](07-connectivity.md)).

---

## Detailed Documentation

Each major subsystem is documented in its own file in this directory:

| Document | Contents |
|----------|----------|
| [01 - Rust Backend](01-rust-backend.md) | Media session state machine, player state machine, playback mode, media items, queue manager, favorites, player backend trait, player controller, playlist system, Tauri commands |
| [02 - Svelte Frontend](02-svelte-frontend.md) | Store structure, music library navigation, playback reporting, repository architecture, playback mode system, database service abstraction, component hierarchy, MiniPlayer, sleep timer, auto-play, navigation guard, playlist management UI |
| [03 - Data Flow](03-data-flow.md) | Repository query flow (cache-first), playback initiation, playback mode transfer, queue navigation, volume control |
| [04 - Type Sync & Threading](04-type-sync-and-threading.md) | Rust/TypeScript type synchronization, Tauri v2 IPC parameter naming convention, thread safety patterns |
| [05 - Platform Backends](05-platform-backends.md) | Player events system, MpvBackend (Linux), ExoPlayerBackend (Android), MediaSession & remote volume, album art caching, backend initialization |
| [06 - Downloads & Offline](06-downloads-and-offline.md) | Download manager, download worker, smart caching engine, download/offline commands, player integration, frontend store, UI components |
| [07 - Connectivity](07-connectivity.md) | HTTP client with retry logic, connectivity monitor, network resilience architecture |
| [08 - Database Design](08-database-design.md) | Entity relationships, all table definitions (servers, users, libraries, items, user_data, downloads, media_streams, sync_queue, thumbnails, playlists), key queries, data flow diagrams, storage estimates |
| [09 - Security](09-security.md) | Authentication token storage, secure storage module, network security, local data protection |

---

## File Structure Summary

```
src-tauri/src/
├── lib.rs                    # Tauri app setup, state initialization
├── commands/                 # Tauri command handlers (90+ commands)
│   ├── mod.rs               # Command exports
│   ├── player.rs            # 16 player commands
│   ├── repository.rs        # 27 repository commands
│   ├── playlist.rs          # 7 playlist commands
│   ├── playback_mode.rs     # 5 playback mode commands
│   ├── connectivity.rs      # 7 connectivity commands
│   ├── storage.rs           # Storage & database commands
│   ├── download.rs          # 7 download commands
│   ├── offline.rs           # 3 offline commands
│   └── sync.rs              # Sync queue commands
├── repository/              # Repository pattern implementation
│   ├── mod.rs               # MediaRepository trait, handle management
│   ├── types.rs             # RepoError, Library, MediaItem, etc.
│   ├── hybrid.rs            # HybridRepository with cache-first racing
│   ├── online.rs            # OnlineRepository (HTTP API)
│   └── offline.rs           # OfflineRepository (SQLite queries)
├── playback_mode/           # Playback mode manager
│   └── mod.rs               # PlaybackMode enum, transfer logic
├── connectivity/            # Connectivity monitoring
│   └── mod.rs               # ConnectivityMonitor, adaptive polling
├── jellyfin/                # Jellyfin API client
│   ├── mod.rs               # Module exports
│   ├── http_client.rs       # HTTP client with retry logic
│   └── client.rs            # JellyfinClient for API calls
├── storage/                 # Database layer
│   ├── mod.rs               # Database struct, migrations
│   ├── db_service.rs        # DatabaseService trait (async wrapper)
│   ├── schema.rs            # Table definitions
│   └── queries/             # Query modules
├── download/                # Download manager module
│   ├── mod.rs               # DownloadManager, DownloadInfo, DownloadTask
│   ├── worker.rs            # DownloadWorker, HTTP streaming, retry logic
│   ├── events.rs            # DownloadEvent enum
│   └── cache.rs             # SmartCache, CacheConfig, LRU eviction
└── player/                  # Player subsystem
    ├── mod.rs               # PlayerController
    ├── session.rs           # MediaSessionManager, MediaSessionType
    ├── state.rs             # PlayerState, PlayerEvent
    ├── media.rs             # MediaItem, MediaSource, MediaType
    ├── queue.rs             # QueueManager, RepeatMode
    ├── backend.rs           # PlayerBackend trait, NullBackend
    ├── events.rs            # PlayerStatusEvent, TauriEventEmitter
    ├── mpv/                 # Linux MPV backend
    │   ├── mod.rs           # MpvBackend implementation
    │   └── event_loop.rs    # Dedicated thread for MPV operations
    └── android/             # Android ExoPlayer backend
        └── mod.rs           # ExoPlayerBackend + JNI bindings

src/lib/
├── api/                     # Thin API layer (~200 lines total)
│   ├── types.ts             # TypeScript type definitions
│   ├── repository-client.ts # RepositoryClient wrapper (~100 lines)
│   ├── client.ts            # JellyfinClient (helper for streaming)
│   └── sessions.ts          # SessionsApi (remote session control)
├── player/                  # Unified player boundary (frontend)
│   ├── index.ts             # playerController facade — the only write-side entry point for playback
│   └── html5Adapter.ts      # Reports webview <video> DOM events back into Rust (player_report_*)
├── services/
│   ├── playerEvents.ts      # Tauri event listener for player events
│   └── playbackReporting.ts # Thin wrapper (~50 lines)
├── stores/                  # Thin reactive wrappers over Rust commands
│   ├── index.ts             # Re-exports
│   ├── auth.ts              # Auth store (calls Rust commands)
│   ├── player.ts            # Player store
│   ├── queue.ts             # Queue store
│   ├── library.ts           # Library store
│   ├── playbackMode.ts      # Playback mode store (~150 lines)
│   ├── connectivity.ts      # Connectivity store (~250 lines)
│   └── downloads.ts         # Downloads store with event listeners
└── components/
    ├── Search.svelte
    ├── player/              # Player UI components
    ├── playlist/            # Playlist modals (Create, AddTo)
    ├── sessions/            # Remote session control UI
    ├── downloads/           # Download UI components
    └── library/             # Library UI components + PlaylistDetailView
```

## Key Architecture Changes

**What moved to Rust (~3,500 lines of business logic):**
1. **HTTP Client** (338 lines) - Retry logic with exponential backoff
2. **Connectivity Monitor** (301 lines) - Reachability derived from real repository traffic, time-window debounce, offline-only recovery probe, event emission
3. **Repository Pattern** (1061 lines) - Cache-first hybrid with parallel racing
4. **Database Service** - Async wrapper preventing UI freezing
5. **Playback Mode** (303 lines) - Local/remote transfer coordination

**Svelte/TypeScript frontend (~20.5k non-test lines, plus ~9.6k test lines):**
- Components + routes (~14.6k lines) — UI and presentation
- Stores (~3.4k lines) — reactive state that invokes Rust commands and listens for events
- api / services / utils (~2.4k lines) — typed clients, event listeners, conversion helpers

The frontend is genuinely UI-heavy; business decisions live in Rust, but the UI owns layout, navigation, and interaction state.

**Total Commands:** 90+ Tauri commands across 14 command modules
