robius-state-management - Claude MCP Skill

# Robius State Management Skill

Best practices for state management and persistence in Makepad applications based on Robrix and Moly codebases.

**Source codebases:**
- **Robrix**: Matrix chat client - AppState, SelectedRoom, persistence via serde
- **Moly**: AI chat application - Central Store pattern, async initialization, Preferences

## Triggers

Use this skill when:
- Designing application state structure
- Implementing state persistence
- Passing state through widget tree
- Managing UI state across sessions
- Keywords: app state, makepad state, persistence, Scope::with_data, save state, load state

## Production Patterns

For production-ready state management patterns, see the `_base/` directory:

| Pattern | Description |
|---------|-------------|
| [06-global-registry](./_base/06-global-registry.md) | Global widget registry with Cx::set_global |
| [07-radio-navigation](./_base/07-radio-navigation.md) | Tab-style navigation with radio buttons |
| [10-state-machine](./_base/10-state-machine.md) | Enum-based state machine widgets |
| [11-theme-switching](./_base/11-theme-switching.md) | Multi-theme support with apply_over |
| [12-local-persistence](./_base/12-local-persistence.md) | Save/load user preferences |

## AppState Structure

### Core State Definition

```rust
use serde::{Serialize, Deserialize};
use std::collections::HashMap;
use matrix_sdk::ruma::OwnedRoomId;

/// App-wide state that is stored persistently across multiple app runs
/// and shared/updated across various parts of the app.
#[derive(Clone, Default, Debug, Serialize, Deserialize)]
pub struct AppState {
    /// The currently-selected room
    pub selected_room: Option<SelectedRoom>,

    /// Saved UI layout state for main view
    pub saved_layout_state: SavedLayoutState,

    /// Per-item saved states (e.g., per-space dock layouts)
    pub saved_state_per_item: HashMap<OwnedRoomId, SavedLayoutState>,

    /// Whether a user is currently logged in
    #[serde(skip)]  // Don't persist login state
    pub logged_in: bool,
}

/// Represents a currently selected item
#[derive(Clone, Debug, Serialize, Deserialize)]
pub enum SelectedRoom {
    JoinedRoom { room_name_id: RoomNameId },
    InvitedRoom { room_name_id: RoomNameId },
    Space { space_name_id: RoomNameId },
}

impl SelectedRoom {
    pub fn room_id(&self) -> &OwnedRoomId {
        match self {
            Self::JoinedRoom { room_name_id } => room_name_id.room_id(),
            Self::InvitedRoom { room_name_id } => room_name_id.room_id(),
            Self::Space { space_name_id } => space_name_id.room_id(),
        }
    }

    /// Upgrade from invited to joined state
    pub fn upgrade_invite_to_joined(&mut self, room_id: &RoomId) -> bool {
        match self {
            Self::InvitedRoom { room_name_id } if room_name_id.room_id() == room_id => {
                let name = room_name_id.clone();
                *self = Self::JoinedRoom { room_name_id: name };
                true
            }
            _ => false,
        }
    }
}

// Equality based on room_id only
impl PartialEq for SelectedRoom {
    fn eq(&self, other: &Self) -> bool {
        self.room_id() == other.room_id()
    }
}
impl Eq for SelectedRoom {}
```

### Layout/Dock State Persistence

```rust
/// A snapshot of UI layout state for restoration
#[derive(Clone, Default, Debug, Serialize, Deserialize)]
pub struct SavedLayoutState {
    /// All items contained in the layout, keyed by ID
    pub layout_items: HashMap<LiveIdSerde, LayoutItemSerde>,

    /// Items currently open, keyed by ID
    pub open_items: HashMap<LiveIdSerde, SelectedRoom>,

    /// Order items were opened (chronological)
    pub item_order: Vec<SelectedRoom>,

    /// Currently selected item when state was saved
    pub selected_item: Option<SelectedRoom>,
}

/// Serializable wrapper for LiveId
#[derive(Clone, Debug, Hash, Eq, PartialEq, Serialize, Deserialize)]
pub struct LiveIdSerde(pub u64);

impl From<LiveId> for LiveIdSerde {
    fn from(id: LiveId) -> Self {
        Self(id.0)
    }
}

impl From<LiveIdSerde> for LiveId {
    fn from(s: LiveIdSerde) -> Self {
        LiveId(s.0)
    }
}
```

## State Propagation via Scope

### Passing State Through Widget Tree

```rust
impl AppMain for App {
    fn handle_event(&mut self, cx: &mut Cx, event: &Event) {
        // Forward to MatchEvent
        self.match_event(cx, event);

        // Create Scope with AppState data
        let scope = &mut Scope::with_data(&mut self.app_state);

        // Pass to widget tree - all children can access AppState
        self.ui.handle_event(cx, event, scope);
    }
}
```

### Accessing State in Child Widgets

```rust
impl Widget for RoomScreen {
    fn handle_event(&mut self, cx: &mut Cx, event: &Event, scope: &mut Scope) {
        // Access AppState from scope
        if let Some(app_state) = scope.data.get::<AppState>() {
            if let Some(selected) = &app_state.selected_room {
                self.update_for_room(cx, selected);
            }
        }

        self.view.handle_event(cx, event, scope);
    }
}
```

### Modifying State

```rust
impl Widget for RoomsList {
    fn handle_event(&mut self, cx: &mut Cx, event: &Event, scope: &mut Scope) {
        // Mutable access to AppState
        if let Some(app_state) = scope.data.get_mut::<AppState>() {
            if self.selection_changed {
                app_state.selected_room = self.get_selected();
            }
        }
    }
}
```

## Persistence Layer

### File Paths

```rust
use std::path::{Path, PathBuf};

const LATEST_APP_STATE_FILE_NAME: &str = "latest_app_state.json";
const WINDOW_GEOM_STATE_FILE_NAME: &str = "window_geom_state.json";

/// Get user-specific persistent state directory
fn persistent_state_dir(user_id: &UserId) -> PathBuf {
    app_data_dir()
        .join("users")
        .join(user_id.to_string().replace(':', "_"))
}

/// Get app-wide data directory
fn app_data_dir() -> &'static Path {
    // Platform-specific app data location
    static APP_DATA_DIR: OnceLock<PathBuf> = OnceLock::new();
    APP_DATA_DIR.get_or_init(|| {
        dirs::data_dir()
            .unwrap_or_else(|| PathBuf::from("."))
            .join("myapp")
    })
}
```

### Saving State

```rust
use std::io::Write;

pub fn save_app_state(
    app_state: AppState,
    user_id: OwnedUserId,
) -> anyhow::Result<()> {
    let file = std::fs::File::create(
        persistent_state_dir(&user_id).join(LATEST_APP_STATE_FILE_NAME)
    )?;
    let mut writer = std::io::BufWriter::new(file);
    serde_json::to_writer(&mut writer, &app_state)?;
    writer.flush()?;
    log!("Successfully saved app state to persistent storage.");
    Ok(())
}

/// Save window geometry state (user-agnostic)
pub fn save_window_state(window_ref: WindowRef, cx: &Cx) -> anyhow::Result<()> {
    let inner_size = window_ref.get_inner_size(cx);
    let position = window_ref.get_position(cx);
    let window_geom = WindowGeomState {
        inner_size: (inner_size.x, inner_size.y),
        position: (position.x, position.y),
        is_fullscreen: window_ref.is_fullscreen(cx),
    };
    std::fs::write(
        app_data_dir().join(WINDOW_GEOM_STATE_FILE_NAME),
        serde_json::to_string(&window_geom)?,
    )?;
    Ok(())
}
```

### Loading State

```rust
/// Load app state with graceful fallback
pub async fn load_app_state(user_id: &UserId) -> anyhow::Result<AppState> {
    let state_path = persistent_state_dir(user_id).join(LATEST_APP_STATE_FILE_NAME);

    // Read file
    let file_bytes = match tokio::fs::read(&state_path).await {
        Ok(fb) => fb,
        Err(e) if e.kind() == std::io::ErrorKind::NotFound => {
            log!("No saved app state found, using default.");
            return Ok(AppState::default());
        }
        Err(e) => return Err(e.into()),
    };

    // Deserialize with fallback
    match serde_json::from_slice(&file_bytes) {
        Ok(app_state) => {
            log!("Successfully loaded app state.");
            Ok(app_state)
        }
        Err(e) => {
            error!("Failed to deserialize: {e}. May be incompatible format.");

            // Backup old file
            let backup_path = state_path.with_extension("json.bak");
            if let Err(backup_err) = tokio::fs::rename(&state_path, &backup_path).await {
                error!("Failed to backup old state: {}", backup_err);
            } else {
                log!("Old state backed up to: {:?}", backup_path);
            }

            log!("Using default app state.");
            Ok(AppState::default())
        }
    }
}

/// Load window geometry (synchronous, on UI thread)
pub fn load_window_state(window_ref: WindowRef, cx: &mut Cx) -> anyhow::Result<()> {
    let file = match std::fs::File::open(app_data_dir().join(WINDOW_GEOM_STATE_FILE_NAME)) {
        Ok(file) => file,
        Err(e) if e.kind() == std::io::ErrorKind::NotFound => return Ok(()),
        Err(e) => return Err(e.into()),
    };

    let window_geom: WindowGeomState = serde_json::from_reader(file)?;
    log!("Restoring window geometry: {window_geom:?}");

    window_ref.configure_window(
        cx,
        dvec2(window_geom.inner_size.0, window_geom.inner_size.1),
        dvec2(window_geom.position.0, window_geom.position.1),
        window_geom.is_fullscreen,
        "MyApp".to_string(),
    );
    Ok(())
}
```

### Startup/Shutdown Integration

```rust
impl MatchEvent for App {
    fn handle_startup(&mut self, cx: &mut Cx) {
        // Load window geometry (sync, on UI thread)
        if let Err(e) = persistence::load_window_state(
            self.ui.window(ids!(main_window)), cx
        ) {
            error!("Failed to load window state: {}", e);
        }

        // Trigger async app state load
        let user_id = get_current_user_id();
        tokio::spawn(async move {
            match persistence::load_app_state(&user_id).await {
                Ok(app_state) => {
                    Cx::post_action(AppStateAction::RestoreFromPersistence(app_state));
                    SignalToUI::set_ui_signal();
                }
                Err(e) => error!("Failed to load app state: {}", e),
            }
        });
    }
}

impl AppMain for App {
    fn handle_event(&mut self, cx: &mut Cx, event: &Event) {
        if let Event::Shutdown = event {
            // Save window state (sync)
            if let Err(e) = persistence::save_window_state(
                self.ui.window(ids!(main_window)), cx
            ) {
                error!("Failed to save window state: {e}");
            }

            // Save app state (sync)
            if let Some(user_id) = current_user_id() {
                if let Err(e) = persistence::save_app_state(
                    self.app_state.clone(), user_id
                ) {
                    error!("Failed to save app state: {e}");
                }
            }
        }
        // ...
    }
}
```

## Thread-Local State (UI-Only)

```rust
use std::{cell::RefCell, rc::Rc, collections::HashMap};

thread_local! {
    /// UI-thread-only cache
    static UI_CACHE: Rc<RefCell<HashMap<OwnedRoomId, CachedData>>> =
        Rc::new(RefCell::new(HashMap::new()));
}

/// Get cache reference (requires Cx to ensure UI thread)
pub fn get_ui_cache(_cx: &mut Cx) -> Rc<RefCell<HashMap<OwnedRoomId, CachedData>>> {
    UI_CACHE.with(Rc::clone)
}

/// Clear cache (requires Cx)
pub fn clear_ui_cache(_cx: &mut Cx) {
    UI_CACHE.with(|cache| cache.borrow_mut().clear());
}
```

## Best Practices

1. **Separate persistent vs runtime state**: Use `#[serde(skip)]` for non-persistent fields
2. **Use Scope::with_data() for tree propagation**: Don't pass state through widget refs
3. **Graceful deserialization fallback**: Handle format changes between versions
4. **Backup old state files**: Preserve user data when format changes
5. **User-specific persistent paths**: Separate state per user account
6. **Sync window state, async app state**: Window geometry loads sync on UI thread
7. **Thread-local for UI-only caches**: Use `thread_local!` with Cx parameter guard

## Reference Files

- `references/persistence-patterns.md` - Additional persistence patterns (Robrix)
- `references/state-structures.md` - State structure examples (Robrix)
- `references/moly-state-patterns.md` - Moly-specific patterns
  - Central Store struct containing all state
  - Async Store initialization with `load_into_app()`
  - App state check pattern (early return if not loaded)
  - Submodule state managers (Search, Downloads, Chats)
  - Provider syncing status tracking
  - Store action forwarding to submodules