Layout Restoration

/**
 * Layout restoration implementation for persistent widget state management
 */
class LayoutRestorer implements ILayoutRestorer {
  constructor(options: LayoutRestorer.IOptions);
  
  /** Whether restoration is deferred until later */
  readonly isDeferred: boolean;
  
  /** Promise that resolves when restoration is complete */
  readonly restored: Promise<void>;
  
  /**
   * Add a widget to be tracked for restoration
   * @param widget - Widget to track
   * @param name - Unique name for the widget
   */
  add(widget: Widget, name: string): void;
  
  /**
   * Fetch the saved layout from storage
   * @returns Promise resolving to saved layout or null
   */
  fetch(): Promise<ILabShell.ILayout>;
  
  /**
   * Restore a widget tracker with saved state
   * @param tracker - Widget tracker to restore
   * @param options - Restoration options
   * @returns Promise resolving when restoration is complete
   */
  restore(
    tracker: WidgetTracker,
    options: IRestorer.IOptions<Widget>
  ): Promise<any>;
  
  /**
   * Restore deferred widgets
   * @returns Promise resolving to main area layout or null
   */
  restoreDeferred(): Promise<ILabShell.IMainArea | null>;
  
  /**
   * Save the current layout to storage
   * @param layout - Layout to save
   * @returns Promise resolving when save is complete
   */
  save(layout: ILabShell.ILayout): Promise<void>;
}

import { LayoutRestorer, ILayoutRestorer } from "@jupyterlab/application";
import { StateDB } from "@jupyterlab/statedb";
import { Widget } from "@lumino/widgets";

// Create layout restorer
const restorer = new LayoutRestorer({
  connector: new StateDB(),
  first: Promise.resolve(),
  registry: commandRegistry
});

// Add widgets for tracking
const myWidget = new Widget();
myWidget.id = 'my-important-widget';
restorer.add(myWidget, 'my-important-widget');

// Wait for restoration to complete
await restorer.restored;
console.log('Layout restoration completed');

// Save current layout
const currentLayout = shell.saveLayout();
await restorer.save(currentLayout);

// Restore a widget tracker
await restorer.restore(widgetTracker, {
  command: 'myapp:open-widget',
  args: (widget) => ({ id: widget.id }),
  name: (widget) => widget.id
});

/**
 * Layout restoration service interface
 */
interface ILayoutRestorer extends IRestorer {
  /** Promise that resolves when restoration is complete */
  readonly restored: Promise<void>;
  
  /**
   * Add a widget to be tracked for restoration
   * @param widget - Widget to track  
   * @param name - Unique name for the widget
   */
  add(widget: Widget, name: string): void;
  
  /**
   * Restore a widget tracker with saved state
   * @param tracker - Widget tracker to restore
   * @param options - Restoration options
   * @returns Promise resolving when restoration is complete
   */
  restore<T extends Widget>(
    tracker: WidgetTracker<T>,
    options: IRestorer.IOptions<T>
  ): Promise<any>;
}

/**
 * Service token for layout restoration
 */
const ILayoutRestorer: Token<ILayoutRestorer>;

import { ILayoutRestorer } from "@jupyterlab/application";
import { JupyterFrontEndPlugin } from "@jupyterlab/application";
import { WidgetTracker } from "@jupyterlab/apputils";

const plugin: JupyterFrontEndPlugin<void> = {
  id: 'my-restoration-plugin',
  autoStart: true,
  requires: [ILayoutRestorer],
  activate: (app, restorer: ILayoutRestorer) => {
    const tracker = new WidgetTracker<MyWidget>({ 
      namespace: 'my-widgets' 
    });
    
    // Restore widgets from previous session
    restorer.restore(tracker, {
      command: 'myapp:create-widget',
      args: (widget) => ({ 
        id: widget.id,
        config: widget.config 
      }),
      name: (widget) => widget.id,
      when: app.serviceManager.ready
    });
    
    // Add new widgets to restoration
    tracker.widgetAdded.connect((sender, widget) => {
      restorer.add(widget, widget.id);
    });
  }
};

/**
 * Options for restoring widget trackers (from @jupyterlab/apputils)
 */
interface IRestorer.IOptions<T extends Widget> {
  /**
   * Command to execute when restoring a widget
   */
  command: string;
  
  /**
   * Function to extract command arguments from widget
   * @param widget - Widget to extract args from
   * @returns Command arguments
   */
  args?: (widget: T) => ReadonlyPartialJSONObject;
  
  /**
   * Function to generate unique name for widget
   * @param widget - Widget to name
   * @returns Unique name string
   */
  name: (widget: T) => string;
  
  /**
   * Promise to wait for before restoration
   */
  when?: Promise<any>;
}

namespace LayoutRestorer {
  /**
   * Constructor options for LayoutRestorer
   */
  interface IOptions {
    /**
     * State storage connector
     */
    connector: IDataConnector<ReadonlyPartialJSONObject>;
    
    /**
     * Promise to resolve before restoration begins
     */
    first: Promise<any>;
    
    /**
     * Command registry for executing restoration commands
     */
    registry: CommandRegistry;
  }
}

import { LayoutRestorer } from "@jupyterlab/application";
import { StateDB } from "@jupyterlab/statedb";
import { CommandRegistry } from "@lumino/commands";

// Custom state connector
class CustomStateConnector implements IDataConnector<ReadonlyPartialJSONObject> {
  async fetch(id: string): Promise<ReadonlyPartialJSONObject | undefined> {
    // Custom fetch implementation
    return JSON.parse(localStorage.getItem(id) || '{}');
  }
  
  async save(id: string, value: ReadonlyPartialJSONObject): Promise<void> {
    // Custom save implementation
    localStorage.setItem(id, JSON.stringify(value));
  }
  
  async remove(id: string): Promise<void> {
    localStorage.removeItem(id);
  }
  
  async list(query?: string): Promise<any> {
    // List implementation
    return {};
  }
}

// Create restorer with custom options
const commands = new CommandRegistry();
const restorer = new LayoutRestorer({
  connector: new CustomStateConnector(),
  first: Promise.resolve(), // Or wait for some initialization
  registry: commands
});

// Check if restoration is deferred
if (restorer.isDeferred) {
  console.log('Restoration will happen later');
  
  // Manually trigger deferred restoration
  const deferredLayout = await restorer.restoreDeferred();
  if (deferredLayout) {
    console.log('Deferred widgets restored');
  }
}

// Integration example showing how restoration works with shell
interface ShellRestorationWorkflow {
  /**
   * 1. Shell saves its layout periodically or on shutdown
   */
  saveShellLayout(): Promise<void>;
  
  /**
   * 2. Layout restorer fetches saved layout on startup
   */
  fetchSavedLayout(): Promise<ILabShell.ILayout | null>;
  
  /**
   * 3. Shell restores layout with layout restorer
   */
  restoreShellLayout(layout: ILabShell.ILayout): Promise<void>;
  
  /**
   * 4. Individual widgets are restored via trackers
   */
  restoreWidgetTrackers(): Promise<void>;
}

import { 
  LayoutRestorer, 
  ILayoutRestorer, 
  LabShell, 
  ILabShell 
} from "@jupyterlab/application";
import { StateDB } from "@jupyterlab/statedb";
import { DockPanel } from "@lumino/widgets";

// Complete restoration workflow
async function setupLayoutRestoration(
  shell: LabShell,
  commands: CommandRegistry
) {
  // 1. Create layout restorer
  const restorer = new LayoutRestorer({
    connector: new StateDB(),
    first: Promise.resolve(),
    registry: commands
  });
  
  // 2. Wait for restoration to complete
  await restorer.restored;
  
  // 3. Restore shell layout from saved state
  const savedLayout = await restorer.fetch();
  if (savedLayout) {
    await shell.restoreLayout(
      DockPanel.Mode.Multiple,
      restorer,
      savedLayout
    );
  }
  
  // 4. Set up periodic saving
  let saveTimer: any;
  const scheduleSave = () => {
    clearTimeout(saveTimer);
    saveTimer = setTimeout(async () => {
      const currentLayout = shell.saveLayout();
      await restorer.save(currentLayout);
    }, 1000); // Save after 1 second of inactivity
  };
  
  // Save when layout changes
  shell.layoutModified.connect(scheduleSave);
  
  // Save when widgets are added/removed
  shell.currentChanged.connect(scheduleSave);
  
  return restorer;
}

// Error handling patterns
try {
  await restorer.restore(tracker, options);
} catch (error) {
  if (error instanceof Error) {
    console.warn('Failed to restore widgets:', error.message);
    // Fallback to default layout or create new widgets
  }
}

// Graceful degradation
const layout = await restorer.fetch().catch(() => null);
if (!layout) {
  console.log('No saved layout found, using defaults');
  // Set up default layout
}