lanspread/crates/lanspread-tauri-deno-ts/src/lib/frontendBootstrap.ts

import { type AsyncCleanup } from './asyncOwnership';

export interface FrontendCloseRequest {
    preventDefault: () => void;
}

export interface FrontendBootstrapOptions {
    registerCloseRequested: (
        handler: (event: FrontendCloseRequest) => void | Promise<void>,
    ) => Promise<AsyncCleanup>;
    disposeOwners: () => Promise<void>;
    drainPersistence: () => Promise<void>;
    destroyWindow: () => Promise<void>;
    render: () => void;
    reportFailure: (message: string, error: unknown) => void;
}

const report = (
    options: FrontendBootstrapOptions,
    message: string,
    error: unknown,
): void => {
    try {
        options.reportFailure(message, error);
    } catch {
        // Reporting must not turn a handled bootstrap failure into a rejection.
    }
};

const runHandled = async (
    options: FrontendBootstrapOptions,
    message: string,
    operation: () => void | Promise<void>,
): Promise<void> => {
    try {
        await operation();
    } catch (error) {
        report(options, message, error);
    }
};

/**
 * Installs the webview's close boundary before mounting any React hooks.
 * Registration failure closes the empty realm instead of running without an
 * ownership boundary.
 */
export const bootstrapFrontend = async (
    options: FrontendBootstrapOptions,
): Promise<boolean> => {
    let closing: Promise<void> | undefined;
    let publishCloseCleanup!: (cleanup: AsyncCleanup) => void;
    const closeCleanupReady = new Promise<AsyncCleanup>(resolve => {
        publishCloseCleanup = resolve;
    });

    const finalizeWindow = (): Promise<void> => {
        if (closing !== undefined) return closing;

        // Calling every operation closes its admission or starts its cleanup
        // synchronously, before any asynchronous drain is awaited.
        const ownerDrain = runHandled(
            options,
            'Failed to dispose frontend window owners:',
            options.disposeOwners,
        );
        const persistenceDrain = runHandled(
            options,
            'Failed to drain frontend persistence:',
            options.drainPersistence,
        );
        const listenerDrain = runHandled(
            options,
            'Failed to unregister the window close listener:',
            async () => {
                const cleanup = await closeCleanupReady;
                await cleanup();
            },
        );

        closing = Promise.all([
            ownerDrain,
            persistenceDrain,
            listenerDrain,
        ])
            .then(() => runHandled(
                options,
                'Failed to destroy the frontend window:',
                options.destroyWindow,
            ));
        return closing;
    };

    try {
        const cleanupCloseListener = await options.registerCloseRequested(event => {
            event.preventDefault();
            return finalizeWindow();
        });
        publishCloseCleanup(cleanupCloseListener);
    } catch (error) {
        publishCloseCleanup(() => {});
        report(options, 'Failed to install the frontend close-drain boundary:', error);

        // Nothing has rendered, but close both admissions in case a module-level
        // owner was registered while loading the bundle, then explicitly await
        // destruction of the empty webview.
        await finalizeWindow();
        return false;
    }

    if (closing !== undefined) {
        // A close request may arrive after the native listener is callable but
        // before its registration promise acknowledges ownership. The active
        // finalizer now owns the late cleanup; never mount React into a realm
        // that has already begun closing.
        await closing;
        return false;
    }

    try {
        options.render();
    } catch (error) {
        report(options, 'Failed to render the frontend:', error);
        await finalizeWindow();
        return false;
    }
    return true;
};