common-proxy.cts

import type * as DefaultImport from 'npm-default-import' with { 'resolution-mode': 'import' };

type ImportableHandler<Handler extends (...args: any[]) => unknown> =
    | Handler
    | { default: { default: Handler } }
    | { default: Handler };

let defaultImportProm: Promise<typeof DefaultImport> | null = null;

export const commonProxy = <Handler extends (...args: any[]) => unknown>(
    promiseOfHandler: ImportableHandler<Handler> | Promise<ImportableHandler<Handler>>
): ((...args: Parameters<Handler>) => Promise<Awaited<ReturnType<Handler>>>) => {
    defaultImportProm ??= import('npm-default-import');
    return async (...args): Promise<Awaited<ReturnType<Handler>>> => {
        const [{ defaultImport }, mod] = await Promise.all([defaultImportProm!, promiseOfHandler]);

        const handler = defaultImport(mod);
        return handler(...args) as Awaited<ReturnType<Handler>>;
    };
};