import { ValidatorSpec } from "envalid";
/**
 * Usage:
 *  1.) Add a `<script src="%PUBLIC_URL%/env.js"></script>` tag to your
 *      index.html's <head> at the top most position, i.e.:
 *         <!DOCTYPE html>
 *            <html lang="en">
 *            <head>
 *               <meta charset="utf-8" />
 *               <script src="%PUBLIC_URL%/env.js"></script>
 *          ...
 *  2.) Create your own configuration singleton module in a separate file:
 *
 *          import { fromWeb, requiredStr } from "@protomodule/instruments"
 *
 *          export const config = fromWeb({
 *            REACT_APP_API_URL: requiredStr(),
 *          })
 *
 *  3.) Access environment variables type-safe like so `const BASE_API_URI = config.REACT_APP_API_URL`
 *  4.) You can add your variables to `.env` when running `yarn start`
 *                                    OR
 *      You can set *actual environment variables* when running as a Docker container
 */
declare global {
    interface Window {
        env: {
            [key: string]: string;
        };
    }
}
export declare const yesNo: (spec?: import("envalid").Spec<boolean> | undefined) => ValidatorSpec<boolean>;
export declare const requiredStr: (spec?: import("envalid").Spec<string> | undefined) => ValidatorSpec<string>;
export declare type Schema<T> = {
    [K in keyof T]: ValidatorSpec<T[K]>;
};
export declare const fromWeb: <T>(schema: Schema<T>) => Readonly<T & import("envalid").CleanedEnvAccessors>;