/**
 * Environment variable source compatible with `process.env`, Worker bindings,
 * and edge runtime environment objects.
 *
 * @example
 * ```ts
 * const env: EnvSource = {
 *   NODE_ENV: "staging",
 *   FLAG_NEW_CHECKOUT: "true",
 * };
 * ```
 */
export type EnvSource = Readonly<Partial<Record<string, string | undefined>>>;

/**
 * Selects the active environment for flag defaults.
 *
 * Declared defaults matching `NODE_ENV` win. Otherwise, `development` is used
 * only for `NODE_ENV=development`; every other value falls back to `production`.
 *
 * @example
 * ```ts
 * const environment = resolveEnvironment(
 *   { NODE_ENV: "staging" },
 *   { development: true, staging: true, production: false }
 * );
 * ```
 */
export function resolveEnvironment(
  env: EnvSource = process.env,
  defaults?: Readonly<Record<string, boolean | undefined>>
): string {
  const environment = env.NODE_ENV;

  if (environment !== undefined && defaults?.[environment] !== undefined) {
    return environment;
  }

  return environment === "development" ? "development" : "production";
}