const VAR_PATTERN = /\$\{([A-Za-z_][A-Za-z0-9_]*)(:-([^}]*))?\}/g;

export function interpolateEnv(
  raw: string,
  env: Record<string, string | undefined>
): string {
  return raw.replace(VAR_PATTERN, (_match, name: string, hasDefault: string | undefined, fallback: string | undefined) => {
    const value = env[name];
    if (value !== undefined) return value;
    if (hasDefault !== undefined) return fallback ?? "";
    throw new Error(`Missing environment variable "${name}" referenced in config.yml`);
  });
}