A Function That Executes An Array Of Function Call Instructions In Typescript Using A Helper Function That Generates A Branded Function Call Instruction

inspectRules.ts

export type InspectRulesArgs<T extends (...args: any) => any> =
  | T[]
  | [T, ...Parameters<T>][];
export type InspectRulesResult = "pending" | "approved" | "denied";

declare const brand: unique symbol;

type Branded<T, Brand extends string> = T & {
  [brand]: Brand;
}

const callTuple = <Fn extends (...args: any[]) => InspectRulesResult>(
  fn: Fn,
  ...args: Parameters<Fn>
) => [fn, ...args] as const as Branded<readonly [Fn, ...Parameters<Fn>], "withHelper">;


const inspectRules = (
  ...rules: ReadonlyArray<
    | (() => InspectRulesResult)
    | Branded<readonly [(...args: any[]) => InspectRulesResult, ...any[]], "withHelper">
  >
): InspectRulesResult => {
  const pendingRules = rules.map((rule) => {
    if (typeof rule === "function") {
      return rule();
    } else {
      const [func, ...args] = rule;
      return func(...args);
    }
  });

  if (pendingRules.includes("denied")) {
    return "denied";
  }
  if (pendingRules.includes("pending")) {
    return "pending";
  }
  return "approved";
};

inspectRules(
  () => "pending" as const,
  // @ts-expect-error helper not used
  [(foo: string) => "approved" as const, ""] as const,
  callTuple((foo: string) => "approved" as const, ""),
  // @ts-expect-error wrong arg
  callTuple((foo: number) => "approved" as const, ""),
)