11.ts

// The Readonly<> utility type could replace the use of readonly on the key
type SantaListProtector<ArbitaryType> = {
  readonly [Key in keyof ArbitaryType]: ArbitaryType[Key] extends
    | Record<string, unknown>
    | unknown[]
    ? SantaListProtector<ArbitaryType[Key]>
    : ArbitaryType[Key];
};

// TESTS
import { Expect, Equal } from "type-testing";

type test_0_actual = SantaListProtector<{
  hacksore: () => "naughty";
  trash: string;
  elliot: {
    penny: boolean;
    candace: {
      address: {
        street: {
          name: "candy cane way";
          num: number;
        };
        k: "hello";
      };
      children: [
        "harry",
        {
          saying: ["hey"];
        }
      ];
    };
  };
}>;
type test_0_expected = {
  readonly hacksore: () => "naughty";
  readonly trash: string;
  readonly elliot: {
    readonly penny: boolean;
    readonly candace: {
      readonly address: {
        readonly street: {
          readonly name: "candy cane way";
          readonly num: number;
        };
        readonly k: "hello";
      };
      readonly children: readonly [
        "harry",
        {
          readonly saying: readonly ["hey"];
        }
      ];
    };
  };
};
type test_0 = Expect<Equal<test_0_expected, test_0_actual>>;

type test_1_actual = SantaListProtector<{
  theo: () => "naughty";
  prime: string;
  netflix: {
    isChill: boolean;
  };
}>;
type test_1_expected = {
  readonly theo: () => "naughty";
  readonly prime: string;
  readonly netflix: {
    readonly isChill: boolean;
  };
};
type test_1 = Expect<Equal<test_1_expected, test_1_actual>>;