day12.ts

import { Equal, Expect } from "../../testing-types";

/* Solution */

type TupleBefore<T extends unknown[], U> = T extends [infer F, ...infer R]
  ? Equal<F, U> extends true
    ? []
    : [F, ...TupleBefore<R, U>]
  : [];

type FindSanta<T extends unknown[]> = TupleBefore<
  T,
  "🎅🏼"
>["length"] extends T["length"]
  ? never
  : TupleBefore<T, "🎅🏼">["length"];

/* Challenge */

type Forest0 = ["🎅🏼", "🎄", "🎄", "🎄"];
type test_0_actual = FindSanta<Forest0>;
//   ^?
type test_0_expected = 0;
type test_0 = Expect<Equal<test_0_expected, test_0_actual>>;

type Forest1 = ["🎄", "🎅🏼", "🎄", "🎄", "🎄", "🎄"];
type test_1_actual = FindSanta<Forest1>;
//   ^?
type test_1_expected = 1;
type test_1 = Expect<Equal<test_1_expected, test_1_actual>>;

type Forest2 = ["🎄", "🎄", "🎅🏼", "🎄"];
type test_2_actual = FindSanta<Forest2>;
//   ^?
type test_2_expected = 2;
type test_2 = Expect<Equal<test_2_expected, test_2_actual>>;

type Forest3 = ["🎄", "🎄", "🎄", "🎅🏼", "🎄"];
type test_3_actual = FindSanta<Forest3>;
//   ^?
type test_3_expected = 3;
type test_3 = Expect<Equal<test_3_expected, test_3_actual>>;

type Forest4 = ["🎄", "🎄", "🎄", "🎄"];
type test_4_actual = FindSanta<Forest4>;
//   ^?
type test_4_expected = never;
type test_4 = Expect<Equal<test_4_expected, test_4_actual>>;