ExtractParams.ts

// Unility types begin

type Split<
  S extends string,
  Delimiter extends string
> = S extends `${infer Head}${Delimiter}${infer Tail}`
  ? [Head, ...Split<Tail, Delimiter>]
  : S extends Delimiter
  ? []
  : [S];

type Simplify<T> = { [KeyType in keyof T]: T[KeyType] } & {};

type UnionToIntersection<U> = (U extends any ? (k: U) => void : never) extends (
  k: infer I
) => void
  ? I
  : never;

// Unility types end

// Path types begin

type ExtraxtPathParam<P extends string> = Extract<
  Split<P, "/">[number],
  `:${string}`
>;

type ExtractParamEnum<E extends string> = Split<E, "|">[number];

type ExtraxtParamName<P extends string> = P extends `${infer RP}?`
  ? ExtraxtParamName<RP> extends { [name in infer N]: infer V }
    ? { [name in Extract<N, string>]?: V }
    : never
  : P extends `:${infer N}(${infer E})`
  ? { [name in N]: ExtractParamEnum<E> }
  : P extends `:${infer N}`
  ? { [name in N]: string }
  : never;

type ExtractParams<Path extends string> = Simplify<
  UnionToIntersection<ExtraxtParamName<ExtraxtPathParam<Path>>>
>;

// Path types end

// TEST

type Expect<T extends true> = T;
type Equal<X, Y> = (<T>() => T extends X ? 1 : 2) extends <T>() => T extends Y
  ? 1
  : 2
  ? true
  : false;

// --- //

type Params =
  ExtractParams<"/url/:filter(popular|latest)/:userId/:tag(daily|weekly|monthly)?/:search?">;

type tests = [
  Expect<Equal<ExtractParams<"/url/search">, {}>>,
  Expect<
    Equal<
      ExtractParams<"/url/:search?">,
      {
        search?: string;
      }
    >
  >,
  Expect<
    Equal<
      ExtractParams<"/url/:search">,
      {
        search: string;
      }
    >
  >,
  Expect<
    Equal<
      ExtractParams<"/url/:filter(popular|latest)">,
      {
        filter: "popular" | "latest";
      }
    >
  >,
  Expect<
    Equal<
      ExtractParams<"/url/:filter(popular|latest)?">,
      {
        filter?: "popular" | "latest";
      }
    >
  >,
  Expect<
    Equal<
      ExtractParams<"/url/:filter(popular|latest)/:userId/:tag(daily|weekly|monthly)?/:search?">,
      {
        filter: "popular" | "latest";
        userId: string;
        tag?: "daily" | "weekly" | "monthly";
        search?: string;
      }
    >
  >
];

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