path.ts

// doesn't work K1 evaluates to never. I assume it's because `obj` isn't immediately available
// export function path<S extends object, K1 extends keyof S, K2 extends keyof S[K1], K3 extends keyof S[K1][K2]>(
//   p: [K1, K2, K3]
// ): (obj: S) => S[K1][K2][K3];

// doesn't work can't index that far
// export function path<S extends object>(p: [keyof S, keyof S[keyof S], keyof S[keyof S[keyof S]]): (obj: S) => S[keyof S][keyof S[keyof S]];
export function path<S extends object>(p: [keyof S, keyof S[keyof S]]): (obj: S) => S[keyof S][keyof S[keyof S]];
export function path<S extends object>(p: [keyof S]): (obj: S) => S[keyof S];

export function path<S extends object, K1 extends keyof S>(p: [K1]): (obj: S) => S[K1];

interface IAddress {
  number: string;
  street: string;
  zip: number;
  state: string;
  city: string;
}

interface IUser {
  name: string;
  address: IAddress;
  friends: Array<IUser>;
}

const w: IUser = {
  address: { number: '123', street: 'easy st', zip: 90210, state: 'AK', city: 'blah' },
  friends: [],
  name: 'derp'
};

const x: IUser = {
  address: { number: '123', street: 'easy st', zip: 90210, state: 'AK', city: 'blah' },
  friends: [w],
  name: 'nope'
};

path(['friends'])(x);