Typed idx

typed-idx.ts

interface IPost {
  title: string;
  comments?: string[];
}

interface IUser {
  posts: IPost[];
}

interface IData {
  users: IUser[];
}

const idxf = (o: {}, ...actions: Array<({ }) => {}>) =>
  actions
    .filter((item) => item)
    .reduce((acc, curr) => acc ? curr(acc) : null, o);

const data: IData = {
  users: [{
    posts: [
      { title: 'One', comments: ['Comment one', 'Comment two'] },
      { title: 'Two' }]
  }]
};

const idxf6 = <TData, T1, T2, T3, T4, T5, TResult>(
  data: TData,
  f1: (a: TData) => T1,
  f2: (a: T1) => T2,
  f3: (a: T2) => T3,
  f4: (a: T3) => T4,
  f5: (a: T4) => T5,
  f6: (a: T5) => TResult) =>
    idxf(data, f1, f2, f3, f4, f5, f6) as TResult;

const idxf5 = <TData, T1, T2, T3, T4, TResult>(
  data: TData,
  f1: (a: TData) => T1,
  f2: (a: T1) => T2,
  f3: (a: T2) => T3,
  f4: (a: T3) => T4,
  f5: (a: T4) => TResult) =>
    idxf(data, f1, f2, f3, f4, f5) as TResult;

const idxf4 = <TData, T1, T2, T3, TResult>(
  data: TData,
  f1: (a: TData) => T1,
  f2: (a: T1) => T2,
  f3: (a: T2) => T3,
  f4: (a: T3) => TResult) =>
    idxf(data, f1, f2, f3, f4) as TResult;

const comment1 = idxf6(data,
  (d: Pick<IData, 'users'>) => d.users,
  (users: IUser[]) => users[0],
  (user: Pick<IUser, 'posts'>) => user.posts,
  (posts: IPost[]) => posts[0],
  (post: Pick<IPost, 'comments'>) => post.comments,
  (comments: string[]) => comments[0]);

const comments = idxf5<IData, IUser[], IUser, IPost[], IPost, string[]>(data,
  (d) => d.users,
  (users) => users[0],
  (user) => user.posts,
  (posts) => posts[0],
  (post) => post.comments);

const noComments = idxf5(data,
  (d) => d.users,
  (users) => users[3],
  (user) => user.posts,
  (posts) => posts[0],
  (post) => post.comments);

const post = idxf4(data,
  (d) => d.users,
  (users: IUser[]) => users[0],
  (user) => user.posts,
  (posts: IPost[]) => posts[0]);

console.log("Comment 1", comment1);
console.log("Comments", comments);
console.log("No comments", noComments);
console.log("Post", post);