import wretch, { WretchAddon, WretchResponseChain } from "wretch"

// The addon part //

// Boilerplate type definition
interface TypedJsonAddonResolver<Data> {
  // Mimics the .json() call, with an extra <Data> generic parameter
  json: <T, C extends TypedJsonAddonResolver<Data>, R, CallbackReturn = never>(
    this: C & WretchResponseChain<T, C, R>,
    callback?: (data: Data) => CallbackReturn
  ) => Promise<[CallbackReturn] extends [never] ? Data : CallbackReturn>
}

// Addon implementation
function typedJsonAddon<Data>():  WretchAddon<unknown, TypedJsonAddonResolver<Data>> {
  return {
    resolver: {
      async json(callback) {
        return this.res(res => res.json().then(json => callback ? callback(json) : json))
      }
    }
  }
}

// ------------- //

// Shape of the objects served from the jsonplaceholder website
type Post = {
  userId: number;
  id: number;
  title: string;
  body: string;
}

const client = wretch("https://jsonplaceholder.typicode.com")
const api = {
  posts: {
    // register the addon inside the member functions and define the return types
    get: (id: number) => client.addon(typedJsonAddon<Post>()).get(`/posts/${id}`),
    getAll: () => client.addon(typedJsonAddon<Post[]>()).get("/posts")
  }
}

// 'posts' is correctly typed as an array of posts 👍
const posts = await api.posts.getAll().badRequest(console.error).notFound(console.error).json()
console.log(posts.map(post => post.title).join("\n- "))
// title is correctly typed as a string 👍
const title = await api.posts
  .get(1)
  .badRequest(console.error)
  .notFound(console.error)
  // post is correctly typed as a Post object 👍
  .json(post => post.title)
console.log(title.toLowerCase())

interface ConflictErrorCatcherAddon {
	conflict: <T, C extends ConflictErrorCatcherAddon, R>(
		this: C & WretchResponseChain<T, C, R>,
		cb: WretchErrorCallback<T, C, R>,
	) => this;
}

// Addon implementation
function conflictErrorAddon(): WretchAddon<unknown, ConflictErrorCatcherAddon> {
	return {
		resolver: {
			conflict(cb) {
				return this.error(409, cb);
			},
		},
	};
}