import { AnyRouter } from './Router'
import { inferFetcher, inferRoutes } from './helpers'
import { Config, DEFAULT_CONFIG } from './config'

export type RouteFetcher<TRouter extends AnyRouter> = inferFetcher<
  inferRoutes<TRouter>
>

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

export type CreateRouteFetcherReturn<TRoutes extends AnyRouter> =
  UnionToIntersection<RouteFetcher<TRoutes>>

export type Fetcher = (url: string, params: string) => Promise<Response>

export type FetcherConfiguration = {
  /**
   * Base url of the nextjs backend without '/api'.
   */
  baseUrl: string

  /**
   * Fetcher implementation.
   */
  fetcher?: Fetcher
} & Partial<Config>

const defaultFetcher: Fetcher = (url, params) =>
  fetch(url, {
    method: 'POST',
    body: params,
  })

export const createRouteFetcher = <TRouter extends AnyRouter>({
  baseUrl,
  stringify = DEFAULT_CONFIG.stringify,
  parser = DEFAULT_CONFIG.parser,
  fetcher = defaultFetcher,
}: FetcherConfiguration): CreateRouteFetcherReturn<TRouter> =>
  ((path: unknown, params: unknown) =>
    fetcher(`${baseUrl}/api/${path}`, stringify({ input: params }))
      .then((r) => r.text())
      .then((v) => parser(v).result)) as unknown as CreateRouteFetcherReturn<
    inferRoutes<TRouter>
  >