import { Functor } from './functor'
import { Cartesian } from './cartesian'
import { $, HKT, kind } from '.'

export interface Apply<F extends HKT> extends Cartesian<F>, Functor<F> {
  ap<A, B>(fab: $<F, (a: A) => B>, fa: $<F, A>): $<F, B>
}

export type ApplyInstances = keyof typeof Apply

export namespace Apply {
  const __name = "Apply"
}

export function ap<F extends ApplyInstances, A, B>(fab: $<F, (a: A) => B>, fa: $<F, A>): $<F, B> {
  let instance = Apply[kind<F>(fab)] as Apply<F>
  let faba = instance.product<(a: A) => B, A>(fab, fa)
  return instance.map((aba: [(a: A) => B, A]) => aba[0](aba[1]), faba)
}

export function ap2<F extends ApplyInstances, A, B, C>(fabc: $<F, (a: A, b: B) => C>, fa: $<F, A>, fb: $<F, B>): $<F, C> {
  let instance = Apply[kind<F>(fabc)] as Apply<F>
  return ap<F, [A, B], C>(
    instance.map(
      (f: (a: A, b: B) => C) => (([a, b]: [A, B]) => f(a, b))
      , fabc)
    , instance.product<A, B>(fa, fb)
  )
}