import { Function1 } from "./abstractions"

export function cachedFn<A, B>(f: Function1<A, B>): Function1<A, B>
export function cachedFn(f: Function): any {
  let previous: [any[], any] | null = null
  return function (...args: any[]) {
    if (previous !== null && equals(previous[0], args)) {
      return previous[1]
    }
    const result = f(...args)
    previous = [args, result]
    return result
  }
}

function equals(xs: any[], ys: any[]) {
  if (xs.length !== ys.length) throw Error("Argument count mismatch")
  for (let i = 0; i < xs.length; i++) {
    if (xs[i] !== ys[i]) return false
  }
  return true
}