import { curry, curryN } from './curry.js'
import { dispatch } from './fantasy-land.js'
import { concat as iconcat, iter } from './list.js'

/** @import { Fn, Morphism, InferredMorphism, Predicate } from './types.js' */

/**
 * @template T
 * @param {T} x
 * @returns {x}
 */
export const id = x => x

/**
 * @param {...Fn} fns
 * @returns {(x: any) => any}
 */
export const pipe = (...fns) => x => fns.reduce((v, f) => f(v), x)

export const concat = curry(dispatch(['fantasy-land/concat', 'concat'],
  (b, a) => iconcat(iter(a), iter(b))
))

export const compose = curry(dispatch(['fantasy-land/compose', 'compose'],
  /**
   * @template T, U, V
   * @param {Morphism<U, V>} f
   * @param {Morphism<T, U>} g
   * @param {T} x
   * @returns V
   */
  (f, g, x) => chain(g, chain(f, x))
))

/**
 * @template T
 * @param {T | T[]} a
 * @Returns {T[]}
 */
export const liftA = a => Array.isArray(a) ? a : [a]

/**
 * @template T, U, R
 * @param {(x: T, y: U) => R} binary 
 * @param {T} x
 * @param {U} y
 * @returns {R}
 */
export const liftF = curry((binary, x, y) => binary(x, y))

/**
 * @param {number} a
 * @param {number} b
 * @returns {number}
 */
export const add = (a, b) => a + b

/**
 * @template T
 * @param {T} x
 * @returns {() => T}
 */
export const thunk = x => () => x

/**
 * @template T, U
 * @template {(a: T, b: U, ...rest: any[]) => any} F
 * @param {F} fn 
 * @returns {(b: U, a: T, ...rest: any[]) => any}
 */
export function flip(fn) {
  return curryN(fn.length, function(a, b) {
    const args = Array.prototype.slice.call(arguments, 0)
    args[0] = b
    args[1] = a
    return fn.apply(this, args)
  })
}

export const ifElse = curry(
  /**
   * @template T
   * @param {Predicate<T>} pred 
   * @param {InferredMorphism<T>} pass 
   * @param {InferredMorphism<T>} fail 
   * @param {T} x 
   */
  (pred, pass, fail, x) => (
    pred(x) ? pass(x) : fail(x)))

export const when = curry(
  /**
   * @template T
   * @param {Predicate<T>} pred 
   * @param {InferredMorphism<T>} pass
   * @param {T} x 
   */
  (pred, pass, x) => ifElse(pred, pass, id, x))

export const unless = curry(
  /**
   * @template T
   * @param {Predicate<T>} pred
   * @param {InferredMorphism<T>} fail
   * @param {T} x
   */
  (pred, fail, x) => ifElse(pred, id, fail, x))

/**
 * @template A, B
 * @template {Morphism<A, B>} [F=Morphism<A, B>]
 * @typedef {(f: F, a: A) => B} StaticMorphism
 */

export const ap = curry(dispatch(['fantasy-land/ap', 'ap'],
  /**
    * @template A, B
    * @template {Morphism<A, B>} Ap
    * @param {Ap} f 
    * @param {{ ap: Ap } | Ap} a
    */
  (f, a) => {
    const fs = liftA(f)
    const args = liftA(a)

    const xs = fs.reduce((acc, f) => (
      concat(acc, iter(map(f, args)))
    ), [])

    return [...xs]
  }))

export const chain = curry(dispatch(['fantasy-land/chain', 'chain'],
  (f, a) => f(a)
))

export const map = curry(dispatch(['fantasy-land/map', 'map'],
  (f, a) => chain(f, a)
))

export const reduce = curry(dispatch(['fantasy-land/reduce', 'reduce'],
  (f, acc, xs) => xs.reduce(f, acc)
))

export const repeat = curry((n, x) => {
  const results = []

  for (let i = n; i > 0; i--) {
    results.push(x)
  }

  return results
})