import { it, assert } from 'folktest'
import { Option, Result } from '../../src/index.js'

const Monads = [Option, Result]

const leftIdentity = (M, a, f) => {
  assert(M(a).chain(f).equals(f(a)))
}

const rightIdentity = (M, m) => {
  assert(m.chain(M).equals(m))
}

const associativity = (m, f, g) => {
  assert(m.chain(f).chain(g).equals(m.chain(x => f(x).chain(g))))
}

export const prove = (M, m, a, f, g) => {
  leftIdentity(M, a, f)
  rightIdentity(M, m)
  associativity(m, f, g)
}

const inc = F => x => F.of(x + 1)
const dbl = F => x => F.of(x * 2)

export const Tests = [
  it('unit is a left identity', () => {
    Monads.forEach(monad => {
      const f = inc(monad)
      // NOTE: okay but like, shut up
      // @ts-ignore
      assert(monad.of(1).chain(f).equals(f(1)))
    })
    //prove(
    //  Ctr, M
    //  Ctr(1), m
    //  1, a
    //  x => Ctr(x + 1), f
    //  x => Ctr(x * 2) g
    //)
  }),

  it('unit is a right identity', () => {
    Monads.forEach(monad => {
      const m = monad.of(1)

      assert(
        // NOTE: i heard this one already
        // @ts-ignore
        m.chain(monad.of).equals(m)
      )
    })
  }),

  it('unit is associative', () => {
    Monads.forEach(monad => {
      const m = monad.of(1)
      const f = inc(monad)
      const g = dbl(monad)
      console.log(m.chain(f))

      // NOTE: it was better the first time
      // @ts-ignore
      const x = m.chain(f).chain(g)
      // @ts-ignore
      const y = m.chain(x => f(x).chain(g))

      assert(
        x.equals(y)
      )
    })
  })
]