import test from 'node:test'
import assert from 'node:assert/strict'
import { nextUint32, pure, map, flatMap, intBelow, run } from '../src/random.js'
import { loadFixture, freeze } from './helpers.js'

const fixtureTests = (name, f) => {
  const fx = loadFixture(name)
  fx.cases.forEach((c) =>
    test(`m04 ${fx.function}: ${c.name}`, () => assert.deepStrictEqual(f(...freeze(c.args)), c.expected)))
}

fixtureTests('m04-random', (seed) => run(nextUint32, seed))
fixtureTests('m04-int-below', (n, seed) => run(intBelow(n), seed))

test('m04 the recorded steps chain: each step starts from the previous step\'s seed', () => {
  const cases = loadFixture('m04-random').cases
  cases.forEach((c, i) => {
    if (!c.name.endsWith('-step-1')) assert.equal(c.args[0], cases[i - 1].expected[1])
  })
})

test('m04 pure returns its value and leaves the seed alone', () =>
  assert.deepStrictEqual(run(pure('x'), 99), ['x', 99]))

test('m04 map applies f to the value and keeps the seed from the underlying step', () => {
  const [v, s] = run(nextUint32, 5)
  assert.deepStrictEqual(run(map(nextUint32, (x) => x + 1), 5), [v + 1, s])
})

test('m04 map with the identity function changes nothing', () =>
  assert.deepStrictEqual(run(map(nextUint32, (x) => x), 5), run(nextUint32, 5)))

test('m04 flatMap threads the seed through both steps', () => {
  const [a, s1] = run(nextUint32, 5)
  const [b, s2] = run(nextUint32, s1)
  assert.deepStrictEqual(run(flatMap(nextUint32, (x) => map(nextUint32, (y) => [x, y])), 5), [[a, b], s2])
})

test('m04 flatMap with pure on the left or right changes nothing', () => {
  assert.deepStrictEqual(run(flatMap(pure(3), (x) => map(nextUint32, (v) => v + x)), 5), run(map(nextUint32, (v) => v + 3), 5))
  assert.deepStrictEqual(run(flatMap(nextUint32, pure), 5), run(nextUint32, 5))
})

test('m04 intBelow always lands in [0, n)', () => {
  const draws = (n, seed, count) =>
    count === 0 ? [] : ((([v, s]) => [v, ...draws(n, s, count - 1)])(run(intBelow(n), seed)))
  ;[1, 2, 7, 400].forEach((n) =>
    draws(n, 123, 50).forEach((v) => assert.ok(Number.isInteger(v) && v >= 0 && v < n, `${v} not in [0, ${n})`)))
})

test('m04 running a Random does not mutate anything: same seed, same answer', () =>
  assert.deepStrictEqual(run(nextUint32, 8), run(nextUint32, 8)))