episode mapping test.js

const functions = [
  (e, target, source) => Math.round(e * target / source),
  (e, target, source) => Math.floor(e * target / source),
  (e, target, source) => Math.ceil(e * target / source),
  (e, target, source) => 1 + Math.round((e - 1) * target / source),
  (e, target, source) => 1 + Math.floor((e - 1) * target / source),
  (e, target, source) => 1 + Math.ceil((e - 1) * target / source),
  (e, target, source) => Math.round((e - 1) * target / source),
  (e, target, source) => Math.floor((e - 1) * target / source),
  (e, target, source) => Math.ceil((e - 1) * target / source),
  (e, target, source) => Math.round((e - 1) * target / source) - 1,
  (e, target, source) => Math.floor((e - 1) * target / source) - 1,
  (e, target, source) => Math.ceil((e - 1) * target / source) - 1,
  (e, target, source) => Math.round(e * (target + 1) / (source + 1)),
  (e, target, source) => Math.floor(e * (target + 1) / (source + 1)),
  (e, target, source) => Math.ceil(e * (target + 1) / (source + 1)),
  (e, target, source) => Math.round(e * (target + 1) / (source + 1)) + 1,
  (e, target, source) => Math.floor(e * (target + 1) / (source + 1)) + 1,
  (e, target, source) => Math.ceil(e * (target + 1) / (source + 1)) + 1,
  (e, target, source) => Math.round(e * (target + 1) / (source + 1)) - 1,
  (e, target, source) => Math.floor(e * (target + 1) / (source + 1)) - 1,
  (e, target, source) => Math.ceil(e * (target + 1) / (source + 1)) - 1,
  (e, target, source) => Math.round((e - 1) * (target + 1) / (source + 1)),
  (e, target, source) => Math.floor((e - 1) * (target + 1) / (source + 1)),
  (e, target, source) => Math.ceil((e - 1) * (target + 1) / (source + 1)),
  (e, target, source) => Math.round((e - 1) * (target + 1) / (source + 1)) + 1,
  (e, target, source) => Math.floor((e - 1) * (target + 1) / (source + 1)) + 1,
  (e, target, source) => Math.ceil((e - 1) * (target + 1) / (source + 1)) + 1,
  (e, target, source) => Math.round((e - 1) * (target + 1) / (source + 1)) - 1,
  (e, target, source) => Math.floor((e - 1) * (target + 1) / (source + 1)) - 1,
  (e, target, source) => Math.ceil((e - 1) * (target + 1) / (source + 1)) - 1,
  (e, target, source) => Math.round((e + 1) * (target + 1) / (source + 1)),
  (e, target, source) => Math.floor((e + 1) * (target + 1) / (source + 1)),
  (e, target, source) => Math.ceil((e + 1) * (target + 1) / (source + 1)),
  (e, target, source) => Math.round((e + 1) * (target + 1) / (source + 1)) + 1,
  (e, target, source) => Math.floor((e + 1) * (target + 1) / (source + 1)) + 1,
  (e, target, source) => Math.ceil((e + 1) * (target + 1) / (source + 1)) + 1,
  (e, target, source) => Math.round((e + 1) * (target + 1) / (source + 1)) - 1,
  (e, target, source) => Math.floor((e + 1) * (target + 1) / (source + 1)) - 1,
  (e, target, source) => Math.ceil((e + 1) * (target + 1) / (source + 1)) - 1,
  (e, target, source) => Math.round(e * (target - 1) / (source - 1)),
  (e, target, source) => Math.floor(e * (target - 1) / (source - 1)),
  (e, target, source) => Math.ceil(e * (target - 1) / (source - 1)),
  (e, target, source) => Math.round(e * (target - 1) / (source - 1)) + 1,
  (e, target, source) => Math.floor(e * (target - 1) / (source - 1)) + 1,
  (e, target, source) => Math.ceil(e * (target - 1) / (source - 1)) + 1,
  (e, target, source) => Math.round(e * (target - 1) / (source - 1)) - 1,
  (e, target, source) => Math.floor(e * (target - 1) / (source - 1)) - 1,
  (e, target, source) => Math.ceil(e * (target - 1) / (source - 1)) - 1,
  (e, target, source) => Math.round((e - 1) * (target - 1) / (source - 1)),
  (e, target, source) => Math.floor((e - 1) * (target - 1) / (source - 1)),
  (e, target, source) => Math.ceil((e - 1) * (target - 1) / (source - 1)),
  (e, target, source) => Math.round((e - 1) * (target - 1) / (source - 1)) + 1,
  (e, target, source) => Math.floor((e - 1) * (target - 1) / (source - 1)) + 1,
  (e, target, source) => Math.ceil((e - 1) * (target - 1) / (source - 1)) + 1,
  (e, target, source) => Math.round((e - 1) * (target - 1) / (source - 1)) - 1,
  (e, target, source) => Math.floor((e - 1) * (target - 1) / (source - 1)) - 1,
  (e, target, source) => Math.ceil((e - 1) * (target - 1) / (source - 1)) - 1,
  (e, target, source) => Math.round((e + 1) * (target - 1) / (source - 1)),
  (e, target, source) => Math.floor((e + 1) * (target - 1) / (source - 1)),
  (e, target, source) => Math.ceil((e + 1) * (target - 1) / (source - 1)),
  (e, target, source) => Math.round((e + 1) * (target - 1) / (source - 1)) + 1,
  (e, target, source) => Math.floor((e + 1) * (target - 1) / (source - 1)) + 1,
  (e, target, source) => Math.ceil((e + 1) * (target - 1) / (source - 1)) + 1,
  (e, target, source) => Math.round((e + 1) * (target - 1) / (source - 1)) - 1,
  (e, target, source) => Math.floor((e + 1) * (target - 1) / (source - 1)) - 1,
  (e, target, source) => Math.ceil((e + 1) * (target - 1) / (source - 1)) - 1
]

const wrappers = [
  (fn, e, target, source) => fn(e, target, source),
  (fn, e, target, source) => e === source ? target : fn(e, target, source)
]

const assertions = [
  // Check conversion between Atachin'chi episode ranges from Amazon's to AniList's
  [[1, 330, 662], 0],
  [[2, 330, 662], 1],
  [[661, 330, 662], 329],
  [[662, 330, 662], 330],
  // Check conversion for a normal series
  [[1, 12, 12], 1],
  [[2, 12, 12], 2],
  [[6, 12, 12], 6],
  [[11, 12, 12], 11],
  [[12, 12, 12], 12]
]

const passedFunctions = []
for (const wrapper of wrappers) {
  const wrapperIndex = wrappers.indexOf(wrapper)
  for (const fn of functions) {
    const fnIndex = functions.indexOf(fn)
    let failed = false
    for (const [input, expected] of assertions) {
      const result = wrapper(fn, ...input)
      if (result !== expected) {
        console.log(wrapperIndex + ':' + fnIndex + ' failed: fn(', ...input.map(e => [',', e]).flat().slice(1), ') returned', result, 'expected', expected)
        failed = true
        break
      }
    }
    if (!failed) passedFunctions.push([ wrapper, fn ])
  }
}

// If some function passed the above test, print the entire Atachin'chi mapping and the functions
if (passedFunctions.length) {
  for (let i = 1; i <= 662; i++) {
    console.log(i, ...passedFunctions.map(fn => fn[0](fn[1], i, 330, 662)))
  }

  console.log('passedFunctions:', passedFunctions.map(e => e.map(e => e.toString())))
}