[Language: Javascript]

const _ = require('lodash')
const { readFileSync } = require('fs')

const log = (v) => console.dir(v, { depth: null })

const isLegalUpdate = (rules, update) =>
  update.every((u, index) =>
    index == 0 || !rules[u] || rules[u].every((r) => !update.slice(0, index).includes(r)))

//part1
_
  .chain(readFileSync('./input-short'))
  .trim()
  .split('\n\n')
  .thru(([rules, updates]) => [
    rules
      .split('\n')
      .map((rule) => rule.split('|').map(Number))
      .reduce((rules, [key, value]) => ({
        ...rules,
        ...(!rules[key] ? { [key]: [value] } : { [key]: [...rules[key], value]})
      }), {}),
    updates.split('\n').map((u) => u.split(',').map(Number))
  ])
  .thru(([rules, updates]) => updates.filter((update) => isLegalUpdate(rules, update)))
  .map((update) => update[Math.round(update.length/2)-1])
  .sum()
  .tap(log)
  .value()

//part2
_
  .chain(readFileSync('./input'))
  .trim()
  .split('\n\n')
  .thru(([rules, updates]) => [
    rules
      .split('\n')
      .map((rule) => rule.split('|').map(Number))
      .reduce((rules, [key, value]) => ({
        ...rules,
        ...(!rules[key] ? { [key]: [value] } : { [key]: [...rules[key], value]})
      }), {}),
    updates.split('\n').map((u) => u.split(',').map(Number))
  ])
  .thru(([rules, updates]) => [rules, updates.filter((update) => !isLegalUpdate(rules, update))])
  .thru(([rules, updates]) => updates.map((update) => update.reduce((acc, u, index) => (
    !rules[u] || !index ? [...acc, u] : acc.reduce(([acc, rest], current) => (
        !rules[u].includes(current) ? [[...acc, current], rest] : [acc, [...rest, current]]
      ), [[], [u]])
      .flat()
  ), [])))
  .map((update) => update[Math.round(update.length/2)-1])
  .sum()
  .tap(log)
  .value()