bracketeering.js

const {upTo} = require("@unction/complete")
const {length} = require("@unction/complete")
const {reverse} = require("@unction/complete")
const {shuffle} = require("@unction/complete")
const {sample} = require("@unction/complete")
const {reduceKeys} = require("@unction/complete")
const {reduceWithValueKey} = require("@unction/complete")
const {mapValues} = require("@unction/complete")
const {last} = require("@unction/complete")
const {first} = require("@unction/complete")

const chunk =
  (maximum) =>
    (list) =>
      reduceWithValueKey(
        (accumulated) =>
          (item) =>
            (index) => {
              const [latestChunk, ...previousChunks] = accumulated;

              if ((length(latestChunk) !== maximum) && (length(list) === index + 1)) {
                return reverse([[...latestChunk, item], ...previousChunks]);
              }

              if (length(list) === index + 1) {
                return reverse([[item], ...accumulated]);
              }

              if (length(latestChunk) !== maximum) {
                return [[...latestChunk, item], ...previousChunks]
              }

              return [[item], ...accumulated];
            }
      )(
        [[]]
      )(
        list
      )

// Pairings = Array<Match>
// ReadyPlayers = Array<Player>
// RoundList => ReadyPlayers
function discoverWinners (rounds) {
  return mapValues(battle)(last(rounds))
}
// ReadyPlayers => Pairings
function generateRound (players) {
  return chunk(2)(shuffle(players))
}

// Match = [Player, Player]
// Match => Winner
function battle([left, right]) {
  if (right) {
    return sample([left, right])
  }

  // A buy round
  return left
}

// ReadyPlayers => Player
function fight(players) {
  return reduceKeys((accumulated) => (index) => {
    if (accumulated.length == index - 1) {
      return first(accumulated)
    }

    return [...accumulated, generateRound(discoverWinners(accumulated))]
  })([generateRound(players)])(upTo(Math.floor(players.length / 2)))
}

console.log(
  fight(["Jesus", "Salino", "Richard", "Hong", "Janus", "Alejandro", "Cortez", "Yun", "Inhani"])
)