pk-lab-xhs/web/lib/bracket.js

export function buildMatches(pool) {
  const matches = [];
  for (let index = 0; index < pool.length; index += 2) {
    matches.push({
      left: pool[index],
      right: pool[index + 1] || null,
      winner: pool[index + 1] ? null : pool[index]
    });
  }
  return matches;
}

export function createBracket(candidates) {
  return {
    round: 1,
    pool: [...candidates],
    matches: buildMatches(candidates),
    eliminated: [],
    decisions: [],
    offset: 0
  };
}

export function chooseMatch(state, matchIndex, side) {
  const match = state.matches[matchIndex];
  if (!match?.right || match.winner) return { state, finished: false };
  const winner = side === 'right' ? match.right : match.left;
  const loser = side === 'right' ? match.left : match.right;
  const matches = state.matches.map((item, index) =>
    index === matchIndex ? { ...item, winner } : item
  );
  let next = {
    ...state,
    matches,
    eliminated: [loser, ...state.eliminated],
    decisions: [...state.decisions, {
      round: state.round,
      left_id: match.left.id,
      right_id: match.right.id,
      winner_id: winner.id
    }]
  };
  if (matches.every(item => item.winner)) {
    const pool = matches.map(item => item.winner);
    if (pool.length === 1) return { state: { ...next, pool }, finished: true };
    next = { ...next, round: state.round + 1, pool, matches: buildMatches(pool), offset: 0 };
  }
  return { state: next, finished: false };
}

export function firstOpenMatch(state) {
  return state.matches.findIndex(match => match.right && !match.winner);
}