aoc-15.js

const fs = require('fs');

const [WALL, EMPTY, ELF, GOB] = [0, 1, 'elf', 'gob'];
const maxDist = 200;

const ents = [];
const coord = (x, y) => ({ x, y });
const delta = (pos, x, y) => ({ x: pos.x + x, y: pos.y + y });
const cell = pos => board[pos.y][pos.x];
const setCell = (pos, v) => board[pos.y][pos.x] = v;
const addEnt = (x, y, type) => {
  const ent = { x, y, hp: 200, type };
  ents.push(ent);
  return ent;
}

console._log = console.constructor.prototype.log.bind(console);
console.log = () => {};
const board = 
  fs.readFileSync('input', 'utf-8')
  .split('\n')
  .map((l, y) => 
    l.split('')
    .map((c, x) => {
      switch (c) {
        case '#': return WALL;
        case '.': return EMPTY;
        case 'E': return addEnt(x, y, ELF);
        case 'G': return addEnt(x, y, GOB);
      }
      console.log('wut', c, x, y)
    }));

const log = () => {
  let str = board.map(l => l.map(c => 
      c === WALL ? '#'
    : c === EMPTY ? '.'
    : c.type === ELF ? 'E'
    : c.type === GOB ? 'G'
    : '?'
  ).join('')).join('\n')
  console._log(str);
  console._log(ents.map(e => [e.type, e.hp]).join('|'))
}


const getNeighbours = pos => [
  delta(pos, 0, -1),
  delta(pos, -1, 0),
  delta(pos, 1, 0),
  delta(pos, 0, 1)
];

const checkTile = (ent, pos) => {

  const checked = [ent, pos];
  let toCheck = getNeighbours(pos);
  let nextCheck = [];

  let dist = 0;
  distCheck: 
  while(++dist < maxDist) {
    for(const pos of toCheck) {
      const v = cell(pos);

      if (v === EMPTY) {
        const neighbours = getNeighbours(pos)
        .filter(p => {
          if (checked.some(q => q.x === p.x && q.y === p.y) || nextCheck.some(q => q.x === p.x && q.y === p.y)) {
            return false;
          }

          const c = cell(p);

          return c === EMPTY || c.dead || (c.type && c.type !== ent.type);
        });

        nextCheck.push(...neighbours)
      }

      if (!v.dead && v.type && v.type !== ent.type) {
        break distCheck;
      }

      checked.push(pos);
    };
    toCheck = nextCheck;
    nextCheck = [];
  }

  return dist;
}
const getNextTile = ent => {
  const tiles = getNeighbours(ent)
    .filter(p => cell(p) === EMPTY)
    .map(p => ({ x: p.x, y: p.y, v: checkTile(ent, p) }))
    .filter(c => c.v < maxDist);

  return tiles.sort((a, b) => a.v - b.v || a.y - b.y || a.x - b.x)[0];
}

const getNextEnemy = ent => {
  return getNeighbours(ent)
    .map(p => cell(p))
    .filter(c => !c.dead && c.type && c.type !== ent.type)
    .sort((a, b) => a.hp - b.hp || a.y - b.y || a.x - b.x)
    [0];
}
  
let rounds = 0;
loop: while(++rounds < 10000) {
  ents.sort((a, b) => a.y - b.y || a.x - b.x);

  log()

  for(let i = 0; i < ents.length; ++i) {
    const ent = ents[i];
    console.log('trying', i, ent);
    console.group();

    if (ent.dead) {
      console.groupEnd();
      continue;
    }

    const enemy = getNextEnemy(ent);

    if (enemy) {
      console.log({ enemy })
      enemy.hp -= 3;

      if (enemy.hp <= 0) {
        enemy.dead = true;
      }
    } else {
      const nextTile = getNextTile(ent);
      console.log({ nextTile })

      if (nextTile) {
        setCell(ent, EMPTY);

        ent.x = nextTile.x;
        ent.y = nextTile.y;

        setCell(ent, ent);
      }

      const enemy = getNextEnemy(ent);

      if (enemy) {
        enemy.hp -= 3;

        if (enemy.hp <= 0) {
          enemy.dead = true;
        }
      }
    }
    console.groupEnd();
  }

  let type = ents[0].type;
  let allTypesSame = true;
  for(let i = 0; i < ents.length; ++i) {
    const ent = ents[i];

    if (ent.dead) {
      setCell(ent, EMPTY);
      ents.splice(i, 1);
      --i;
    } else {
      if (type !== ent.type) {
        allTypesSame = false;
      }
    }
  }

  if (allTypesSame) {
    console._log('ended in ' + rounds);
    const sum = ents.reduce((a, e) => a + e.hp, 0);
    console._log(sum, sum * (rounds-1));
    //console._log(ents);

    break;
  }
}