joke-app/packages/games/src/marble/bot.ts

/**
 * 주사위 땅따먹기 computer player: buys and builds while it keeps a cash reserve against the tolls ahead, sells the
 * cheapest thing that covers a debt, escapes the island early in the game, flies to the best square on 우주여행,
 * never proposes trades and only accepts clearly good ones.
 */
import type { BotStrategy } from '../bots/types';
import { answerRequests, best, pick, playable, typeOf } from '../bots/policy';
import { GROUPS, SPACES, investment, type Level } from './board';
import type { MarbleAction, MarbleView } from './index';

type Act<T extends MarbleAction['type']> = Extract<MarbleAction, { type: T }>;

export const marbleBot: BotStrategy<MarbleView, MarbleAction> = ({ me, view, legal, random }) => {
  const req = answerRequests(legal);
  if (req) return req;
  const find = <T extends MarbleAction['type']>(t: T) => legal.find((a) => a.type === t) as Act<T> | undefined;
  const meP = view.players.find((p) => p.id === me)!;
  const cash = meP.cash;
  const owner = new Map(view.owned.map((o) => [o.pos, o]));
  const theirs = view.owned.filter((o) => o.owner !== me);

  // Keep enough cash for a bad landing in the next lap; less as the round limit approaches
  // (then cash and land count the same for the final ranking).
  const maxToll = Math.max(0, ...theirs.map((o) => o.toll));
  let reserve = Math.min(150, Math.max(20, 0.6 * maxToll));
  if (view.maxRounds > 0) reserve *= Math.min(1, (view.maxRounds - view.round + 1) / 5);
  /** Owning the rest of a colour group makes this square worth more (and can win with 독점). */
  const groupBonus = (pos: number) => {
    const g = SPACES[pos]!.group;
    if (!g) return 0;
    const mine = GROUPS[g].filter((p) => owner.get(p)?.owner === me).length;
    return mine * (view.options.monopolyWin ? 20 : 8);
  };

  // Trade offered to me: accept only when I get clearly more than I give (book value).
  const respond = legal.filter((a) => a.type === 'TRADE_RESPOND') as Act<'TRADE_RESPOND'>[];
  if (respond.length && view.trade) {
    const worth = (o: { lands: number[]; cash: number }) => o.cash + o.lands.reduce((s, p) => s + investment(p, (owner.get(p)?.level ?? 0) as Level), 0);
    const good = worth(view.trade.give) >= 1.3 * worth(view.trade.take) + 5 && cash + view.trade.give.cash - view.trade.take.cash >= 0;
    return respond.find((a) => a.accept === good) ?? respond[0]!;
  }

  // Debt: the smallest single sale that covers it, else the biggest sale (top stages before whole lands).
  const sells = legal.filter((a) => a.type === 'SELL') as Act<'SELL'>[];
  if (sells.length && view.my?.sell) {
    const short = view.debt?.short ?? 0;
    const amount = (a: Act<'SELL'>) => view.my!.sell!.find((o) => o.pos === a.pos && o.what === a.what)?.amount ?? 0;
    const covers = sells.filter((a) => amount(a) >= short);
    if (covers.length) return best(covers, (a) => -amount(a) - groupBonus(a.pos) + (a.what === 'top' ? 1 : 0), random);
    return best(sells, (a) => amount(a) + (a.what === 'top' ? 100 : 0) - groupBonus(a.pos), random);
  }

  // Landed on a square: buy / build / take over while the reserve stays.
  const d = view.my?.decide;
  if (d) {
    const buy = find('BUY');
    if (buy && d.buy !== null && cash - d.buy >= reserve - groupBonus(d.pos)) return buy;
    const build = find('BUILD');
    if (build && d.build && cash - d.build.cost >= reserve) return build;
    const take = find('TAKEOVER');
    if (take && d.takeover !== null && cash - d.takeover >= 1.5 * reserve + 20) return take;
    return find('PASS') ?? pick(playable(legal), random);
  }

  // 우주여행: pick the destination worth most.
  const space = legal.filter((a) => a.type === 'SPACE_TRAVEL') as Act<'SPACE_TRAVEL'>[];
  if (space.length && view.spacePreview) {
    const prev = new Map(view.spacePreview.map((p) => [p.dest, p]));
    const score = (dest: number): number => {
      const p = prev.get(dest);
      const sp = SPACES[dest]!;
      let v = (p?.salary ? view.options.salary : 0) - (p?.toll ?? 0) * 1.5;
      const o = owner.get(dest);
      if (sp.price !== null && !o && cash - (p?.fare ?? 0) - sp.price >= reserve) v += 15 + sp.price / 2 + groupBonus(dest);
      if (o?.owner === me && sp.kind === 'city' && o.level < 3) v += 8;
      if (sp.kind === 'fundIn') v += view.fund;
      if (sp.kind === 'island') v -= 30;
      if (sp.kind === 'fundOut') v -= 15;
      return v + random();
    };
    return best(space, (a) => score(a.dest), random);
  }

  // Island: use an escape card, or pay the fee while the game is young and cash is plentiful.
  if (view.my?.island) {
    const card = find('USE_ESCAPE_CARD');
    if (card) return card;
    const fee = find('PAY_ISLAND_FEE');
    const early = view.maxRounds === 0 || view.round <= view.maxRounds / 2;
    if (fee && early && cash - (view.my.island.fee ?? 0) >= 2 * reserve) return fee;
  }
  // Never start trades: roll.
  const rest = playable(legal).filter((a) => typeOf(a) !== 'PROPOSE_TRADE');
  return find('ROLL') ?? pick(rest.length ? rest : legal, random);
};