ecs-observable/examples/blackjack/game.ts

// ── Blackjack game logic (pure functions, no ECS dependency) ──

export const SUITS = ["♠", "♥", "♦", "♣"] as const;
export const RANKS = [
  "A",
  "2",
  "3",
  "4",
  "5",
  "6",
  "7",
  "8",
  "9",
  "10",
  "J",
  "Q",
  "K",
] as const;

export interface CardData {
  rank: string;
  suit: string;
}

// ── Hand evaluation ──────────────────────────────────
/** Numeric value of a single card rank. */
export function rankValue(rank: string): number {
  if (rank === "A") return 11;
  if (rank === "K" || rank === "Q" || rank === "J") return 10;
  return parseInt(rank, 10);
}

/** Best total for a hand (aces count as 1 or 11). */
export function handValue(cards: CardData[]): number {
  let total = 0;
  let aces = 0;
  for (const c of cards) {
    total += rankValue(c.rank);
    if (c.rank === "A") aces++;
  }
  while (total > 21 && aces > 0) {
    total -= 10;
    aces--;
  }
  return total;
}

export function isBust(cards: CardData[]): boolean {
  return handValue(cards) > 21;
}

export function isBlackjack(cards: CardData[]): boolean {
  return cards.length === 2 && handValue(cards) === 21;
}

export function isSoft(cards: CardData[]): boolean {
  let total = 0;
  let aces = 0;
  for (const c of cards) {
    total += rankValue(c.rank);
    if (c.rank === "A") aces++;
  }
  return aces > 0 && total <= 21;
}

// ── Dealer logic ─────────────────────────────────────
/** Dealer must hit on soft 17 in this variant. */
export function dealerShouldHit(cards: CardData[]): boolean {
  const val = handValue(cards);
  if (val < 17) return true;
  if (val === 17 && isSoft(cards)) return true;
  return false;
}

// ── Outcome ──────────────────────────────────────────
export type Outcome = "win" | "lose" | "push" | "blackjack";

export function determineOutcome(
  playerCards: CardData[],
  dealerCards: CardData[],
): Outcome {
  if (isBust(playerCards)) return "lose";
  if (isBust(dealerCards)) return "win";
  if (isBlackjack(playerCards) && !isBlackjack(dealerCards)) return "blackjack";
  const pv = handValue(playerCards);
  const dv = handValue(dealerCards);
  if (pv > dv) return "win";
  if (pv < dv) return "lose";
  return "push";
}

/** Payout multiplier. Blackjack pays 3:2, win pays 1:1. */
export function payout(outcome: Outcome, bet: number): number {
  switch (outcome) {
    case "blackjack":
      return Math.floor(bet * 1.5);
    case "win":
      return bet;
    case "push":
      return 0;
    case "lose":
      return -bet;
  }
}