aurorabot/shared/games/blackjack/blackjack.plugin.ts

import type { GamePlugin, GameResult, GameOverResult, RoundSettlement } from "../types";
import type {
    BlackjackState, BlackjackAction, BlackjackPlayerView,
    BlackjackSpectatorView, PlayerHandView, PlayerSeatView,
    Card, Suit, Rank, PlayerHand, PlayerSeat,
} from "./blackjack.types";

// ── Constants ──

const MAX_HANDS_PER_PLAYER = 4; // max 3 splits
const RESHUFFLE_THRESHOLD = 15; // reshuffle when deck drops below this

// ── Card helpers ──

const SUITS: Suit[] = ["hearts", "diamonds", "clubs", "spades"];
const RANKS: Rank[] = ["A", "2", "3", "4", "5", "6", "7", "8", "9", "10", "J", "Q", "K"];

function createDeck(): Card[] {
    const deck: Card[] = [];
    for (const suit of SUITS) {
        for (const rank of RANKS) {
            deck.push({ suit, rank });
        }
    }
    return deck;
}

function shuffleDeck(deck: Card[]): Card[] {
    const shuffled = [...deck];
    for (let i = shuffled.length - 1; i > 0; i--) {
        const j = Math.floor(Math.random() * (i + 1));
        [shuffled[i]!, shuffled[j]!] = [shuffled[j]!, shuffled[i]!];
    }
    return shuffled;
}

function cardValue(rank: Rank): number {
    if (rank === "A") return 11;
    if (["K", "Q", "J"].includes(rank)) return 10;
    return parseInt(rank);
}

/** Calculate the best hand value (accounting for soft aces). */
export function handValue(hand: Card[]): number {
    let total = 0;
    let aces = 0;
    for (const card of hand) {
        total += cardValue(card.rank);
        if (card.rank === "A") aces++;
    }
    while (total > 21 && aces > 0) {
        total -= 10;
        aces--;
    }
    return total;
}

function isBust(hand: Card[]): boolean {
    return handValue(hand) > 21;
}

function isNaturalBlackjack(hand: Card[]): boolean {
    return hand.length === 2 && handValue(hand) === 21;
}

function drawCard(deck: Card[]): [Card, Card[]] {
    return [deck[0]!, deck.slice(1)];
}

/** Check if two cards can be split (same rank). */
function canSplitHand(hand: PlayerHand, totalHands: number): boolean {
    if (hand.cards.length !== 2) return false;
    if (hand.status !== "playing") return false;
    if (totalHands >= MAX_HANDS_PER_PLAYER) return false;
    return cardValue(hand.cards[0]!.rank) === cardValue(hand.cards[1]!.rank);
}

/** Check if a hand can be doubled down (exactly 2 cards, still playing). */
function canDoubleHand(hand: PlayerHand): boolean {
    return hand.cards.length === 2 && hand.status === "playing";
}

/** Play dealer hand: hit until 17+. */
function playDealerHand(dealerHand: Card[], deck: Card[]): { dealerHand: Card[]; deck: Card[] } {
    let hand = [...dealerHand];
    let remaining = [...deck];
    while (handValue(hand) < 17) {
        const [card, rest] = drawCard(remaining);
        hand = [...hand, card];
        remaining = rest;
    }
    return { dealerHand: hand, deck: remaining };
}

/** Find the next player who has a "playing" hand, starting after the given index. */
function findNextActivePlayer(state: BlackjackState, afterIndex: number): { playerIndex: number; handIndex: number } {
    for (let i = afterIndex + 1; i < state.turnOrder.length; i++) {
        const seat = state.seats[state.turnOrder[i]!];
        if (!seat) continue;
        const hi = seat.hands.findIndex(h => h.status === "playing");
        if (hi !== -1) return { playerIndex: i, handIndex: hi };
    }
    return { playerIndex: -1, handIndex: -1 };
}

/** Advance to the next hand within the current player, or to the next player. */
function advanceTurn(state: BlackjackState): BlackjackState {
    const activeId = state.turnOrder[state.activePlayerIndex];
    if (!activeId) return finishPlayerTurns(state);

    const seat = state.seats[activeId];
    if (!seat) return finishPlayerTurns(state);

    // Try next hand in current player's seat
    for (let hi = seat.activeHandIndex + 1; hi < seat.hands.length; hi++) {
        if (seat.hands[hi]!.status === "playing") {
            return {
                ...state,
                seats: {
                    ...state.seats,
                    [activeId]: { ...seat, activeHandIndex: hi },
                },
            };
        }
    }

    // No more hands for this player — move to next player
    const next = findNextActivePlayer(state, state.activePlayerIndex);
    if (next.playerIndex === -1) {
        return finishPlayerTurns(state);
    }

    const nextId = state.turnOrder[next.playerIndex]!;
    const nextSeat = state.seats[nextId]!;
    return {
        ...state,
        activePlayerIndex: next.playerIndex,
        seats: {
            ...state.seats,
            [activeId]: { ...seat, activeHandIndex: -1 },
            [nextId]: { ...nextSeat, activeHandIndex: next.handIndex },
        },
    };
}

/** Resolve a single hand against the dealer. */
function resolveHand(hand: PlayerHand, dealerHand: Card[]): PlayerHand {
    if (hand.result) return hand; // already resolved (bust, etc.)

    const dealerVal = handValue(dealerHand);
    const dealerBust = isBust(dealerHand);
    const playerVal = handValue(hand.cards);

    if (hand.status === "bust") {
        return { ...hand, result: "lose", resultReason: "Player busts" };
    }

    if (hand.status === "blackjack") {
        if (isNaturalBlackjack(dealerHand)) {
            return { ...hand, result: "push", resultReason: "Both have Blackjack" };
        }
        return { ...hand, result: "blackjack", resultReason: "Blackjack!" };
    }

    if (dealerBust) {
        return { ...hand, result: "win", resultReason: "Dealer busts" };
    }
    if (playerVal > dealerVal) {
        return { ...hand, result: "win", resultReason: "Higher hand" };
    }
    if (playerVal < dealerVal) {
        return { ...hand, result: "lose", resultReason: "Dealer has higher hand" };
    }
    return { ...hand, result: "push", resultReason: "Push" };
}

function calculateHandPayout(hand: Pick<PlayerHand, "bet" | "result">, betAmount: number): number {
    if (betAmount <= 0 || hand.result === null) return 0;

    switch (hand.result) {
        case "blackjack":
            return Math.round(hand.bet * betAmount * 2.5);
        case "win":
            return hand.bet * betAmount * 2;
        case "push":
            return hand.bet * betAmount;
        case "lose":
            return 0;
    }
}

function calculateHandNet(hand: Pick<PlayerHand, "bet" | "result">, betAmount: number): number | null {
    if (hand.result === null) return null;
    const wager = hand.bet * betAmount;
    return calculateHandPayout(hand, betAmount) - wager;
}

function calculateSeatRoundSettlement(seat: PlayerSeat, betAmount: number): RoundSettlement {
    const wager = seat.hands.reduce((sum, hand) => sum + (hand.bet * betAmount), 0);
    const payout = seat.hands.reduce((sum, hand) => sum + calculateHandPayout(hand, betAmount), 0);

    return {
        wager,
        payout,
        net: payout - wager,
    };
}

function calculateRoundSettlements(seats: Record<string, PlayerSeat>, betAmount: number): Record<string, RoundSettlement> {
    const settlements: Record<string, RoundSettlement> = {};

    for (const [playerId, seat] of Object.entries(seats)) {
        settlements[playerId] = calculateSeatRoundSettlement(seat, betAmount);
    }

    return settlements;
}

/** Transition to dealer turn + resolve all hands. */
function finishPlayerTurns(state: BlackjackState): BlackjackState {
    const anyStood = Object.values(state.seats).some(
        seat => seat.hands.some(h => h.status === "stood" || h.status === "blackjack"),
    );

    let dealerHand = state.dealerHand;
    let deck = state.deck;

    if (anyStood) {
        const dealer = playDealerHand(dealerHand, deck);
        dealerHand = dealer.dealerHand;
        deck = dealer.deck;
    }

    const resolvedSeats: Record<string, PlayerSeat> = {};
    for (const [id, seat] of Object.entries(state.seats)) {
        const resolvedHands = seat.hands.map(h => resolveHand(h, dealerHand));
        const settlement = calculateSeatRoundSettlement({ ...seat, hands: resolvedHands }, state.betAmount);

        resolvedSeats[id] = {
            ...seat,
            activeHandIndex: -1,
            hands: resolvedHands,
            cumulativePnl: (seat.cumulativePnl ?? 0) + settlement.net,
        };
    }

    return {
        ...state,
        deck,
        dealerHand,
        seats: resolvedSeats,
        activePlayerIndex: -1,
        phase: "resolved",
    };
}

/** Build the dealer hand for views — hole card hidden during player_turns/betting. */
function dealerVisibleHand(state: BlackjackState): Card[] {
    if (state.phase === "resolved") return state.dealerHand;
    if (state.dealerHand.length === 0) return [];
    return [state.dealerHand[0]!, { suit: "spades", rank: "?" as Rank }];
}

/** Convert internal PlayerHand to a view. */
function toHandView(hand: PlayerHand, betAmount: number): PlayerHandView {
    return {
        cards: hand.cards,
        value: handValue(hand.cards),
        status: hand.status,
        result: hand.result,
        resultReason: hand.resultReason,
        bet: hand.bet,
        wager: hand.bet * betAmount,
        payout: hand.result === null ? null : calculateHandPayout(hand, betAmount),
        net: calculateHandNet(hand, betAmount),
        fromSplit: hand.fromSplit,
    };
}

/** Convert internal PlayerSeat to a view. */
function toSeatView(seat: PlayerSeat, betAmount: number): PlayerSeatView {
    const settlement = seat.hands.every(hand => hand.result !== null)
        ? calculateSeatRoundSettlement(seat, betAmount)
        : null;

    return {
        hands: seat.hands.map(hand => toHandView(hand, betAmount)),
        activeHandIndex: seat.activeHandIndex,
        hasBet: seat.hasBet,
        totalWager: seat.hands.reduce((sum, hand) => sum + (hand.bet * betAmount), 0),
        roundNet: settlement?.net ?? null,
        cumulativePnl: seat.cumulativePnl,
    };
}

/** Deal cards to all seated players and the dealer. */
function dealRound(state: BlackjackState): BlackjackState {
    let deck = state.deck.length < RESHUFFLE_THRESHOLD
        ? shuffleDeck(createDeck())
        : [...state.deck];

    const seats: Record<string, PlayerSeat> = {};

    // Deal 2 cards to each player
    for (const pid of state.turnOrder) {
        const cards: Card[] = [];
        let card: Card;
        [card, deck] = drawCard(deck); cards.push(card);
        [card, deck] = drawCard(deck); cards.push(card);

        const isBlackjack = isNaturalBlackjack(cards);
        seats[pid] = {
            hands: [{
                cards,
                status: isBlackjack ? "blackjack" : "playing",
                result: null,
                resultReason: null,
                bet: 1,
                fromSplit: false,
            }],
            activeHandIndex: -1,
            hasBet: true,
            cumulativePnl: state.seats[pid]?.cumulativePnl ?? 0,
        };
    }

    // Deal 2 cards to dealer
    const dealerHand: Card[] = [];
    let card: Card;
    [card, deck] = drawCard(deck); dealerHand.push(card);
    [card, deck] = drawCard(deck); dealerHand.push(card);

    let newState: BlackjackState = {
        ...state,
        deck,
        dealerHand,
        seats,
        activePlayerIndex: 0,
        phase: "player_turns",
    };

    // Find first player that needs to act (skip natural blackjacks)
    const first = findNextActivePlayer(newState, -1);
    if (first.playerIndex === -1) {
        // All players have blackjack — resolve immediately
        return finishPlayerTurns(newState);
    }

    newState.activePlayerIndex = first.playerIndex;
    const firstId = newState.turnOrder[first.playerIndex]!;
    newState.seats = {
        ...newState.seats,
        [firstId]: { ...newState.seats[firstId]!, activeHandIndex: first.handIndex },
    };

    return newState;
}

/** Get the active player's active hand, or null. */
function getActiveHand(state: BlackjackState): { playerId: string; seat: PlayerSeat; hand: PlayerHand } | null {
    if (state.phase !== "player_turns" || state.activePlayerIndex < 0) return null;
    const playerId = state.turnOrder[state.activePlayerIndex];
    if (!playerId) return null;
    const seat = state.seats[playerId];
    if (!seat || seat.activeHandIndex < 0) return null;
    const hand = seat.hands[seat.activeHandIndex];
    if (!hand) return null;
    return { playerId, seat, hand };
}

// ── Plugin ──

export const blackjackPlugin: GamePlugin<BlackjackState, BlackjackAction> = {
    slug: "blackjack",
    name: "Blackjack",
    minPlayers: 1,
    maxPlayers: 6,
    manualStart: true,

    createInitialState(players: string[], options?: Record<string, unknown>): BlackjackState {
        const betAmount = typeof options?.betAmount === 'number' ? options.betAmount : 0;
        const seats: Record<string, PlayerSeat> = {};
        for (const pid of players) {
            seats[pid] = {
                hands: [],
                activeHandIndex: -1,
                hasBet: false,
                cumulativePnl: 0,
            };
        }

        return {
            deck: shuffleDeck(createDeck()),
            dealerHand: [],
            seats,
            turnOrder: [...players],
            activePlayerIndex: -1,
            phase: "betting",
            roundNumber: 1,
            betAmount,
        };
    },

    getActionCost(state: BlackjackState, action: BlackjackAction, _playerId: string): number {
        switch (action.type) {
            case "place_bet": return 1;
            case "split": return 1;
            case "double_down": return 1;
            default: return 0;
        }
    },

    isSpectatorAction(action: BlackjackAction): boolean {
        return action.type === "sit_down";
    },

    handleAction(state: BlackjackState, action: BlackjackAction, playerId: string): GameResult<BlackjackState> {
        switch (action.type) {
            case "place_bet":
                return handlePlaceBet(state, playerId);
            case "hit":
                return handleHit(state, playerId);
            case "stand":
                return handleStand(state, playerId);
            case "split":
                return handleSplit(state, playerId);
            case "double_down":
                return handleDoubleDown(state, playerId);
            case "leave_table":
                return handleLeaveTable(state, playerId);
            case "sit_down":
                return handleSitDown(state, playerId);
            default:
                return { ok: false, error: "Unknown action type" };
        }
    },

    getPlayerView(state: BlackjackState, playerId: string): BlackjackPlayerView {
        const visibleDealer = dealerVisibleHand(state);
        const seatsView: Record<string, PlayerSeatView> = {};
        for (const [id, seat] of Object.entries(state.seats)) {
            seatsView[id] = toSeatView(seat, state.betAmount);
        }

        const activeId = state.activePlayerIndex >= 0
            ? state.turnOrder[state.activePlayerIndex] ?? null
            : null;

        const isMyTurn = activeId === playerId && state.phase === "player_turns";
        const mySeat = state.seats[playerId];
        const myActiveHand = mySeat && mySeat.activeHandIndex >= 0
            ? mySeat.hands[mySeat.activeHandIndex] ?? null
            : null;

        // Determine active hand index for the view
        const activeHandIdx = activeId && state.seats[activeId]
            ? state.seats[activeId]!.activeHandIndex
            : -1;

        return {
            dealerHand: visibleDealer,
            dealerVisibleValue: state.dealerHand.length > 0 ? cardValue(state.dealerHand[0]!.rank) : 0,
            dealerFullValue: state.phase === "resolved" ? handValue(state.dealerHand) : null,
            seats: seatsView,
            turnOrder: state.turnOrder,
            activePlayerId: activeId,
            activeHandIndex: activeHandIdx,
            myPlayerId: playerId,
            phase: state.phase,
            canAct: isMyTurn,
            canSplit: isMyTurn && myActiveHand !== null && mySeat !== undefined && canSplitHand(myActiveHand, mySeat.hands.length),
            canDoubleDown: isMyTurn && myActiveHand !== null && canDoubleHand(myActiveHand),
            roundNumber: state.roundNumber,
            myCumulativePnl: mySeat?.cumulativePnl ?? 0,
        };
    },

    getSpectatorView(state: BlackjackState): BlackjackSpectatorView {
        const visibleDealer = dealerVisibleHand(state);
        const seatsView: Record<string, PlayerSeatView> = {};
        for (const [id, seat] of Object.entries(state.seats)) {
            seatsView[id] = toSeatView(seat, state.betAmount);
        }

        const activeId = state.activePlayerIndex >= 0
            ? state.turnOrder[state.activePlayerIndex] ?? null
            : null;

        const activeHandIdx = activeId && state.seats[activeId]
            ? state.seats[activeId]!.activeHandIndex
            : -1;

        return {
            dealerHand: visibleDealer,
            dealerVisibleValue: state.dealerHand.length > 0 ? cardValue(state.dealerHand[0]!.rank) : 0,
            dealerFullValue: state.phase === "resolved" ? handValue(state.dealerHand) : null,
            seats: seatsView,
            turnOrder: state.turnOrder,
            activePlayerId: activeId,
            activeHandIndex: activeHandIdx,
            phase: state.phase,
            roundNumber: state.roundNumber,
        };
    },

    isGameOver(state: BlackjackState): GameOverResult | null {
        if (state.turnOrder.length === 0) {
            return { winner: null, reason: "All players left the table", payouts: {} };
        }
        return null;
    },

    onPlayerDisconnect(state: BlackjackState, playerId: string): BlackjackState {
        return removePlayer(state, playerId);
    },
};

// ── Action handlers ──

function handlePlaceBet(state: BlackjackState, playerId: string): GameResult<BlackjackState> {
    if (state.phase !== "betting" && state.phase !== "resolved") {
        return { ok: false, error: "Cannot place bets right now" };
    }
    if (!state.turnOrder.includes(playerId)) {
        return { ok: false, error: "You are not seated at this table" };
    }

    let newState = { ...state };

    // Transition from resolved to betting for a new round
    if (state.phase === "resolved") {
        const deck = state.deck.length < RESHUFFLE_THRESHOLD
            ? shuffleDeck(createDeck())
            : state.deck;

        const resetSeats: Record<string, PlayerSeat> = {};
        for (const pid of state.turnOrder) {
            // Preserve cumulativePnl from previous round
            resetSeats[pid] = {
                hands: [],
                activeHandIndex: -1,
                hasBet: false,
                cumulativePnl: state.seats[pid]?.cumulativePnl ?? 0,
            };
        }

        newState = {
            ...state,
            deck,
            dealerHand: [],
            seats: resetSeats,
            activePlayerIndex: -1,
            phase: "betting",
            roundNumber: state.roundNumber + 1,
        };
    }

    const seat = newState.seats[playerId];
    if (!seat) return { ok: false, error: "Seat not found" };
    if (seat.hasBet) return { ok: false, error: "You have already placed your bet" };

    newState = {
        ...newState,
        seats: {
            ...newState.seats,
            [playerId]: { ...seat, hasBet: true },
        },
    };

    // Check if all seated players have bet
    const allBet = newState.turnOrder.every(pid => newState.seats[pid]?.hasBet);
    if (allBet) {
        const dealtState = dealRound(newState);
        if (dealtState.phase === "resolved") {
            // All players got blackjack — round is already over
            return { ok: true, state: dealtState, roundSettlements: calculateRoundSettlements(dealtState.seats, dealtState.betAmount) };
        }
        return { ok: true, state: dealtState };
    }

    return { ok: true, state: newState };
}

function handleHit(state: BlackjackState, playerId: string): GameResult<BlackjackState> {
    const active = getActiveHand(state);
    if (!active) return { ok: false, error: "Game is not in play" };
    if (active.playerId !== playerId) return { ok: false, error: "It's not your turn" };

    const [card, remaining] = drawCard(state.deck);
    const newCards = [...active.hand.cards, card];
    const bust = isBust(newCards);
    const got21 = handValue(newCards) === 21;

    const newHand: PlayerHand = {
        ...active.hand,
        cards: newCards,
        status: bust ? "bust" : got21 ? "stood" : "playing",
        result: bust ? "lose" : null,
        resultReason: bust ? "Player busts" : null,
    };

    const newHands = [...active.seat.hands];
    newHands[active.seat.activeHandIndex] = newHand;

    let newState: BlackjackState = {
        ...state,
        deck: remaining,
        seats: {
            ...state.seats,
            [playerId]: { ...active.seat, hands: newHands },
        },
    };

    if (bust || got21) {
        newState = advanceTurn(newState);
    }

    if (newState.phase === "resolved") {
        return { ok: true, state: newState, roundSettlements: calculateRoundSettlements(newState.seats, newState.betAmount) };
    }
    return { ok: true, state: newState };
}

function handleStand(state: BlackjackState, playerId: string): GameResult<BlackjackState> {
    const active = getActiveHand(state);
    if (!active) return { ok: false, error: "Game is not in play" };
    if (active.playerId !== playerId) return { ok: false, error: "It's not your turn" };

    const newHand: PlayerHand = { ...active.hand, status: "stood" };
    const newHands = [...active.seat.hands];
    newHands[active.seat.activeHandIndex] = newHand;

    let newState: BlackjackState = {
        ...state,
        seats: {
            ...state.seats,
            [playerId]: { ...active.seat, hands: newHands },
        },
    };

    newState = advanceTurn(newState);

    if (newState.phase === "resolved") {
        return { ok: true, state: newState, roundSettlements: calculateRoundSettlements(newState.seats, newState.betAmount) };
    }
    return { ok: true, state: newState };
}

function handleSplit(state: BlackjackState, playerId: string): GameResult<BlackjackState> {
    const active = getActiveHand(state);
    if (!active) return { ok: false, error: "Game is not in play" };
    if (active.playerId !== playerId) return { ok: false, error: "It's not your turn" };

    if (!canSplitHand(active.hand, active.seat.hands.length)) {
        return { ok: false, error: "Cannot split this hand" };
    }

    const [card1, deck1] = drawCard(state.deck);
    const [card2, deck2] = drawCard(deck1);

    const isAceSplit = active.hand.cards[0]!.rank === "A";

    const hand1Cards = [active.hand.cards[0]!, card1];
    const hand2Cards = [active.hand.cards[1]!, card2];

    // Split aces: auto-stand, and 21 on split is not blackjack
    const hand1Status = isAceSplit ? "stood" as const
        : handValue(hand1Cards) === 21 ? "stood" as const
        : "playing" as const;
    const hand2Status = isAceSplit ? "stood" as const
        : handValue(hand2Cards) === 21 ? "stood" as const
        : "playing" as const;

    const hand1: PlayerHand = {
        cards: hand1Cards,
        status: hand1Status,
        result: null,
        resultReason: null,
        bet: 1,
        fromSplit: true,
    };

    const hand2: PlayerHand = {
        cards: hand2Cards,
        status: hand2Status,
        result: null,
        resultReason: null,
        bet: 1,
        fromSplit: true,
    };

    const newHands = [...active.seat.hands];
    newHands.splice(active.seat.activeHandIndex, 1, hand1, hand2);

    // Find the first playable hand starting from the split position
    let newActiveHandIndex = active.seat.activeHandIndex;
    if (hand1.status !== "playing") {
        if (hand2.status !== "playing") {
            newActiveHandIndex = -1; // both auto-stood
        } else {
            newActiveHandIndex = active.seat.activeHandIndex + 1;
        }
    }

    let newState: BlackjackState = {
        ...state,
        deck: deck2,
        seats: {
            ...state.seats,
            [playerId]: {
                ...active.seat,
                hands: newHands,
                activeHandIndex: newActiveHandIndex,
            },
        },
    };

    // If both split hands auto-stood (aces), advance turn
    if (newActiveHandIndex === -1 || newHands[newActiveHandIndex]?.status !== "playing") {
        newState = advanceTurn(newState);
    }

    if (newState.phase === "resolved") {
        return { ok: true, state: newState, roundSettlements: calculateRoundSettlements(newState.seats, newState.betAmount) };
    }
    return { ok: true, state: newState };
}

function handleDoubleDown(state: BlackjackState, playerId: string): GameResult<BlackjackState> {
    const active = getActiveHand(state);
    if (!active) return { ok: false, error: "Game is not in play" };
    if (active.playerId !== playerId) return { ok: false, error: "It's not your turn" };

    if (!canDoubleHand(active.hand)) {
        return { ok: false, error: "Cannot double down on this hand" };
    }

    const [card, remaining] = drawCard(state.deck);
    const newCards = [...active.hand.cards, card];
    const bust = isBust(newCards);

    const newHand: PlayerHand = {
        ...active.hand,
        cards: newCards,
        bet: 2,
        status: bust ? "bust" : "stood",
        result: bust ? "lose" : null,
        resultReason: bust ? "Player busts" : null,
    };

    const newHands = [...active.seat.hands];
    newHands[active.seat.activeHandIndex] = newHand;

    let newState: BlackjackState = {
        ...state,
        deck: remaining,
        seats: {
            ...state.seats,
            [playerId]: { ...active.seat, hands: newHands },
        },
    };

    newState = advanceTurn(newState);

    if (newState.phase === "resolved") {
        return { ok: true, state: newState, roundSettlements: calculateRoundSettlements(newState.seats, newState.betAmount) };
    }
    return { ok: true, state: newState };
}

function handleLeaveTable(state: BlackjackState, playerId: string): GameResult<BlackjackState> {
    if (!state.turnOrder.includes(playerId)) {
        return { ok: false, error: "You are not seated at this table" };
    }

    const newState = removePlayer(state, playerId);
    return { ok: true, state: newState };
}

function handleSitDown(state: BlackjackState, playerId: string): GameResult<BlackjackState> {
    if (state.phase !== "betting") {
        return { ok: false, error: "You can only sit down during the betting phase" };
    }
    if (state.turnOrder.includes(playerId)) {
        return { ok: false, error: "You are already seated" };
    }
    if (state.turnOrder.length >= 6) {
        return { ok: false, error: "Table is full" };
    }

    return {
        ok: true,
        state: {
            ...state,
            turnOrder: [...state.turnOrder, playerId],
            seats: {
                ...state.seats,
                [playerId]: {
                    hands: [],
                    activeHandIndex: -1,
                    hasBet: false,
                    cumulativePnl: 0,
                },
            },
        },
    };
}

/** Remove a player from the table, handling mid-round cleanup. */
function removePlayer(state: BlackjackState, playerId: string): BlackjackState {
    if (!state.turnOrder.includes(playerId)) return state;

    const playerIdx = state.turnOrder.indexOf(playerId);
    const newTurnOrder = state.turnOrder.filter(id => id !== playerId);
    const { [playerId]: _, ...remainingSeats } = state.seats;

    let newState: BlackjackState = {
        ...state,
        turnOrder: newTurnOrder,
        seats: remainingSeats,
    };

    // Adjust activePlayerIndex if we're in player_turns
    if (state.phase === "player_turns") {
        const wasActive = state.activePlayerIndex === playerIdx;

        if (wasActive) {
            // The leaving player was the active player — find next
            // Since we removed the player, the index effectively points to the next player
            const adjustedIndex = playerIdx >= newTurnOrder.length ? newTurnOrder.length - 1 : playerIdx;
            newState.activePlayerIndex = adjustedIndex;

            // Try to find a playing hand from this adjusted index onward
            const next = findNextActivePlayer(
                { ...newState, activePlayerIndex: adjustedIndex - 1 },
                adjustedIndex - 1,
            );

            if (next.playerIndex === -1) {
                if (newTurnOrder.length > 0) {
                    newState = finishPlayerTurns(newState);
                }
            } else {
                newState.activePlayerIndex = next.playerIndex;
                const nextId = newTurnOrder[next.playerIndex]!;
                newState.seats = {
                    ...newState.seats,
                    [nextId]: { ...newState.seats[nextId]!, activeHandIndex: next.handIndex },
                };
            }
        } else if (playerIdx < state.activePlayerIndex) {
            // Player was before the active player — shift index down
            newState.activePlayerIndex = state.activePlayerIndex - 1;
        }
    }

    return newState;
}