document.addEventListener('DOMContentLoaded', () => {
    // ====== CONSTANTS & STATE ======
    const suits = ['♥', '♦', '♣', '♠'];
    const values = ['A','2','3','4','5','6','7','8','9','10','J','Q','K'];
    const PILE_BORDER_WIDTH = 2;
    const SPACING_FACE_DOWN = 10;
    const SPACING_FACE_UP = 32;

    let DRAW_COUNT = 3;

    let deck, stock, waste, foundations, tableau;
    let cardElements = {};
    let dragged = { cards: [], sourcePile: null, startIndex: -1, ghostEl: null, offsetX: 0, offsetY: 0 };
    const history = [];
    
    let isAutoCompleting = false;
    let autoCompleteInterval = null;
    let isDealing = false;
    let score = 0;
    let highScore = 0;
    let isActive = false;

    const CARD_BACKS = [
        { id: 'waves', name: 'Blue Waves', className: 'card-back-waves' },
        { id: 'herringbone', name: 'Green Herringbone', className: 'card-back-herringbone' },
        { id: 'sunset', name: 'Gradient Sunset', className: 'card-back-sunset' },
        { id: 'linen', name: 'Cozy Linen', className: 'card-back-linen' },
        { id: 'nordic', name: 'Nordic Cross', className: 'card-back-nordic' },
        { id: 'midnight', name: 'Midnight Grid', className: 'card-back-midnight' },
        { id: 'diamond', name: 'Diamond Weave', className: 'card-back-diamond' },
        { id: 'royal', name: 'Royal Blue Stripe', className: 'card-back-royal' },
        { id: 'fade', name: 'Matte Gradient Fade', className: 'card-back-fade' }
    ];

    // ====== DOM ======
    const klondikeBoard = document.getElementById('klondike-board');
    const restartBtn = document.getElementById('restart-btn');
    const winMessage = document.getElementById('win-message');
    const undoBtn = document.getElementById('undo-btn');
    const drawSelect = document.getElementById('draw-select');
    const cardBackModal = document.getElementById('card-back-modal');
    const openModalBtn = document.getElementById('change-back-btn');
    const closeModalBtn = document.getElementById('modal-close-btn');
    const modalOverlay = document.querySelector('.modal-overlay');
    const cardBackOptionsContainer = document.getElementById('card-back-options');
    const checkMovesBtn = document.getElementById('check-moves-btn');
    const autoCompleteBtn = document.getElementById('autocomplete-btn');
    const scoreEl = document.getElementById('current-score');
    const highScoreEl = document.getElementById('high-score');


    // ====== SAVE / LOAD ======
    function saveGame() {
        const gameState = { stock, waste, foundations, tableau, history, drawCount: DRAW_COUNT, score };
        localStorage.setItem('solitaire-save-game', JSON.stringify(gameState));
    }
    function loadGame() {
        const savedGame = localStorage.getItem('solitaire-save-game');
        if (!savedGame) return false;
        try {
            const gameState = JSON.parse(savedGame);
            stock = gameState.stock;
            waste = gameState.waste;
            foundations = gameState.foundations;
            tableau = gameState.tableau;
            history.length = 0;
            history.push(...gameState.history);
            DRAW_COUNT = gameState.drawCount || 3;
            score = gameState.score || 0;
            highScore = parseInt(localStorage.getItem('solitaire-high-score'), 10) || 0;
            drawSelect.value = DRAW_COUNT;
            Object.values(cardElements).forEach(el => el.remove());
            cardElements = {};
            const allCards = [...stock, ...waste, ...foundations.flat(), ...tableau.flat()];
            allCards.forEach(cardData => {
                if (!cardElements[cardData.id]) {
                    const el = createCardElement(cardData);
                    cardElements[cardData.id] = el;
                    klondikeBoard.appendChild(el);
                }
            });
            winMessage.classList.add('hidden');
            updateScoreDisplay();
            updateBoard(true);
            return true;
        } catch (e) {
            console.error("Failed to load saved game:", e);
            localStorage.removeItem('solitaire-save-game');
            return false;
        }
    }

    // ====== UNDO SNAPSHOTS ======
    const snapshotState = () => JSON.stringify({ stock, waste, foundations, tableau, score });
    const restoreState = (json) => {
        const s = JSON.parse(json);
        stock = s.stock; waste = s.waste; foundations = s.foundations; tableau = s.tableau;
        score = s.score !== undefined ? s.score : score;
    };
    const pushHistory = () => {
        if (history.length > 50) history.shift();
        history.push(snapshotState());
    };

    // ====== SETUP ======
    function initState() {
        score = 0;
        highScore = parseInt(localStorage.getItem('solitaire-high-score'), 10) || 0;
        updateScoreDisplay();

        isAutoCompleting = false;
        if (autoCompleteInterval) clearInterval(autoCompleteInterval);
        
        Object.values(cardElements).forEach(el => el.remove());
        cardElements = {};
        deck = []; stock = []; waste = [];
        foundations = [[],[],[],[]];
        tableau = Array(7).fill(null).map(()=>[]);
        suits.forEach(suit => values.forEach(value => {
            deck.push({ suit, value, faceUp:false, id:`${value}${suit}-${Math.random().toString(36).slice(2,8)}` });
        }));
        for (let i = deck.length - 1; i > 0; i--) {
            const j = Math.floor(Math.random()*(i+1));
            [deck[i], deck[j]] = [deck[j], deck[i]];
        }
        deck.forEach(cardData => {
            const el = createCardElement(cardData);
            cardElements[cardData.id] = el;
            klondikeBoard.appendChild(el);
            // Initially position cards at the stock location to animate out from there
            const stockEl = document.getElementById('stock');
            if (stockEl) {
                const rect = stockEl.getBoundingClientRect();
                const boardRect = klondikeBoard.getBoundingClientRect();
                el.style.top = `${rect.top - boardRect.top + PILE_BORDER_WIDTH}px`;
                el.style.left = `${rect.left - boardRect.left + PILE_BORDER_WIDTH}px`;
            }
        });

        // Separate cards for tableau and stock
        const tableauCards = [];
        for (let i=0; i<7; i++){
            for (let j=i; j<7; j++) {
                const card = deck.pop();
                tableau[j].push(card);
                tableauCards.push({ card, pileIndex: j });
            }
        }
        stock = deck;

        winMessage.classList.add('hidden');
        history.length = 0;
        pushHistory();
        
        // Start dealing animation
        dealTableauSequentially(tableauCards);
    }

    async function dealTableauSequentially(cardsToDeal) {
        isDealing = true;
        // Turn off interactivity during deal
        klondikeBoard.style.pointerEvents = 'none';

        for (let i = 0; i < cardsToDeal.length; i++) {
            const { card, pileIndex } = cardsToDeal[i];
            // Only flip the last card of each pile
            const pile = tableau[pileIndex];
            if (card === pile[pile.length - 1]) {
                card.faceUp = true;
            }
            updateBoard(true);
            await new Promise(r => setTimeout(r, 60));
        }

        isDealing = false;
        klondikeBoard.style.pointerEvents = 'auto';
        updateBoard();
        saveGame();
    }

    // ====== RENDER ======
    function updateBoard(initial=false) {
        if (!isActive) return;
        updateScoreDisplay();
        const gameBoardRect = klondikeBoard.getBoundingClientRect();
        const updatePile = (pileData, pileEl, type) => {
            if (!pileEl) return;
            const { top, left } = pileEl.getBoundingClientRect();
            const baseTop = top - gameBoardRect.top + PILE_BORDER_WIDTH;
            const baseLeft = left - gameBoardRect.left + PILE_BORDER_WIDTH;
            let currentOffset = 0;
            pileData.forEach((cardData, i) => {
                const cardEl = cardElements[cardData.id];
                if(!cardEl) return;
                // Don't update position for cards being dragged (ghost)
                if (dragged.ghostEl && dragged.cards.some(c => c.id === cardData.id)) {
                     cardEl.style.visibility = 'hidden'; // Hide the original card
                     return;
                } else {
                     cardEl.style.visibility = 'visible';
                }

                if (type === 'tableau') {
                    cardEl.style.top = `${baseTop + currentOffset}px`;
                    currentOffset += cardData.faceUp ? SPACING_FACE_UP : SPACING_FACE_DOWN;
                } else {
                    cardEl.style.top = `${baseTop}px`;
                }
                cardEl.style.left = `${baseLeft}px`;
                cardEl.style.pointerEvents = 'auto';
                cardEl.classList.toggle('is-stacked', i < pileData.length - 1 && type !== 'tableau');
                if (cardData.faceUp) {
                    cardEl.classList.add('is-flipped');
                    cardEl.draggable = true;
                } else {
                    cardEl.classList.remove('is-flipped');
                    cardEl.draggable = false;
                }
                const zBase = type === 'tableau' ? 100 : type === 'foundation' ? 400 : 600;
                cardEl.style.zIndex = zBase + i;
            });
        };
        tableau.forEach((p,i)=>updatePile(p, document.getElementById(`tableau-${i}`), 'tableau'));
        foundations.forEach((p,i)=>updatePile(p, document.getElementById(`foundation-${i}`), 'foundation'));
        updatePile(stock, document.getElementById('stock'), 'stock');
        stock.forEach(cardData => { if(cardElements[cardData.id]) cardElements[cardData.id].style.pointerEvents = 'none'; });
        const wasteEl = document.getElementById('waste');
        if (wasteEl) {
            const { top:wt, left:wl } = wasteEl.getBoundingClientRect();
            const baseTop = wt - gameBoardRect.top + PILE_BORDER_WIDTH;
            const baseLeft = wl - gameBoardRect.left + PILE_BORDER_WIDTH;
            waste.forEach((cardData, i) => {
                const cardEl = cardElements[cardData.id];
                if(!cardEl) return;

                if (dragged.ghostEl && dragged.cards.some(c => c.id === cardData.id)) {
                    cardEl.style.visibility = 'hidden';
                    return;
                } else {
                    cardEl.style.visibility = 'visible';
                }

                const isTopCard = i === waste.length - 1;
                const visibleFanIndexStart = Math.max(0, waste.length - DRAW_COUNT);
                let leftOffset = 0;
                if (i >= visibleFanIndexStart) {
                    leftOffset = (i - visibleFanIndexStart) * 18;
                }
                cardEl.style.top  = `${baseTop}px`;
                cardEl.style.left = `${baseLeft + leftOffset}px`;
                cardEl.style.zIndex = 800 + i;
                cardEl.classList.add('is-flipped');
                cardEl.classList.toggle('is-stacked', !isTopCard);
                cardEl.draggable = isTopCard;
                cardEl.style.pointerEvents = isTopCard ? 'auto' : 'none';
            });
        }
        if (!initial) checkWin();
    }
    function createCardElement(cardData) {
        const el = document.createElement('div');
        el.classList.add('card');
        el.dataset.id = cardData.id;
        const cardInner = document.createElement('div');
        cardInner.classList.add('card-inner');
        const color = (cardData.suit === '♥' || cardData.suit === '♦') ? 'red' : 'black';
        const front = document.createElement('div');
        front.className = `card-face card-face--front ${color}`;
        front.innerHTML = `
            <div class="card-value-display--top"><span class="card-rank">${cardData.value}</span><span class="card-suit">${cardData.suit}</span></div>
            <div class="card-value-display--bottom"><span class="card-rank">${cardData.value}</span><span class="card-suit">${cardData.suit}</span></div>
            <div class="card-watermark">${cardData.suit}</div>`;
        const back = document.createElement('div');
        back.className = 'card-face card-face--back';
        cardInner.append(front, back);
        el.appendChild(cardInner);
        return el;
    }

    // ====== THEMES & MODAL ======
    function applyCardBack(backId) {
        const back = CARD_BACKS.find(b => b.id === backId) || CARD_BACKS[0];
        CARD_BACKS.forEach(b => document.body.classList.remove(b.className));
        document.body.classList.add(back.className);
        document.querySelectorAll('.back-option').forEach(el => el.classList.toggle('active', el.dataset.id === backId));
    }
    function setupThemeSelector() {
        if (!cardBackOptionsContainer) return;
        cardBackOptionsContainer.innerHTML = '';
        CARD_BACKS.forEach(back => {
            const optionEl = document.createElement('div');
            optionEl.className = `back-option ${back.className}`;
            optionEl.dataset.id = back.id;
            optionEl.title = back.name;
            const previewInner = document.createElement('div');
            previewInner.className = 'card-face card-face--back';
            optionEl.appendChild(previewInner);
            cardBackOptionsContainer.appendChild(optionEl);
        });
        cardBackOptionsContainer.addEventListener('click', e => {
            const target = e.target.closest('.back-option');
            if (target) {
                const backId = target.dataset.id;
                applyCardBack(backId);
                localStorage.setItem('solitaire-card-back', backId);
                cardBackModal.classList.add('hidden');
            }
        });
        const savedBack = localStorage.getItem('solitaire-card-back');
        applyCardBack(savedBack || 'waves');
    }

    // ====== HELPERS ======
    function updateScoreDisplay() {
        if (!isActive) return;
        scoreEl.textContent = score;
        highScoreEl.textContent = highScore;
    }
    function getValueRank(v) { if (v==='A') return 1; if (v==='K') return 13; if (v==='Q') return 12; if (v==='J') return 11; return parseInt(v,10); }
    function getPileArrayFromElement(el) {
        if (!el) return null;
        const [type, index] = el.id.split('-');
        if (type === 'tableau') return tableau[Number(index)];
        if (type === 'foundation') return foundations[Number(index)];
        if (type === 'waste') return waste;
        if (type === 'stock') return stock;
        return null;
    }

    // Helper to get the actual pile that a card belongs to
    function getPileContainingCard(cardId) {
        const checkPile = (pile) => pile.find(c => c.id === cardId);

        if (checkPile(waste)) return waste;
        for (const pile of tableau) {
            if (checkPile(pile)) return pile;
        }
        for (const pile of foundations) {
            if (checkPile(pile)) return pile;
        }
        return null;
    }

    function findCardData(cardEl) {
        const id = cardEl.dataset.id;
        let cardIndex;
        
        // Check waste (only top card can be moved)
        if (waste.length > 0 && waste[waste.length - 1].id === id) {
            return { sourcePile: waste, cardIndex: waste.length - 1, card: waste[waste.length - 1], cardsToMove: [waste[waste.length - 1]] };
        }

        // Check tableau piles (any face-up card and cards above it can be moved)
        for (const pile of tableau) {
            cardIndex = pile.findIndex(c => c.id === id);
            if (cardIndex > -1 && pile[cardIndex].faceUp) {
                const cardsToMove = pile.slice(cardIndex);
                return { sourcePile: pile, cardIndex, card: cardsToMove[0], cardsToMove };
            }
        }
        // Check foundations (only top card can be moved)
        for (const pile of foundations) {
            if (pile.length > 0 && pile[pile.length - 1].id === id) {
                return { sourcePile: pile, cardIndex: pile.length - 1, card: pile[pile.length - 1], cardsToMove: [pile[pile.length - 1]] };
            }
        }
        return {}; // Return empty object if card not found or not movable
    }

    function canMove(card, destPile) {
        if (!card || !destPile) return false;
        
        // Prevent moving to the stock pile
        if (destPile === stock) return false;

        const destType = (foundations.includes(destPile)) ? 'foundation' : (tableau.includes(destPile)) ? 'tableau' : 'other';
        if (destType === 'other' && destPile !== waste) return false; // Only allow tableau, foundation, or waste as actual destinations

        // Waste pile can only receive cards if it's not the source for the current drag (handled by dragged.sourcePile check)
        // Also, waste doesn't typically accept cards from other piles in Klondike.
        // We ensure we don't try to drop on the waste pile itself unless it's for internal logic like recycling stock.
        if (destPile === waste) return false; // Generally, cards don't move TO waste.

        if (destPile.length === 0) {
            return (destType==='tableau' && card.value==='K') || (destType==='foundation' && card.value==='A');
        }
        const top = destPile[destPile.length - 1];
        if (destType === 'tableau') {
            const opposite = ((['♥','♦'].includes(card.suit) && ['♣','♠'].includes(top.suit)) || (['♣','♠'].includes(card.suit) && ['♥','♦'].includes(top.suit)));
            return opposite && getValueRank(card.value) === getValueRank(top.value) - 1;
        } else if (destType === 'foundation') {
            return card.suit === top.suit && getValueRank(card.value) === getValueRank(top.value) + 1;
        }
        return false;
    }
    
    function moveSequence(sourcePile, startIndex, destPile) {
        const seq = sourcePile.splice(startIndex);
        destPile.push(...seq);
    }
    function performMoveCleanup(sourcePile) {
        if (tableau.includes(sourcePile) && sourcePile.length > 0) {
            const topCard = sourcePile[sourcePile.length - 1];
            if (!topCard.faceUp) {
                topCard.faceUp = true;
                score += 5;
            }
        }
        updateBoard();
        saveGame();
        if (!isAutoCompleting) {
            checkAndTriggerAutoComplete();
        }
    }
    function checkWin() {
        if (foundations.every(p=>p.length===13)) {
            if (score > highScore) {
                highScore = score;
                localStorage.setItem('solitaire-high-score', highScore);
                updateScoreDisplay();
            }
            winMessage.classList.remove('hidden');
            triggerBouncingCards();
        }
    }

    function triggerBouncingCards() {
        const boardRect = klondikeBoard.getBoundingClientRect();
        const cardsToBounce = [];

        // Gather all top cards from foundations to start the bounce sequence
        // We'll process them one suit at a time for the classic effect
        const animationFoundations = foundations.map(f => [...f]); // Clone

        function bounceNextCard() {
            let cardFound = false;
            for (let i = 0; i < 4; i++) {
                if (animationFoundations[i].length > 0) {
                    const cardData = animationFoundations[i].pop();
                    const cardEl = cardElements[cardData.id];
                    if (cardEl) {
                        startCardPhysics(cardEl);
                        cardFound = true;
                        break; // One card per trigger
                    }
                }
            }
            if (cardFound) {
                setTimeout(bounceNextCard, 180);
            }
        }

        function startCardPhysics(el) {
            const rect = el.getBoundingClientRect();
            let x = rect.left;
            let y = rect.top;
            let vx = (Math.random() * 4 + 2) * (Math.random() > 0.5 ? 1 : -1);
            let vy = Math.random() * -5 - 2;
            const gravity = 0.5;
            const friction = 0.75;

            // Remove transition for physics
            el.style.transition = 'none';
            el.style.position = 'fixed';
            el.style.zIndex = 3000;
            el.style.pointerEvents = 'none';

            function step() {
                x += vx;
                y += vy;
                vy += gravity;

                if (y + rect.height > window.innerHeight) {
                    y = window.innerHeight - rect.height;
                    vy *= -friction;
                    if (Math.abs(vy) < 2) vy = 0; // Stop vertical bounce if too small
                }

                if (x + rect.width < 0 || x > window.innerWidth) {
                    el.remove();
                    return; // Card off screen
                }

                el.style.left = `${x}px`;
                el.style.top = `${y}px`;

                if (Math.abs(vx) > 0.1 || Math.abs(vy) > 0.1 || y < window.innerHeight - rect.height) {
                    requestAnimationFrame(step);
                } else {
                    // Small slide before stopping
                    vx *= 0.95;
                    if (Math.abs(vx) > 0.1) requestAnimationFrame(step);
                    else el.remove();
                }
            }
            requestAnimationFrame(step);
        }

        bounceNextCard();
    }
    window.triggerBouncingCards = triggerBouncingCards;

    // ====== ACTIONS ======
    function handleStockClick() {
        if (isAutoCompleting) return;
        pushHistory();
        if (stock.length > 0) {
            const drawCount = Math.min(stock.length, DRAW_COUNT);
            const cardsToMove = stock.splice(stock.length - drawCount, drawCount).reverse();
            cardsToMove.forEach(c => c.faceUp = true);
            waste.push(...cardsToMove);
        } else if (waste.length > 0) {
            score = Math.max(0, score - 20);
            stock = waste.reverse();
            stock.forEach(c => c.faceUp = false);
            waste = [];
        }
        updateBoard();
        saveGame();
    }
    
    function performAutoMove(cardEl) {
        if (isAutoCompleting) return;
        const { sourcePile, cardIndex, cardsToMove } = findCardData(cardEl);
        
        if (!sourcePile || !cardsToMove || cardsToMove.length === 0) return;
        const cardToMove = cardsToMove[0];

        // Priority 1: Try to move a single card to a foundation.
        if (cardsToMove.length === 1) {
            for (const f of foundations) {
                if (canMove(cardToMove, f)) {
                    score += 10;
                    pushHistory();
                    moveSequence(sourcePile, cardIndex, f);
                    performMoveCleanup(sourcePile);
                    return;
                }
            }
        }

        // Priority 2: Try to move a stack to another tableau pile.
        for (const t of tableau) {
            if (t !== sourcePile && canMove(cardToMove, t)) {
                if (sourcePile === waste) score += 5;
                if (foundations.includes(sourcePile)) score -= 15;
                
                pushHistory();
                moveSequence(sourcePile, cardIndex, t);
                performMoveCleanup(sourcePile);
                return;
            }
        }
    }

    function undo() {
        if (isAutoCompleting) return;
        if (history.length <= 1) return;
        history.pop();
        restoreState(history[history.length-1]);
        winMessage.classList.add('hidden');
        updateBoard(true);
        saveGame();
    }

    function checkAndTriggerAutoComplete() {
        if (isAutoCompleting) return;
        const isWinnable = stock.length === 0 && tableau.flat().every(card => card.faceUp);
        if (isWinnable) {
            autoComplete();
        }
    }

    function autoComplete() {
        const isWinnable = stock.length === 0 && tableau.flat().every(card => card.faceUp);
        if (!isWinnable) {
            Swal.fire({
                title: 'Cannot Auto-Complete',
                text: 'You can only auto-complete when all cards are face-up and the stock is empty.',
                icon: 'info'
            });
            return;
        }
        isAutoCompleting = true;
        autoCompleteInterval = setInterval(() => {
            let movedCard = false;
            let source = null;

            if (waste.length > 0) {
                const card = waste[waste.length - 1];
                for (const f of foundations) {
                    if (canMove(card, f)) {
                        score += 10;
                        source = waste;
                        moveSequence(source, source.length - 1, f);
                        movedCard = true;
                        break;
                    }
                }
            }
            
            if (!movedCard) {
                for (const t of tableau) {
                    if (t.length > 0) {
                        const card = t[t.length - 1];
                        for (const f of foundations) {
                            if (canMove(card, f)) {
                                score += 10;
                                source = t;
                                moveSequence(source, source.length - 1, f);
                                movedCard = true;
                                break;
                            }
                        }
                    }
                    if (movedCard) break;
                }
            }
            
            if (source) performMoveCleanup(source);
            
            if (!movedCard) {
                clearInterval(autoCompleteInterval);
                autoCompleteInterval = null;
                isAutoCompleting = false;
                checkWin();
            }
        }, 120);
    }
    
    function checkForAnyAvailableMove() {
        const topWasteCard = waste.length > 0 ? waste[waste.length - 1] : null;
        if (topWasteCard) {
            for (const f of foundations) if (canMove(topWasteCard, f)) return true;
            for (const t of tableau) if (canMove(topWasteCard, t)) return true;
        }
        for (const sourcePile of tableau) {
            if (sourcePile.length > 0) {
                const topCard = sourcePile[sourcePile.length-1];
                for(const f of foundations) if(canMove(topCard, f)) return true;

                const movableStackIndex = sourcePile.findIndex(card => card.faceUp);
                if (movableStackIndex > -1) {
                    const cardToMove = sourcePile[movableStackIndex];
                    for (const destPile of tableau) {
                        if (sourcePile !== destPile && canMove(cardToMove, destPile)) return true;
                    }
                }
            }
        }
        return false;
    }

    function handleStuckCheck() {
        if (checkForAnyAvailableMove()) {
            Swal.fire({
                title: 'Hint!',
                text: 'A move is available on the board!',
                icon: 'info'
            });
            return;
        }
        let tempStock = JSON.parse(JSON.stringify(stock));
        let tempWaste = JSON.parse(JSON.stringify(waste));
        const originalStockSize = tempStock.length + tempWaste.length;
        if (originalStockSize === 0) {
            Swal.fire({
                title: 'No Moves Found',
                text: 'The game appears to be unwinnable from this state.',
                icon: 'warning'
            });
            return;
        }
        let cardsCycled = 0;
        while (cardsCycled < originalStockSize) {
            if (tempStock.length === 0) {
                tempStock = tempWaste.reverse();
                tempWaste = [];
            }
            const draw = Math.min(tempStock.length, DRAW_COUNT);
            const drawnCards = tempStock.splice(tempStock.length - draw, draw);
            tempWaste.push(...drawnCards);
            cardsCycled += drawnCards.length;
            const newTopWasteCard = tempWaste.length > 0 ? tempWaste[tempWaste.length - 1] : null;
            if (newTopWasteCard) {
                const hintText = "A move will become available by drawing from the stock!";
                for (const f of foundations) if (canMove(newTopWasteCard, f)) {
                    Swal.fire({ title: 'Hint!', text: hintText, icon: 'info' });
                    return;
                }
                for (const t of tableau) if (canMove(newTopWasteCard, t)) {
                    Swal.fire({ title: 'Hint!', text: hintText, icon: 'info' });
                    return;
                }
            }
        }
        Swal.fire({
            title: 'No Moves Found',
            text: 'The game appears to be unwinnable from this state.',
            icon: 'warning'
        });
    }

    // ====== INPUT HANDLERS ======
    klondikeBoard.addEventListener('click', e => {
        if (!isActive || isAutoCompleting) return;

        const clickedCardEl = e.target.closest('.card');
        const clickedPileEl = e.target.closest('.pile');

        // If the stock pile background was clicked, draw cards.
        if (clickedPileEl && clickedPileEl.id === 'stock' && !clickedCardEl) {
            handleStockClick();
            return;
        }

        // If a card was clicked, attempt to auto-move it.
        if (clickedCardEl) {
            performAutoMove(clickedCardEl);
            return;
        }
        
        // Clicks on anything else (background, empty piles, etc.) will do nothing.
    });
    
    // Custom drag and drop functionality
    klondikeBoard.addEventListener('dragstart', e => {
        if (!isActive || isAutoCompleting) { e.preventDefault(); return; }
        const cardEl = e.target.closest('.card');
        if (!cardEl) { e.preventDefault(); return; }

        const { sourcePile, cardIndex, cardsToMove } = findCardData(cardEl);
        if (!sourcePile || !cardsToMove.length) { e.preventDefault(); return; }

        const rect = cardEl.getBoundingClientRect();
        dragged.offsetX = e.clientX - rect.left;
        dragged.offsetY = e.clientY - rect.top;
        dragged.cards = cardsToMove;
        dragged.sourcePile = sourcePile;
        dragged.startIndex = cardIndex;

        // Create a "ghost" element for visual feedback
        dragged.ghostEl = document.createElement('div');
        dragged.ghostEl.classList.add('card-ghost-stack');
        // Add classes for card back if applicable
        const currentBackClass = document.body.className.match(/card-back-\w+/);
        if (currentBackClass) {
            dragged.ghostEl.classList.add(currentBackClass[0]);
        }
        
        cardsToMove.forEach((cardData, i) => {
            const el = cardElements[cardData.id].cloneNode(true);
            el.style.position = 'absolute'; // Position relative to ghostEl
            el.style.top = `${i * SPACING_FACE_UP}px`;
            el.style.left = '0';
            el.style.zIndex = i + 1; // Stack visually
            el.classList.add('is-flipped'); // Ensure ghost cards are flipped
            el.style.visibility = 'visible';
            dragged.ghostEl.appendChild(el);
        });

        dragged.ghostEl.style.position = 'fixed';
        dragged.ghostEl.style.pointerEvents = 'none'; // Ensure it doesn't interfere with drop targets
        dragged.ghostEl.style.zIndex = 2000; // Above everything else
        dragged.ghostEl.style.width = cardEl.offsetWidth + 'px'; // Match card width
        dragged.ghostEl.style.height = (cardEl.offsetHeight + (cardsToMove.length - 1) * SPACING_FACE_UP) + 'px';

        document.body.appendChild(dragged.ghostEl);

        // Hide the original cards visually while dragging
        cardsToMove.forEach(c => cardElements[c.id].style.visibility = 'hidden');

        // Set custom drag image (a tiny transparent image) to prevent default ghost
        const img = new Image();
        img.src = 'data:image/gif;base64,R0lGODlhAQABAIAAAAAAAP///yH5BAEAAAAALAAAAAABAAEAAAIBRAA7';
        e.dataTransfer.setDragImage(img, 0, 0);

        // Initial position for the ghost
        dragged.ghostEl.style.left = `${e.clientX - dragged.offsetX}px`;
        dragged.ghostEl.style.top = `${e.clientY - dragged.offsetY}px`;
    });

    klondikeBoard.addEventListener('drag', e => {
        if (dragged.ghostEl && e.clientX !== 0) {
            // Update ghost element position to follow the cursor
            dragged.ghostEl.style.left = `${e.clientX - dragged.offsetX}px`;
            dragged.ghostEl.style.top = `${e.clientY - dragged.offsetY}px`;
        }
    });

    klondikeBoard.addEventListener('dragover', e => {
        e.preventDefault();
        
        const targetEl = e.target.closest('.card, .pile');
        let potentialDestPileEl = null;

        if (targetEl) {
            if (targetEl.classList.contains('card')) {
                potentialDestPileEl = targetEl.closest('.pile');
            } else if (targetEl.classList.contains('pile')) {
                potentialDestPileEl = targetEl;
            }
        }

        const currentlyHighlighted = document.querySelector('.pile.drag-over');
        if (currentlyHighlighted && currentlyHighlighted !== potentialDestPileEl) {
            currentlyHighlighted.classList.remove('drag-over');
        }

        if (potentialDestPileEl && dragged.cards.length > 0) {
            const destPileData = getPileArrayFromElement(potentialDestPileEl);
            if (canMove(dragged.cards[0], destPileData)) {
                potentialDestPileEl.classList.add('drag-over');
            }
        }
    });

    klondikeBoard.addEventListener('dragend', () => {
        // Clean up ghost element and reset state
        if (dragged.ghostEl) {
            dragged.ghostEl.remove();
            dragged.ghostEl = null;
        }
        // Make original cards visible again (updateBoard will re-position them)
        dragged.cards.forEach(c => cardElements[c.id].style.visibility = 'visible');
        dragged = { cards: [], sourcePile: null, startIndex: -1, ghostEl: null };
        document.querySelectorAll('.drag-over').forEach(p => p.classList.remove('drag-over'));
        updateBoard(); // Re-render to ensure everything is correct
    });

    klondikeBoard.addEventListener('drop', e => {
        e.preventDefault();
        document.querySelectorAll('.drag-over').forEach(p => p.classList.remove('drag-over'));

        if (!dragged.cards.length) return;

        const dropTargetEl = e.target.closest('.card, .pile');
        if (!dropTargetEl) return;

        let destPile = null;
        if (dropTargetEl.classList.contains('card')) {
            // If dropped on a card, find the pile that card belongs to
            const cardId = dropTargetEl.dataset.id;
            const targetCardPile = getPileContainingCard(cardId);
            if (targetCardPile) {
                // We need to ensure it's the TOP card of the pile to drop ONTO it effectively
                if (targetCardPile[targetCardPile.length - 1].id === cardId) {
                    destPile = targetCardPile;
                }
            }
        } else if (dropTargetEl.classList.contains('pile')) {
            // If dropped directly on a pile (e.g., an empty tableau slot)
            destPile = getPileArrayFromElement(dropTargetEl);
        }

        if (destPile && canMove(dragged.cards[0], destPile)) {
            // --- SCORING LOGIC ---
            if (foundations.includes(destPile)) score += 10;
            if (tableau.includes(destPile) && dragged.sourcePile === waste) score += 5;
            if (tableau.includes(destPile) && foundations.includes(dragged.sourcePile)) score -= 15;
            // --- END SCORING LOGIC ---
            pushHistory();
            moveSequence(dragged.sourcePile, dragged.startIndex, destPile);
            performMoveCleanup(dragged.sourcePile);
        }
        // dragend will handle cleanup regardless of success
    });

    document.addEventListener('keydown', (e)=>{
        if (!isActive || isAutoCompleting) return;
        if (e.code === 'Space') { e.preventDefault(); handleStockClick(); }
        if (e.key.toLowerCase() === 'u' || (e.ctrlKey && e.key.toLowerCase() === 'z')) {
            e.preventDefault();
            undo();
        }
    });
    
    // ====== BUTTONS & MODAL LISTENERS ======
    restartBtn?.addEventListener('click', () => {
        if (isActive) initState();
    });
    undoBtn?.addEventListener('click', undo);
    drawSelect?.addEventListener('change', () => { DRAW_COUNT = parseInt(drawSelect.value, 10) || 3; initState(); });
    openModalBtn?.addEventListener('click', () => cardBackModal.classList.remove('hidden'));
    closeModalBtn?.addEventListener('click', () => cardBackModal.classList.add('hidden'));
    modalOverlay?.addEventListener('click', () => cardBackModal.classList.add('hidden'));
    checkMovesBtn?.addEventListener('click', handleStuckCheck);
    autoCompleteBtn?.addEventListener('click', autoComplete);

    document.addEventListener('gameModeChanged', (e) => {
        isActive = (e.detail === 'klondike');
        if (isActive) {
            updateScoreDisplay();
            updateBoard();
        }
    });

    // ====== INIT ======
    setupThemeSelector();
    isActive = (localStorage.getItem('solitaire-mode') !== 'pyramid');
    if (isActive) {
        if (!loadGame()) {
            initState();
        }
    } else {
        loadGame();
    }
    window.addEventListener('resize', () => { if (isActive) updateBoard(true); });
});