// --- CONFIG ---
    const CURRICULUM = [
        { name: "Year 1", numbers: [1, 2, 5, 10], targetXP: 150 }, 
        { name: "Year 2", numbers: [3, 4], targetXP: 150 },        
        { name: "Year 3", numbers: [9, 11], targetXP: 200 },       
        { name: "Year 4", numbers: [6, 7], targetXP: 250 },        
        { name: "Year 5", numbers: [8, 12], targetXP: 300 },       
        { name: "N.E.W.T.s", numbers: [1,2,3,4,5,6,7,8,9,10,11,12], targetXP: 5000 }
    ];

    const SHOP_ITEMS = [
        { id: 'auto_quill', name: "Auto-Quill", type: 'consumable', category: 'Supplies', price: 15, desc: "Writes the first digit." },
        { id: 'choc_frog', name: "Chocolate Frog", type: 'consumable', category: 'Supplies', price: 25, desc: "Clears Dementors instantly." },
        { id: 'liquid_luck', name: "Liquid Luck", type: 'consumable', category: 'Supplies', price: 40, desc: "Solves problem instantly." },
        { id: 'time_turner', name: "Time Turner", type: 'consumable', category: 'Magic Items', price: 60, desc: "Slows Dementors for 5 spells." },
        { id: 'study_spell', name: "Study Spell", type: 'consumable', category: 'Daily Specials', price: 30, desc: "+25 XP instantly (Mon/Thu).", availableDays: ['Mon','Thu'] },
        { id: 'vault_key', name: "Vault Key", type: 'consumable', category: 'Daily Specials', price: 50, desc: "+100 Gold (Sun only).", availableDays: ['Sun'] },
        { id: 'phoenix_feather', name: "Phoenix Feather", type: 'consumable', category: 'Daily Specials', price: 45, desc: "Boost streak to 5 (Tue/Fri).", availableDays: ['Tue','Fri'] },
        { id: 'shield_charm', name: "Shield Charm", type: 'consumable', category: 'Daily Specials', price: 35, desc: "Reset & slow Dementors for 2 turns (Wed/Sat).", availableDays: ['Wed','Sat'] },
        { id: 'astral_map', name: "Astral Map", type: 'consumable', category: 'Daily Specials', price: 40, desc: "Shows a star hint for this question (Sun/Tue/Thu).", availableDays: ['Sun','Tue','Thu'] },
        // PETS
        { id: 'pet_owl', name: "Snowy Owl", type: 'pet', category: 'Familiars', price: 120, desc: "Faithful post owl companion.", class: 'pet-owl', icon: '🦉' },
        { id: 'pet_cat', name: "Kneazle Cat", type: 'pet', category: 'Familiars', price: 110, desc: "Clever feline lookout.", class: 'pet-cat', icon: '🐈' },
        { id: 'pet_rat', name: "Garden Rat", type: 'pet', category: 'Familiars', price: 90, desc: "Surprisingly loyal.", class: 'pet-rat', icon: '🐀' },
        { id: 'pet_toad', name: "Pad-Pad Toad", type: 'pet', category: 'Familiars', price: 80, desc: "Keeps calm in the classroom.", class: 'pet-toad', icon: '🐸' },
        { id: 'pet_ferret', name: "Mischief Ferret", type: 'pet', category: 'Familiars', price: 130, desc: "Fast distraction in duels.", class: 'pet-ferret', icon: '🦦' },
        // SKINS (Hogwarts Houses + specials)
        { id: 'skin_gryffindor', name: "Gryffindor", type: 'skin', category: 'Card Skins', price: 100, desc: "Scarlet and gold bravery motif.", class: "skin-gryffindor" },
        { id: 'skin_slytherin', name: "Slytherin", type: 'skin', category: 'Card Skins', price: 100, desc: "Emerald and silver ambition motif.", class: "skin-slytherin" },
        { id: 'skin_ravenclaw', name: "Ravenclaw", type: 'skin', category: 'Card Skins', price: 100, desc: "Bronze and blue wit motif.", class: "skin-ravenclaw" },
        { id: 'skin_hufflepuff', name: "Hufflepuff", type: 'skin', category: 'Card Skins', price: 100, desc: "Honey and charcoal loyalty motif.", class: "skin-hufflepuff" },
        { id: 'skin_map', name: "Marauder's Map", type: 'skin', category: 'Card Skins', price: 140, desc: "Footprints on aged parchment.", class: "skin-map" },
        { id: 'skin_spellbook', name: "Spellbook", type: 'skin', category: 'Card Skins', price: 140, desc: "Worn leather and gold filigree.", class: "skin-spellbook" },
        // TRAILS
        { id: 'trail_sparks', name: "Sparks Trail", type: 'trail', category: 'Wand Effects', price: 120, desc: "Golden sparks.", class: "trail-sparks" },
        { id: 'trail_ice', name: "Frost Trail", type: 'trail', category: 'Wand Effects', price: 120, desc: "Icy crystals.", class: "trail-ice" },
        { id: 'trail_slime', name: "Troll Slime", type: 'trail', category: 'Wand Effects', price: 80, desc: "Sticky green trail.", class: "trail-slime" },
    ];

    function getFactsForLevel(levelIndex) {
        const level = CURRICULUM[levelIndex];
        const facts = new Set();
        for (const num1 of level.numbers) {
            for (let num2 = 1; num2 <= 12; num2++) {
                const fact = [num1, num2].sort((a, b) => a - b);
                facts.add(`${fact[0]}x${fact[1]}`);
            }
        }
        return Array.from(facts);
    }

    function getLevelTargetXP() {
        const levelData = CURRICULUM[state.levelIndex];
        const requiredCount = getFactsForLevel(state.levelIndex).length;
        const scaled = requiredCount * 12; // scales with how many facts are in the level
        return Math.max(levelData.targetXP, scaled);
    }

    function allFactsMastered(levelIndex) {
        const requiredFacts = getFactsForLevel(levelIndex);
        const masteredFactsInLevel = state.masteredFacts.filter(fact => requiredFacts.includes(fact));
        return masteredFactsInLevel.length === requiredFacts.length;
    }

    // --- STATE ---
    let state = { 
        levelIndex: 0, currentLevelXP: 0, streak: 0, gold: 0, 
        troubleList: [], masteredFacts: [],
        totalQuestions: 0, correctAnswers: 0, fastestTime: null,
        inventory: {}, 
        activeSkin: 'skin-default', activeTrail: '', activeBackground: 'bg-default',
        activePet: '', activePetIcon: '',
        studentName: '',
        focusQueue: [],
        lastFactId: ''
    };
    
    let game = {
        active: false,
        currentFact: { n1: 0, n2: 0, ans: 0 },
        currentInput: "",
        attempts: 0,
        startTime: 0,
        timeTurnerCharges: 0,
        forcedAnswer: false
    };

    let dementor = { interval: null, progress: 0, timedOut: false };
    let snitchTimer = null;
    let cheatClicks = 0;

    // --- INIT ---
    function init() {
        loadData();
        const card = document.getElementById('main-card');
        const overlay = document.getElementById('dementor-overlay');
        if (card && overlay && overlay.parentElement !== card) {
            card.prepend(overlay);
        }

        if (!state.studentName) {
            const hashName = window.location.hash.substring(1);
            if (hashName) {
                state.studentName = hashName.substring(0, 12);
                saveData();
                updateLetterGreeting();
                document.querySelector('.letter .signature').insertAdjacentHTML('beforebegin', `<p>We await your owl, ${state.studentName}.</p>`);
            } else {
                Swal.fire({
                    title: 'Welcome, young wizard!',
                    text: 'Please state your name for the Hogwarts registry.',
                    input: 'text',
                    inputPlaceholder: 'Your Name',
                    allowOutsideClick: false,
                    allowEscapeKey: false,
                    customClass: {
                        popup: 'hogwarts-popup',
                        confirmButton: 'hogwarts-button',
                        title: 'hogwarts-title',
                    },
                    preConfirm: (name) => {
                        if (!name) {
                            Swal.showValidationMessage('You must provide a name to enroll!')
                        }
                        return name
                    }
                }).then((result) => {
                    state.studentName = result.value.substring(0, 12);
                    saveData();
                    updateLetterGreeting();
                    document.querySelector('.letter .signature').insertAdjacentHTML('beforebegin', `<p>We await your owl, ${state.studentName}.</p>`);
                });
            }
        } else {
            updateLetterGreeting();
            document.querySelector('.letter .signature').insertAdjacentHTML('beforebegin', `<p>We await your owl, ${state.studentName}.</p>`);
        }

        applyCosmetics();
        updateUI();
        scheduleSnitch();
        
        document.addEventListener('touchmove', handleTouchTrail, {passive: false});
        document.addEventListener('mousemove', handleMouseTrail);
        document.addEventListener('keydown', handleKeydown);

        // CHEAT LISTENER (Tap Year X 5 times)
        document.getElementById('level-name').addEventListener('click', () => {
            cheatClicks++;
            if (cheatClicks === 5) {
                state.gold += 500;
                document.getElementById('feedback-msg').style.color = '#d4af37';
                document.getElementById('feedback-msg').innerText = "Gringotts Vault Opened! +500G";
                saveData(); updateUI(); cheatClicks = 0;
            }
            setTimeout(() => cheatClicks = 0, 2000); 
        });

        const skip = localStorage.getItem('arithmancySkipIntro');
        if (skip === 'true') startGame(); else openIntro();
    }

    // --- CORE LOOP ---
    function startGame() { 
        game.active = true; 
        generateQuestion(); 
    }

    function generateQuestion() {
        resetDementor();
        game.currentInput = "";
        game.attempts = 0;
        game.forcedAnswer = false;
        game.startTime = Date.now();
        
        document.getElementById('answer-display').innerText = "";
        document.getElementById('feedback-msg').innerText = "";
        const hintGrid = document.getElementById('hint-grid');
        hintGrid.innerHTML = "";
        hintGrid.classList.remove('has-stars');
        const castBtn = document.querySelector('.key-cast');
        const answerDisplay = document.getElementById('answer-display');
        if (castBtn) castBtn.classList.remove('ready-cast');
        if (answerDisplay) answerDisplay.classList.remove('forced-answer');
        
        if (game.timeTurnerCharges > 0) {
            game.timeTurnerCharges--;
            updateBuffDisplay();
        } else {
            updateBuffDisplay();
        }
        
        const levelData = CURRICULUM[state.levelIndex];
        const allowedNumbers = levelData.numbers;
        const relevantTrouble = state.troubleList.filter(t => allowedNumbers.includes(t.n1) || allowedNumbers.includes(t.n2));

        let n1, n2;
        const makeId = (a, b) => {
            const [s, l] = a < b ? [a, b] : [b, a];
            return `${s}x${l}`;
        };
        const lastId = state.lastFactId;

        if (state.focusQueue.length > 0) {
            const factId = state.focusQueue.shift();
            const parts = factId.split('x').map(Number);
            [n1, n2] = parts;
        } else {
            let attempts = 0;
            while (attempts < 6) {
                if (relevantTrouble.length > 0 && Math.random() < 0.5) {
                    const struggle = relevantTrouble[Math.floor(Math.random() * relevantTrouble.length)];
                    n1 = struggle.n1; n2 = struggle.n2;
                } else {
                    n1 = allowedNumbers[Math.floor(Math.random() * allowedNumbers.length)];
                    n2 = Math.floor(Math.random() * 12) + 1;
                    if (Math.random() > 0.5) [n1, n2] = [n2, n1];
                }
                const cid = makeId(n1, n2);
                if (cid !== lastId || attempts === 5) break;
                attempts++;
            }
        }

        game.currentFact = { n1, n2, ans: n1 * n2 };
        state.lastFactId = makeId(n1, n2);
        document.getElementById('equation-display').innerText = `${n1} × ${n2}`;
        startDementor();
    }

    function checkAnswer() {
        if (!game.active || game.currentInput === "") return;
        
        state.totalQuestions++;
        const userAns = parseInt(game.currentInput);
        const feedback = document.getElementById('feedback-msg');
        const card = document.querySelector('.card-container');
        const levelData = CURRICULUM[state.levelIndex];

        if (userAns === game.currentFact.ans) {
            state.correctAnswers++;
            const answerTime = Date.now() - game.startTime;
            if (state.fastestTime === null || answerTime < state.fastestTime) {
                state.fastestTime = answerTime;
            }
            state.streak++;
            const goldGain = game.attempts === 0 ? 2 : 1;
            state.gold += goldGain;
            const xpGain = game.attempts === 0 ? 10 : 5;
        state.currentLevelXP += xpGain;
        applyXPToMastery();

            const xpPop = document.createElement('div');
            xpPop.className = 'xp-gain-pop';
            xpPop.innerText = `+${xpGain} XP`;
            card.appendChild(xpPop);
            setTimeout(() => xpPop.remove(), 1000);

            if (game.attempts === 0) {
                const fact = [game.currentFact.n1, game.currentFact.n2].sort((a, b) => a - b);
                const factId = `${fact[0]}x${fact[1]}`;
                if (!state.masteredFacts.includes(factId)) {
                    state.masteredFacts.push(factId);
                }
                removeFromTroubleList(game.currentFact.n1, game.currentFact.n2);
            }

            castPatronus();
            feedback.style.color = '#7cff9a';
            feedback.innerText = `Expecto Patronum! (+${goldGain} G)`;

            if (allFactsMastered(state.levelIndex) && state.levelIndex < CURRICULUM.length - 1) {
                state.levelIndex++; 
                state.currentLevelXP = 0;
                state.masteredFacts = [];
                state.focusQueue = [];

                Swal.fire({
                    title: 'LEVEL UP!',
                    text: `Welcome to ${CURRICULUM[state.levelIndex].name}`,
                    icon: 'success',
                    customClass: {
                        popup: 'hogwarts-popup',
                        confirmButton: 'hogwarts-button',
                        title: 'hogwarts-title',
                    }
                });

                saveData(); updateUI(); setTimeout(generateQuestion, 2500);
                return;
            }
            saveData(); updateUI(); setTimeout(generateQuestion, 1000);
        } else {
            handleWrongAttempt();
        }
    }

    // --- SHOP & INVENTORY ---
    function openShop() {
        game.active = false;
        clearInterval(dementor.interval);
        document.getElementById('dementor-overlay').style.display = 'none';
        renderShop();
        document.getElementById('shop-modal').classList.add('visible');
    }
    function closeShop() {
        document.getElementById('shop-modal').classList.remove('visible');
        document.getElementById('dementor-overlay').style.display = 'block';
        game.active = true;
        startDementor(true);
    }

    function availableShopItems() {
        const dayMap = ['Sun','Mon','Tue','Wed','Thu','Fri','Sat'];
        const today = dayMap[new Date().getDay()];
        return SHOP_ITEMS.filter(item => {
            const owned = (state.inventory[item.id] || 0) > 0;
            if (!item.availableDays) return true;
            if (owned) return true;
            return item.availableDays.includes(today);
        });
    }

    function renderShop() {
        const list = document.getElementById('shop-list');
        document.getElementById('shop-gold').innerText = state.gold;
        list.innerHTML = "";
        const itemsToShow = availableShopItems();
        const categories = [...new Set(itemsToShow.map(i => i.category))];
        
        categories.forEach(cat => {
            const catHeader = document.createElement('div');
            catHeader.className = 'shop-category'; catHeader.innerText = cat; list.appendChild(catHeader);
            itemsToShow.filter(i => i.category === cat).forEach(item => {
                
                const qty = state.inventory[item.id] || 0;
                const div = document.createElement('div'); 
                div.className = `shop-item ${qty > 0 ? 'purchased' : ''}`;
                
                let actionHtml = `<div class="shop-actions">`;
                
                if (item.type === 'skin' || item.type === 'trail' || item.type === 'background' || item.type === 'pet') {
                    if (qty > 0) {
                        const isEquipped = (item.type === 'skin' && state.activeSkin === item.class) || 
                                           (item.type === 'trail' && state.activeTrail === item.class) ||
                                           (item.type === 'background' && state.activeBackground === item.class) ||
                                           (item.type === 'pet' && state.activePet === item.class);
                        if (isEquipped) {
                            actionHtml += `<button class="buy-btn unequip-btn" onclick="unequipItem('${item.id}')">Unequip</button>`;
                        } else {
                            actionHtml += `<button class="buy-btn equip-btn" onclick="equipItem('${item.id}')">Equip</button>`;
                        }
                    } else {
                        actionHtml += `<button class="buy-btn" onclick="buyItem('${item.id}')" ${state.gold < item.price ? 'disabled' : ''}>${item.price}G</button>`;
                    }
                } else {
                    if (qty > 0) {
                        actionHtml += `<div class="qty-badge">Owned: ${qty}</div>`;
                        actionHtml += `<button class="buy-btn use-btn" onclick="useConsumable('${item.id}')">Use</button>`;
                        actionHtml += `<button class="buy-btn" onclick="buyItem('${item.id}')" ${state.gold < item.price ? 'disabled' : ''} style="margin-top:5px; font-size:0.7rem;">Buy (+1)</button>`;
                    } else {
                        actionHtml += `<button class="buy-btn" onclick="buyItem('${item.id}')" ${state.gold < item.price ? 'disabled' : ''}>${item.price}G</button>`;
                    }
                }
                
                actionHtml += `</div>`;
                div.innerHTML = `<div class="item-details"><h4>${item.name}</h4><p>${item.desc}</p></div>${actionHtml}`;
                list.appendChild(div);
            });
        });
    }

    function buyItem(id) {
        const item = SHOP_ITEMS.find(i => i.id === id);
        if (state.gold >= item.price) {
            state.gold -= item.price;
            if (!state.inventory[id]) state.inventory[id] = 0;
            state.inventory[id]++;
            saveData(); updateUI(); renderShop();
        }
    }

    function equipItem(id) {
        const item = SHOP_ITEMS.find(i => i.id === id);
        if (item.type === 'skin') state.activeSkin = item.class;
        if (item.type === 'trail') state.activeTrail = item.class;
        if (item.type === 'background') state.activeBackground = item.class;
        if (item.type === 'pet') { state.activePet = item.class; state.activePetIcon = item.icon || ''; }
        applyCosmetics(); saveData(); renderShop();
    }
    
    function unequipItem(id) {
        const item = SHOP_ITEMS.find(i => i.id === id);
        if (item.type === 'skin') state.activeSkin = 'skin-default';
        if (item.type === 'trail') state.activeTrail = '';
        if (item.type === 'background') state.activeBackground = 'bg-default';
        if (item.type === 'pet') { state.activePet = ''; state.activePetIcon = ''; }
        applyCosmetics(); saveData(); renderShop();
    }

    function useConsumable(id) {
        if (!state.inventory[id] || state.inventory[id] <= 0) return;
        
        const feedback = document.getElementById('feedback-msg');
        const fromShop = document.getElementById('shop-modal')?.classList.contains('visible');

        if (id === 'time_turner') {
            game.timeTurnerCharges = 5;
            feedback.style.color = '#d4af37'; feedback.innerText = "Time Turner Active (5 turns)";
        } 
        else if (id === 'liquid_luck') {
            game.currentInput = game.currentFact.ans.toString();
            document.getElementById('answer-display').innerText = game.currentInput;
            feedback.style.color = '#d4af37'; feedback.innerText = "Liquid Luck applied!";
        } 
        else if (id === 'choc_frog') {
            resetDementor();
            feedback.style.color = '#740001'; feedback.innerText = "Ate Chocolate Frog. You feel better.";
        } 
        else if (id === 'auto_quill') {
            const strAns = game.currentFact.ans.toString();
            game.currentInput = strAns.charAt(0);
            document.getElementById('answer-display').innerText = game.currentInput;
            feedback.style.color = '#d4af37'; feedback.innerText = "The Quill writes...";
        }
        else if (id === 'study_spell') {
            state.currentLevelXP += 25;
            feedback.style.color = '#d4af37'; feedback.innerText = "+25 XP from Study Spell!";
        }
        else if (id === 'vault_key') {
            state.gold += 100;
            feedback.style.color = '#d4af37'; feedback.innerText = "Gringotts vault refilled! +100G";
        }
        else if (id === 'phoenix_feather') {
            state.streak = Math.max(state.streak, 5);
            feedback.style.color = '#d4af37'; feedback.innerText = "Phoenix Feather restored your focus (Streak 5).";
        }
        else if (id === 'shield_charm') {
            resetDementor();
            game.timeTurnerCharges = Math.max(game.timeTurnerCharges, 2);
            updateBuffDisplay();
            feedback.style.color = '#d4af37'; feedback.innerText = "Shield charm up (slow Dementors 2 turns).";
        }
        else if (id === 'astral_map') {
            drawHintGrid(game.currentFact.n1 || 1, game.currentFact.n2 || 1);
            feedback.style.color = '#d4af37'; feedback.innerText = "The stars reveal the path.";
        }

        state.inventory[id]--;
        saveData();
        renderQuickConsumables();
        if (fromShop) closeShop(); else updateUI();
    }
    
    function updateBuffDisplay() {
        const bar = document.getElementById('buff-bar');
        bar.innerHTML = "";
        if (game.timeTurnerCharges > 0) {
            const badge = document.createElement('div');
            badge.className = 'buff-tag';
            badge.innerText = `⏳ ${game.timeTurnerCharges}`;
            bar.appendChild(badge);
        }
    }

    function renderQuickConsumables() {
        const holder = document.getElementById('quick-consumables');
        if (!holder) return;
        holder.innerHTML = "";
        const consumables = SHOP_ITEMS.filter(i => i.type === 'consumable' && (state.inventory[i.id] || 0) > 0);
        if (consumables.length === 0) {
            holder.innerHTML = `<div style="font-size:0.8rem; color:#555;">No consumables on hand.</div>`;
            return;
        }
        consumables.forEach(item => {
            const qty = state.inventory[item.id] || 0;
            const card = document.createElement('div');
            card.className = 'consumable-card';
            card.innerHTML = `
                <h5>${item.name}</h5>
                <div class="qty">Owned: ${qty}</div>
                <button ${qty <= 0 ? 'disabled' : ''} onclick="useConsumable('${item.id}')">Use</button>
            `;
            holder.appendChild(card);
        });
    }

    // --- VISUALS ---
    function applyCosmetics() {
        const card = document.getElementById('main-card');
        const allowedSkins = ['skin-default','skin-gryffindor','skin-slytherin','skin-ravenclaw','skin-hufflepuff','skin-map','skin-spellbook'];
        if (!allowedSkins.includes(state.activeSkin)) {
            state.activeSkin = 'skin-default';
        }
        card.className = `card-container ${state.activeSkin}`;
        const allowedBackgrounds = ['bg-default'];
        if (!allowedBackgrounds.includes(state.activeBackground)) {
            state.activeBackground = 'bg-default';
        }
        document.body.className = state.activeBackground;
        renderPet();
    }
    function handleTouchTrail(e) {
        if (!state.activeTrail) return;
        const touch = e.touches[0]; createParticle(touch.clientX, touch.clientY);
    }
    function handleMouseTrail(e) {
        if (!state.activeTrail || e.buttons === 0) return;
        createParticle(e.clientX, e.clientY);
    }
    function createParticle(x, y) {
        const p = document.createElement('div');
        p.className = `particle ${state.activeTrail}`;
        p.style.left = `${x}px`; p.style.top = `${y}px`;
        document.body.appendChild(p); setTimeout(() => p.remove(), 800);
    }

    function handleKeydown(e) {
        const activeEl = document.activeElement;
        if (activeEl && (activeEl.tagName === 'INPUT' || activeEl.tagName === 'TEXTAREA')) return;
        if (document.querySelector('.modal-overlay.visible')) return;
        if (!game.active && !game.forcedAnswer) return;
        const k = e.key;
        if (k >= '0' && k <= '9') {
            pressKey(Number(k));
        } else if (k === 'Backspace') {
            e.preventDefault();
            pressKey('BS');
        } else if (k === 'Enter') {
            checkAnswer();
        } else if (k === 'c' || k === 'C' || k === 'Escape') {
            pressKey('C');
        }
    }

    function openStats() {
        game.active = false;
        clearInterval(dementor.interval);
        document.getElementById('dementor-overlay').style.display = 'none';
        renderStats();
        document.getElementById('stats-modal').classList.add('visible');
    }

    function closeStats() {
        document.getElementById('stats-modal').classList.remove('visible');
        document.getElementById('dementor-overlay').style.display = 'block';
        game.active = true;
        startDementor(true);
    }

    function renderStats() {
        const statsList = document.getElementById('stats-list');
        const levelData = CURRICULUM[state.levelIndex];
        const accuracy = state.totalQuestions === 0 ? 0 : (state.correctAnswers / state.totalQuestions) * 100;
        const fastestTime = state.fastestTime === null ? 'N/A' : `${(state.fastestTime / 1000).toFixed(2)}s`;
        const requiredFacts = getFactsForLevel(state.levelIndex);
        const masteredFactsInLevel = state.masteredFacts.filter(fact => requiredFacts.includes(fact));
        const masteryPct = requiredFacts.length === 0 ? 0 : (masteredFactsInLevel.length / requiredFacts.length) * 100;
        const targetXP = getLevelTargetXP();
        const xpPct = Math.min((state.currentLevelXP / targetXP) * 100, 100);
        const grade =
            accuracy >= 95 ? 'O' :
            accuracy >= 85 ? 'E' :
            accuracy >= 75 ? 'A' :
            accuracy >= 65 ? 'P' :
            accuracy >= 50 ? 'D' : 'T';

        const troubleFacts = state.troubleList.map(fact => `<span class="trouble-chip">${fact.n1} × ${fact.n2}</span>`).join('');

        statsList.innerHTML = `
            <div class="report-card">
                <div class="report-heading">
                    <div class="report-title-block">
                        <div class="report-title-row">
                            <span class="report-icon" aria-hidden="true">📜</span>
                            <div class="report-title">Report Card</div>
                        </div>
                        <div class="report-subtitle">${state.studentName || 'Student'} • ${levelData.name}</div>
                    </div>
                    <div class="report-actions">
                        <div class="grade-badge">Grade ${grade}</div>
                        <button class="report-btn" onclick="changeStudentName()">Change Name</button>
                    </div>
                </div>

                <div class="grade-grid">
                    <div class="grade-row">
                        <div class="grade-label">Accuracy</div>
                        <div class="grade-value">${accuracy.toFixed(1)}%</div>
                        <div class="grade-meter"><span style="width:${Math.min(accuracy, 100)}%"></span></div>
                    </div>
                    <div class="grade-row">
                        <div class="grade-label">Mastery</div>
                        <div class="grade-value">${masteredFactsInLevel.length} / ${requiredFacts.length}</div>
                        <div class="grade-meter"><span style="width:${masteryPct}%"></span></div>
                    </div>
                    <div class="grade-row">
                        <div class="grade-label">XP This Year</div>
                        <div class="grade-value">${state.currentLevelXP} / ${targetXP}</div>
                        <div class="grade-meter"><span style="width:${xpPct}%"></span></div>
                    </div>
                </div>

                <div class="metric-cards">
                    <div class="metric-card">
                        <div class="metric-label">Total Questions</div>
                        <div class="metric-value">${state.totalQuestions}</div>
                    </div>
                    <div class="metric-card">
                        <div class="metric-label">Correct Answers</div>
                        <div class="metric-value">${state.correctAnswers}</div>
                    </div>
                    <div class="metric-card">
                        <div class="metric-label">Fastest Answer</div>
                        <div class="metric-value">${fastestTime}</div>
                    </div>
                    <div class="metric-card">
                        <div class="metric-label">Current Streak</div>
                        <div class="metric-value">${state.streak}</div>
                    </div>
                </div>

                <div class="report-footer">
                    <div class="report-subsection-title">Trouble Facts</div>
                    ${
                        troubleFacts
                            ? `<div class="trouble-chips">${troubleFacts}</div>`
                            : `<div class="report-note">Looks clear for now. Keep casting to reveal any weak spots.</div>`
                    }
                </div>
            </div>
        `;
    }
    
    // --- HELPERS ---
    function updateLetterGreeting() {
        const greetingEl = document.getElementById('student-greeting');
        if (!greetingEl) return;
        const name = state.studentName && state.studentName.trim() ? state.studentName : 'Student';
        greetingEl.innerHTML = `<strong>Dear ${name},</strong>`;
    }

    function changeStudentName() {
        Swal.fire({
            title: 'Change your name?',
            text: 'This updates the Hogwarts registry.',
            icon: 'question',
            showCancelButton: true,
            confirmButtonColor: '#740001',
            cancelButtonColor: '#3085d6',
            confirmButtonText: 'Yes, change it'
        }).then(result => {
            if (!result.isConfirmed) return;
            Swal.fire({
                title: 'Enter your new name',
                input: 'text',
                inputPlaceholder: 'New Name',
                showCancelButton: true,
                confirmButtonText: 'Save',
                preConfirm: (name) => {
                    if (!name || !name.trim()) {
                        Swal.showValidationMessage('Name cannot be empty');
                    }
                    return name;
                }
            }).then(res => {
                if (!res.isConfirmed) return;
                state.studentName = res.value.trim().substring(0, 12);
                saveData();
                updateLetterGreeting();
                updateUI();
                renderStats();
            });
        });
    }

    function pressKey(key) {
        if (!game.active) return;
        if (key === 'C') game.currentInput = "";
        else if (key === 'BS') game.currentInput = game.currentInput.slice(0, -1);
        else if (game.currentInput.length < 4) game.currentInput += key;
        document.getElementById('answer-display').innerText = game.currentInput;
    }

    function updateUI() {
        const levelData = CURRICULUM[state.levelIndex];
        document.getElementById('level-name').innerText = levelData.name;
        document.getElementById('gold-display').innerText = state.gold;
        const targetXP = getLevelTargetXP();
        document.getElementById('xp-text').innerText = `${state.currentLevelXP} / ${targetXP} XP`;

        const requiredFacts = getFactsForLevel(state.levelIndex);
        const masteredFactsInLevel = state.masteredFacts.filter(fact => requiredFacts.includes(fact));
        
        document.getElementById('mastery-display').innerText = `Mastered: ${masteredFactsInLevel.length} / ${requiredFacts.length}`;
        
        let pct = (masteredFactsInLevel.length / requiredFacts.length) * 100;
        if(pct > 100) pct = 100;
        document.getElementById('progress-bar').style.width = `${pct}%`;

        updateBuffDisplay();
        renderQuickConsumables();
    }

    function startDementor(resume = false) {
        clearInterval(dementor.interval);
        if (!resume) dementor.progress = 0;
        dementor.timedOut = false;
        const difficulty = Math.max(game.currentFact.n1 || 1, game.currentFact.n2 || 1);
        let totalMs = 10000 + difficulty * 500; // base + more time for harder facts
        let tickMs = 200;
        if (game.timeTurnerCharges > 0) {
            tickMs = 400;
            totalMs *= 1.6;
        }
        const step = tickMs / totalMs;

        updateDementorVisuals();
        dementor.interval = setInterval(() => {
            if (!game.active) return;
            if (dementor.progress < 1) {
                dementor.progress += step; updateDementorVisuals();
            } else if (!dementor.timedOut) {
                dementor.timedOut = true;
                handleDementorTimeout();
            }
        }, tickMs);
    }

    function updateDementorVisuals() {
        const overlay = document.getElementById('dementor-overlay');
        const p = dementor.progress > 1 ? 1 : dementor.progress;
        const opacity = 0.12 + (p * 0.6); // darker as time passes
        const size = 18 + (p * 82); // spread further toward center over time, nearly full cover
        const darkness = 0.4 + (p * 0.55);
        const vignette = 0.2 + (p * 0.32);
        const blur = 0 + (p * 0.8);
        const glow = Math.min(2.0, 0.5 + (p * 1.5)); // stronger glow as it darkens
        overlay.style.opacity = opacity;
        overlay.style.setProperty('--circle-size', `${size}%`);
        overlay.style.setProperty('--circle-strength', darkness.toFixed(2));
        overlay.style.setProperty('--circle-blur', `${blur}px`);
        overlay.style.setProperty('--vignette-strength', vignette.toFixed(2));
        overlay.style.background = buildDementorBackground(p, size, darkness, vignette);
        const castTimer = document.getElementById('cast-timer-fill');
        if (castTimer) castTimer.style.width = `${Math.max(0, 100 - p * 100)}%`;
        document.documentElement.style.setProperty('--focus-glow', glow.toFixed(2));
        const uiGlow = Math.min(1.2, 0.15 + (p * 1.05));
        document.documentElement.style.setProperty('--ui-glow', uiGlow.toFixed(2));
    }
    
    function resetDementor() {
        clearInterval(dementor.interval); dementor.progress = 0;
        const overlay = document.getElementById('dementor-overlay');
        overlay.style.opacity = 0; 
        overlay.style.setProperty('--circle-size', '12%');
        overlay.style.setProperty('--circle-strength', '0.42');
        overlay.style.setProperty('--circle-blur', '0px');
        overlay.style.setProperty('--vignette-strength', '0.18');
        overlay.style.background = 'transparent';
        const castTimer = document.getElementById('cast-timer-fill');
        if (castTimer) castTimer.style.width = '100%';
        document.documentElement.style.setProperty('--focus-glow', '0');
        document.documentElement.style.setProperty('--ui-glow', '0');
        saveData();
        dementor.timedOut = false;
    }

    function buildDementorBackground(progress, size, strength, vignette) {
        const circles = [
            { pos: '0% 12%', s: 1.0 },
            { pos: '100% 12%', s: 1.0 },
            { pos: '0% 88%', s: 1.0 },
            { pos: '100% 88%', s: 1.0 },
            { pos: '0% 50%', s: 1.1 },
            { pos: '100% 50%', s: 1.1 },
            { pos: '50% 0%', s: 1.05 },
            { pos: '50% 100%', s: 1.05 }
        ];
        const activeCount = Math.max(1, Math.min(circles.length, Math.floor(progress * circles.length) + 1));
        const gradients = [];
        for (let i = 0; i < activeCount; i++) {
            const c = circles[i];
            gradients.push(
                `radial-gradient(circle at ${c.pos}, rgba(0,0,0,${(strength * c.s).toFixed(2)}) 0%, rgba(0,0,0,${(strength * c.s).toFixed(2)}) ${Math.max(size * 0.55, 6)}%, transparent ${size}%)`
            );
        }
        gradients.push(`radial-gradient(circle at 50% 50%, transparent 60%, rgba(0,0,0,${(vignette * 0.35).toFixed(2)}) 78%, rgba(0,0,0,${vignette.toFixed(2)}) 92%, rgba(0,0,0,${(vignette * 1.05).toFixed(2)}) 100%)`);
        return gradients.join(',');
    }

    function castPatronus() {
        clearInterval(dementor.interval);
        const overlay = document.getElementById('dementor-overlay');
        overlay.classList.add('patronus-flash');
        setTimeout(() => { resetDementor(); overlay.classList.remove('patronus-flash'); }, 500);
    }

    function addToTroubleList(n1, n2) {
        const [s, b] = n1 < n2 ? [n1, n2] : [n2, n1];
        const id = `${s}x${b}`;
        if (!state.troubleList.some(t => t.id === id)) state.troubleList.push({ id, n1: s, n2: b });
    }
    function removeFromTroubleList(n1, n2) {
        const [s, b] = n1 < n2 ? [n1, n2] : [n2, n1];
        const id = `${s}x${b}`;
        state.troubleList = state.troubleList.filter(t => t.id !== id);
    }
    
    function drawHintGrid(rows, cols) {
        const grid = document.getElementById('hint-grid');
        grid.innerHTML = "";
        grid.classList.toggle('has-stars', false);
        if (!rows || !cols) return;
        grid.style.gridTemplateColumns = `repeat(${rows}, 1fr)`; // flip to spread horizontally first
        for (let i = 0; i < (rows * cols); i++) {
            const dot = document.createElement('div'); dot.className = 'star-dot'; grid.appendChild(dot);
        }
        grid.classList.add('has-stars');
    }

    function applyPenalty(amount) {
        if (!amount) return;
        state.currentLevelXP = Math.max(0, state.currentLevelXP - amount);
    }

    function handleWrongAttempt(options = {}) {
        const { timedOut = false } = options;
        const feedback = document.getElementById('feedback-msg');
        const card = document.querySelector('.card-container');
        state.streak = 0;
        game.attempts = timedOut ? 3 : game.attempts + 1;
        const penalty = game.attempts >= 3 || timedOut ? 10 : (game.attempts === 2 ? 5 : 0);
        if (card) {
            card.classList.add('apply-shake');
            setTimeout(() => card.classList.remove('apply-shake'), 500);
        }
        if (!timedOut) {
            dementor.progress += 0.2; updateDementorVisuals();
            game.currentInput = "";
            document.getElementById('answer-display').innerText = "";
        }
        if (penalty > 0) applyPenalty(penalty);
        if (game.attempts >= 3) {
            revealAnswerAndAdvance(timedOut ? 2000 : 0, timedOut, penalty);
            return;
        }
        if (game.attempts === 2) {
            feedback.style.color = '#ffb0b0';
            feedback.innerText = `Count the stars... (-${penalty} XP)`;
            drawHintGrid(game.currentFact.n1, game.currentFact.n2);
        } else {
            feedback.style.color = '#ffb0b0';
            feedback.innerText = "Try again!";
        }
        saveData(); updateUI();
    }

    function revealAnswerAndAdvance(delayMs = 0, timedOut = false, penalty = 0) {
        const feedback = document.getElementById('feedback-msg');
        const card = document.querySelector('.card-container');
        const factId = `${Math.min(game.currentFact.n1, game.currentFact.n2)}x${Math.max(game.currentFact.n1, game.currentFact.n2)}`;
        game.active = false;
        setTimeout(() => {
            // guard in case question changed
            const currentId = `${Math.min(game.currentFact.n1, game.currentFact.n2)}x${Math.max(game.currentFact.n1, game.currentFact.n2)}`;
            if (currentId !== factId) return;
            if (card) {
                card.classList.add('apply-shake');
                setTimeout(() => card.classList.remove('apply-shake'), 500);
            }
            feedback.style.color = '#ffb0b0';
            feedback.innerText = `Answer is ${game.currentFact.ans}.${penalty ? ` (-${penalty} XP)` : ''} Press CAST to continue.`;
            addToTroubleList(game.currentFact.n1, game.currentFact.n2);
            game.currentInput = game.currentFact.ans.toString();
            const answerDisplay = document.getElementById('answer-display');
            if (answerDisplay) {
                answerDisplay.innerText = game.currentInput;
                answerDisplay.classList.add('forced-answer');
            }
            const castBtn = document.querySelector('.key-cast');
            if (castBtn) castBtn.classList.add('ready-cast');
            game.forcedAnswer = true;
            resetDementor();
            saveData(); updateUI();
            game.active = true;
        }, delayMs);
    }

    function handleDementorTimeout() {
        const factId = `${Math.min(game.currentFact.n1, game.currentFact.n2)}x${Math.max(game.currentFact.n1, game.currentFact.n2)}`;
        game.active = false;
        setTimeout(() => {
            const currentId = `${Math.min(game.currentFact.n1, game.currentFact.n2)}x${Math.max(game.currentFact.n1, game.currentFact.n2)}`;
            if (currentId !== factId) return;
            const feedback = document.getElementById('feedback-msg');
            if (feedback) {
                feedback.style.color = '#ffb0b0';
                feedback.innerText = "Saved by a Professor...";
            }
            handleWrongAttempt({ timedOut: true });
        }, 2000);
    }

    function applyXPToMastery() {
        const levelData = CURRICULUM[state.levelIndex];
        const requiredFacts = getFactsForLevel(state.levelIndex);
        const targetXP = levelData.targetXP;
        const queued = new Set(state.focusQueue);
        const unmastered = () => requiredFacts.filter(f => !state.masteredFacts.includes(f));

        while (state.currentLevelXP >= targetXP && unmastered().length > 0) {
            state.currentLevelXP -= targetXP;
            const available = unmastered().filter(f => !queued.has(f));
            if (available.length === 0) break;

            const troubleIds = state.troubleList.map(t => `${Math.min(t.n1, t.n2)}x${Math.max(t.n1, t.n2)}`);
            const troubleCandidate = available.find(id => troubleIds.includes(id));
            const pickedId = troubleCandidate || available[Math.floor(Math.random() * available.length)];

            state.focusQueue.push(pickedId);
            queued.add(pickedId);
        }
    }

    function renderPet() {
        const perch = document.getElementById('pet-perch');
        if (!perch) return;
        perch.innerHTML = "";
        if (!state.activePet) return;
        const pet = document.createElement('div');
        pet.className = `pet-icon ${state.activePet}`;
        pet.innerText = state.activePetIcon || '🐾';
        perch.appendChild(pet);
    }
    
    function saveData() { localStorage.setItem('arithmancyDataV17', JSON.stringify(state)); }
    function loadData() {
        const saved = localStorage.getItem('arithmancyDataV17');
        if (saved) {
            const parsed = JSON.parse(saved);
            if (parsed.masteredFacts && Array.isArray(parsed.masteredFacts)) {
                state = { ...state, ...parsed };
            }
        }
    }
    
    function openIntro() { 
        document.getElementById('intro-modal').classList.add('visible'); 
        document.getElementById('dont-show-again').checked = (localStorage.getItem('arithmancySkipIntro') === 'true');
        game.active = false; clearInterval(dementor.interval); 
    }
    
    function closeIntro() { 
        document.getElementById('intro-modal').classList.remove('visible');
        const checkbox = document.getElementById('dont-show-again');
        if(checkbox.checked) localStorage.setItem('arithmancySkipIntro', 'true');
        else localStorage.removeItem('arithmancySkipIntro');
        if(game.currentFact.ans === 0) startGame(); else { game.active = true; startDementor(true); }
    }
    window.addEventListener('beforeunload', function (e) {
        e.preventDefault();
        e.returnValue = '';
    });

    document.addEventListener('DOMContentLoaded', init);

    // --- GOLDEN SNITCH EVENT ---
    function scheduleSnitch() {
        if (snitchTimer) clearTimeout(snitchTimer);
        const delay = 45000 + Math.random() * 30000; // 45–75s
        snitchTimer = setTimeout(spawnSnitch, delay);
    }

    function spawnSnitch() {
        const layer = document.getElementById('snitch-layer');
        if (!layer || document.querySelector('.flying-snitch')) {
            scheduleSnitch();
            return;
        }
        if (dementor.progress > 0.6) { // scared off by looming dementor
            scheduleSnitch();
            return;
        }
        const snitch = document.createElement('div');
        snitch.className = 'flying-snitch';
        const fromLeft = Math.random() > 0.5;
        snitch.classList.toggle('from-right', !fromLeft);
        snitch.style.top = `${10 + Math.random() * 70}%`;
        snitch.addEventListener('click', () => claimSnitch(snitch));
        layer.appendChild(snitch);
        setTimeout(() => {
            snitch.remove();
            scheduleSnitch();
        }, 8000);
    }

    function claimSnitch(el) {
        el.remove();
        const reward = 50;
        state.gold += reward;
        saveData(); updateUI();
        const feedback = document.getElementById('feedback-msg');
        feedback.style.color = '#d4af37';
        feedback.innerText = `Caught the Snitch! +${reward}G`;
        scheduleSnitch();
    }