/**
 * Cosmic Garden - Main Game Engine
 * Handles game state, tick loop, and core logic
 */

const Game = {
    // Core game state
    state: {
        stardust: 0,
        totalStardust: 0,
        totalClicks: 0,
        clickPower: 1,
        startTime: Date.now(),
        lastSaveTime: Date.now(),
        buildings: {},
        upgrades: [],
        achievements: [],
        stellarEssence: 0,
        prestigeCount: 0,
        totalPrestigeEssence: 0,
        prestigeUpgrades: [],

        // Save Slot System
        activeSlot: 0,   // index of the currently selected save slot (0..SLOTS-1)
        autoSave: true,  // whether the periodic autosave loop is running

        // Golden Starbloom random event state
        goldenBlooms: {
            active: false,      // is a bloom currently visible on screen?
            timer: 0,           // seconds until the bloom vanishes
            lastSpawn: Date.now(), // ms when we last (re)spawned one
            totalClaimed: 0     // lifetime count of blooms the player has clicked
        }
    },

    // Configuration
    config: {
        tickRate: 100, // ms per tick (10 ticks/sec)
        autoSaveInterval: 30000, // 30 seconds
        costScaling: 1.15, // Cost multiplier per building level

        // Save Slot System - number of independent save slots available
        SLOTS: 3,

        goldenBloomMinMs: 45000, // min ms between bloom spawns (45s)
        goldenBloomMaxMs: 90000, // max ms between bloom spawns (90s)
        goldenBloomDuration: 12, // seconds a visible bloom stays before vanishing
        goldenBloomBonusMult: 15  // production-per-second worth of stardust awarded
    },

    /**
     * Initialize the game
     */
    init() {
        this.loadState();
        this.setupEventListeners();
        this.startGameLoop();
        this.startAutoSave();
        Audio.init();
        UI.init();
        Stats.init();
        PrestigeUI.init();
        console.log('🌌 Cosmic Garden initialized!');
    },

    /**
     * Setup event listeners
     */
    setupEventListeners() {
        // Track which slot the user has selected for importing.
        this.importSlot = 0;

        // Harvest button - support both click and touch
        const harvestBtn = document.getElementById('harvest-btn');

        harvestBtn.addEventListener('click', (e) => {
            this.harvest(e);
            this.createRipple(harvestBtn, e);
            this.animateClickButton(harvestBtn);
        });

        // Touch support for better mobile experience
        harvestBtn.addEventListener('touchstart', (e) => {
            e.preventDefault(); // Prevent double-fire with click
            const touch = e.touches[0];
            const clickEvent = new MouseEvent('click', {
                clientX: touch.clientX,
                clientY: touch.clientY,
                bubbles: true
            });

            // Create ripple effect for touch
            this.createRipple(harvestBtn, { clientX: touch.clientX, clientY: touch.clientY });
            this.animateClickButton(harvestBtn);
        }, { passive: false });

        // Save buttons
        document.getElementById('save-btn').addEventListener('click', () => {
            this.save();
            UI.showNotification('Game saved!', 'success');
        });

        document.getElementById('export-btn').addEventListener('click', () => {
            SaveSystem.exportSave();
        });

        document.getElementById('import-btn').addEventListener('click', () => {
            UI.showImportModal();
        });

        document.getElementById('confirm-import').addEventListener('click', () => {
            const data = document.getElementById('import-data').value;
            if (data) {
                const ok = this.importSlotFromData(data, this.importSlot);
                UI.hideImportModal();
                if (ok) {
                    // If the import landed in the active slot, switchSlot already re-rendered.
                    UI.update();
                }
            }
        });

        document.getElementById('cancel-import').addEventListener('click', () => {
            UI.hideImportModal();
        });

        // Buy All upgrades button.
        const buyAllBtn = document.getElementById('buy-all-upgrades');
        if (buyAllBtn) {
            buyAllBtn.addEventListener('click', () => {
                Game.buyAllUpgrades();
            });
        }

        // Buy All buildings button - buy as many of every building at once.
        const buyAllBuildingsBtn = document.getElementById('buy-all-buildings');
        if (buyAllBuildingsBtn) {
            buyAllBuildingsBtn.addEventListener('click', () => {
                Game.buyAllBuildings();
            });
        }

        document.getElementById('reset-btn').addEventListener('click', () => {
            if (confirm('Are you sure you want to reset all progress? This cannot be undone!')) {
                this.reset();
            }
        });

        // Save Slot System: slot selection buttons.
        document.querySelectorAll('.slot-btn').forEach(btn => {
            btn.addEventListener('click', () => {
                if (this.state.activeSlot === parseInt(btn.dataset.slot, 10)) {
                    UI.showNotification(`Already on Slot ${parseInt(btn.dataset.slot, 10) + 1}`, 'info');
                    return;
                }
                if (confirm(`Switch to Slot ${parseInt(btn.dataset.slot, 10) + 1}?\nUnsaved changes will be saved first.`)) {
                    this.save(); // Persist current slot before switching.
                    this.switchSlot(parseInt(btn.dataset.slot, 10));
                }
            });
        });

        // Autosave toggle button.
        document.getElementById('autosave-btn').addEventListener('click', () => {
            this.state.autoSave = !this.state.autoSave;
            const btn = document.getElementById('autosave-btn');
            if (this.state.autoSave) {
                btn.classList.add('on');
                btn.textContent = 'ON';
                UI.showNotification('Autosave enabled', 'success');
            } else {
                btn.classList.remove('on');
                btn.textContent = 'OFF';
                UI.showNotification('Autosave disabled', 'info');
            }
            // Persist the toggle preference immediately.
            localStorage.setItem('cosmicGardenAutoSave', String(this.state.autoSave));
        });

        // Tab switching
        document.querySelectorAll('.tab-btn').forEach(btn => {
            btn.addEventListener('click', (e) => {
                const tab = e.target.dataset.tab;
                document.querySelectorAll('.tab-btn').forEach(b => b.classList.remove('active'));
                document.querySelectorAll('.tab-content').forEach(c => c.classList.remove('active'));
                e.target.classList.add('active');
                document.getElementById(`${tab}-tab`).classList.add('active');
            });
        });

        // Import slot selector buttons.
        document.querySelectorAll('[data-import-slot]').forEach(btn => {
            btn.addEventListener('click', () => {
                this.importSlot = parseInt(btn.dataset.importSlot, 10);
                UI.showNotification(`Importing into Slot ${this.importSlot + 1}`, 'info');
            });
        });
    },

    /**
     * Harvest stardust by clicking
     */
    harvest(event) {
        const amount = this.getClickPower();
        this.addStardust(amount);
        this.state.totalClicks++;

        // Audio feedback
        Audio.playClick();

        // Visual feedback
        UI.showFloatingText(event.clientX, event.clientY, `+${this.formatNumber(amount)}`);
        Particles.createClickParticles(event.clientX, event.clientY, 8);
        UI.update();
    },

    /**
     * Add stardust to the game
     */
    addStardust(amount) {
        this.state.stardust += amount;
        this.state.totalStardust += amount;
    },

    /**
     * Get current click power
     */
    getClickPower() {
        let power = 1;
        
        // Apply upgrade bonuses
        for (const upgradeId of this.state.upgrades) {
            const upgrade = UPGRADES[upgradeId];
            if (upgrade && upgrade.clickPowerBonus) {
                power *= upgrade.clickPowerBonus;
            }
        }
        
        // Apply prestige multipliers
        const prestigeMultiplier = PRESTIGE.getMultiplier();
        power *= prestigeMultiplier;
        
        // Apply prestige upgrades
        for (const upgradeId of (this.state.prestigeUpgrades || [])) {
            const upgrade = PRESTIGE_UPGRADES[upgradeId];
            if (upgrade && upgrade.effect === 'clickMultiplier') {
                power *= upgrade.value;
            }
        }
        
        return Math.floor(power);
    },

    /**
     * Calculate production per second
     */
    getProductionPerSecond() {
        let total = 0;
        
        for (const [buildingId, count] of Object.entries(this.state.buildings)) {
            if (count === 0) continue;
            
            const building = BUILDINGS[buildingId];
            if (!building) continue;
            
            let production = building.baseProduction * count;
            
            // Apply prestige multiplier
            const prestigeMultiplier = PRESTIGE.getMultiplier();
            production *= prestigeMultiplier;
            
            // Apply Golden Starbloom temporary production boost (+50%)
            if (this.state.productionBoostUntil && this.state.productionBoostUntil > Date.now()) {
                production *= 1.5;
            }
            // Apply prestige upgrades
            for (const upgradeId of (this.state.prestigeUpgrades || [])) {
                const upgrade = PRESTIGE_UPGRADES[upgradeId];
                if (upgrade && upgrade.effect === 'productionMultiplier') {
                    production *= upgrade.value;
                }
            }
            
            // Apply upgrade bonuses
            for (const upgradeId of this.state.upgrades) {
                const upgrade = UPGRADES[upgradeId];
                if (upgrade && upgrade.buildingBonus && upgrade.buildingBonus[buildingId]) {
                    production *= upgrade.buildingBonus[buildingId];
                }
                if (upgrade && upgrade.globalBonus) {
                    production *= upgrade.globalBonus;
                }
            }
            
            total += production;
        }
        
        return total;
    },

    /**
     * Get building cost
     */
    getBuildingCost(buildingId) {
        const building = BUILDINGS[buildingId];
        const count = this.state.buildings[buildingId] || 0;
        let cost = Math.floor(building.baseCost * Math.pow(this.config.costScaling, count));
        
        // Apply prestige cost reduction
        for (const upgradeId of (this.state.prestigeUpgrades || [])) {
            const upgrade = PRESTIGE_UPGRADES[upgradeId];
            if (upgrade && upgrade.effect === 'costReduction') {
                cost *= upgrade.value;
            }
        }
        
        return Math.floor(cost);
    },

    /**
     * Buy a single building
     */
    buyBuilding(buildingId) {
        const cost = this.getBuildingCost(buildingId);
        
        if (this.state.stardust >= cost) {
            this.state.stardust -= cost;
            this.state.buildings[buildingId] = (this.state.buildings[buildingId] || 0) + 1;
            
            UI.showNotification(`Bought ${BUILDINGS[buildingId].name}!`, 'success');

            // Audio feedback
            Audio.playPurchase();

            // Particle effect on building purchase
            const card = document.getElementById(`building-${buildingId}`);
            if (card) {
                const rect = card.getBoundingClientRect();
                Particles.createBuildingEffect(rect.left + rect.width / 2, rect.top + rect.height / 2);
            }
            
            UI.update();
            return true;
        }
        
        return false;
    },

    /**
     * Calculate how many of a building the player can currently afford.
     * Does not modify game state.
     */
    getMaxAffordable(buildingId) {
        const building = BUILDINGS[buildingId];
        if (!building) return 0;

        let stardust = this.state.stardust;
        let count = 0;
        let owned = this.state.buildings[buildingId] || 0;

        while (true) {
            const cost = Math.floor(building.baseCost * Math.pow(this.config.costScaling, owned + count));
            if (stardust < cost) break;
            stardust -= cost;
            count++;
        }

        return count;
    },

    /**
     * Buy as many of a building as the player can afford at once.
     * Returns the number purchased.
     */
    buyMaxBuilding(buildingId) {
        const building = BUILDINGS[buildingId];
        if (!building) return 0;

        let count = 0;
        while (this.state.stardust >= this.getBuildingCost(buildingId)) {
            const cost = this.getBuildingCost(buildingId);
            this.state.stardust -= cost;
            this.state.buildings[buildingId] = (this.state.buildings[buildingId] || 0) + 1;
            count++;
        }

        if (count > 0) {
            UI.showNotification(`Bought ${count}x ${building.name}!`, 'success');

            // Audio feedback
            Audio.playPurchase();

            // Particle effect on building purchase
            const card = document.getElementById(`building-${buildingId}`);
            if (card) {
                const rect = card.getBoundingClientRect();
                Particles.createBuildingEffect(rect.left + rect.width / 2, rect.top + rect.height / 2);
            }

            UI.update();
        }

        return count;
    },

    /**
     * Buy as many of EVERY building the player can currently afford at once,
     * across all building types. Returns the total number purchased. Buildings
     * cost-scales independently per type, so this loops until a full pass buys
     * nothing (kept for symmetry with buyAllUpgrades / buyMaxPrestigeUpgrades
     * and to stay safe if future buildings gain requirement gates); in practice
     * a single pass suffices. Mirrors buyMaxBuilding per building.
     */
    buyAllBuildings() {
        let totalBought = 0;

        // Loop until a full pass purchases nothing (buying one building type
        // never unlocks another, but the loop keeps us safe against future
        // requirement gates and matches the bulk-buy convention elsewhere).
        let progress = true;
        while (progress) {
            progress = false;
            for (const buildingId of Object.keys(BUILDINGS)) {
                const bought = this.buyMaxBuilding(buildingId);
                if (bought > 0) {
                    totalBought += bought;
                    progress = true;
                }
            }
        }

        return totalBought;
    },

    /**
     * Buy an upgrade
     */
    buyUpgrade(upgradeId) {
        const upgrade = UPGRADES[upgradeId];
        if (!upgrade || this.state.upgrades.includes(upgradeId)) {
            return false;
        }
        
        if (this.state.stardust >= upgrade.cost) {
            // Check requirements
            if (upgrade.requirements) {
                for (const [reqId, reqCount] of Object.entries(upgrade.requirements)) {
                    const currentCount = this.state.buildings[reqId] || 0;
                    if (currentCount < reqCount) {
                        UI.showNotification('Requirements not met!', 'warning');
                        return false;
                    }
                }
            }
            
            this.state.stardust -= upgrade.cost;
            this.state.upgrades.push(upgradeId);
            
            UI.showNotification(`Unlocked: ${upgrade.name}!`, 'success');
            UI.update();
            return true;
        }
        
        return false;
    },

    /**
     * Buy every upgrade the player can currently afford at once.
     * Returns an object describing what happened: { bought: count, ids: [...] }.
     * Upgrades are one-time purchases, so we loop until nothing affordable remains.
     */
    buyAllUpgrades() {
        const bought = [];
        // Loop until a pass buys nothing (each purchase may unlock new affordability).
        let progress = true;
        while (progress) {
            progress = false;
            for (const [id, upgrade] of Object.entries(UPGRADES)) {
                if (this.state.upgrades.includes(id)) continue;
                // Respect requirements before attempting purchase.
                if (upgrade.requirements) {
                    let met = true;
                    for (const [reqId, reqCount] of Object.entries(upgrade.requirements)) {
                        if ((this.state.buildings[reqId] || 0) < reqCount) {
                            met = false;
                            break;
                        }
                    }
                    if (!met) continue;
                }
                if (this.state.stardust >= upgrade.cost) {
                    this.state.stardust -= upgrade.cost;
                    this.state.upgrades.push(id);
                    bought.push(id);
                    progress = true; // another purchase may have unlocked more affordability
                }
            }
        }

        if (bought.length > 0) {
            UI.showNotification(`Bought ${bought.length} upgrade(s)!`, 'success');
            Audio.playPurchase();
            UI.update();
        }

        return { bought: bought.length, ids: bought };
    },

    /**
     * Buy every prestige upgrade the player can currently afford at once,
     * paid from Stellar Essence. Returns an object describing what happened:
     * { bought: count, ids: [...] }. Prestige upgrades are one-time purchases,
     * so we loop until a full pass buys nothing (purchasing one never unlocks
     * another, but the loop is kept for symmetry with buyAllUpgrades and to
     * stay safe should future prestige upgrades gain requirement gates).
     */
    buyMaxPrestigeUpgrades() {
        const bought = [];
        let progress = true;
        while (progress) {
            progress = false;
            for (const [id, upgrade] of Object.entries(PRESTIGE_UPGRADES)) {
                if ((this.state.prestigeUpgrades || []).includes(id)) continue;
                // Respect requirements before attempting purchase, mirroring
                // PRESTIGE.buyUpgrade semantics.
                if (upgrade.requirements) {
                    let met = true;
                    for (const [reqId, reqCount] of Object.entries(upgrade.requirements)) {
                        if ((this.state.buildings[reqId] || 0) < reqCount) {
                            met = false;
                            break;
                        }
                    }
                    if (!met) continue;
                }
                if ((this.state.stellarEssence || 0) >= upgrade.cost) {
                    this.state.prestigeUpgrades = this.state.prestigeUpgrades || [];
                    this.state.prestigeUpgrades.push(id);
                    // Spend Stellar Essence, mirroring PRESTIGE.buyUpgrade.
                    this.state.stellarEssence -= upgrade.cost;
                    bought.push(id);
                    progress = true;
                }
            }
        }

        if (bought.length > 0) {
            UI.showNotification(`Bought ${bought.length} prestige upgrade(s)!`, 'achievement');
            Audio.playPurchase();
            UI.update();
        }

        return { bought: bought.length, ids: bought };
    },

    /**
     * Golden Starbloom - random event system.
     * A rare, time-limited bloom occasionally appears on screen. Clicking it
     * awards a stardust bonus and grants a temporary production boost.
     */

    /**
     * Seconds remaining until the current bloom vanishes (0 if none active).
     */
    getGoldenBloomRemaining() {
        return this.state.goldenBlooms.active ? Math.ceil(this.state.goldenBlooms.timer) : 0;
    },

    /**
     * Award a Golden Starbloom bonus and apply the production multiplier.
     * Called when the player clicks a visible bloom. Returns the amount earned.
     */
    claimGoldenBloom(x, y) {
        const state = this.state.goldenBlooms;

        // No active bloom - nothing to claim.
        if (!state.active) return 0;

        state.active = false;
        state.timer = 0;
        state.totalClaimed++;

        // Bonus: goldenBloomBonusMult x current production per second (min 1).
        const bonus = Math.max(1, Math.floor(this.getProductionPerSecond() * this.config.goldenBloomBonusMult));
        this.addStardust(bonus);

        // Temporary production boost: +50% for 30 seconds.
        this.state.productionBoostUntil = Date.now() + 30000;

        UI.showNotification('⭐ Golden Starbloom! +' + this.formatNumber(bonus) + ' ✨', 'achievement');
        Audio.playGoldenBloom();
        Particles.createGoldenEffect(x, y);
        UI.update();
        return bonus;
    },

    /**
     * Update golden bloom scheduling on each tick.
     * Spawns a new bloom if none is active and enough time has elapsed;
     * decrements the countdown of an active bloom until it vanishes.
     */
    updateGoldenBloom(dtSeconds) {
        const state = this.state.goldenBlooms;

        // If a bloom is still on screen, count down its lifetime.
        if (state.active) {
            state.timer -= dtSeconds;
            if (state.timer <= 0) {
                state.active = false;
                state.timer = 0;
            }
            return;
        }

        // Otherwise, check whether it is time to spawn the next bloom.
        const elapsed = Date.now() - state.lastSpawn;
        const minMs = this.config.goldenBloomMinMs;
        const maxMs = this.config.goldenBloomMaxMs;
        if (elapsed >= minMs) {
            // Wait until somewhere in [min, max] before spawning.
            if (elapsed >= maxMs || Math.random() < 0.05) {
                state.active = true;
                state.timer = this.config.goldenBloomDuration;
                state.lastSpawn = Date.now();
                UI.spawnGoldenBloom();
            }
        }
    },

    /**
     * Whether the temporary production boost is currently active, and how
     * many seconds remain.
     */
    getProductionBoostInfo() {
        const until = this.state.productionBoostUntil || 0;
        if (until <= Date.now()) return { active: false, remaining: 0 };
        return { active: true, remaining: Math.ceil((until - Date.now()) / 1000) };
    },

    /**
     * Game tick - called every config.tickRate ms
     */
    tick() {
        const production = this.getProductionPerSecond();
        const tickSeconds = this.config.tickRate / 1000;
        
        if (production > 0) {
            this.addStardust(production * tickSeconds);
        }
        
        // Advance the Golden Starbloom random event clock.
        this.updateGoldenBloom(tickSeconds);
        
        UI.update();
        Achievements.check();
    },

    /**
     * Start the game loop
     */
    startGameLoop() {
        setInterval(() => this.tick(), this.config.tickRate);
    },

    /**
     * Start auto-save
     */
    startAutoSave() {
        setInterval(() => {
            // Only autosave when the player has enabled it (default on).
            if (!this.state.autoSave) return;
            this.save();
            document.getElementById('last-saved').textContent = 
                `Last saved: ${new Date().toLocaleTimeString()}`;
        }, this.config.autoSaveInterval);
    },

    /**
     * localStorage key for a given slot's save data.
     */
    getSaveKey(slot) {
        return `cosmicGardenSave-${slot}`;
    },

    /**
     * The key holding the selected slot index across page loads.
     */
    getActiveSlotKey() {
        return 'cosmicGardenActiveSlot';
    },

    /**
     * Save game state to the currently active slot.
     */
    save() {
        this.state.lastSaveTime = Date.now();
        localStorage.setItem(this.getSaveKey(this.state.activeSlot), JSON.stringify(this.state));
    },

    /**
     * Load game state
     */
    loadState() {
        // Restore the persisted selected-slot index before reading its data.
        const persistedSlot = localStorage.getItem(this.getActiveSlotKey());
        if (persistedSlot !== null) {
            this.state.activeSlot = parseInt(persistedSlot, 10) || 0;
        }

        const saved = localStorage.getItem(this.getSaveKey(this.state.activeSlot));
        if (saved) {
            try {
                const parsed = JSON.parse(saved);
                this.state = { ...this.state, ...parsed };
                // The explicitly-persisted slot selection always wins.
                if (persistedSlot !== null) {
                    this.state.activeSlot = parseInt(persistedSlot, 10) || 0;
                }
                
                // Calculate offline progress
                const offlineTime = (Date.now() - this.state.lastSaveTime) / 1000;
                if (offlineTime > 60) {
                    const production = this.getProductionPerSecond();
                    let offlineRate = 0.5; // 50% offline efficiency
                    for (const upgradeId of (this.state.prestigeUpgrades || [])) {
                        const upgrade = PRESTIGE_UPGRADES[upgradeId];
                        if (upgrade && upgrade.effect === 'offlineBonus') {
                            offlineRate = upgrade.value;
                        }
                    }
                    const offlineEarnings = production * offlineTime * offlineRate;
                    if (offlineEarnings > 0) {
                        this.addStardust(offlineEarnings);
                        UI.showNotification(
                            `Welcome back! Earned ${this.formatNumber(offlineEarnings)} ✨ while away`,
                            'success'
                        );
                    }
                }
            } catch (e) {
                console.error('Failed to load save:', e);
            }
        }
    },

    /**
     * Load from imported data
     */
    loadFromData(data) {
        try {
            const parsed = JSON.parse(atob(data));
            this.state = { ...this.state, ...parsed };
            UI.update();
        } catch (e) {
            UI.showNotification('Invalid save data!', 'warning');
        }
    },

    /**
     * Load the data stored in a specific slot index (without changing it).
     * Returns the parsed state, or null if that slot is empty.
     */
    loadSlot(slot) {
        const raw = localStorage.getItem(this.getSaveKey(slot));
        if (!raw) return null;
        try {
            return JSON.parse(raw);
        } catch (e) {
            console.error(`Failed to read slot ${slot}:`, e);
            return null;
        }
    },

    /**
     * Build a lightweight preview of a given save slot WITHOUT mutating the
     * live game state. Returns an object describing what that slot holds:
     *   - present: whether the slot has any saved data
     *   - stardust: current (live) stardust production/sec for the slot
     *   - totalStardust: lifetime stardust earned in the slot
     *   - buildings: total number of buildings owned in the slot
     *   - achievements: count/total of achievements unlocked in the slot
     *   - prestigeCount: how many times the slot has been prestiged
     *   - lastSaved: human-readable "time ago" string for the slot's save time
     * An empty/unreadable slot returns present:false with zeroed fields.
     */
    getSlotPreview(slot) {
        const data = this.loadSlot(slot);
        if (!data) {
            return {
                present: false,
                stardust: 0,
                totalStardust: 0,
                buildings: 0,
                achievements: [0, 33],
                prestigeCount: 0,
                lastSaved: 'never'
            };
        }

        const buildingCount = Object.values(data.buildings || {})
            .reduce((sum, c) => sum + (Number(c) || 0), 0);

        let timeAgo = 'never';
        if (typeof data.lastSaveTime === 'number') {
            const secs = Math.max(0, Math.floor((Date.now() - data.lastSaveTime) / 1000));
            timeAgo = this.formatTimeAgo(secs);
        }

        return {
            present: true,
            stardust: Number(data.stardust) || 0,
            totalStardust: Number(data.totalStardust) || 0,
            buildings: buildingCount,
            achievements: [
                Array.isArray(data.achievements) ? data.achievements.length : 0,
                33
            ],
            prestigeCount: Number(data.prestigeCount) || 0,
            lastSaved: timeAgo
        };
    },

    /**
     * Format a number of seconds as a compact "time ago" string
     * (e.g. "just now", "1m ago", "3h ago", "2d ago"). Used by slot previews.
     */
    formatTimeAgo(secs) {
        if (secs < 5) return 'just now';

        // Largest units first; each entry is [thresholdSeconds, label].
        const buckets = [
            [365 * 86400, 'y'],
            [30 * 86400, 'mo'],
            [86400, 'd'],
            [3600, 'h'],
            [60, 'm']
        ];

        for (const [threshold, label] of buckets) {
            if (secs >= threshold) {
                const value = Math.floor(secs / threshold);
                return `${value}${label} ago`;
            }
        }

        // Below one minute.
        return `${Math.max(1, secs)}s ago`;
    },

    /**
     * Switch the active save slot. Persists the selection and reloads that
     * slot's data from localStorage into the live game state, preserving
     * prestige-related counters that should carry across slots only when
     * present in the target slot.
     */
    switchSlot(slot) {
        slot = ((parseInt(slot, 10) || 0) + this.config.SLOTS) % this.config.SLOTS;

        // Persist the selection first so loadState() reads it back.
        localStorage.setItem(this.getActiveSlotKey(), String(slot));
        this.state.activeSlot = slot;

        const data = this.loadSlot(slot);
        if (data) {
            try {
                const parsed = JSON.parse(JSON.stringify(data));
                this.state = { ...this.state, ...parsed };
                // Ensure the slot index stays consistent.
                this.state.activeSlot = slot;

                UI.showNotification(
                    `Saved to Slot ${slot + 1}!`, 'success'
                );
            } catch (e) {
                console.error('Failed to load selected slot:', e);
                UI.showNotification('Could not load that slot!', 'warning');
            }
        } else {
            // Target slot is empty: reset to a fresh start but keep essence.
            this.state = {
                stardust: 0,
                totalStardust: 0,
                totalClicks: 0,
                clickPower: 1,
                startTime: Date.now(),
                lastSaveTime: Date.now(),
                buildings: {},
                upgrades: [],
                achievements: [],
                stellarEssence: this.state.stellarEssence || 0,
                prestigeCount: this.state.prestigeCount || 0,
                totalPrestigeEssence: this.state.totalPrestigeEssence || 0,
                prestigeUpgrades: this.state.prestigeUpgrades || [],
                goldenBlooms: { active: false, timer: 0, lastSpawn: Date.now(), totalClaimed: 0 },
                // Reset the temporary golden-bloom production boost so a boost
                // from a previous slot cannot leak into a fresh slot.
                productionBoostUntil: 0,
                activeSlot: slot,
                autoSave: this.state.autoSave
            };
            UI.showNotification(
                `Empty Slot ${slot + 1} - new game started!`, 'success'
            );
        }

        // Re-render dynamic UI and refresh the golden-bloom badge.
        UI.init();
        UI.update();
    },

    /**
     * Export a single slot's save as base64 (for backup or transfer).
     */
    exportSlotToBase64(slot) {
        const data = this.loadSlot(slot);
        if (!data) {
            UI.showNotification(`Slot ${slot + 1} is empty!`, 'warning');
            return null;
        }
        const encoded = btoa(JSON.stringify(data));
        navigator.clipboard.writeText(encoded).then(() => {
            UI.showNotification(`Slot ${slot + 1} copied to clipboard!`, 'success');
        });
        return encoded;
    },

    /**
     * Import base64 save data into a chosen slot.
     */
    importSlotFromData(data, slot) {
        try {
            const parsed = JSON.parse(atob(data));
            localStorage.setItem(this.getSaveKey(slot), JSON.stringify(parsed));
            UI.showNotification(`Imported into Slot ${slot + 1}!`, 'success');

            // If we imported into the active slot, reload it.
            if (parseInt(slot, 10) === this.state.activeSlot) {
                this.switchSlot(slot);
            } else {
                UI.update();
            }
            return true;
        } catch (e) {
            UI.showNotification('Invalid save data!', 'warning');
            return false;
        }
    },

    /**
     * Export save as base64
     */
    exportSave() {
        this.save();
        const data = btoa(JSON.stringify(this.state));
        navigator.clipboard.writeText(data).then(() => {
            UI.showNotification('Save copied to clipboard!', 'success');
        });
    },

    /**
     * Reset game
     */
    reset() {
        localStorage.removeItem('cosmicGardenSave');
        this.state = {
            stardust: 0,
            totalStardust: 0,
            totalClicks: 0,
            clickPower: 1,
            startTime: Date.now(),
            lastSaveTime: Date.now(),
            buildings: {},
            upgrades: [],
            achievements: [],
            stellarEssence: 0,
            prestigeCount: 0,
            totalPrestigeEssence: 0,
            prestigeUpgrades: [],
            goldenBlooms: { active: false, timer: 0, lastSpawn: Date.now(), totalClaimed: 0 },
            activeSlot: this.state.activeSlot,
            autoSave: this.state.autoSave
        };
        UI.update();
        UI.showNotification('Game reset!', 'warning');
    },

    /**
     * Format numbers with commas
     */
    formatNumber(num) {
        if (num >= 1e12) return (num / 1e12).toFixed(2) + 'T';
        if (num >= 1e9) return (num / 1e9).toFixed(2) + 'B';
        if (num >= 1e6) return (num / 1e6).toFixed(2) + 'M';
        if (num >= 1e3) return (num / 1e3).toFixed(2) + 'K';
        return Math.floor(num).toLocaleString();
    },

    /**
     * Create ripple effect on button click
     */
    createRipple(button, event) {
        const ripple = document.createElement('span');
        ripple.className = 'ripple';

        const rect = button.getBoundingClientRect();
        const size = Math.max(rect.width, rect.height);
        const x = event.clientX - rect.left - size / 2;
        const y = event.clientY - rect.top - size / 2;

        ripple.style.width = ripple.style.height = `${size}px`;
        ripple.style.left = `${x}px`;
        ripple.style.top = `${y}px`;

        button.appendChild(ripple);
        setTimeout(() => ripple.remove(), 600);
    },

    /**
     * Animate click button with glow effect
     */
    animateClickButton(button) {
        button.classList.add('clicked');
        setTimeout(() => button.classList.remove('clicked'), 200);
    }
};

// Make Game globally accessible
window.Game = Game;