document.addEventListener('DOMContentLoaded', () => {
    const canvas = document.getElementById('gameCanvas');
    const ctx = canvas.getContext('2d');
    const scoreEl = document.getElementById('score');
    const bestScoreEl = document.getElementById('best-score');
    const playBtn = document.getElementById('play-btn');
    const startScreen = document.getElementById('start-screen');

    const settingsBtn = document.getElementById('settings-btn');
    const closeSettingsBtn = document.getElementById('close-settings-btn');
    const settingsBackdrop = document.getElementById('settings-backdrop');
    const difficultyBtns = document.getElementById('difficulty-btns');
    const themeToggle = document.getElementById('theme-toggle');

    const gridSize = 20;
    canvas.width = 600;
    canvas.height = 600;

    let snake = [{ x: 15, y: 15 }];
    let food = {};
    let direction = 'right';
    let score = 0;
    let bestScore = 0;
    let speed = 200;
    let gameInterval;
    let levelThreshold = 5;
    let gameRunning = false;
    let isGamePausedBySettings = false;

    // --- Settings ---
    function openSettings() {
        if (gameRunning) {
            clearInterval(gameInterval);
            isGamePausedBySettings = true;
        }
        settingsBackdrop.classList.remove('hidden');
    }

    function closeSettings() {
        if (isGamePausedBySettings) {
            gameInterval = setInterval(update, speed);
            isGamePausedBySettings = false;
        }
        settingsBackdrop.classList.add('hidden');
    }

    function setDifficulty(difficulty) {
        switch (difficulty) {
            case 'easy':
                speed = 250;
                break;
            case 'normal':
                speed = 150;
                break;
            case 'hard':
                speed = 75;
                break;
        }
        document.querySelectorAll('.difficulty-btn').forEach(btn => {
            btn.classList.toggle('active', btn.dataset.difficulty === difficulty);
        });
        localStorage.setItem('snakeDifficulty', difficulty);
    }

    function applyTheme(theme) {
        document.body.classList.toggle('light-theme', theme === 'light');
        document.body.classList.toggle('dark-theme', theme === 'dark');
        themeToggle.checked = theme === 'dark';
        localStorage.setItem('snakeTheme', theme);
        draw();
    }

    settingsBtn.addEventListener('click', openSettings);
    closeSettingsBtn.addEventListener('click', closeSettings);
    settingsBackdrop.addEventListener('click', (e) => {
        if (e.target === settingsBackdrop) {
            closeSettings();
        }
    });

    difficultyBtns.addEventListener('click', (e) => {
        if (e.target.classList.contains('difficulty-btn')) {
            setDifficulty(e.target.dataset.difficulty);
        }
    });

    themeToggle.addEventListener('change', () => {
        applyTheme(themeToggle.checked ? 'dark' : 'light');
    });

    const savedDifficulty = localStorage.getItem('snakeDifficulty') || 'normal';
    setDifficulty(savedDifficulty);

    const savedTheme = localStorage.getItem('snakeTheme') || 'dark';
    applyTheme(savedTheme);

    bestScore = localStorage.getItem('snakeBestScore') || 0;
    bestScoreEl.textContent = bestScore;


    // --- Game Logic ---
    function placeFood() {
        food = {
            x: Math.floor(Math.random() * (canvas.width / gridSize)),
            y: Math.floor(Math.random() * (canvas.height / gridSize))
        };
        for (let segment of snake) {
            if (segment.x === food.x && segment.y === food.y) {
                placeFood();
                return;
            }
        }
    }

    function draw() {
        const canvasBg = getComputedStyle(document.body).getPropertyValue('--canvas-bg').trim();

        ctx.fillStyle = canvasBg;
        ctx.fillRect(0, 0, canvas.width, canvas.height);

        snake.forEach((segment, index) => {
            const hue = (segment.x * 5 + segment.y * 5) % 360;
            ctx.fillStyle = `hsl(${hue}, 100%, 50%)`;
            if (index === 0) {
                ctx.fillRect(segment.x * gridSize, segment.y * gridSize, gridSize, gridSize);
            } else {
                ctx.fillRect(segment.x * gridSize + 1, segment.y * gridSize + 1, gridSize - 2, gridSize - 2);
            }
        });

        const foodX = food.x * gridSize;
        const foodY = food.y * gridSize;
        const foodRadius = gridSize / 2.5;

        ctx.save();

        ctx.shadowColor = '#A020F0';
        ctx.shadowBlur = 20;

        const gradient = ctx.createRadialGradient(
            foodX + foodRadius, foodY + foodRadius, foodRadius * 0.1,
            foodX + foodRadius, foodY + foodRadius, foodRadius
        );
        gradient.addColorStop(0, '#E0B0FF');
        gradient.addColorStop(1, '#8A2BE2');

        ctx.fillStyle = gradient;
        ctx.beginPath();
        ctx.arc(foodX + gridSize / 2, foodY + gridSize / 2, foodRadius, 0, 2 * Math.PI);
        ctx.fill();

        ctx.restore();
    }

    function update() {
        if (!gameRunning) return;

        const head = { ...snake[0] };
        switch (direction) {
            case 'up': head.y--; break;
            case 'down': head.y++; break;
            case 'left': head.x--; break;
            case 'right': head.x++; break;
        }

        if (head.x < 0 || head.x >= canvas.width / gridSize || head.y < 0 || head.y >= canvas.height / gridSize) {
            return gameOver();
        }

        for (let i = 1; i < snake.length; i++) {
            if (head.x === snake[i].x && head.y === snake[i].y) {
                return gameOver();
            }
        }

        snake.unshift(head);

        if (head.x === food.x && head.y === food.y) {
            score++;
            scoreEl.textContent = score;
            placeFood();
            if (score % levelThreshold === 0) {
                increaseSpeed();
            }
        } else {
            snake.pop();
        }

        draw();
    }

    function increaseSpeed() {
        clearInterval(gameInterval);
        speed = Math.max(50, speed * 0.9);
        gameInterval = setInterval(update, speed);
    }

    function gameOver() {
        clearInterval(gameInterval);
        isGamePausedBySettings = false;

        if (score > bestScore) {
            bestScore = score;
            localStorage.setItem('snakeBestScore', bestScore);
            bestScoreEl.textContent = bestScore;
        }

        startScreen.style.display = 'flex';
        startScreen.querySelector('h1').textContent = 'Game Over';
        playBtn.textContent = 'Play Again';
        gameRunning = false;
    }

    function startGame() {
        snake = [{ x: 15, y: 15 }];
        direction = 'right';
        score = 0;
        scoreEl.textContent = score;
        gameRunning = true;
        isGamePausedBySettings = false;
        startScreen.style.display = 'none';
        
        const currentDifficulty = localStorage.getItem('snakeDifficulty') || 'normal';
        setDifficulty(currentDifficulty);

        placeFood();
        clearInterval(gameInterval);
        gameInterval = setInterval(update, speed);
    }

    playBtn.addEventListener('click', startGame);

    document.addEventListener('keydown', e => {
        const key = e.key;
        if ((key === 'ArrowUp' || key.toLowerCase() === 'w') && direction !== 'down') direction = 'up';
        if ((key === 'ArrowDown' || key.toLowerCase() === 's') && direction !== 'up') direction = 'down';
        if ((key === 'ArrowLeft' || key.toLowerCase() === 'a') && direction !== 'right') direction = 'left';
        if ((key === 'ArrowRight' || key.toLowerCase() === 'd') && direction !== 'left') direction = 'right';
    });

    draw();
});