// Snake Game Logic
(function () {
  'use strict';

  const canvas = document.getElementById('gameCanvas');
  const ctx = canvas.getContext('2d');
  const scoreEl = document.getElementById('score');
  const highScoreEl = document.getElementById('high-score');
  const restartBtn = document.getElementById('restartBtn');

  const GRID_SIZE = 20;          // size of each cell in pixels
  const COLS = canvas.width / GRID_SIZE;
  const ROWS = canvas.height / GRID_SIZE;

  let snake, direction, nextDirection, food, score, highScore, gameOver, gameLoop;

  highScore = Number(localStorage.getItem('snakeHighScore')) || 0;
  highScoreEl.textContent = highScore;

  // Initialize a new game state
  function init() {
    snake = [
      { x: 10, y: 10 },
      { x: 9, y: 10 },
      { x: 8, y: 10 }
    ];
    direction = { x: 1, y: 0 };
    nextDirection = { x: 1, y: 0 };
    score = 0;
    gameOver = false;
    scoreEl.textContent = score;
    placeFood();

    if (gameLoop) clearInterval(gameLoop);
    gameLoop = setInterval(update, 100);
  }

  // Place food at a random empty cell
  function placeFood() {
    let newFood;
    do {
      newFood = {
        x: Math.floor(Math.random() * COLS),
        y: Math.floor(Math.random() * ROWS)
      };
    } while (snake.some(seg => seg.x === newFood.x && seg.y === newFood.y));
    food = newFood;
  }

  // Update game state each tick
  function update() {
    if (gameOver) return;

    direction = nextDirection;

    const head = {
      x: snake[0].x + direction.x,
      y: snake[0].y + direction.y
    };

    // Wall collision
    if (head.x < 0 || head.x >= COLS || head.y < 0 || head.y >= ROWS) {
      return endGame();
    }

    // Self collision
    if (snake.some(seg => seg.x === head.x && seg.y === head.y)) {
      return endGame();
    }

    snake.unshift(head);

    // Eat food
    if (head.x === food.x && head.y === food.y) {
      score += 10;
      scoreEl.textContent = score;
      if (score > highScore) {
        highScore = score;
        highScoreEl.textContent = highScore;
        localStorage.setItem('snakeHighScore', highScore);
      }
      placeFood();
    } else {
      snake.pop();
    }

    draw();
  }

  // Draw everything on the canvas
  function draw() {
    // Background
    ctx.fillStyle = '#16213e';
    ctx.fillRect(0, 0, canvas.width, canvas.height);

    // Grid lines (subtle)
    ctx.strokeStyle = 'rgba(78, 204, 163, 0.08)';
    for (let i = 1; i < COLS; i++) {
      ctx.beginPath();
      ctx.moveTo(i * GRID_SIZE, 0);
      ctx.lineTo(i * GRID_SIZE, canvas.height);
      ctx.stroke();
    }
    for (let j = 1; j < ROWS; j++) {
      ctx.beginPath();
      ctx.moveTo(0, j * GRID_SIZE);
      ctx.lineTo(canvas.width, j * GRID_SIZE);
      ctx.stroke();
    }

    // Food
    ctx.fillStyle = '#e94560';
    ctx.beginPath();
    ctx.arc(
      food.x * GRID_SIZE + GRID_SIZE / 2,
      food.y * GRID_SIZE + GRID_SIZE / 2,
      GRID_SIZE / 2 - 2,
      0,
      Math.PI * 2
    );
    ctx.fill();

    // Snake
    snake.forEach((seg, i) => {
      ctx.fillStyle = i === 0 ? '#4ecca3' : '#3aa886';
      ctx.fillRect(
        seg.x * GRID_SIZE + 1,
        seg.y * GRID_SIZE + 1,
        GRID_SIZE - 2,
        GRID_SIZE - 2
      );
    });

    // Game over overlay
    if (gameOver) {
      ctx.fillStyle = 'rgba(0, 0, 0, 0.7)';
      ctx.fillRect(0, 0, canvas.width, canvas.height);
      ctx.fillStyle = '#e94560';
      ctx.font = 'bold 32px sans-serif';
      ctx.textAlign = 'center';
      ctx.fillText('Game Over', canvas.width / 2, canvas.height / 2 - 10);
      ctx.fillStyle = '#eee';
      ctx.font = '18px sans-serif';
      ctx.fillText('Press Restart to play again', canvas.width / 2, canvas.height / 2 + 30);
    }
  }

  // End the game
  function endGame() {
    gameOver = true;
    clearInterval(gameLoop);
    draw();
  }

  // Keyboard controls
  document.addEventListener('keydown', (e) => {
    const key = e.key.toLowerCase();
    let newDir = null;

    if (key === 'arrowup' || key === 'w') newDir = { x: 0, y: -1 };
    else if (key === 'arrowdown' || key === 's') newDir = { x: 0, y: 1 };
    else if (key === 'arrowleft' || key === 'a') newDir = { x: -1, y: 0 };
    else if (key === 'arrowright' || key === 'd') newDir = { x: 1, y: 0 };

    if (!newDir) return;
    e.preventDefault();

    // Prevent reversing direction
    if (newDir.x === -direction.x && newDir.y === -direction.y) return;
    nextDirection = newDir;
  });

  restartBtn.addEventListener('click', init);

  // Start the game
  init();
})();