// get elements from page
const info = document.getElementById("info");
const highscore = document.getElementById("highscore");
const canvas = document.getElementById("canvas");

const ctx = canvas.getContext("2d");
const game = {
  size: 15,
  speed: 1000 / 15, // 15 frames per second
  snek: {
    body: [
      [3, 7],
      [4, 7],
      [5, 7],
      [6, 7],
      [7, 7],
    ],
    dir: null,
    newdir: null,
  },
  apple: [12, 7],
  highscore: 0,
};

// reset the game board (but not the highscore)
function reset() {
  game.apple = [12, 7];
  game.snek.body = [
    [3, 7],
    [4, 7],
    [5, 7],
    [6, 7],
    [7, 7],
  ];
  game.snek.dir = null;
  game.snek.newdir = null;
}

// check if the x and y coordinate is part of the snek
function inSnek(x, y) {
  for (let part of game.snek.body) {
    if (part[0] === x && part[1] === y) return true;
  }
  return false;
}

// draw the game board
function draw() {
  const size = 25;
  ctx.clearRect(0, 0, 500, 500);
  for (let i = 0; i < game.size; i++) {
    for (let j = 0; j < game.size; j++) {
      ctx.fillStyle = inSnek(i, j)
        ? "#38e070"
        : i === game.apple[0] && j === game.apple[1]
        ? "#eb4034"
        : "#333333";
      ctx.fillRect(i * size, j * size, size, size);
    }
  }
}

// update the game board
function update() {
  game.snek.dir = game.snek.newdir;

  const b = game.snek.body;
  const l = b[b.length - 1];
  const next = move();

  // check if the snek ate the apple
  if (game.apple[0] === next[0] && game.apple[1] === next[1]) {
    // the apple shouldnt be on top of the snek
    // try 30 times to place the apple
    for (let i = 0; i < 30; i++) {
      const x = Math.floor(Math.random() * game.size);
      const y = Math.floor(Math.random() * game.size);
      game.apple = [x, y];

      if (!inSnek(game.apple[0], game.apple[1])) break;
    }
  } else {
    b.shift();
  }

  // check if the snek crashed into itself
  if (inSnek(next[0], next[1])) {
    reset();
  }

  // check if the snek fell out of the world
  if (l[0] < 0 || l[0] >= game.size || l[1] < 0 || l[1] >= game.size) {
    reset();
  }

  // uncomment to wrap
  // if (next[0] < 0) next[0] = game.size - 1;
  // if (next[0] >= game.size) next[0] = 0;
  // if (next[1] < 0 ) next[1] = game.size - 1;
  // if (next[1] >= game.size) next[1] = 0;

  b.push(next); // move the snek

  // update score display
  if (game.snek.dir !== null) {
    const score = b.length - 5;
    if (score > game.highscore) game.highscore = score; // update high score if necessary
    info.innerText = `${score < 15 ? "length" : "longth"}: ${score}`;
    highscore.innerText = `highscore: ${game.highscore}\n`;
  }

  // calculate where the snek will move to
  function move() {
    const [x, y] = l;
    switch (game.snek.dir) {
      case "left":
        return [x - 1, y];
      case "right":
        return [x + 1, y];
      case "up":
        return [x, y - 1];
      case "down":
        return [x, y + 1];
      default:
        return [x, y];
    }
  }
}

// change direction on keypress
document.addEventListener("keydown", (e) => {
  if (e.ctrlKey || e.shiftKey) return;

  const s = game.snek;
  if (s.dir !== s.newdir) update(); // avoid snek from crashing into itself
  e.preventDefault();
  switch (e.key) {
    case "ArrowLeft":
      return s.dir !== "right" ? (s.newdir = "left") : 0;
    case "ArrowRight":
      return s.dir !== "left" ? (s.newdir = "right") : 0;
    case "ArrowUp":
      return s.dir !== "down" ? (s.newdir = "up") : 0;
    case "ArrowDown":
      return s.dir !== "up" ? (s.newdir = "down") : 0;
  }
});

// the main game loop
setInterval(() => {
  update();
  draw();
}, game.speed);