// snake
var snake = {
// the positions of all the parts
positions: [],
// the radius of the snake
radius: 1,
// the color of the snake
color: '#ffff00',

// inits the snake
init: function() {
  this.positions.push({
  x: canvas.width / 2,
  y: canvas.height / 2
});

for (let i = 1; i < 200; i++) {
  this.positions.push({
    x: canvas.width / 2,
    y: canvas.height / 2 + 2 * i * this.radius
  });
 }
},

// renders the snake
render: function() {
 ctx.clearRect(0, 0, canvas.width, canvas.height);

 ctx.fillStyle = this.color;

  for (let i = 0; i < this.positions.length; i++) {
  ctx.beginPath();

  ctx.arc(
    this.positions[i].x,
    this.positions[i].y,
    this.radius,
    0, 2 * Math.PI
  );

  ctx.closePath();
  ctx.fill();
 }
 },

// moves the snake to a new point
moveTo: function(x, y) {
// positions[0] is the head of the snake
this.positions[0].x = x;
this.positions[0].y = y;

this.join();
},

join: function() {
// loop through each position
for (let i = 1; i < this.positions.length; i++) {
  // get last and current position
  var last = this.positions[i - 1];
  var curr = this.positions[i];

  // get difference in x and y of each position
  var dx = curr.x - last.x;
  var dy = curr.y - last.y;

  // calculate the angle between the two parts of the snake
  var angle = Math.atan2(dy, dx);

  // get the new x and new y using polar coordinates
  var nx = 2 * this.radius * Math.cos(angle);
  var ny = 2 * this.radius * Math.sin(angle);

  // add the new x and new y to the last snake's position to "join" the two
  //together without a gap
  curr.x = nx + last.x;
  curr.y = ny + last.y;
}
},

// slithers the snake smoothly to a new point
slither (x, y) {
var head = snake.positions[0];

// smooth movement
var nx = head.x + (x - head.x)/10 ;
var ny = head.y + (y - head.y) /10;

this.moveTo(nx, ny);
}
};

// inits the snake
snake.init();

var mouse = false;
window.addEventListener('mousemove', function(e) {
mouse = {
x: e.clientX,
y: e.clientY
};
});

window.requestAnimationFrame(function loop() {
window.requestAnimationFrame(loop);

// slithers the snake to a new point
if (mouse) {
snake.slither(mouse.x, mouse.y);
 }

// renders the snake
snake.render();