const START_SEGMENTS = 10;
const SEG_LEN = 10;
const SPEED = 4;
const WIDTH = 300;
const HEIGHT = 300;
const APPLE_SIZE = 20;
const APPLE_R = APPLE_SIZE/2;
const SPACE_BAR = 32;
let head;
let tail;
let apple;
let turn = 0;
let speedup = 0;

const isOutside = (aVec) => (
        aVec.x > WIDTH ||
        aVec.x < 0 ||
        aVec.y > HEIGHT ||
        aVec.y < 0);


function setup() {
  // put setup code here
  apple = new Vector(random(APPLE_R,WIDTH-APPLE_R),
                        random(APPLE_R,HEIGHT-APPLE_R));
  tail = new Segment(WIDTH/2, 0, 10, HALF_PI);
  head = tail
  for(let i = 0; i < START_SEGMENTS; i++){
    let pos = head.end();
    head.child = new Segment(pos.x, pos.y, 10, HALF_PI);
    head.child.parent = head;
    head = head.child;
  }
  createCanvas(300,300);
  frameRate(15);
}

function draw() {
  // put drawing code here
  background(0);
  for(let current = tail; current !== null; current= current.child){
    current.draw();
  }
  fill(0, 255, 0);
  noStroke();
  circle(apple.x, apple.y, APPLE_SIZE);
  // update
  head.heading += turn * PI/18;
  head.start.add(p5.Vector.fromAngle(head.heading, SPEED*(1+speedup)));
  head.update();
  head_end = head.end();
  if(Vector.sub(head_end, apple).mag() < APPLE_SIZE){
        apple = new Vector(random(APPLE_R,WIDTH-APPLE_R),
                            random(APPLE_R,HEIGHT-APPLE_R));
        for(let i=1; i<=3; i++){
            let end = tail.end();
            let heading = tail.heading;
            tail = tail.expand_parent(end.x, end.y, SEG_LEN, heading+ PI);
        }
  }
  // Game over
  if(isOutside(head_end) || head.eats_parents())
  {
    background(128);
    textSize(HEIGHT/10);
    textAlign(CENTER);
    text("Game Over! Refresh page to restart.",
            0.1*WIDTH, 0.1*HEIGHT,
            0.8*WIDTH, 0.8*HEIGHT)
    noLoop();
  };
}

function keyPressed(){
    switch(keyCode){
        case LEFT_ARROW:
            turn = -1;
            break;
        case RIGHT_ARROW:
            turn = +1;
            break;
        case SPACE_BAR:
            speedup = 1;
            break;
    }
}

function keyReleased(){
    switch(keyCode){
        case LEFT_ARROW:
        case RIGHT_ARROW:
            turn = 0;
            break;
        case SPACE_BAR:
            speedup = 0;
            break;
    }
}