snake.js

import { getInputDirection } from './input.js';

const steps = [10, 20, 30, 40, 50];
const DEFAULT_SNAKE_SPEED = 5;
const HEAD = 0;
const snakeBody = [{ x: 13, y: 13 }];
let snakeSpeed = DEFAULT_SNAKE_SPEED;
let newSegments = 0;

export function getSpeed() {
  return snakeSpeed;
}

export function update() {
  addSegment();

  const direction = getInputDirection();

  for (let i = snakeBody.length - 2; i >= HEAD; i--) {
    snakeBody[i + 1] = { ...snakeBody[i] };
  }
  snakeBody[HEAD].x += direction.x;
  snakeBody[HEAD].y += direction.y;
}

export function draw(gameboard) {
  snakeBody.forEach((element, index) => {
    const snakeElement = document.createElement('div');
    snakeElement.style.gridRowStart = element.y;
    snakeElement.style.gridColumnStart = element.x;
    snakeElement.classList.add('snake');
    gameboard.appendChild(snakeElement);
  });
}

export function expandSnake(amount) {
  newSegments += amount;
}

export function onSnake(position, { ignoreHead = false } = {}) {
  return snakeBody.some((element, index) => {
    if (ignoreHead && index === HEAD) return false;
    return equalPosition(element, position);
  });
}

export function getSnakeHead() {
  return snakeBody[HEAD];
}

export function snakeIntersection() {
  return onSnake(getSnakeHead(), { ignoreHead: true });
}

function equalPosition(pos1, pos2) {
  return pos1.x === pos2.x && pos1.y === pos2.y;
}

function addSegment() {
  for (let i = 0; i < newSegments; i++) {
    snakeBody.push({ ...snakeBody[snakeBody.length - 1] });

    if (steps.includes(snakeBody.length)) {
      snakeSpeed++;
    }
  }
  newSegments = 0;
}