const SMALLEST_SIZE = 4.0;
const LARGEST_SIZE = 48.0;

const DEFAULT_SIZE = 24.0;

class State {
  updateWindowSize(w, h) {
    this.w = w;
    this.h = h;
    this.canvas.width = w;
    this.canvas.height = h;
    this.data = {};
  }

  constructor(canvas, ctx, w, h) {
    this.canvas = canvas;
    this.ctx = ctx;
    this.updateWindowSize(w, h);
    this.size = DEFAULT_SIZE;
    this.mode = 'square';
  }

  scroll(delta) {
    this.size += delta / 30.0;
    if (this.size < SMALLEST_SIZE) {
      this.size = SMALLEST_SIZE;
    } else if (this.size > LARGEST_SIZE) {
      this.size = LARGEST_SIZE;
    }
  }

  draw(mouseLoc) {
    this.ctx.clearRect(0, 0, this.w, this.h);

    if (mouseLoc !== null) {
      let [fx, fy] = mouseLoc;
      this.ctx.fillStyle = '#f00';

      if (this.mode === 'square') {
        fx = Math.floor(fx / this.size);
        fy = Math.floor(fy / this.size);
        this.ctx.fillRect(fx * this.size, fy * this.size, this.size, this.size);
      } else {
        this.ctx.strokeStyle = '#f00';
        const half = this.size / 2
        fx = Math.floor((fx + half) / this.size);
        fy = Math.floor((fy + half) / this.size);
        this.ctx.moveTo(fx * this.size, fy * this.size);
        this.ctx.arc(fx * this.size, fy * this.size, 5, 0, Math.PI * 2, true);
        this.ctx.stroke();
      }
    }

    this.ctx.strokeStyle = '#000';
    for (let x = 0; Math.floor(x / this.size < this.w); x++) {
      this.ctx.beginPath();
      this.ctx.moveTo(x * this.size, 0);
      this.ctx.lineTo(x * this.size, this.h);
      this.ctx.stroke();
    }

    for (let y = 0; Math.floor(y / this.size < this.h); y++) {
      this.ctx.beginPath();
      this.ctx.moveTo(0, y * this.size);
      this.ctx.lineTo(this.w, y * this.size);
      this.ctx.stroke();
    }
  }
}

let main = () => {
  const canvas = document.getElementById('cv');

  const w = window.innerWidth;
  const h = window.innerHeight;

  const ctx = canvas.getContext('2d');

  let state = new State(canvas, ctx, w, h);
  let last_mouse = null;
  state.draw(last_mouse);

  document.addEventListener('mousemove', e => {
    last_mouse = [e.clientX, e.clientY];
    state.draw(last_mouse);
  });

  document.addEventListener('wheel', e => {
    state.scroll(-e.deltaY);
    state.draw(last_mouse);
  });

  window.addEventListener('resize', () => {
    state.updateWindowSize(
      window.innerWidth,
      window.innerHeight,
    );
    state.draw(last_mouse);
  });

  document.addEventListener('keydown', e => {
    if (e.key === ' ') {
      if (state.mode === 'square')
        state.mode = 'dot';
      else
        state.mode = 'square';
    }
    state.draw(last_mouse);
  });
};

window.onload = main;