let graphics = []; 
let gSprite; 
let flakes = []; 

const SPRITE_AMOUNT = 6;
const DENSITY = .5;
let N = 1;
const DRAW_SIZE_MIN = 20;
const DRAW_SIZE_MAX = 50;

let DRAW_SPRITE = false;

function setup() {
  N = Math.floor(DENSITY * (windowWidth*windowHeight)/(DRAW_SIZE_MAX* DRAW_SIZE_MAX));
  
  createCanvas(windowWidth, windowHeight);
  imageMode(CENTER);
  rectMode(CENTER);
  
  generate_snowflake_sprite();
  
  for (var x = 0; x < N; x++) {
    flakes.push(new Snowflake(random(width), random(height)));
  }
}

function generate_snowflake_sprite() {
   gSprite = createGraphics(100 * SPRITE_AMOUNT, 100);
   graphics=[];
  for (let x = 0; x < SPRITE_AMOUNT; x++) {
    var g = createGraphics(100,100);
    generateSnowflake(g); 
    gSprite.image(g, x*100, 0);
    graphics.push(g);  
  }
  
  
  document.getElementById("snowflake_sprite").setAttribute("src", gSprite.canvas.toDataURL());
}


function windowResized() {
  N = Math.floor(DENSITY * (windowWidth*windowHeight)/(DRAW_SIZE_MAX* DRAW_SIZE_MAX));
  flakes = [];
  
  resizeCanvas(windowWidth, windowHeight);
  
  
  for (var x = 0; x < N; x++) {
    flakes[x] = (new Snowflake(random(width), random(height)));
  }
}

function draw() {
  clear();
  for (var x = flakes.length - 1 ; x >=0; x--) {
    let fl = flakes[x];
    fl.update();
    fl.draw();  
    if (fl.isOutOfView()) {
      flakes[x] = new Snowflake();
    }
  }
  
  if (DRAW_SPRITE) {
    var scale_factor = 1;
    if (gSprite.width > width) scale_factor =  width / gSprite.width;
    fill(0);
    rect(width/2,height/2,(gSprite.width + 10)*scale_factor, (gSprite.height + 10)*scale_factor);
    image(gSprite,width/2,height/2, gSprite.width * scale_factor, gSprite.height * scale_factor);
  }
}

function mouseReleased(e) {
  if (e.button == 0) {
    generate_snowflake_sprite();
    //DRAW_SPRITE = !DRAW_SPRITE;
  }
  
}

function Snowflake(x,y) {
  this.size = random(DRAW_SIZE_MAX - DRAW_SIZE_MIN) + DRAW_SIZE_MIN;
  if (typeof x == "undefined") x = random(width)
  if (typeof y == "undefined") y = -this.size;  
  this.pos = createVector(x,y);
  this.vel = createVector(0,1);
  this.index = Math.floor(random(SPRITE_AMOUNT));
  
  this.spriteSize = 100;
  this.rot = random(TWO_PI); 
  this.rotNoiseX = random(1000);
}
Snowflake.prototype.update = function() {
  let v = this.vel.copy();
  v.mult(this.size*this.size / 1000);
  
  this.pos.add(v);
  
  this.vel.rotate(random(-.05, .05));
  
  this.rot += (noise(this.rotNoiseX) - .5) / 10; 
  this.rotNoiseX += .01;
}
Snowflake.prototype.draw = function() {
  push();
  translate(this.pos.x, this.pos.y);
  rotate(this.rot);
  image(gSprite, 0, 0, this.size, this.size, 
        this.spriteSize*this.index, 0, this.spriteSize, this.spriteSize);
  pop();
}
Snowflake.prototype.isOutOfView = function() {
  return (this.pos.x < -this.size || this.pos.y < -this.size || this.pos.x > width + this.size || this.pos.y > height + this.size);
}


function generateSnowflake(g) {
  let snowflake = [];
  g.translate(g.width/2, g.height/2);
  g.rotate(PI/6);
  let current = new Particle(height/2, 0);
  
  while(true) {
    let count = 0;
    while (!current.finished() && !current.intersects(snowflake)) {
      current.update();
      count++;
    }
    snowflake.push(current);
    current = new Particle(g.height/2, 0);

    
    // If a particle doesn't move at all we're done
    // This is an exit condition not implemented in the video
    if (count == 0) {
      
      for (let i = 0; i < 6; i++) {
        g.rotate(PI/3);
        for (let p of snowflake) {
          p.show(g);
        }

        g.push();
        g.scale(1, -1);
        for (let p of snowflake) {
          p.show(g);
        }
        g.pop();
      }
      
      return;
    }
    
  }
}

// Coding Challenge 127: Brownian Motion Snowflake
// Daniel Shiffman
// https://thecodingtrain.com/CodingChallenges/127-brownian-snowflake.html
// https://youtu.be/XUA8UREROYE

class Particle {

  constructor(radius, angle) {
    this.pos = p5.Vector.fromAngle(angle);
    this.pos.mult(radius);
    this.r = 1;
  }

  update() {
    this.pos.x -= 1;
    this.pos.y += random(-2, 2);

    let angle = this.pos.heading();
    angle = constrain(angle, 0, PI/6);
    let magnitude = this.pos.mag();
    this.pos = p5.Vector.fromAngle(angle);
    this.pos.setMag(magnitude);
  }

  show(g) {
    g.fill(255);
    g.noStroke();
    g.ellipse(this.pos.x, this.pos.y, this.r * 2);
  }

  intersects(snowflake) {
    let result = false;
    for (let s of snowflake) {
      let d = dist(s.pos.x, s.pos.y, this.pos.x, this.pos.y); 
      if (d < this.r * 2) {
        result = true;
        break;
      }
    }
    return result;
  }

  finished() {
    return (this.pos.x < 1);
  }
}