let params = {
  letterCount: 10,
  letterSize: 12, letterSizeMin: 1, letterSizeMax: 48,
  letterSizeVariance: 0.0, letterSizeVarianceMin: 0.0, letterSizeVarianceMax: 1.0, letterSizeVarianceStep: 0.01,
  
  speed: 0.5, speedMin: 0.1, speedMax: 4.0, speedStep: 0.01,
  speedVariance: 0.0, speedVarianceMin: 0.0, speedVarianceMax: 10.0, speedVarianceStep: 0.01,
  
  color: '#0fff00',
  
  fadeRate: 0.1, fadeRateMin: 0, fadeRateMax: 0.3, fadeRateStep: 0.01,
  
  characterSet: [
    'unknown',
  ]
};
let letters;

let characterSets = [
  ['latin', 'A', 'Z'],
  ['cjk', '一', '龯'],
  // ['cuneiform', '𒀀', '𒎙'],
  ['runic', 'ᚠ', 'ᛪ'],
  ['greek', 'α', 'ω'],
];

function randomChar(min, max) {

}

function randomLetter() {
  for (let [name, min, max] of characterSets) {
    if (params.characterSet == name) {
      return String.fromCharCode(
        random(
          min.charCodeAt(0),
          max.charCodeAt(0) + 1
        )
      );
    }
  }
       
  return '☹️';
}

class Letter {
  constructor(c, x, s) {
    this.x = x; 
    this.y = -1 * random(height);
    this.c = c;
    this.s = s + (
      s
      * (random() + 0.5)
      * params.letterSizeVariance
    );
    this.sv = (random() - 0.5) * params.speedVariance;
  }
  
  update() {
    this.y += (
      this.s * params.speed
      + this.sv * params.speed
    );
  }
  
  draw() {
    textSize(this.s);
    noStroke();
    fill(params.color);
    text(this.c, this.x, this.y);
  }
}

class Letters {
  constructor() {
    this.letters = [];
  }
  
  update() {
    while (this.letters.length < params.letterCount) {
      this.letters.push(new Letter(
        randomLetter(),
        random(width),
        params.letterSize
      ));
    }
    
    for (let letter of this.letters) {
      letter.update();
    }
    
    for (let i = 0; i < this.letters.length; i++) {
      if (this.letters[i].y > height && random() > 0.95) {
        this.letters.splice(i, 1);
        i--;
      }
    }
  }
  
  draw() {
    for (let letter of this.letters) {
      letter.draw();
    }
  }
}

function setup() {
  createCanvas(400, 400);
  background(0);
  
  params.characterSet = [];
  for (let [name, min, max] of characterSets) {
    params.characterSet.push(name);
  }
  
  gui = createGuiPanel('params');
  gui.addObject(params);
  gui.setPosition(420, 0);

  letters = new Letters();
}

function draw() {
  background(0, parseInt(255 * params.fadeRate));
  
  letters.update();
  letters.draw();
}