class Clock{
  constructor(layers){
    layers = (typeof(layers === 'number') && layers > 0) ?
      Math.floor(layers) :
      1;
    this.__ticktime = 1000;
    this.__dt = -1;
    this.__out = [];
    this.__cl = 0;
    for (let i=0; i < layers; i++)
      this.__out.push([]);
  }

  get hz(){return Math.floor(1000 / this.__ticktime);}
  set hz(hz){
    if(hz >= 1){
      this.__ticktime = 1000 / hz;
      this.__dt = -1;
    }
  }

  get layers(){return this.__out.length;}

  clk(fn, layer){
    layer = (typeof(layer === 'number') && layer >= 0) ?
      Math.floor(layer) :
      0;
    if (layer < 0 || layer >= this.__out.length)
      throw new RangeError("Layer out of bounds.");

    if (typeof(fn) === 'function')
      this.__out[layer].push(fn);
    return this;
  }

  // NOTE: dt in milliseconds.
  tick(dt){
    let extraTick = false;
    if (this.__dt < 0){
      this.__dt = 0;
      extraTick = true;
    }
    let proc = (ddt) => {
      this.__out[this.__cl].forEach((fn)=>{fn();});
      if (ddt)
        this.__dt -= this.__ticktime;
      if (this.__out.length > 1)
        this.__cl = (this.__cl === this.__out.length - 1) ? 0 : this.__cl + 1;
    };


    this.__dt += dt;
    while(this.__dt > this.__ticktime)
      proc(true);
    if (extraTick)
      proc(false);

    return this;
  }
}


module.exports = Clock;