var round1 = makeRoundFunction(1);
var round4 = makeRoundFunction(4);
var beats = new beatsConstructor(10);

$(function(){
    var bpmText = $('#bpm');
    var quarter = $('#quarter');
    var half = $('#half');
    var one = $('#one');
    var two = $('#two');
    var four = $('#four');
    $(document).keydown(function(event){
        bpmText.css('background', "#ffff66");
        beats.add(new Date().getTime());
        var period = beats.getPeriod();
        if (period == 0) return;
        bpmText.html(round1(60.0 / period));
        quarter.html(round4(period / 4.0));
        half.html(round4(period / 2.0));
        one.html(round4(period));
        two.html(round4(period * 2));
        four.html(round4(period * 4));
    }).keyup(function(event){
        bpmText.css('background', "#ffffff")
    });
    
});

function makeRoundFunction(places){
    var multiplier = 1;
    for (var i = 0; i < places; i++) {
        multiplier *= 10;
    }
    return function(number){
        return Math.round(number * multiplier) / multiplier
    };
}

function beatsConstructor(maxBeats){
   this.lastTime = new Date().getTime();
   this.maxBeats = maxBeats;
   this.array = new Array();
   this.add = function(t){
      if ((t - this.lastTime) > 3000) this.array = new Array();
      this.lastTime = t;
      this.array.push(t);
      if (this.array.length >= this.maxBeats) this.array.shift();
   }
   this.getPeriod = function(){
      if (this.array.length < 2) return 0;
      return (-0.0 + this.array[this.array.length-1] - this.array[0]) / (this.array.length -1) / 1000;
   }
   
}