var bankcalc = {
  _init: function() {
    $("#calcualte-sum").bind('click', this._handleCalculate);
  },
  _handleCalculate: function() {
    var price = parseInt($("#item-price").val());
    var payInSum = parseInt($("#pay-in-sum").val());
    var payIn = parseInt($("#pay-in").val()) / 100 * price;
    var intress = parseFloat($("#payment-intress").html()) / 100;
    var NPV = price - (payInSum || payIn);
    var r = intress/12;
    var n = parseInt($("#payment-period").val());
    var P = (NPV * r) / (1-Math.pow((1+r), n*(-1)));
    var IK = (n * P) - NPV;
    
    $("#monthly-payment").html(Math.round(P));
    $("#intress-sum").html(Math.round(IK));

  }
};

$.widget("ui.bankcalc", bankcalc); // create the widget