google app script (spreadsheet) pmt ipmt ppmt

function ppmt_sum(rate, number_of_periods, present_value, number_of_sum_period)
{
  var sum = 0;
  var remain_rounds = number_of_sum_period;  
    
  while (remain_rounds > 0)
  {
    sum += this._my_ppmt(rate, remain_rounds, number_of_periods, present_value) ;
    remain_rounds--;
  }
  
  return sum;
}

//PPMT(rate, period, number_of_periods, present_value, [future_value, end_or_beginning])
function _my_ppmt(rate, period, number_of_periods, present_value, future_value, end_or_beginning) 
{
  if (period < 1 || (period >= number_of_periods + 1)) return null;

  var pmt = this._my_pmt(rate, number_of_periods, present_value, future_value, end_or_beginning);
  var ipmt = this._inner_ipmt(rate, period - 1, pmt, present_value);
  
  return pmt - ipmt;
}

//IPMT(rate, period, number_of_periods, present_value, [future_value], [end_or_beginning])
function _my_ipmt(rate, period, number_of_periods, present_value, future_value, end_or_beginning) 
{
  var pmt = this._my_pmt(rate, number_of_periods, present_value, future_value, end_or_beginning);
  var ppmt = this._my_ppmt(rate, period, number_of_periods, present_value, future_value, end_or_beginning);

  return pmt - ppmt;
}

function _inner_ipmt(rate, period, number_of_periods, present_value) 
{
  var tmp = Math.pow(1 + rate, period);
  return 0 - (present_value * tmp * rate + number_of_periods * (tmp - 1));
}

//PMT(rate, number_of_periods, present_value, [future_value, end_or_beginning])
function _my_pmt(rate, number_of_periods, present_value, future_value, end_or_beginning) 
{
  if (!future_value) future_value = 0;
  if (!end_or_beginning) end_or_beginning = 0;

  if (rate == 0) return -(present_value + future_value)/number_of_periods;
		
  var pvif = Math.pow(1 + rate, number_of_periods);
  var pmt = rate / (pvif - 1) * -(present_value * pvif + future_value);

  if (end_or_beginning == 1) {
	pmt /= (1 + rate);
  };

  return pmt;
}