package org.apache.poi.ss.formula.functions;


/**
  * Implementation of the financial functions pmt, fv, ppmt, ipmt.
  * 
  * @author Mike Argyriou micharg@gmail.com
  */
public class Finance {

	/**
     * Emulates Excel/Calc's PMT(interest_rate, number_payments, PV, FV, Type)
     * function, which calculates the payments for a loan or the future value of an investment
     * 
     * @param r
     *            - periodic interest rate represented as a decimal.
     * @param nper
     *            - number of total payments / periods.
     * @param pv
     *            - present value -- borrowed or invested principal.
     * @param fv
     *            - future value of loan or annuity.
     * @param type
     *            - when payment is made: beginning of period is 1; end, 0.
     * @return <code>double</code> representing periodic payment amount.
     */
	// http://arachnoid.com/lutusp/finance.html
	static public double pmt(double r, int nper, double pv, double fv, int type) {
	    double pmt = -r * (pv * Math.pow(1 + r, nper) + fv) / ((1 + r*type) * (Math.pow(1 + r, nper) - 1));
	    return pmt;
	}


	/**
     * Overloaded pmt() call omitting type, which defaults to 0.
     * 
     * @see #pmt(double, int, double, double, int)
     */
	static public double pmt(double r, int nper, double pv, double fv) {
	    return pmt(r, nper, pv, fv, 0);
	}
	
	/**
     * Overloaded pmt() call omitting fv and type, which both default to 0.
     * 
     * @see #pmt(double, int, double, double, int)
     */
	static public double pmt(double r, int nper, double pv) {
	    return pmt(r, nper, pv, 0);
	}
	
	
	/**
     * Emulates Excel/Calc's IPMT(interest_rate, period, number_payments, PV,
     * FV, Type) function, which calculates the portion of the payment at a
     * given period that is the interest on previous balance.
     * 
     * @param r
     *            - periodic interest rate represented as a decimal.
     * @param per
     *            - period (payment number) to check value at.
     * @param nper
     *            - number of total payments / periods.
     * @param pv
     *            - present value -- borrowed or invested principal.
     * @param fv
     *            - future value of loan or annuity.
     * @param type
     *            - when payment is made: beginning of period is 1; end, 0.
     * @return <code>double</code> representing interest portion of payment.
     * 
     * @see #pmt(double, int, double, double, int)
     * @see #fv(double, int, double, double, int)
     */
	// http://doc.optadata.com/en/dokumentation/application/expression/functions/financial.html
	static public double ipmt(double r, int per, int nper, double pv, double fv, int type) {
	    double ipmt = fv(r, per - 1, pmt(r, nper, pv, fv, type), pv, type) * r;
	    if (type==1) ipmt /= (1 + r);
	    return ipmt;
	}
	
	static public double ipmt(double r, int per, int nper, double pv, double fv) {
		return ipmt(r, per, nper, pv, fv, 0);
	}
	
	static public double ipmt(double r, int per, int nper, double pv) {
		return ipmt(r, per, nper, pv, 0);
	}
	 
	/**
     * Emulates Excel/Calc's PPMT(interest_rate, period, number_payments, PV,
     * FV, Type) function, which calculates the portion of the payment at a
     * given period that will apply to principal.
     * 
     * @param r
     *            - periodic interest rate represented as a decimal.
     * @param per
     *            - period (payment number) to check value at.
     * @param nper
     *            - number of total payments / periods.
     * @param pv
     *            - present value -- borrowed or invested principal.
     * @param fv
     *            - future value of loan or annuity.
     * @param type
     *            - when payment is made: beginning of period is 1; end, 0.
     * @return <code>double</code> representing principal portion of payment.
     * 
     * @see #pmt(double, int, double, double, int)
     * @see #ipmt(double, int, int, double, double, boolean)
     */
	static public double ppmt(double r, int per, int nper, double pv, double fv, int type) {
	    return pmt(r, nper, pv, fv, type) - ipmt(r, per, nper, pv, fv, type);
	}
	
	static public double ppmt(double r, int per, int nper, double pv, double fv) {
	    return pmt(r, nper, pv, fv) - ipmt(r, per, nper, pv, fv);
	}
	
	static public double ppmt(double r, int per, int nper, double pv) {
	    return pmt(r, nper, pv) - ipmt(r, per, nper, pv);
	}
	
    /**
     * Emulates Excel/Calc's FV(interest_rate, number_payments, payment, PV,
     * Type) function, which calculates future value or principal at period N.
     * 
     * @param r
     *            - periodic interest rate represented as a decimal.
     * @param nper
     *            - number of total payments / periods.
     * @param pmt
     *            - periodic payment amount.
     * @param pv
     *            - present value -- borrowed or invested principal.
     * @param type
     *            - when payment is made: beginning of period is 1; end, 0.
     * @return <code>double</code> representing future principal value.
     */
	//http://en.wikipedia.org/wiki/Future_value
	static public double fv(double r, int nper, double pmt, double pv, int type) {
	    double fv = -(pv * Math.pow(1 + r, nper) + pmt * (1+r*type) * (Math.pow(1 + r, nper) - 1) / r);
	    return fv;
	}
	
	/**
     * Overloaded fv() call omitting type, which defaults to 0.
     * 
     * @see #fv(double, int, double, double, int)
     */
	static public double fv(double r, int nper, double c, double pv) {
		return fv(r, nper, c, pv, 0);
	}
}