/* -*- mode: c++; tab-width: 4; indent-tabs-mode: nil; c-basic-offset: 4 -*- */

/*
 Copyright (C) 2006 Banca Profilo S.p.A.
 Copyright (C) 2006 StatPro Italia srl

 This file is part of QuantLib, a free-software/open-source library
 for financial quantitative analysts and developers - http://quantlib.org/

 QuantLib is free software: you can redistribute it and/or modify it
 under the terms of the QuantLib license.  You should have received a
 copy of the license along with this program; if not, please email
 <quantlib-dev@lists.sf.net>. The license is also available online at
 <http://quantlib.org/license.shtml>.

 This program is distributed in the hope that it will be useful, but WITHOUT
 ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS
 FOR A PARTICULAR PURPOSE.  See the license for more details.
*/

#include <ql/pricingengines/capfloor/mchullwhiteengine.hpp>

namespace QuantLib {

    HullWhiteCapFloorPricer::HullWhiteCapFloorPricer(
                                    const CapFloor::arguments& args,
                                    const boost::shared_ptr<HullWhite>& model,
                                    Time forwardMeasureTime)
    : args_(args), model_(model), forwardMeasureTime_(forwardMeasureTime) {
        endDiscount_ = model_->termStructure()->discount(forwardMeasureTime_);
    }

    Real HullWhiteCapFloorPricer::operator()(const Path& path) const {

        bool isCap = (args_.type == CapFloor::Cap);
        Real npv = 0.0;
        Time Tb = forwardMeasureTime_;

        Size pastFixings = 0;
        for (Size i = 0; i<args_.fixingTimes.size(); i++) {
            Time tau = args_.accrualTimes[i];
            Time start = args_.startTimes[i],
                 end = args_.endTimes[i],
                 fixing = args_.fixingTimes[i];
            if (end <= 0.0) {
                // the fixing is in the past...
                pastFixings++;
                // ...and the caplet is expired; nothing more to do.
            } else {
                Rate ri_1, ri_2, currentLibor;
                if (fixing <= 0.0) {
                    // current caplet. The fixing is in the past...
                    pastFixings++;
                    // ...so it is determined.
                    currentLibor = args_.forwards[i];
                    // However, the short rate at caplet expiry is not.
                    ri_2 = path[i-pastFixings+2];
                } else {
                    // future caplet. Everything is to be forecast.
                    // The number of past fixings is used as an offset
                    // to index into the path.
                    ri_1 = path[i-pastFixings+1];
                    ri_2 = path[i-pastFixings+2];

                    DiscountFactor d1 =
                        model_->discountBond(fixing, start, ri_1);
                    DiscountFactor d2 =
                        model_->discountBond(fixing, end, ri_1);
                    currentLibor = (d1/d2-1)/tau;
                }

                Real accrualFactor = 1.0/model_->discountBond(end, Tb, ri_2);

                Rate strike = isCap? args_.capRates[i] : args_.floorRates[i];
                Real payoff = isCap?
                    std::max(currentLibor - strike, 0.0):
                    std::max(strike - currentLibor, 0.0);

                npv += payoff * tau * args_.gearings[i] *
                    args_.nominals[i] * accrualFactor;
            }
        }
        npv *= endDiscount_;
        return  npv;
    }

}