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

/*

 Copyright (C) 2011 Master IMAFA - Polytech'Nice Sophia - Université de Nice Sophia Antipolis

 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

 <https://www.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/exercise.hpp>

#include <ql/pricingengines/asian/continuousarithmeticasianlevyengine.hpp>

#include <ql/math/distributions/normaldistribution.hpp>

#include <ql/pricingengines/blackcalculator.hpp>

#include <utility>

using namespace std;

namespace QuantLib {

    ContinuousArithmeticAsianLevyEngine::ContinuousArithmeticAsianLevyEngine(

        ext::shared_ptr<GeneralizedBlackScholesProcess> process,

        Handle<Quote> currentAverage)

    : process_(std::move(process)), currentAverage_(std::move(currentAverage)) {

        registerWith(process_);

        registerWith(currentAverage_);

    }

    ContinuousArithmeticAsianLevyEngine::ContinuousArithmeticAsianLevyEngine(

        ext::shared_ptr<GeneralizedBlackScholesProcess> process,

        Handle<Quote> currentAverage,

        Date startDate)

    : process_(std::move(process)), currentAverage_(std::move(currentAverage)),

      startDate_(startDate) {

        registerWith(process_);

        registerWith(currentAverage_);

    }

    void ContinuousArithmeticAsianLevyEngine::calculate() const {

        QL_REQUIRE(arguments_.averageType == Average::Arithmetic,

                   "not an Arithmetic average option");

        QL_REQUIRE(arguments_.exercise->type() == Exercise::European,

                   "not an European Option");

        // Prefer start date from option if available, otherwise use constructor parameter.

        // At least one must be specified.

        Date startDate = (arguments_.startDate != Date()) ? arguments_.startDate : startDate_;

        QL_REQUIRE(startDate != Date(), "start date not provided");

        QL_REQUIRE(startDate <= process_->riskFreeRate()->referenceDate(),

                   "start date must be earlier than or equal to reference date");

        DayCounter rfdc  = process_->riskFreeRate()->dayCounter();

        DayCounter divdc = process_->dividendYield()->dayCounter();

        DayCounter voldc = process_->blackVolatility()->dayCounter();

        Real spot = process_->stateVariable()->value();

        // payoff

        ext::shared_ptr<StrikedTypePayoff> payoff =

            ext::dynamic_pointer_cast<StrikedTypePayoff>(arguments_.payoff);

        QL_REQUIRE(payoff, "non-plain payoff given");

        // original time to maturity

        Date maturity = arguments_.exercise->lastDate();

        Time T = rfdc.yearFraction(startDate,

                                   arguments_.exercise->lastDate());

        // remaining time to maturity

        Time T2 = rfdc.yearFraction(process_->riskFreeRate()->referenceDate(),

                                    arguments_.exercise->lastDate());

        Real strike = payoff->strike();

        Volatility volatility =

            process_->blackVolatility()->blackVol(maturity, strike);

        CumulativeNormalDistribution N;

        Rate riskFreeRate = process_->riskFreeRate()->

            zeroRate(maturity, rfdc, Continuous, NoFrequency);

        Rate dividendYield = process_->dividendYield()->

            zeroRate(maturity, divdc, Continuous, NoFrequency);

        Real b = riskFreeRate - dividendYield;

        Real Se = (std::fabs(b) > 1000*QL_EPSILON) 

            ? Real((spot/(T*b))*(exp((b-riskFreeRate)*T2)-exp(-riskFreeRate*T2)))

            : Real(spot*T2/T * std::exp(-riskFreeRate*T2));

        Real X;

        if (T2 < T) {

            QL_REQUIRE(!currentAverage_.empty() && currentAverage_->isValid(),

                       "current average required for seasoned option");

            X = strike - ((T-T2)/T)*currentAverage_->value();

        } else {

            X = strike;

        }

        Real m = (std::fabs(b) > 1000*QL_EPSILON) ? ((exp(b*T2)-1)/b) : T2;

        Real M = (2*spot*spot/(b+volatility*volatility)) *

            (((exp((2*b+volatility*volatility)*T2)-1)

              / (2*b+volatility*volatility))-m);

        Real D = M/(T*T);

        Real V = log(D)-2*(riskFreeRate*T2+log(Se));

        Real d1 = (1/sqrt(V))*((log(D)/2)-log(X));

        Real d2 = d1-sqrt(V);

        if(payoff->optionType()==Option::Call)

            results_.value = Se*N(d1) - X*exp(-riskFreeRate*T2)*N(d2);

        else

            results_.value = Se*N(d1) - X*exp(-riskFreeRate*T2)*N(d2)

                             - Se + X*exp(-riskFreeRate*T2);

    }

}