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

/*
 Copyright (C) 2003 Neil Firth
 Copyright (C) 2002, 2003 Ferdinando Ametrano
 Copyright (C) 2002, 2003 Sadruddin Rejeb
 Copyright (C) 2000, 2001, 2002, 2003 RiskMap 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.
*/

/*! \file mcdigitalengine.hpp
    \brief digital option Monte Carlo engine
*/

#ifndef quantlib_digital_mc_engine_hpp
#define quantlib_digital_mc_engine_hpp

#include <ql/exercise.hpp>
#include <ql/yieldtermstructure.hpp>
#include <ql/voltermstructure.hpp>
#include <ql/methods/montecarlo/mctraits.hpp>
#include <ql/pricingengines/vanilla/mcvanillaengine.hpp>
#include <ql/processes/blackscholesprocess.hpp>

namespace QuantLib {

    //! Pricing engine for digital options using Monte Carlo simulation
    /*! Uses the Brownian Bridge correction for the barrier found in
        <i>
        Going to Extremes: Correcting Simulation Bias in Exotic
        Option Valuation - D.R. Beaglehole, P.H. Dybvig and G. Zhou
        Financial Analysts Journal; Jan/Feb 1997; 53, 1. pg. 62-68
        </i>
        and
        <i>
        Simulating path-dependent options: A new approach -
        M. El Babsiri and G. Noel
        Journal of Derivatives; Winter 1998; 6, 2; pg. 65-83
        </i>

        \ingroup vanillaengines

        \test the correctness of the returned value in case of
              cash-or-nothing at-hit digital payoff is tested by
              reproducing known good results.
    */
    template<class RNG = PseudoRandom, class S = Statistics>
    class MCDigitalEngine : public MCVanillaEngine<SingleVariate,RNG,S> {
      public:
        typedef
        typename MCVanillaEngine<SingleVariate,RNG,S>::path_generator_type
            path_generator_type;
        typedef
        typename MCVanillaEngine<SingleVariate,RNG,S>::path_pricer_type
            path_pricer_type;
        typedef typename MCVanillaEngine<SingleVariate,RNG,S>::stats_type
            stats_type;
        // constructor
        MCDigitalEngine(Size timeSteps,
                        Size timeStepsPerYear,
                        bool brownianBridge,
                        bool antitheticVariate,
                        bool controlVariate,
                        Size requiredSamples,
                        Real requiredTolerance,
                        Size maxSamples,
                        BigNatural seed);
      protected:
        // McSimulation implementation
        boost::shared_ptr<path_pricer_type> pathPricer() const;
    };

    //! Monte Carlo digital engine factory
    template <class RNG = PseudoRandom, class S = Statistics>
    class MakeMCDigitalEngine {
      public:
        MakeMCDigitalEngine();
        // named parameters
        MakeMCDigitalEngine& withSteps(Size steps);
        MakeMCDigitalEngine& withStepsPerYear(Size steps);
        MakeMCDigitalEngine& withBrownianBridge(bool b = true);
        MakeMCDigitalEngine& withSamples(Size samples);
        MakeMCDigitalEngine& withTolerance(Real tolerance);
        MakeMCDigitalEngine& withMaxSamples(Size samples);
        MakeMCDigitalEngine& withSeed(BigNatural seed);
        MakeMCDigitalEngine& withAntitheticVariate(bool b = true);
        MakeMCDigitalEngine& withControlVariate(bool b = true);
        // conversion to pricing engine
        operator boost::shared_ptr<PricingEngine>() const;
      private:
        bool antithetic_, controlVariate_;
        Size steps_, stepsPerYear_, samples_, maxSamples_;
        Real tolerance_;
        bool brownianBridge_;
        BigNatural seed_;
    };

    class DigitalPathPricer : public PathPricer<Path> {
      public:
        DigitalPathPricer(
                    const boost::shared_ptr<CashOrNothingPayoff>& payoff,
                    const boost::shared_ptr<AmericanExercise>& exercise,
                    const Handle<YieldTermStructure>& discountTS,
                    const boost::shared_ptr<StochasticProcess1D>& diffProcess,
                    const PseudoRandom::ursg_type& sequenceGen);
        Real operator()(const Path& path) const;
      private:
        boost::shared_ptr<CashOrNothingPayoff> payoff_;
        boost::shared_ptr<AmericanExercise> exercise_;
        boost::shared_ptr<StochasticProcess1D> diffProcess_;
        PseudoRandom::ursg_type sequenceGen_;
        Handle<YieldTermStructure> discountTS_;
    };



    // template definitions

    template<class RNG, class S>
    MCDigitalEngine<RNG,S>::MCDigitalEngine(Size timeSteps,
                                            Size timeStepsPerYear,
                                            bool brownianBridge,
                                            bool antitheticVariate,
                                            bool controlVariate,
                                            Size requiredSamples,
                                            Real requiredTolerance,
                                            Size maxSamples,
                                            BigNatural seed)
    : MCVanillaEngine<SingleVariate,RNG,S>(timeSteps,
                                           timeStepsPerYear,
                                           brownianBridge,
                                           antitheticVariate,
                                           controlVariate,
                                           requiredSamples,
                                           requiredTolerance,
                                           maxSamples,
                                           seed) {}

    template <class RNG, class S>
    inline
    boost::shared_ptr<QL_TYPENAME MCDigitalEngine<RNG,S>::path_pricer_type>
    MCDigitalEngine<RNG,S>::pathPricer() const {

        boost::shared_ptr<CashOrNothingPayoff> payoff =
            boost::dynamic_pointer_cast<CashOrNothingPayoff>(
                this->arguments_.payoff);
        QL_REQUIRE(payoff, "wrong payoff given");

        boost::shared_ptr<AmericanExercise> exercise =
            boost::dynamic_pointer_cast<AmericanExercise>(
                this->arguments_.exercise);
        QL_REQUIRE(exercise, "wrong exercise given");

        boost::shared_ptr<GeneralizedBlackScholesProcess> process =
            boost::dynamic_pointer_cast<GeneralizedBlackScholesProcess>(
                                          this->arguments_.stochasticProcess);
        QL_REQUIRE(process, "Black-Scholes process required");

        TimeGrid grid = this->timeGrid();
        PseudoRandom::ursg_type sequenceGen(grid.size()-1,
                                            PseudoRandom::urng_type(76));

        return boost::shared_ptr<
                        QL_TYPENAME MCDigitalEngine<RNG,S>::path_pricer_type>(
          new DigitalPathPricer(payoff,
                                exercise,
                                process->riskFreeRate(),
                                process,
                                sequenceGen));
    }


    template <class RNG, class S>
    inline MakeMCDigitalEngine<RNG,S>::MakeMCDigitalEngine()
    : antithetic_(false), controlVariate_(false),
      steps_(Null<Size>()), stepsPerYear_(Null<Size>()),
      samples_(Null<Size>()), maxSamples_(Null<Size>()),
      tolerance_(Null<Real>()), brownianBridge_(false), seed_(0) {}

    template <class RNG, class S>
    inline MakeMCDigitalEngine<RNG,S>&
    MakeMCDigitalEngine<RNG,S>::withSteps(Size steps) {
        steps_ = steps;
        return *this;
    }

    template <class RNG, class S>
    inline MakeMCDigitalEngine<RNG,S>&
    MakeMCDigitalEngine<RNG,S>::withStepsPerYear(Size steps) {
        stepsPerYear_ = steps;
        return *this;
    }

    template <class RNG, class S>
    inline MakeMCDigitalEngine<RNG,S>&
    MakeMCDigitalEngine<RNG,S>::withSamples(Size samples) {
        QL_REQUIRE(tolerance_ == Null<Real>(),
                   "tolerance already set");
        samples_ = samples;
        return *this;
    }

    template <class RNG, class S>
    inline MakeMCDigitalEngine<RNG,S>&
    MakeMCDigitalEngine<RNG,S>::withTolerance(Real tolerance) {
        QL_REQUIRE(samples_ == Null<Size>(),
                   "number of samples already set");
        QL_REQUIRE(RNG::allowsErrorEstimate,
                   "chosen random generator policy "
                   "does not allow an error estimate");
        tolerance_ = tolerance;
        return *this;
    }

    template <class RNG, class S>
    inline MakeMCDigitalEngine<RNG,S>&
    MakeMCDigitalEngine<RNG,S>::withMaxSamples(Size samples) {
        maxSamples_ = samples;
        return *this;
    }

    template <class RNG, class S>
    inline MakeMCDigitalEngine<RNG,S>&
    MakeMCDigitalEngine<RNG,S>::withSeed(BigNatural seed) {
        seed_ = seed;
        return *this;
    }

    template <class RNG, class S>
    inline MakeMCDigitalEngine<RNG,S>&
    MakeMCDigitalEngine<RNG,S>::withBrownianBridge(bool brownianBridge) {
        brownianBridge_ = brownianBridge;
        return *this;
    }

    template <class RNG, class S>
    inline MakeMCDigitalEngine<RNG,S>&
    MakeMCDigitalEngine<RNG,S>::withAntitheticVariate(bool b) {
        antithetic_ = b;
        return *this;
    }

    template <class RNG, class S>
    inline MakeMCDigitalEngine<RNG,S>&
    MakeMCDigitalEngine<RNG,S>::withControlVariate(bool b) {
        controlVariate_ = b;
        return *this;
    }

    template <class RNG, class S>
    inline
    MakeMCDigitalEngine<RNG,S>::operator boost::shared_ptr<PricingEngine>()
                                                                      const {
        QL_REQUIRE(steps_ != Null<Size>() || stepsPerYear_ != Null<Size>(),
                   "number of steps not given");
        QL_REQUIRE(steps_ == Null<Size>() || stepsPerYear_ == Null<Size>(),
                   "number of steps overspecified");
        return boost::shared_ptr<PricingEngine>(new
            MCDigitalEngine<RNG,S>(steps_,
                                   stepsPerYear_,
                                   brownianBridge_,
                                   antithetic_,
                                   controlVariate_,
                                   samples_, tolerance_,
                                   maxSamples_,
                                   seed_));
    }

}


#endif