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

/*

 Copyright (C) 2018 Klaus Spanderen

 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/math/ode/adaptiverungekutta.hpp>

#include <ql/methods/finitedifferences/schemes/methodoflinesscheme.hpp>

#include <utility>

namespace QuantLib {

    MethodOfLinesScheme::MethodOfLinesScheme(const Real eps,

                                             const Real relInitStepSize,

                                             ext::shared_ptr<FdmLinearOpComposite> map,

                                             const bc_set& bcSet)

    : dt_(Null<Real>()), eps_(eps), relInitStepSize_(relInitStepSize), map_(std::move(map)),

      bcSet_(bcSet) {}

    std::vector<Real> MethodOfLinesScheme::apply(Time t, const std::vector<Real>& u) const {

        map_->setTime(t, t + 0.0001);

        bcSet_.applyBeforeApplying(*map_);

        const Array dxdt = -map_->apply(Array(u.begin(), u.end()));

        return std::vector<Real>(dxdt.begin(), dxdt.end());

    }

    void MethodOfLinesScheme::step(array_type& a, Time t) {

        QL_REQUIRE(t-dt_ > -1e-8, "a step towards negative time given");

        const std::vector<Real> v =

           AdaptiveRungeKutta<Real>(eps_, relInitStepSize_*dt_)(

               [&](Time _t, const std::vector<Real>& _u){ return apply(_t, _u); },

               std::vector<Real>(a.begin(), a.end()),

               t, std::max(0.0, t-dt_));

        Array y(v.begin(), v.end());

        bcSet_.applyAfterSolving(y);

        a = y;

    }

    void MethodOfLinesScheme::setStep(Time dt) {

        dt_ = dt;

    }

}