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

/*
 Copyright (C) 2002, 2003 Ferdinando Ametrano
 Copyright (C) 2026 Yassine Idyiahia

 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/termstructures/volatility/equityfx/blackvoltermstructure.hpp>
#include <ql/termstructures/volatility/smilesection.hpp>

namespace QuantLib {

    namespace {

        class BlackVolSmileSectionAdapter : public SmileSection {
          public:
            BlackVolSmileSectionAdapter(
                ext::shared_ptr<const BlackVolTermStructure> vol,
                Time t)
            : SmileSection(t, vol->dayCounter()), vol_(std::move(vol)) {}
            Real minStrike() const override { return vol_->minStrike(); }
            Real maxStrike() const override { return vol_->maxStrike(); }
            Real atmLevel() const override {
                return vol_->atmLevel(exerciseTime());
            }
          protected:
            Volatility volatilityImpl(Rate strike) const override {
                return vol_->blackVol(exerciseTime(), strike, true);
            }
          private:
            ext::shared_ptr<const BlackVolTermStructure> vol_;
        };

    }

    BlackVolTermStructure::BlackVolTermStructure(BusinessDayConvention bdc,
                                                 const DayCounter& dc)
    : VolatilityTermStructure(bdc, dc) {}

    BlackVolTermStructure::BlackVolTermStructure(const Date& refDate,
                                                 const Calendar& cal,
                                                 BusinessDayConvention bdc,
                                                 const DayCounter& dc)
    : VolatilityTermStructure(refDate, cal, bdc, dc) {}

    BlackVolTermStructure::BlackVolTermStructure(Natural settlDays,
                                                 const Calendar& cal,
                                                 BusinessDayConvention bdc,
                                                 const DayCounter& dc)
    : VolatilityTermStructure(settlDays, cal, bdc, dc) {}

    Volatility BlackVolTermStructure::blackForwardVol(const Date& date1,
                                                      const Date& date2,
                                                      Real strike,
                                                      bool extrapolate) const {
        // (redundant) date-based checks
        QL_REQUIRE(date1 <= date2,
                   date1 << " later than " << date2);
        checkRange(date2, extrapolate);

        // using the time implementation
        Time time1 = timeFromReference(date1);
        Time time2 = timeFromReference(date2);
        return blackForwardVol(time1, time2, strike, extrapolate);
    }

    Volatility BlackVolTermStructure::blackForwardVol(Time time1,
                                                      Time time2,
                                                      Real strike,
                                                      bool extrapolate) const {
        QL_REQUIRE(time1 <= time2,
                   time1 << " later than " << time2);
        checkRange(time2, extrapolate);
        checkStrike(strike, extrapolate);
        if (time2==time1) {
            if (time1==0.0) {
                Time epsilon = 1.0e-5;
                Real var = blackVarianceImpl(epsilon, strike);
                return std::sqrt(var/epsilon);
            } else {
                Time epsilon = std::min<Time>(1.0e-5, time1);
                Real var1 = blackVarianceImpl(time1-epsilon, strike);
                Real var2 = blackVarianceImpl(time1+epsilon, strike);
                QL_ENSURE(var2>=var1,
                          "variances must be non-decreasing");
                return std::sqrt((var2-var1)/(2*epsilon));
            }
        } else {
            Real var1 = blackVarianceImpl(time1, strike);
            Real var2 = blackVarianceImpl(time2, strike);
            QL_ENSURE(var2 >= var1,
                      "variances must be non-decreasing");
            return std::sqrt((var2-var1)/(time2-time1));
        }
    }

    Real BlackVolTermStructure::blackForwardVariance(const Date& date1,
                                                     const Date& date2,
                                                     Real strike,
                                                     bool extrapolate)
                                                                      const {
        // (redundant) date-based checks
        QL_REQUIRE(date1 <= date2,
                   date1 << " later than " << date2);
        checkRange(date2, extrapolate);

        // using the time implementation
        Time time1 = timeFromReference(date1);
        Time time2 = timeFromReference(date2);
        return blackForwardVariance(time1, time2, strike, extrapolate);
    }

    Real BlackVolTermStructure::blackForwardVariance(Time time1,
                                                     Time time2,
                                                     Real strike,
                                                     bool extrapolate) const {
        QL_REQUIRE(time1 <= time2,
                   time1 << " later than " << time2);
        checkRange(time2, extrapolate);
        checkStrike(strike, extrapolate);
        Real v1 = blackVarianceImpl(time1, strike);
        Real v2 = blackVarianceImpl(time2, strike);
        QL_ENSURE(v2 >= v1,
                  "variances must be non-decreasing");
        return v2-v1;
    }

    BlackVolatilityTermStructure::BlackVolatilityTermStructure(
                                                    BusinessDayConvention bdc,
                                                    const DayCounter& dc)
    : BlackVolTermStructure(bdc, dc) {}

    BlackVolatilityTermStructure::BlackVolatilityTermStructure(
                                                    const Date& refDate,
                                                    const Calendar& cal,
                                                    BusinessDayConvention bdc,
                                                    const DayCounter& dc)
    : BlackVolTermStructure(refDate, cal, bdc, dc) {}

    BlackVolatilityTermStructure::BlackVolatilityTermStructure(
                                                    Natural settlementDays,
                                                    const Calendar& cal,
                                                    BusinessDayConvention bdc,
                                                    const DayCounter& dc)
    : BlackVolTermStructure(settlementDays, cal, bdc, dc) {}

    BlackVarianceTermStructure::BlackVarianceTermStructure(
                                                    BusinessDayConvention bdc,
                                                    const DayCounter& dc)
    : BlackVolTermStructure(bdc, dc) {}

    BlackVarianceTermStructure::BlackVarianceTermStructure(
                                                    const Date& refDate,
                                                    const Calendar& cal,
                                                    BusinessDayConvention bdc,
                                                    const DayCounter& dc)
    : BlackVolTermStructure(refDate, cal, bdc, dc) {}

    BlackVarianceTermStructure::BlackVarianceTermStructure(
                                                    Natural settlementDays,
                                                    const Calendar& cal,
                                                    BusinessDayConvention bdc,
                                                    const DayCounter& dc)
    : BlackVolTermStructure(settlementDays, cal, bdc, dc) {}

    ext::shared_ptr<SmileSection>
    BlackVolTermStructure::smileSectionImpl(Time t) const {
        try {
            return ext::make_shared<BlackVolSmileSectionAdapter>(
#ifdef QL_ENABLE_THREAD_SAFE_OBSERVER_PATTERN
                ext::dynamic_pointer_cast<const BlackVolTermStructure>(
                    shared_from_this()),
#else
                shared_from_this(),
#endif
                t);
        } catch (const ext::bad_weak_ptr&) {
            QL_FAIL("smileSection() requires the BlackVolTermStructure "
                    "to be held by a shared_ptr");
        }
    }

}
