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

/*

 Copyright (C) 2023 Marcin Rybacki

 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/indexes/equityindex.hpp>

#include <ql/settings.hpp>

#include <utility>

namespace QuantLib {

    namespace {

        Real resolveSpot(const Handle<Quote>& spot, Real lastFixing) {

            QL_REQUIRE(!spot.empty() || lastFixing != Null<Real>(),

                       "Cannot forecast equity index, missing both spot and historical index");

            return spot.empty() ? lastFixing : spot->value();

        }

    }

    EquityIndex::EquityIndex(std::string name,

                             Calendar fixingCalendar,

                             Currency currency,

                             Handle<YieldTermStructure> interest,

                             Handle<YieldTermStructure> dividend,

                             Handle<Quote> spot)

    : name_(std::move(name)), fixingCalendar_(std::move(fixingCalendar)),

      currency_(std::move(currency)), interest_(std::move(interest)),

      dividend_(std::move(dividend)), spot_(std::move(spot)) {

        registerWith(interest_);

        registerWith(dividend_);

        registerWith(spot_);

        registerWith(Settings::instance().evaluationDate());

        registerWith(notifier());

    }

    Real EquityIndex::fixing(const Date& fixingDate, bool forecastTodaysFixing) const {

        QL_REQUIRE(isValidFixingDate(fixingDate), "Fixing date " << fixingDate << " is not valid");

        Date today = Settings::instance().evaluationDate();

        if (fixingDate > today || (fixingDate == today && forecastTodaysFixing))

            return forecastFixing(fixingDate);

        Real result = pastFixing(fixingDate);

        if (result != Null<Real>())

            // if historical fixing is present use it

            return result;

        if (fixingDate == today && !spot_.empty())

            // Today's fixing is missing, but spot is

            // provided, so use it as proxy

            return spot_->value();

        QL_FAIL("Missing " << name() << " fixing for " << fixingDate);

    }

    Real EquityIndex::forecastFixing(const Date& fixingDate) const {

        QL_REQUIRE(!interest_.empty(),

                   "null interest rate term structure set to this instance of " << name());

        Date today = Settings::instance().evaluationDate();

        Date lastFixingDate = fixingCalendar_.adjust(today, BusinessDayConvention::Preceding);

        Real spot = resolveSpot(spot_, pastFixing(lastFixingDate));

        Real forward;

        if (!dividend_.empty()) {

            forward = spot * dividend_->discount(fixingDate) / interest_->discount(fixingDate);

        } else {

            forward = spot / interest_->discount(fixingDate);

        }

        return forward;

    }

    ext::shared_ptr<EquityIndex> EquityIndex::clone(const Handle<YieldTermStructure>& interest,

                                                    const Handle<YieldTermStructure>& dividend,

                                                    const Handle<Quote>& spot) const {

        return ext::make_shared<EquityIndex>(name(), fixingCalendar(), currency(), interest,

                                             dividend, spot);

    }

}