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

/*

 Copyright (C) 2007 Chris Kenyon

 Copyright (C) 2021 Ralf Konrad Eckel

 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/inflationindex.hpp>

#include <ql/termstructures/inflationtermstructure.hpp>

#include <ql/time/calendars/nullcalendar.hpp>

#include <utility>

namespace QuantLib {

    Real CPI::laggedFixing(const ext::shared_ptr<ZeroInflationIndex>& index,

                           const Date& date,

                           const Period& observationLag,

                           CPI::InterpolationType interpolationType) {

        switch (interpolationType) {

          QL_DEPRECATED_DISABLE_WARNING

          case AsIndex:

          QL_DEPRECATED_ENABLE_WARNING

          case Flat: {

              auto fixingPeriod = inflationPeriod(date - observationLag, index->frequency());

              return index->fixing(fixingPeriod.first);

          }

          case Linear: {

              auto fixingPeriod = inflationPeriod(date - observationLag, index->frequency());

              auto interpolationPeriod = inflationPeriod(date, index->frequency());

              auto I0 = index->fixing(fixingPeriod.first);

              if (date == interpolationPeriod.first) {

                  // special case; no interpolation.  This avoids asking for

                  // the fixing at the end of the period, which might need a

                  // forecast curve to be set.

                  return I0;

              }

              static const auto oneDay = Period(1, Days);

              auto I1 = index->fixing(fixingPeriod.second + oneDay);

              return I0 + (I1 - I0) * (date - interpolationPeriod.first) /

                  (Real)((interpolationPeriod.second + oneDay) - interpolationPeriod.first);

          }

          default:

            QL_FAIL("unknown CPI interpolation type: " << int(interpolationType));

        }

    }

    Real CPI::laggedYoYRate(const ext::shared_ptr<YoYInflationIndex>& index,

                            const Date& date,

                            const Period& observationLag,

                            CPI::InterpolationType interpolationType) {

        switch (interpolationType) {

          QL_DEPRECATED_DISABLE_WARNING

          case AsIndex: {

              return index->fixing(date - observationLag);

          }

          QL_DEPRECATED_ENABLE_WARNING

          case Flat: {

              auto fixingPeriod = inflationPeriod(date - observationLag, index->frequency());

              return index->fixing(fixingPeriod.first);

          }

          case Linear: {

              if (index->ratio() && !index->needsForecast(date)) {

                  // in the case of a ratio, the convention seems to be to interpolate

                  // the underlying index fixings first, then take the ratio.  This is

                  // not the same as taking the ratios and then interpolate, which is

                  // equivalent to what the else clause does.

                  // However, we can only do this if the fixings we need are in the past,

                  // because forecasts need to be done through the YoY forecast curve,

                  // and not the underlying index.

                  auto underlying = index->underlyingIndex();

                  Rate Z1 = CPI::laggedFixing(underlying, date, observationLag, interpolationType);

                  Rate Z0 = CPI::laggedFixing(underlying, date - 1*Years, observationLag, interpolationType);

                  return Z1/Z0 - 1.0;

              } else {

                  static const auto oneDay = Period(1, Days);

                  auto fixingPeriod = inflationPeriod(date - observationLag, index->frequency());

                  auto interpolationPeriod = inflationPeriod(date, index->frequency());

                  auto Y0 = index->fixing(fixingPeriod.first);

                  if (date == interpolationPeriod.first) {

                      // special case; no interpolation anyway.

                      return Y0;

                  }

                  auto Y1 = index->fixing(fixingPeriod.second + oneDay);

                  return Y0 + (Y1 - Y0) * (date - interpolationPeriod.first) /

                      (Real)((interpolationPeriod.second + oneDay) - interpolationPeriod.first);

              }

          }

          default:

            QL_FAIL("unknown CPI interpolation type: " << int(interpolationType));

        }

    }

    InflationIndex::InflationIndex(std::string familyName,

                                   Region region,

                                   bool revised,

                                   Frequency frequency,

                                   const Period& availabilityLag,

                                   Currency currency)

    : familyName_(std::move(familyName)), region_(std::move(region)), revised_(revised),

      frequency_(frequency), availabilityLag_(availabilityLag), currency_(std::move(currency)) {

        name_ = region_.name() + " " + familyName_;

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

        registerWith(notifier());

    }

    Calendar InflationIndex::fixingCalendar() const {

        static NullCalendar c;

        return c;

    }

    void InflationIndex::addFixing(const Date& fixingDate,

                                   Real fixing,

                                   bool forceOverwrite) {

        std::pair<Date,Date> lim = inflationPeriod(fixingDate, frequency_);

        Size n = static_cast<QuantLib::Size>(lim.second - lim.first) + 1;

        std::vector<Date> dates(n);

        std::vector<Rate> rates(n);

        for (Size i=0; i<n; ++i) {

            dates[i] = lim.first + i;

            rates[i] = fixing;

        }

        Index::addFixings(dates.begin(), dates.end(),

                          rates.begin(), forceOverwrite);

    }

    ZeroInflationIndex::ZeroInflationIndex(const std::string& familyName,

                                           const Region& region,

                                           bool revised,

                                           Frequency frequency,

                                           const Period& availabilityLag,

                                           const Currency& currency,

                                           Handle<ZeroInflationTermStructure> zeroInflation)

    : InflationIndex(familyName, region, revised, frequency, availabilityLag, currency),

      zeroInflation_(std::move(zeroInflation)) {

        registerWith(zeroInflation_);

    }

    Real ZeroInflationIndex::fixing(const Date& fixingDate,

                                    bool /*forecastTodaysFixing*/) const {

        if (!needsForecast(fixingDate)) {

            const Real I1 = pastFixing(fixingDate);

            QL_REQUIRE(I1 != Null<Real>(),

                       "Missing " << name() << " fixing for "

                       << inflationPeriod(fixingDate, frequency_).first);

            return I1;

        } else {

            return forecastFixing(fixingDate);

        }

    }

    Real ZeroInflationIndex::pastFixing(const Date& fixingDate) const {

        const auto p = inflationPeriod(fixingDate, frequency_);

        const auto& ts = timeSeries();

        return ts[p.first];

    }

    Date ZeroInflationIndex::lastFixingDate() const {

        const auto& fixings = timeSeries();

        QL_REQUIRE(!fixings.empty(), "no fixings stored for " << name());

        // attribute fixing to first day of the underlying period

        return inflationPeriod(fixings.lastDate(), frequency_).first;

    }

    bool ZeroInflationIndex::needsForecast(const Date& fixingDate) const {

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

        auto latestPossibleHistoricalFixingPeriod =

            inflationPeriod(today - availabilityLag_, frequency_);

        // Zero-index fixings are always non-interpolated.

        auto fixingPeriod = inflationPeriod(fixingDate, frequency_);

        Date latestNeededDate = fixingPeriod.first;

        if (latestNeededDate < latestPossibleHistoricalFixingPeriod.first) {

            // the fixing date is well before the availability lag, so

            // we know that fixings must be provided.

            return false;

        } else if (latestNeededDate > latestPossibleHistoricalFixingPeriod.second) {

            // the fixing can't be available yet

            return true;

        } else {

            // we're not sure, but the fixing might be there so we check.

            Real f = timeSeries()[latestNeededDate];

            return (f == Null<Real>());

        }

    }

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

        // the term structure is relative to the fixing value at the base date.

        Date baseDate = zeroInflation_->baseDate();

        QL_REQUIRE(!needsForecast(baseDate),

                   name() << " index fixing at base date " << baseDate << " is not available");

        Real baseFixing = fixing(baseDate);

        std::pair<Date, Date> fixingPeriod = inflationPeriod(fixingDate, frequency_);

        Date firstDateInPeriod = fixingPeriod.first;

        Rate Z1 = zeroInflation_->zeroRate(firstDateInPeriod, false);

        Time t1 = inflationYearFraction(frequency_, false, zeroInflation_->dayCounter(),

                                        baseDate, firstDateInPeriod);

        // During bootstrapping, extrapolated rates can temporarily go below -1.

        // Guard against pow of a negative base with non-integer exponent.

        if (Z1 <= -1.0)

            return 0.0;

        return baseFixing * std::pow(1.0 + Z1, t1);

    }

    ext::shared_ptr<ZeroInflationIndex> ZeroInflationIndex::clone(

                          const Handle<ZeroInflationTermStructure>& h) const {

        return ext::make_shared<ZeroInflationIndex>(

            familyName_, region_, revised_, frequency_, availabilityLag_, currency_, h);

    }

    QL_DEPRECATED_DISABLE_WARNING

    YoYInflationIndex::YoYInflationIndex(const ext::shared_ptr<ZeroInflationIndex>& underlyingIndex,

                                         Handle<YoYInflationTermStructure> yoyInflation)

    : InflationIndex("YYR_" + underlyingIndex->familyName(), underlyingIndex->region(),

                     underlyingIndex->revised(), underlyingIndex->frequency(),

                     underlyingIndex->availabilityLag(), underlyingIndex->currency()),

      ratio_(true), underlyingIndex_(underlyingIndex),

      yoyInflation_(std::move(yoyInflation)) {

        registerWith(underlyingIndex_);

        registerWith(yoyInflation_);

    }

    YoYInflationIndex::YoYInflationIndex(const std::string& familyName,

                                         const Region& region,

                                         bool revised,

                                         Frequency frequency,

                                         const Period& availabilityLag,

                                         const Currency& currency,

                                         Handle<YoYInflationTermStructure> yoyInflation)

    : InflationIndex(familyName, region, revised, frequency, availabilityLag, currency),

      ratio_(false), yoyInflation_(std::move(yoyInflation)) {

        registerWith(yoyInflation_);

    }

    QL_DEPRECATED_ENABLE_WARNING

    Rate YoYInflationIndex::fixing(const Date& fixingDate,

                                   bool /*forecastTodaysFixing*/) const {

        if (needsForecast(fixingDate)) {

            return forecastFixing(fixingDate);

        } else {

            return pastFixing(fixingDate);

        }

    }

    Date YoYInflationIndex::lastFixingDate() const {

        if (ratio()) {

            return underlyingIndex_->lastFixingDate();

        } else {

            const auto& fixings = timeSeries();

            QL_REQUIRE(!fixings.empty(), "no fixings stored for " << name());

            // attribute fixing to first day of the underlying period

            return inflationPeriod(fixings.lastDate(), frequency_).first;

        }

    }

    bool YoYInflationIndex::needsForecast(const Date& fixingDate) const {

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

        auto fixingPeriod = inflationPeriod(fixingDate, frequency_);

        Date latestNeededDate;

        QL_DEPRECATED_DISABLE_WARNING

        if (!interpolated() || fixingDate == fixingPeriod.first)

            latestNeededDate = fixingPeriod.first;

        else

            latestNeededDate = fixingPeriod.second + 1;

        QL_DEPRECATED_ENABLE_WARNING

        if (ratio()) {

            return underlyingIndex_->needsForecast(latestNeededDate);

        } else {

            auto latestPossibleHistoricalFixingPeriod =

                inflationPeriod(today - availabilityLag_, frequency_);

            if (latestNeededDate < latestPossibleHistoricalFixingPeriod.first) {

                // the fixing date is well before the availability lag, so

                // we know that fixings must be provided.

                return false;

            } else if (latestNeededDate > latestPossibleHistoricalFixingPeriod.second) {

                // the fixing can't be available yet

                return true;

            } else {

                // we're not sure, but the fixing might be there so we check.

                Real f = timeSeries()[latestNeededDate];

                return (f == Null<Real>());

            }

        }

    }

    Real YoYInflationIndex::pastFixing(const Date& fixingDate) const {

        if (ratio()) {

            QL_DEPRECATED_DISABLE_WARNING

            auto interpolationType = interpolated() ? CPI::Linear : CPI::Flat;

            QL_DEPRECATED_ENABLE_WARNING

            Rate pastFixing = CPI::laggedFixing(underlyingIndex_, fixingDate, Period(0, Months), interpolationType);

            Rate previousFixing = CPI::laggedFixing(underlyingIndex_, fixingDate - 1*Years, Period(0, Months), interpolationType);

            return pastFixing/previousFixing - 1.0;

        } else {  // NOT ratio

            const auto& ts = timeSeries();

            auto [periodStart, periodEnd] = inflationPeriod(fixingDate, frequency_);

            Rate YY0 = ts[periodStart];

            QL_REQUIRE(YY0 != Null<Rate>(),

                       "Missing " << name() << " fixing for " << periodStart);

            QL_DEPRECATED_DISABLE_WARNING

            bool is_interpolated = interpolated();

            QL_DEPRECATED_ENABLE_WARNING

            if (!is_interpolated || /* degenerate case */ fixingDate == periodStart) {

                return YY0;

            } else {

                Real dp = periodEnd + 1 - periodStart;

                Real dl = fixingDate - periodStart;

                Rate YY1 = ts[periodEnd+1];

                QL_REQUIRE(YY1 != Null<Rate>(),

                           "Missing " << name() << " fixing for " << periodEnd+1);

                return YY0 + (YY1 - YY0) * dl / dp;

            }

        }

    }

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

        Date d;

        QL_DEPRECATED_DISABLE_WARNING

        bool is_interpolated = interpolated();

        QL_DEPRECATED_ENABLE_WARNING

        if (is_interpolated) {

            d = fixingDate;

        } else {

            // if the value is not interpolated use the starting value

            // by internal convention this will be consistent

            std::pair<Date,Date> fixingPeriod = inflationPeriod(fixingDate, frequency_);

            d = fixingPeriod.first;

        }

        return yoyInflation_->yoyRate(d);

    }

    ext::shared_ptr<YoYInflationIndex> YoYInflationIndex::clone(

                           const Handle<YoYInflationTermStructure>& h) const {

        if (ratio_) {

            return ext::make_shared<YoYInflationIndex>(underlyingIndex_, h);

        } else {

            return ext::make_shared<YoYInflationIndex>(familyName_, region_, revised_,

                                                       frequency_, availabilityLag_,

                                                       currency_, h);

        }

    }

    CPI::InterpolationType

    detail::CPI::effectiveInterpolationType(const QuantLib::CPI::InterpolationType& type) {

        QL_DEPRECATED_DISABLE_WARNING

        if (type == QuantLib::CPI::AsIndex) {

            return QuantLib::CPI::Flat;

        } else {

            return type;

        }

        QL_DEPRECATED_ENABLE_WARNING

    }

    CPI::InterpolationType

    detail::CPI::effectiveInterpolationType(const QuantLib::CPI::InterpolationType& type,

                                            const ext::shared_ptr<YoYInflationIndex>& index) {

        QL_DEPRECATED_DISABLE_WARNING

        if (type == QuantLib::CPI::AsIndex) {

            return index->interpolated() ? QuantLib::CPI::Linear : QuantLib::CPI::Flat;

        } else {

            return type;

        }

        QL_DEPRECATED_ENABLE_WARNING

    }

    bool detail::CPI::isInterpolated(const QuantLib::CPI::InterpolationType& type) {

        return detail::CPI::effectiveInterpolationType(type) == QuantLib::CPI::Linear;

    }

    bool detail::CPI::isInterpolated(const QuantLib::CPI::InterpolationType& type,

                                     const ext::shared_ptr<YoYInflationIndex>& index) {

        return detail::CPI::effectiveInterpolationType(type, index) == QuantLib::CPI::Linear;

    }

}