/*
  Copyright 2020 Equinor ASA.

  This file is part of the Open Porous Media project (OPM).

  OPM is free software: you can redistribute it and/or modify
  it under the terms of the GNU General Public License as published by
  the Free Software Foundation, either version 3 of the License, or
  (at your option) any later version.

  OPM 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
  GNU General Public License for more details.

  You should have received a copy of the GNU General Public License
  along with OPM.  If not, see <http://www.gnu.org/licenses/>.
*/

#include <config.h>
#include <opm/simulators/wells/GasLiftSingleWellGeneric.hpp>

#include <opm/input/eclipse/Schedule/GasLiftOpt.hpp>
#include <opm/input/eclipse/Schedule/Schedule.hpp>

#include <opm/simulators/utils/DeferredLogger.hpp>
#include <opm/simulators/wells/GasLiftWellState.hpp>
#include <opm/simulators/wells/WellState.hpp>
#include <opm/simulators/wells/GroupState.hpp>


#include <fmt/format.h>

#include <cassert>
#include <sstream>

namespace Opm
{

GasLiftSingleWellGeneric::GasLiftSingleWellGeneric(
    DeferredLogger& deferred_logger,
    WellState& well_state,
    const GroupState& group_state,
    const Well& ecl_well,
    const SummaryState& summary_state,
    GasLiftGroupInfo& group_info,
    const PhaseUsage& phase_usage,
    const Schedule& schedule,
    const int report_step_idx,
    GLiftSyncGroups& sync_groups,
    const Parallel::Communication& comm,
    bool glift_debug
) :
    GasLiftCommon(well_state, deferred_logger, comm, glift_debug)
    , group_state_{group_state}
    , ecl_well_{ecl_well}
    , summary_state_{summary_state}
    , group_info_{group_info}
    , phase_usage_{phase_usage}
    , sync_groups_{sync_groups}
    , controls_{ecl_well_.productionControls(summary_state_)}
    , debug_limit_increase_decrease_{false}
{
    this->well_name_ = ecl_well_.name();
    const GasLiftOpt& glo = schedule.glo(report_step_idx);
    // NOTE: According to LIFTOPT, item 1:
    //   "Increment size for lift gas injection rate. Lift gas is
    //   allocated to individual wells in whole numbers of the increment
    //   size. If gas lift optimization is no longer required, it can be
    //   turned off by entering a zero or negative number."
    // NOTE: This condition was checked in doGasLiftOptimize() in StandardWell
    //   so it can be assumed that increment_ > 0
    this->increment_ = glo.gaslift_increment();
    assert( this->increment_ > 0);
    // NOTE: The manual (see LIFTOPT, item 2) does not mention
    //  any default value or restrictions on the economic gradient.
    // TODO: The value of the gradient would most likely be a positive
    //  number. Should we warn or fail on a negative value?
    //  A negative value for the economic gradient would mean that
    //  the oil production is decreasing with increased liftgas
    //  injection (which seems strange)
    this->eco_grad_ = glo.min_eco_gradient();
    gl_well_ = &glo.well(this->well_name_);
}

/****************************************
 * Public methods in alphabetical order
 ****************************************/
// NOTE: Used from GasLiftStage2
std::optional<GasLiftSingleWellGeneric::GradInfo>
GasLiftSingleWellGeneric::
calcIncOrDecGradient(double oil_rate, double gas_rate, double alq, bool increase) const
{
    auto [new_alq_opt, alq_is_limited] = addOrSubtractAlqIncrement_(alq, increase);
    // TODO: What to do if ALQ is limited and new_alq != alq?
    if (!new_alq_opt)
        return std::nullopt;
    double new_alq = *new_alq_opt;
    if (auto bhp = computeBhpAtThpLimit_(new_alq)) {
        auto [new_bhp, bhp_is_limited] = getBhpWithLimit_(*bhp);
        // TODO: What to do if BHP is limited?
        auto rates = computeWellRates_(new_bhp, bhp_is_limited);
        double new_oil_rate, new_gas_rate, new_water_rate;
        bool oil_is_limited, gas_is_limited, water_is_limited;
        std::tie(new_oil_rate, oil_is_limited) = getOilRateWithLimit_(rates);
        std::tie(new_gas_rate, gas_is_limited) = getGasRateWithLimit_(rates);
        std::tie(new_water_rate, water_is_limited) = getWaterRateWithLimit_(rates);
        if (!increase && new_oil_rate < 0 ) {
            return std::nullopt;
        }
        auto grad = calcEcoGradient_(
            oil_rate, new_oil_rate, gas_rate, new_gas_rate, increase);
        return GradInfo(grad, new_oil_rate, oil_is_limited,
            new_gas_rate, gas_is_limited, new_water_rate, water_is_limited,
            new_alq, alq_is_limited);
    }
    else {
        return std::nullopt;
    }
}

std::unique_ptr<GasLiftWellState>
GasLiftSingleWellGeneric::
runOptimize(const int iteration_idx)
{
    std::unique_ptr<GasLiftWellState> state;
    if (this->optimize_) {
        if (this->debug_limit_increase_decrease_) {
            state = runOptimize1_();
        }
        else {
            state = runOptimize2_();
        }
        if (state) {
            // NOTE: that state->increase() returns a std::optional<bool>, if
            //  this is std::nullopt it means that we was not able to change ALQ
            //  (either increase or decrease)
            if (state->increase()) {  // ALQ changed..
                double alq = state->alq();
                if (this->debug)
                    logSuccess_(alq, iteration_idx);
                this->well_state_.setALQ(this->well_name_, alq);
                const auto& pu = this->phase_usage_;
                std::vector<double> well_pot(pu.num_phases, 0.0);
                if(pu.phase_used[BlackoilPhases::PhaseIndex::Liquid])
                    well_pot[pu.phase_pos[BlackoilPhases::PhaseIndex::Liquid]] = state->oilRate();
                if(pu.phase_used[BlackoilPhases::PhaseIndex::Aqua])
                    well_pot[pu.phase_pos[BlackoilPhases::PhaseIndex::Aqua]] = state->waterRate();
                if(pu.phase_used[BlackoilPhases::PhaseIndex::Vapour])
                    well_pot[pu.phase_pos[BlackoilPhases::PhaseIndex::Vapour]] = state->gasRate();

                this->well_state_[this->well_name_].well_potentials = well_pot;
            }
        }
    }
    return state;
}

/****************************************
 * Protected methods in alphabetical order
 ****************************************/

std::pair<std::optional<double>, bool>
GasLiftSingleWellGeneric::
addOrSubtractAlqIncrement_(double alq, bool increase) const
{
    bool limited = false;
    double orig_alq = alq;
    if (increase) {
        alq += this->increment_;
        // NOTE: if max_alq_ was defaulted in WLIFTOPT, item 3, it has
        //   already been set to the largest value in the VFP table in
        //   the contructor of GasLiftSingleWell
        if (alq > this->max_alq_) {
            alq = this->max_alq_;
            limited = true;
        }
    }
    else { // we are decreasing ALQ
        alq -= this->increment_;
        if (this->min_alq_ > 0) {
            // According to WLIFTOPT item 5: If a positive value is
            // specified (min_alq_), the well is allocated at least that amount
            // of lift gas, unless the well is unable to flow with
            // that rate of lift gas injection, or unless the well can
            // already meet one of its own rate limits before
            // receiving its minimum lift gas rate.
            if (alq < this->min_alq_) {
                alq = this->min_alq_;
                limited = true;
            }
        }
        else {
            if (alq < 0) {
                alq = 0.0;
                limited = true;
            }
        }
    }
    std::optional<double> alq_opt {alq};
    // If we were not able to change ALQ (to within rounding error), we
    //   return std::nullopt
    if (limited && checkALQequal_(orig_alq,alq))
        alq_opt = std::nullopt;

    return {alq_opt, limited};
}

double
GasLiftSingleWellGeneric::
calcEcoGradient_(double oil_rate, double new_oil_rate, double gas_rate,
                 double new_gas_rate, bool increase) const
{
    auto dqo = new_oil_rate - oil_rate;
    auto dqg = new_gas_rate - gas_rate;
    // TODO: Should the gas rate term in the denominator be subject to the constraint:
    //
    //    alpha_g_ * dqg >= 0.0
    //
    //   ?
    auto gradient = (this->alpha_w_ * dqo) / (this->increment_ + this->alpha_g_*dqg);
    // TODO: Should we do any error checks on the calculation of the
    //   gradient?

    if (!increase) gradient = -gradient;
    return gradient;
}

bool
GasLiftSingleWellGeneric::
checkALQequal_(double alq1, double alq2) const
{
    return std::fabs(alq1-alq2) < (this->increment_*ALQ_EPSILON);
}

bool
GasLiftSingleWellGeneric::
checkGroupTargetsViolated(
         const BasicRates& rates, const BasicRates& new_rates) const
{
    const auto &pairs =
        this->group_info_.getWellGroups(this->well_name_);
    for (const auto &[group_name, efficiency] : pairs) {
        for (const auto rate_type : {Rate::oil, Rate::gas, Rate::water, Rate::liquid}) {
            auto target_opt = this->group_info_.getTarget(rate_type, group_name);
            if (target_opt) {
                auto delta_rate = new_rates[rate_type] - rates[rate_type];
                auto new_group_rate = this->group_info_.getRate(rate_type, group_name)
                                                       + efficiency * delta_rate;
                if (new_group_rate > *target_opt) {
                    if (this->debug) {
                        const std::string msg = fmt::format(
                            "Group {} : {} rate {} exceeds target {}. Stopping iteration",
                            group_name, GasLiftGroupInfo::rateToString(rate_type),
                            new_group_rate, *target_opt);
                        displayDebugMessage_(msg);
                    }
                    return true;
                }
            }
        }
    }
    return false;
}

bool
GasLiftSingleWellGeneric::
checkInitialALQmodified_(double alq, double initial_alq) const
{
    if (checkALQequal_(alq,initial_alq)) {
        return false;
    }
    else {
        const std::string msg = fmt::format("initial ALQ changed from {} "
            "to {} before iteration starts..", initial_alq, alq);
        displayDebugMessage_(msg);
        return true;
    }
}

bool
GasLiftSingleWellGeneric::
checkThpControl_() const
{
    const int well_index = this->well_state_.index(this->well_name_).value();
    const Well::ProducerCMode& control_mode =
                         this->well_state_.well(well_index).production_cmode;
    bool thp_control = control_mode == Well::ProducerCMode::THP;
    if (this->debug) {
        if (!thp_control) {
            displayDebugMessage_("Well is not under THP control, skipping iteration..");
        }
    }
    return thp_control;
}

std::pair<std::optional<double>,double>
GasLiftSingleWellGeneric::
computeConvergedBhpAtThpLimitByMaybeIncreasingALQ_() const
{
    auto alq = this->orig_alq_;
    double new_alq = alq;
    std::optional<double> bhp;
    while (alq <= (this->max_alq_ + this->increment_)) {
        if (bhp = computeBhpAtThpLimit_(alq); bhp) {
            new_alq = alq;
            break;
        }
        alq += this->increment_;
    }
    return {bhp, new_alq};
}

std::pair<std::optional<GasLiftSingleWellGeneric::BasicRates>,double>
GasLiftSingleWellGeneric::
computeInitialWellRates_() const
{
    std::optional<BasicRates> rates;
    double initial_alq = this->orig_alq_;
    //auto alq = initial_alq;
    //if (auto bhp = computeBhpAtThpLimit_(this->orig_alq_); bhp) {
    if (auto [bhp, alq] = computeConvergedBhpAtThpLimitByMaybeIncreasingALQ_(); bhp) {
        {
            const std::string msg = fmt::format(
                "computed initial bhp {} given thp limit and given alq {}", *bhp, alq);
            displayDebugMessage_(msg);
        }
        initial_alq = alq;
        auto [new_bhp, bhp_is_limited] = getBhpWithLimit_(*bhp);
        rates = computeWellRates_(new_bhp, bhp_is_limited);
        if (rates) {
            const std::string msg = fmt::format(
                "computed initial well potentials given bhp, "
                "oil: {}, gas: {}, water: {}",
                rates->oil, rates->gas, rates->water);
            displayDebugMessage_(msg);
        }
    }
    else {
        displayDebugMessage_("Aborting optimization.");
    }
    return {rates, initial_alq};
}

std::optional<GasLiftSingleWellGeneric::LimitedRates>
GasLiftSingleWellGeneric::
computeLimitedWellRatesWithALQ_(double alq) const
{
    std::optional<LimitedRates> limited_rates;
    if (auto rates = computeWellRatesWithALQ_(alq); rates) {
        limited_rates = getLimitedRatesFromRates_(*rates);
    }
    return limited_rates;
}

std::optional<GasLiftSingleWellGeneric::BasicRates>
GasLiftSingleWellGeneric::
computeWellRatesWithALQ_(double alq) const
{
    std::optional<BasicRates> rates;
    auto bhp_opt = computeBhpAtThpLimit_(alq);
    if (bhp_opt) {
        auto [bhp, bhp_is_limited] = getBhpWithLimit_(*bhp_opt);
        rates = computeWellRates_(bhp, bhp_is_limited);
    }
    return rates;
}

void
GasLiftSingleWellGeneric::
debugCheckNegativeGradient_(double grad, double alq, double new_alq,
                            double oil_rate, double new_oil_rate,
                            double gas_rate, double new_gas_rate, bool increase) const
{
    {
        const std::string msg = fmt::format("calculating gradient: "
            "new_oil_rate = {}, oil_rate = {}, grad = {}", new_oil_rate, oil_rate, grad);
        displayDebugMessage_(msg);
    }
    if (grad < 0 ) {
        const std::string msg = fmt::format("negative {} gradient detected ({}) : "
            "alq: {}, new_alq: {}, "
            "oil_rate: {}, new_oil_rate: {}, gas_rate: {}, new_gas_rate: {}",
            (increase ? "incremental" : "decremental"),
            grad, alq, new_alq, oil_rate, new_oil_rate, gas_rate, new_gas_rate);
        displayDebugMessage_(msg);
    }
}

void
GasLiftSingleWellGeneric::
debugShowAlqIncreaseDecreaseCounts_()
{
    auto inc_count = this->well_state_.gliftGetAlqIncreaseCount(this->well_name_);
    auto dec_count = this->well_state_.gliftGetAlqDecreaseCount(this->well_name_);
    const std::string msg =
        fmt::format("ALQ increase/decrease count : {}/{}", inc_count, dec_count);
    displayDebugMessage_(msg);
}

void
GasLiftSingleWellGeneric::
debugShowBhpAlqTable_()
{
    double alq = 0.0;
    const std::string fmt_fmt1 {"{:^12s} {:^12s} {:^12s} {:^12s}"};
    const std::string fmt_fmt2 {"{:>12.5g} {:>12.5g} {:>12.5g} {:>12.5g}"};
    const std::string header = fmt::format(fmt_fmt1, "ALQ", "BHP", "oil", "gas");
    displayDebugMessage_(header);
    auto max_it = 50;
    auto it = 1;
    while (alq <= (this->max_alq_+this->increment_)) {
        auto bhp_at_thp_limit = computeBhpAtThpLimit_(alq);
        if (!bhp_at_thp_limit) {
            const std::string msg = fmt::format("Failed to get converged potentials "
                "for ALQ = {}. Skipping.", alq );
            displayDebugMessage_(msg);
        }
        else {
            auto [bhp, bhp_is_limited] = getBhpWithLimit_(*bhp_at_thp_limit);
            auto rates = computeWellRates_(bhp, bhp_is_limited, /*debug_out=*/false);
            const std::string msg = fmt::format(
                fmt_fmt2, alq, bhp, rates.oil, rates.gas);
            displayDebugMessage_(msg);
        }
        alq += this->increment_;
        if (it > max_it) {
            const std::string msg = fmt::format(
                "ALQ table : max iterations {} reached. Stopping iteration.", max_it);
            displayDebugMessage_(msg);
            break;
        }
        it++;
    }
}

void
GasLiftSingleWellGeneric::
debugShowLimitingTargets_(const LimitedRates& rates) const
{
    if (rates.limited()) {
        if (rates.oil_is_limited) {
            const std::string msg = fmt::format(
                     "oil rate {} is limited by {} target",
                     rates.oil,
                     GasLiftGroupInfo::rateToString(*(rates.oil_limiting_target)));
            displayDebugMessage_(msg);
        }
        if (rates.gas_is_limited) {
            const std::string msg = fmt::format(
                     "gas rate {} is limited by GRAT target",
                     rates.gas);
            displayDebugMessage_(msg);
        }
        if (rates.water_is_limited) {
            const std::string msg = fmt::format(
                     "water rate {} is limited by {} target",
                     rates.water,
                     GasLiftGroupInfo::rateToString(*(rates.water_limiting_target)));
            displayDebugMessage_(msg);
        }
    }
    else {
        displayDebugMessage_("no rates are currently limited by a target");
    }
}

void
GasLiftSingleWellGeneric::
debugShowProducerControlMode() const
{
    const int well_index = this->well_state_.index(this->well_name_).value();
    const Well::ProducerCMode& control_mode =
                         this->well_state_.well(well_index).production_cmode;
    const std::string msg = fmt::format("Current control mode is: {}",
        Well::ProducerCMode2String(control_mode));
    displayDebugMessage_(msg);
}

void
GasLiftSingleWellGeneric::
debugShowStartIteration_(double alq, bool increase, double oil_rate)
{
    const std::string msg =
        fmt::format("starting {} iteration, ALQ = {}, oilrate = {}",
            (increase ? "increase" : "decrease"),
            alq, oil_rate);
    displayDebugMessage_(msg);
}

void
GasLiftSingleWellGeneric::
debugShowTargets_()
{
    if (this->controls_.hasControl(Well::ProducerCMode::ORAT)) {
        auto target = this->controls_.oil_rate;
        const std::string msg = fmt::format("has ORAT control with target {}", target);
        displayDebugMessage_(msg);
    }
    if (this->controls_.hasControl(Well::ProducerCMode::GRAT)) {
        auto target = this->controls_.gas_rate;
        const std::string msg = fmt::format("has GRAT control with target {}", target);
        displayDebugMessage_(msg);
    }
    if (this->controls_.hasControl(Well::ProducerCMode::LRAT)) {
        auto target = this->controls_.liquid_rate;
        const std::string msg = fmt::format("has LRAT control with target {}", target);
        displayDebugMessage_(msg);
    }
}

void
GasLiftSingleWellGeneric::
displayDebugMessage_(const std::string& msg) const
{

    if (this->debug) {
        const std::string message = fmt::format("Well {} : {}", this->well_name_, msg);
        logMessage_(/*prefix=*/"GLIFT", message);
    }
}

void
GasLiftSingleWellGeneric::
displayWarning_(const std::string& msg)
{
    const std::string message = fmt::format("WELL {} : {}", this->well_name_, msg);
    logMessage_(/*prefix=*/"GLIFT", msg, MessageType::WARNING);
}

std::pair<double, bool>
GasLiftSingleWellGeneric::
getBhpWithLimit_(double bhp) const
{
    bool limited = false;
    if (this->controls_.hasControl(Well::ProducerCMode::BHP)) {
        auto limit = this->controls_.bhp_limit;
        if (bhp < limit) {
            bhp = limit;
            limited = true;
        }
    }
    return {bhp, limited};
}


// TODO: what if the gas_rate_target_ has been defaulted
//   (i.e. value == 0, meaning: "No limit") but the
//   oil_rate_target_ has not been defaulted ?
//   If the new_oil_rate exceeds the oil_rate_target_ it is cut back,
//   but the same cut-back will not happen for the new_gas_rate
//   Seems like an inconsistency, since alq should in this
//   case also be adjusted (to the smaller value that would
//   give oil target rate) but then the gas rate would also be smaller?
//   The effect of not reducing the gas rate (if it should be
//   reduced?) is that a too large value is used in the
//   computation of the economic gradient making the gradient
//   smaller than it should be since the term appears in the denominator.
std::pair<double, bool>
GasLiftSingleWellGeneric::
getGasRateWithLimit_(const BasicRates& rates) const
{
    auto [rate, target_type] = getRateWithLimit_(Rate::gas, rates);
    bool limited = target_type.has_value();
    return {rate, limited};
}

// NOTE: If the computed oil rate is larger than the target
//   rate of the well, we reduce it to the target rate. This
//   will make the economic gradient smaller than it would be
//   if we did not reduce the rate, and it is less
//   likely that the current gas lift increment will be
//   accepted.
// TODO: If it still is accepted, we should ideally reduce the alq
//  also since we also reduced the rate. This might involve
//   some sort of iteration though..
std::pair<double, bool>
GasLiftSingleWellGeneric::
getOilRateWithLimit_(const BasicRates& rates) const
{
    auto [rate, target_type] = getRateWithLimit_(Rate::oil, rates);
    bool limited = target_type.has_value();
    return {rate, limited};
}

std::pair<double, std::optional<GasLiftSingleWellGeneric::Rate>>
GasLiftSingleWellGeneric::
getOilRateWithLimit2_(const BasicRates& rates) const
{
    return getRateWithLimit_(Rate::oil, rates);
}

std::pair<double, bool>
GasLiftSingleWellGeneric::
getWaterRateWithLimit_(const BasicRates& rates) const
{
    auto [rate, target_type] = getRateWithLimit_(Rate::water, rates);
    bool limited = target_type.has_value();
    return {rate, limited};
}

std::pair<double, std::optional<GasLiftSingleWellGeneric::Rate>>
GasLiftSingleWellGeneric::
getWaterRateWithLimit2_(const BasicRates& rates) const
{
    return getRateWithLimit_(Rate::water, rates);
}

double
GasLiftSingleWellGeneric::
getRate_(Rate rate, const BasicRates& rates) const
{
    switch (rate) {
    case Rate::oil:
        return rates.oil;
    case Rate::gas:
        return rates.gas;
    case Rate::water:
        return rates.water;
    case Rate::liquid:
        return rates.oil + rates.water;
    default:
        // Need this to avoid compiler warning : control reaches end of non-void function
        throw std::runtime_error("This should not happen");
    }
}

double
GasLiftSingleWellGeneric::
getProductionTarget_(Rate rate) const
{
    switch (rate) {
    case Rate::oil:
        return this->controls_.oil_rate;
    case Rate::gas:
        return this->controls_.gas_rate;
    case Rate::water:
        return this->controls_.water_rate;
    case Rate::liquid:
        return this->controls_.liquid_rate;
    default:
        // Need this to avoid compiler warning : control reaches end of non-void function
        throw std::runtime_error("This should not happen");
    }
}

std::pair<double, std::optional<GasLiftSingleWellGeneric::Rate>>
GasLiftSingleWellGeneric::
getRateWithLimit_(Rate rate_type, const BasicRates &rates) const
{
    double new_rate = getRate_(rate_type, rates);
    // If "target_type" is empty at the end of this method, it means the rate
    //   was not limited. Otherwise, target_type gives the reason (the type of target)
    //   for why the rate was limited.
    std::optional<Rate> target_type;

    if (hasProductionControl_(rate_type)) {
        auto target = getProductionTarget_(rate_type);
        if (new_rate > target) {
            const std::string msg = fmt::format("limiting {} rate to target: "
                                                "computed rate: {}, target: {}",
                  GasLiftGroupInfo::rateToString(rate_type), new_rate, target);
            displayDebugMessage_(msg);
            new_rate = target;
            target_type = rate_type;
        }
    }
    if (((rate_type == Rate::oil) || (rate_type == Rate::water))
            && hasProductionControl_(Rate::liquid))
    {
        double rate2;
        if (rate_type == Rate::oil) {
            rate2 = getRate_(Rate::water, rates);
        }
        else {
            rate2 = getRate_(Rate::oil, rates);
        }
        // Note: Since "new_rate" was first updated for ORAT or WRAT, see first "if"
        //   statement in the method, the rate is limited due to LRAT only if
        //   it becomes less than the rate limited by a WRAT or ORAT target..
        double liq_rate = new_rate + rate2;

        auto liq_target = getProductionTarget_(Rate::liquid);
        if (liq_rate > liq_target) {
            double fraction = new_rate / liq_rate;
            // NOTE: since
            //      fraction * liq_rate = new_rate,
            //  we must have
            //      fraction * liq_target < new_rate
            //  since
            //      liq_target < liq_rate
            //  therefore new_rate will become less than it original was and
            //  limited = true.
            new_rate = fraction * liq_target;
            target_type = Rate::liquid;
            const std::string msg = fmt::format(
                "limiting {} rate to {} due to LRAT target: "
                "computed LRAT: {}, target LRAT: {}",
                GasLiftGroupInfo::rateToString(rate_type), new_rate,
                liq_rate, liq_target);
            displayDebugMessage_(msg);
        }
    }
    // TODO: Also check RESV target?
    return { new_rate, target_type};
}

std::pair<double, bool>
GasLiftSingleWellGeneric::
getOilRateWithGroupLimit_(double new_oil_rate, double oil_rate) const
{
    [[maybe_unused]] auto [rate, gr_name, efficiency]
        = getRateWithGroupLimit_(Rate::oil, new_oil_rate, oil_rate);
    bool limited = gr_name != nullptr;
    return {rate, limited};
}

std::pair<double, bool>
GasLiftSingleWellGeneric::
getGasRateWithGroupLimit_(double new_gas_rate, double gas_rate) const
{
    [[maybe_unused]] auto [rate, gr_name, efficiency]
        = getRateWithGroupLimit_(Rate::gas, new_gas_rate, gas_rate);
    bool limited = gr_name != nullptr;
    return {rate, limited};
}

std::pair<double, bool>
GasLiftSingleWellGeneric::
getWaterRateWithGroupLimit_(double new_water_rate, double water_rate) const
{
    [[maybe_unused]] auto [rate, gr_name, efficiency] = getRateWithGroupLimit_(
                                            Rate::water, new_water_rate, water_rate);
    bool limited = gr_name != nullptr;
    return {rate, limited};
}

std::tuple<double, double, bool, bool>
GasLiftSingleWellGeneric::
getLiquidRateWithGroupLimit_(const double new_oil_rate, const double oil_rate,
                             const double new_water_rate, const double water_rate) const
{
    auto liquid_rate = oil_rate + water_rate;
    auto new_liquid_rate = new_oil_rate + new_water_rate;
    auto [liquid_rate_limited, group_name, efficiency]
        = getRateWithGroupLimit_(Rate::liquid, new_liquid_rate, liquid_rate);
    bool limited = group_name != nullptr;
    if (limited) {
        // the oil, gas, and water cases can be handled directly by
        //  getRateWithGroupLimit_() above. However, for the liquid case
        //  we must do some postprocessing. I chose to include it here
        //  instead of cluttering up getRateWithGroupLimit_() with this
        //  special case.
        double delta_water = new_water_rate - water_rate;
        double delta_oil = new_oil_rate - oil_rate;

        double gr_water_rate = this->group_info_.waterRate(*group_name);
        double gr_oil_rate = this->group_info_.oilRate(*group_name);

        // NOTE: these rates are too large according to the limited liquid rate
        //  but it does not matter since we are only using them to calculate
        //  the fraction of the liquid corresponding to the oil phase
        double new_gr_water_rate = gr_water_rate + efficiency * delta_water;
        double new_gr_oil_rate = gr_oil_rate + efficiency * delta_oil;
        double new_gr_liquid_rate = new_gr_water_rate + new_gr_oil_rate;

        double oil_fraction = new_gr_oil_rate / new_gr_liquid_rate;
        double delta_liquid = liquid_rate_limited - liquid_rate;
        auto limited_oil_rate = oil_rate + oil_fraction * delta_liquid;
        auto limited_water_rate = water_rate + (1.0 - oil_fraction) * delta_liquid;
        return {limited_oil_rate, limited_water_rate, limited, limited};
    }
    return {new_oil_rate, new_water_rate, limited, limited};
}

std::tuple<double, const std::string*, double>
GasLiftSingleWellGeneric::
getRateWithGroupLimit_(
    Rate rate_type, const double new_rate, const double old_rate) const
{
    const double delta_rate = new_rate - old_rate;
    if (delta_rate > 0) {
      // It is required that the production rate for a given group is
      // is less than or equal to its target rate, see assert() below.
      // Then it only makes sense to check if the group target is exceeded
      //  if delta_rate > 0
      const auto &pairs =
          this->group_info_.getWellGroups(this->well_name_);
      double limited_rate = new_rate;
      double gr_target, new_gr_rate, efficiency;
      const std::string *group_name = nullptr;
      for (const auto& [group_name_temp, efficiency_temp] : pairs) {
          auto gr_target_opt = this->group_info_.getTarget(rate_type, group_name_temp);
          if (gr_target_opt) {
            double gr_target_temp = *gr_target_opt;
            double gr_rate_temp =
                this->group_info_.getRate(rate_type, group_name_temp);
            if (gr_rate_temp > gr_target_temp) {
                if (this->debug) {
                    debugInfoGroupRatesExceedTarget(
                        rate_type, group_name_temp, gr_rate_temp, gr_target_temp);
                }
                group_name = &group_name_temp;
                efficiency = efficiency_temp;
                limited_rate = old_rate;
                gr_target = gr_target_temp;
                new_gr_rate = gr_rate_temp;
                break;
            }
            double new_gr_rate_temp = gr_rate_temp + efficiency_temp * delta_rate;
            if (new_gr_rate_temp > gr_target_temp) {
                double limited_rate_temp =
                    old_rate + (gr_target_temp - gr_rate_temp) / efficiency_temp;
                if (limited_rate_temp < limited_rate) {
                    group_name = &group_name_temp;
                    efficiency = efficiency_temp;
                    limited_rate = limited_rate_temp;
                    gr_target = gr_target_temp;
                    new_gr_rate = new_gr_rate_temp;
                }
            }
         }
      }
      if (group_name) {
          if (this->debug) {
              const std::string msg = fmt::format(
                  "limiting {} rate from {} to {} to meet group target {} "
                  "for group {}. Computed group rate was: {}",
                  GasLiftGroupInfo::rateToString(rate_type),
                  new_rate, limited_rate, gr_target,
                  *group_name, new_gr_rate);
              displayDebugMessage_(msg);
          }
          return { limited_rate, group_name, efficiency };
      }
    }
    return { new_rate, /*group_name =*/nullptr, /*efficiency dummy value*/0.0 };
}


std::pair<std::optional<GasLiftSingleWellGeneric::LimitedRates>, double>
GasLiftSingleWellGeneric::
getInitialRatesWithLimit_() const
{
    std::optional<LimitedRates> limited_rates;
    double initial_alq = this->orig_alq_;
    if (auto [rates, alq] = computeInitialWellRates_(); rates) {
        if (this->debug) {
            displayDebugMessage_(
                             "Maybe limiting initial rates before optimize loop..");
        }
        auto temp_rates = getLimitedRatesFromRates_(*rates);
        BasicRates old_rates = getWellStateRates_();
        limited_rates = updateRatesToGroupLimits_(old_rates, temp_rates);
        initial_alq = alq;
    }
    return {limited_rates, initial_alq};
}

GasLiftSingleWellGeneric::LimitedRates
GasLiftSingleWellGeneric::
getLimitedRatesFromRates_(const BasicRates& rates) const
{
    auto [oil_rate, oil_limiting_target] = getOilRateWithLimit2_(rates);
    auto [gas_rate, gas_is_limited] = getGasRateWithLimit_(rates);
    auto [water_rate, water_limiting_target] = getWaterRateWithLimit2_(rates);
    bool oil_is_limited = oil_limiting_target.has_value();
    bool water_is_limited = water_limiting_target.has_value();
    return LimitedRates{
        oil_rate, gas_rate, water_rate,
        oil_is_limited, gas_is_limited, water_is_limited, rates.bhp_is_limited,
        oil_limiting_target, water_limiting_target};
}

GasLiftSingleWellGeneric::BasicRates
GasLiftSingleWellGeneric::
getWellStateRates_() const
{
    const int well_index = this->well_state_.index(this->well_name_).value();
    const auto& pu = this->phase_usage_;
    const auto& ws= this->well_state_.well(well_index);
    const auto& wrate = ws.well_potentials;

    const auto oil_rate = pu.phase_used[Oil]
        ? wrate[pu.phase_pos[Oil]]
        : 0.0;

    const auto gas_rate = pu.phase_used[Gas]
        ? wrate[pu.phase_pos[Gas]]
        : 0.0;

    const auto water_rate = pu.phase_used[Water]
        ? wrate[pu.phase_pos[Water]]
        : 0.0;
    if (this->debug) {
        const std::string msg = fmt::format("Initial surface rates: oil : {}, "
            "gas : {}, water : {}", oil_rate, gas_rate, water_rate);
        displayDebugMessage_(msg);
    }
    return BasicRates{oil_rate, water_rate, gas_rate, /*bhp_is_limited=*/false};
}


bool
GasLiftSingleWellGeneric::
hasProductionControl_(Rate rate) const
{
    switch (rate) {
    case Rate::oil:
        return this->controls_.hasControl(Well::ProducerCMode::ORAT);
    case Rate::gas:
        return this->controls_.hasControl(Well::ProducerCMode::GRAT);
    case Rate::water:
        return this->controls_.hasControl(Well::ProducerCMode::WRAT);
    case Rate::liquid:
        return this->controls_.hasControl(Well::ProducerCMode::LRAT);
    default:
        // Need this to avoid compiler warning : control reaches end of non-void function
        throw std::runtime_error("This should not happen");
    }
}


std::pair<GasLiftSingleWellGeneric::LimitedRates, double>
GasLiftSingleWellGeneric::
increaseALQtoPositiveOilRate_(double alq, const LimitedRates& orig_rates) const
{
    bool stop_iteration = false;
    double temp_alq = alq;
    // use the copy constructor to only copy the rates
    BasicRates rates = orig_rates;
    while(!stop_iteration) {
        temp_alq += this->increment_;
        if (temp_alq > this->max_alq_) break;
        auto temp_rates = computeWellRatesWithALQ_(temp_alq);
        if (!temp_rates) break;
        alq = temp_alq;
        rates = *temp_rates;
        if (rates.oil > 0) break;
    }
    // TODO: what about group limits?
    return {getLimitedRatesFromRates_(rates), alq};
}

std::pair<GasLiftSingleWellGeneric::LimitedRates, double>
GasLiftSingleWellGeneric::
increaseALQtoMinALQ_(const double orig_alq, const LimitedRates& orig_rates) const
{
    auto min_alq = this->min_alq_;
    assert(min_alq >= 0);
    assert(orig_alq < min_alq);
    assert(min_alq < this->max_alq_);
    bool stop_iteration = false;
    double alq = orig_alq;
    LimitedRates rates = orig_rates;
    while(!stop_iteration) {
        double temp_alq = alq + this->increment_;
        if (temp_alq >= min_alq) break;
        auto temp_rates = computeLimitedWellRatesWithALQ_(temp_alq);
        if (!temp_rates) break;
        alq = temp_alq;
        rates = *temp_rates;
        if (rates.limited()) break;
    }
    return std::make_pair(rates, alq);
}

void
GasLiftSingleWellGeneric::
logSuccess_(double alq, const int iteration_idx)
{
    const std::string message = fmt::format(
         "GLIFT, IT={}, WELL {} : {} ALQ from {} to {}",
         iteration_idx,
         this->well_name_,
         ((alq > this->orig_alq_) ? "increased" : "decreased"),
         this->orig_alq_, alq);
    this->deferred_logger_.info(message);
}

std::pair<GasLiftSingleWellGeneric::LimitedRates, double>
GasLiftSingleWellGeneric::
maybeAdjustALQbeforeOptimizeLoop_(
      const LimitedRates& orig_rates, const double orig_alq, const bool increase) const
{
    double alq = orig_alq;
    LimitedRates rates = orig_rates;

    if (this->debug) {
        const std::string msg = fmt::format("initial ALQ: {}", alq);
        displayDebugMessage_(msg);
    }
    if (!increase) {
        // NOTE: Try to decrease ALQ down to a value where the groups
        // maximum alq target and the total gas + alq target is not violated
        std::tie(rates, alq) = reduceALQtoGroupAlqLimits_(alq, orig_rates);
        if(orig_rates.limited()) {
            // NOTE: Try to decrease ALQ down to a value where the well target is
            //   not exceeded.
            // NOTE: This may reduce ALQ below the minimum value set in WLIFTOPT
            //   item 5. However, this is OK since the rate target is met and there
            //   is no point in using a higher ALQ value then.
            auto [rates1, alq1] = reduceALQtoWellTarget_(alq, orig_rates);
            auto [rates2, alq2] = reduceALQtoGroupTarget(alq, orig_rates);
            if (alq1 < alq2) {
                alq = alq1;
                rates = rates1;
            }
            else {
                alq = alq2;
                rates = rates2;
            }
        }
    } else {
        if (orig_rates.oil < 0) {
            // Try to increase ALQ up to a value where oil_rate is positive
            std::tie(rates, alq) = increaseALQtoPositiveOilRate_(alq, rates);
        }
        if ((this->min_alq_> 0) && (alq < this->min_alq_)) {
            // Try to increase ALQ up to the minimum limit without checking
            //   the economic gradient..
            std::tie(rates, alq) = increaseALQtoMinALQ_(alq, rates);
        }
    }
    if (orig_alq != alq) {
        if (this->debug) {
            const std::string msg = fmt::format("adjusted ALQ to: {}", alq);
            displayDebugMessage_(msg);
        }
        double delta_alq = alq - orig_alq;
        updateGroupRates_(orig_rates, rates, delta_alq);
    }
    return {rates, alq};
}

bool has_control(int controls, Group::InjectionCMode cmode) {
    return ((controls & static_cast<int>(cmode)) != 0);
}

// Reduce ALQ to the lowest value greater than zero that still makes at
//   least one rate limited w.r.t. group targets, or reduce ALQ to zero if
//   such positive ALQ value cannot be found.
std::pair<GasLiftSingleWellGeneric::LimitedRates, double>
GasLiftSingleWellGeneric::
reduceALQtoGroupAlqLimits_(const double orig_alq, const LimitedRates& orig_rates) const
{
    bool stop_this_iteration = false;
    double alq = orig_alq;
    BasicRates rates{ orig_rates };
    double temp_alq = orig_alq;
    while(!stop_this_iteration) {
        if (temp_alq == 0) break;
        temp_alq -= this->increment_;
        if (temp_alq < 0) temp_alq = 0;
        auto new_rates = computeWellRatesWithALQ_(temp_alq);
        if (!new_rates) break;
        auto delta_alq = temp_alq - orig_alq;
        auto delta_gas_rate = new_rates->gas - orig_rates.gas;
        if (!checkGroupTotalRateExceeded(delta_alq, delta_gas_rate)) {
            break;
        }
        rates = *new_rates;
        alq = temp_alq;
    }
    if (alq == orig_alq) {
        return {orig_rates, orig_alq};
    }
    else {
        LimitedRates limited_rates = getLimitedRatesFromRates_(rates);
        return {limited_rates, alq};
    }
}
// Reduce ALQ to the lowest value greater than zero that still makes at
//   least one rate limited w.r.t. group targets, or reduce ALQ to zero if
//   such positive ALQ value cannot be found.
std::pair<GasLiftSingleWellGeneric::LimitedRates, double>
GasLiftSingleWellGeneric::
reduceALQtoGroupTarget(const double orig_alq, const LimitedRates& orig_rates) const
{
    bool stop_this_iteration = true;
    const std::vector<std::pair<std::string,double>>& pairs =
        this->group_info_.getWellGroups(this->well_name_);
    for (const auto &pair /*<group_name, efficiency>*/ : pairs) {
        const auto& group_name = pair.first;
        if (!this->group_state_.has_production_control(group_name))
            continue;
        if (this->group_info_.hasAnyTarget(group_name)) {
            stop_this_iteration = false;
            displayDebugMessage_(
                "Reducing ALQ to meet group target(s) before iteration starts.");
            break;
        }
    }
    double alq = orig_alq;
    BasicRates rates{ orig_rates };
    double temp_alq = orig_alq;
    while(!stop_this_iteration) {
        if (temp_alq == 0) break;
        temp_alq -= this->increment_;
        if (temp_alq < 0) temp_alq = 0;
        auto new_rates = computeWellRatesWithALQ_(temp_alq);
        if (!new_rates) break;
        if (!checkGroupTargetsViolated(rates, *new_rates)) {
            break;
        }
        rates = *new_rates;
        alq = temp_alq;
    }
    if (alq == orig_alq) {
        return {orig_rates, orig_alq};
    }
    else {
        LimitedRates limited_rates = getLimitedRatesFromRates_(rates);
        return {limited_rates, alq};
    }
}

// Reduce ALQ to the lowest value greater than zero that still makes at
//   least one rate limited w.r.t. well targets, or reduce ALQ to zero if
//   such positive ALQ value cannot be found.
std::pair<GasLiftSingleWellGeneric::LimitedRates, double>
GasLiftSingleWellGeneric::
reduceALQtoWellTarget_(const double orig_alq, const LimitedRates& rates) const
{
    // this method should only be called if "rates" is limited
    assert(rates.limited());
    if (this->debug) {
        displayDebugMessage_(
             "Reducing ALQ to meet well targets before iteration starts..");
        debugShowLimitingTargets_(rates);
    }
    double alq = orig_alq;
    double temp_alq = alq;
    std::optional<LimitedRates> new_rates;
    bool stop_iteration = false;
    while(!stop_iteration) {
        if (temp_alq == 0) break;
        temp_alq -= this->increment_;
        if (temp_alq < 0) temp_alq = 0;
        auto temp_rates = computeLimitedWellRatesWithALQ_(temp_alq);
        if (!temp_rates) break; // failed to compute BHP given THP limit and ALQ
        // keep iterating until no rate is limited
        if (!temp_rates->limited()) break;
        alq = temp_alq;
        new_rates = temp_rates;
    }
    assert( alq <= orig_alq );
    if (this->debug) {
        if (alq < orig_alq) {
            // NOTE: ALQ may drop below zero before we are able to meet the target
            const std::string msg = fmt::format(
                "Reduced ALQ from {} to {} to meet rate targets. Rates (new, old) : "
                "oil(({}, {}), gas({}, {}), water({}, {})",
                orig_alq, alq,
                new_rates->oil, rates.oil,
                new_rates->gas, rates.gas,
                new_rates->water, rates.water);
            displayDebugMessage_(msg);
        }
        else if (alq == orig_alq) {
            // We might not be able to reduce ALQ, for example if ALQ starts out at zero.
            const std::string msg = fmt::format(
                       "Not able to reduce ALQ {} further. ", orig_alq);
            displayDebugMessage_(msg);
        }
    }
    if (new_rates) {
        return {*new_rates, alq};
    }
    else {
        return {rates, orig_alq};
    }
}

// INPUT:
//  - increase (boolean) :
//   - true  : try increase the lift gas supply,
//   - false : try decrease lift gas supply.
//
// OUTPUT:
//
//  - return value: a new GasLiftWellState or nullptr
//
std::unique_ptr<GasLiftWellState>
GasLiftSingleWellGeneric::
runOptimizeLoop_(bool increase)
{
    if (this->debug) debugShowProducerControlMode();
    std::unique_ptr<GasLiftWellState> ret_value; // nullptr initially
    auto [rates, cur_alq] = getInitialRatesWithLimit_();
    if (!rates) return ret_value;
    // if (this->debug) debugShowBhpAlqTable_();
    if (this->debug) debugShowAlqIncreaseDecreaseCounts_();
    if (this->debug) debugShowTargets_();
    bool success = false;  // did we succeed to increase alq?
    bool alq_is_limited = false;
    LimitedRates new_rates = *rates;
    auto [temp_rates2, new_alq] = maybeAdjustALQbeforeOptimizeLoop_(
                                                 *rates, cur_alq, increase);
    if (checkInitialALQmodified_(new_alq, this->orig_alq_)) {
        auto delta_alq = new_alq - cur_alq;
        new_rates = temp_rates2;
        cur_alq = new_alq;
        success = true;
        updateGroupRates_(*rates, new_rates, delta_alq);
    }

    OptimizeState state {*this, increase};
    auto temp_alq = cur_alq;
    if (checkThpControl_()) {
        if (this->debug) debugShowStartIteration_(temp_alq, increase, new_rates.oil);
    }
    else {
        // If the well is not under THP control, we can still use the previous
        //   initial adjustment of ALQ by using the well's THP limit to calculate
        //   BHP and then well rates from that.
        //   This is useful for example for wells under group control to reduce
        //   their gaslift. A typical case for this could be that a new well opens up.
        //   Then gaslift can be reduced while still keeping the group target.
        state.stop_iteration = true;
    }
    while (!state.stop_iteration && (++state.it <= this->max_iterations_)) {
        if (state.checkRatesViolated(new_rates)) break;
        if (state.checkAlqOutsideLimits(temp_alq, new_rates.oil)) break;
        std::optional<double> alq_opt;
        std::tie(alq_opt, alq_is_limited) = state.addOrSubtractAlqIncrement(temp_alq);
        if (!alq_opt) break;
        auto delta_alq = *alq_opt - temp_alq;
        if (checkGroupALQrateExceeded(delta_alq)) break;

        temp_alq = *alq_opt;
        if (this->debug) state.debugShowIterationInfo(temp_alq);
        rates = new_rates;
        auto temp_rates = computeLimitedWellRatesWithALQ_(temp_alq);
        if (!temp_rates) break;
        if (temp_rates->bhp_is_limited)
            state.stop_iteration = true;
        temp_rates = updateRatesToGroupLimits_(*rates, *temp_rates);

        auto delta_gas_rate = temp_rates->gas - rates->gas;
        if (checkGroupTotalRateExceeded(delta_alq, delta_gas_rate)) break;

/*        if (this->debug_abort_if_increase_and_gas_is_limited_) {
            if (gas_is_limited && increase) {
                // if gas is limited we do not want to increase
                displayDebugMessage_(
                    "increasing ALQ and gas is limited -> aborting iteration");
                break;
            }
        }
*/
        auto gradient = state.calcEcoGradient(
            rates->oil, temp_rates->oil, rates->gas, temp_rates->gas);
        if (this->debug)
            debugCheckNegativeGradient_(
                gradient, cur_alq, temp_alq, rates->oil, temp_rates->oil,
                rates->gas, temp_rates->gas, increase);
        if (state.checkEcoGradient(gradient)) break;
        cur_alq = temp_alq;
        success = true;
        new_rates = *temp_rates;
        updateGroupRates_(*rates, new_rates, delta_alq);
    }
    if (state.it > this->max_iterations_) {
        warnMaxIterationsExceeded_();
    }
    std::optional<bool> increase_opt;
    if (success) {
        this->well_state_.gliftUpdateAlqIncreaseCount(this->well_name_, increase);
        increase_opt = increase;
    }
    else {
        increase_opt = std::nullopt;
    }
    ret_value = std::make_unique<GasLiftWellState>(
        new_rates.oil, new_rates.oil_is_limited,
        new_rates.gas, new_rates.gas_is_limited,
        cur_alq, alq_is_limited, new_rates.water, increase_opt);
    return ret_value;
}

std::unique_ptr<GasLiftWellState>
GasLiftSingleWellGeneric::
runOptimize1_()
{
    std::unique_ptr<GasLiftWellState> state;
    int inc_count = this->well_state_.gliftGetAlqIncreaseCount(this->well_name_);
    int dec_count = this->well_state_.gliftGetAlqDecreaseCount(this->well_name_);
    if (dec_count == 0 && inc_count == 0) {
        state = tryIncreaseLiftGas_();
        if (!state || !(state->alqChanged())) {
            state = tryDecreaseLiftGas_();
        }
    }
    else if (dec_count == 0) {
        assert(inc_count > 0);
        state = tryIncreaseLiftGas_();
    }
    else if (inc_count == 0) {
        assert(dec_count > 0);
        state = tryDecreaseLiftGas_();
    }
    return state;
}

std::unique_ptr<GasLiftWellState>
GasLiftSingleWellGeneric::
runOptimize2_()
{
    std::unique_ptr<GasLiftWellState> state;
    state = tryIncreaseLiftGas_();
    if (!state || !(state->alqChanged())) {
        state = tryDecreaseLiftGas_();
    }
    return state;
}

std::unique_ptr<GasLiftWellState>
GasLiftSingleWellGeneric::
tryDecreaseLiftGas_()
{
    return runOptimizeLoop_(/*increase=*/ false);
}

std::unique_ptr<GasLiftWellState>
GasLiftSingleWellGeneric::
tryIncreaseLiftGas_()
{
    return runOptimizeLoop_(/*increase=*/ true);
}

void
GasLiftSingleWellGeneric::
setAlqMinRate_(const GasLiftOpt::Well& well)
{
    // NOTE:  According to WLIFTOPT item 5 :
    //   if min_rate() is negative, it means: allocate at least enough lift gas
    //   to enable the well to flow
    // NOTE: "to enable the well to flow" : How to interpret this?
    //   We choose to interpret it to mean a positive oil rate as returned from
    //
    //    computeWellRates_(bhp, cur_potentials);
    //
    //   So even if the well is producing gas, if the oil rate is zero
    //   we say that the "well is not flowing".
    //
    //   Note that if WECON item 2 is set, the well can be shut off
    //   before the flow rate reaches zero. Also,
    //   if bhp drops below the bhp lower limit, the well might switch to bhp
    //   control before the oil rate becomes zero.

    this->min_alq_ = well.min_rate();
    if (this->min_alq_ > 0) {
        if (this->min_alq_ >= this->max_alq_) {
            // NOTE: We reset the value to a negative value.
            //   negative value means: Allocate at least enough lift gas
            //   to allow the well to flow.
            // TODO: Consider other options for resetting the value..
            this->min_alq_ = -1;
            displayWarning_("Minimum ALQ value is larger than maximum ALQ value!"
                " Resetting value.");
        }
    }
}

void
GasLiftSingleWellGeneric::
updateGroupRates_(
    const LimitedRates& rates, const LimitedRates& new_rates, double delta_alq) const
{
    double delta_oil = new_rates.oil - rates.oil;
    double delta_gas = new_rates.gas - rates.gas;
    double delta_water = new_rates.water - rates.water;
    const auto &pairs =
        this->group_info_.getWellGroups(this->well_name_);
    for (const auto &[group_name, efficiency] : pairs) {
        int idx = this->group_info_.getGroupIdx(group_name);
        // This will notify the optimize loop in BlackoilWellModel, see
        //   gasLiftOptimizationStage1() in BlackoilWellModel_impl.hpp
        // that this group_info needs to be synchronized to the other MPI ranks
        this->sync_groups_.insert(idx);
        this->group_info_.update(group_name,
            efficiency * delta_oil,
            efficiency * delta_gas,
            efficiency * delta_water,
            efficiency * delta_alq);
    }
}

GasLiftSingleWellGeneric::LimitedRates
GasLiftSingleWellGeneric::
updateRatesToGroupLimits_(
    const BasicRates& old_rates, const LimitedRates& rates) const
{
    LimitedRates new_rates = rates;
    auto [new_oil_rate, oil_is_limited] = getOilRateWithGroupLimit_(
        new_rates.oil, old_rates.oil);
    if (oil_is_limited) {
        new_rates.oil_limiting_target = Rate::oil;
    }
    auto [new_gas_rate, gas_is_limited] = getGasRateWithGroupLimit_(
        new_rates.gas, old_rates.gas);
    auto [new_water_rate, water_is_limited] = getWaterRateWithGroupLimit_(
        new_rates.water, old_rates.water);
    if (water_is_limited) {
        new_rates.water_limiting_target = Rate::water;
    }
    auto [new_oil_rate2, new_water_rate2, oil_is_limited2, water_is_limited2]
        = getLiquidRateWithGroupLimit_(
            new_oil_rate, old_rates.oil, new_water_rate, old_rates.water);
    if (oil_is_limited2) {
        new_rates.oil_limiting_target = Rate::liquid;
    }
    if (water_is_limited2) {
        new_rates.water_limiting_target = Rate::liquid;
    }
    new_rates.oil = new_oil_rate2;
    new_rates.gas = new_gas_rate;
    new_rates.water = new_water_rate2;
    new_rates.oil_is_limited = rates.oil_is_limited || oil_is_limited || oil_is_limited2;
    new_rates.gas_is_limited = rates.gas_is_limited || gas_is_limited;
    new_rates.water_is_limited =
                      rates.water_is_limited || water_is_limited || water_is_limited2;
    if (oil_is_limited || oil_is_limited2 || gas_is_limited
                       || water_is_limited || water_is_limited2) {
        new_rates.limit_type = LimitedRates::LimitType::group;
    }
    return new_rates;
}

// Called when we should use a fixed ALQ value
void
GasLiftSingleWellGeneric::
updateWellStateAlqFixedValue_(const GasLiftOpt::Well& well)
{
    auto& max_alq_optional = well.max_rate();
    if (max_alq_optional) {
        // According to WLIFTOPT, item 3:
        // If item 2 is NO, then item 3 is regarded as the fixed
        // lift gas injection rate for the well.
        auto new_alq = *max_alq_optional;
        this->well_state_.setALQ(this->well_name_, new_alq);
    }
    // else {
    //    // If item 3 is defaulted, the lift gas rate remains
    //    // unchanged at its current value.
    //}

}

// Determine if we should use a fixed ALQ value.
//
// From the manual for WLIFTOPT, item 2:
//   Is the well's lift gas injection rate to be calculated by the
//   optimization facility?
// - YES : The well's lift gas injection rate is calculated by the
//   optimization facility.
// - NO  : The well's lift gas injection rate remains fixed at a
//   value that can be set either in Item 3 of this keyword, or in
//   Item 12 of keyword WCONPROD, or with keyword WELTARG.
bool
GasLiftSingleWellGeneric::
useFixedAlq_(const GasLiftOpt::Well& well)
{
    auto wliftopt_item2 = well.use_glo();
    if (wliftopt_item2) {
        return false;
    }
    else {
        displayDebugMessage_("WLIFTOPT item2 = NO. Skipping optimization.");
        //  auto& max_alq_optional = well.max_rate();
        //  if (max_alq_optional) {
               // According to WLIFTOPT, item 3:
               // If item 2 is NO, then item 3 is regarded as the fixed
               // lift gas injection rate for the well.
        //  }
        //  else {
              // If item 3 is defaulted, the lift gas rate remains
              // unchanged at its current value.
        //  }
        return true;
    }
}

void
GasLiftSingleWellGeneric::
debugInfoGroupRatesExceedTarget(
    Rate rate_type, const std::string& gr_name, double rate, double target) const
{
    const std::string msg = fmt::format("{} rate for group {} exceeds target: "
        "rate = {}, target = {}, the old rate is kept.",
        GasLiftGroupInfo::rateToString(rate_type),
        gr_name, rate, target);
    displayDebugMessage_(msg);
}

void
GasLiftSingleWellGeneric::
warnMaxIterationsExceeded_()
{
    const std::string msg = fmt::format(
        "Max iterations ({}) exceeded", this->max_iterations_);
    displayWarning_(msg);
}

/****************************************
 * Methods declared in OptimizeState
 ****************************************/

std::pair<std::optional<double>, bool>
GasLiftSingleWellGeneric::OptimizeState::
addOrSubtractAlqIncrement(double alq)
{
    auto [alq_opt, limited]
        = this->parent.addOrSubtractAlqIncrement_(alq, this->increase);
    if (!alq_opt) {
        const std::string msg = fmt::format(
            "iteration {}, alq = {} : not able to {} ALQ increment",
            this->it, alq, (this->increase ? "add" : "subtract"));
    }
    return {alq_opt, limited};
}

double
GasLiftSingleWellGeneric::OptimizeState::
calcEcoGradient(double oil_rate, double new_oil_rate,
                double gas_rate, double new_gas_rate)
{
    return this->parent.calcEcoGradient_(oil_rate, new_oil_rate,
                                         gas_rate, new_gas_rate, this->increase);
}

// NOTE:  According to WLIFTOPT item 5 :
//   if min_rate() is negative, it means: allocate at least enough lift gas
//   to enable the well to flow
//  We will interpret this as (see discussion above GasLiftSingleWell()
//   in this file): Allocate at least the amount of lift gas needed to
//   get a positive oil production rate.
bool
GasLiftSingleWellGeneric::OptimizeState::
checkAlqOutsideLimits(double alq, [[maybe_unused]] double oil_rate)
{
    std::ostringstream ss;
    bool result = false;

    if (this->increase) {
        if (alq >= this->parent.max_alq_) {
            ss << "ALQ >= " << this->parent.max_alq_ << " (max limit), "
               << "stopping iteration";
            result = true;
        }
        else { // checking the minimum limit...
            // NOTE: A negative min_alq_ means: allocate at least enough lift gas
            //  to enable the well to flow, see WLIFTOPT item 5.
            if (this->parent.min_alq_ < 0) {
                // - if oil rate is negative (i.e. the well is not flowing), continue to
                //    increase ALQ (according WLIFTOPT item 5) and try make the well
                //    flow.
                // - else if oil rate is already positive, there is no minimum
                //    limit for ALQ in this case
                result = false;
            }
            else {
                // NOTE: checking for a lower limit is not necessary
                //   when increasing alq. If ALQ was smaller than the minimum when
                //   we entered the runOptimizeLoop_() method,
                //   increaseALQtoMinALQ_() will ensure that ALQ >= min_alq
                assert(alq >= this->parent.min_alq_ );
                result = false;
            }
        }
    }
    else { // we are decreasing lift gas
        if ( alq == 0 ) {
            ss << "ALQ is zero, cannot decrease further. Stopping iteration.";
            result = true;
        }
        else if ( alq < 0 ) {
            ss << "Negative ALQ: " << alq << ". Stopping iteration.";
            result = true;
        }
        // NOTE: A negative min_alq_ means: allocate at least enough lift gas
        //  to enable the well to flow, see WLIFTOPT item 5.
        if (this->parent.min_alq_ < 0) {
            // We know that the well is flowing (oil_rate > 0) since that was
            //  already checked in runOptimizeLoop_() by calling checkNegativeOilRate()
            assert(oil_rate >= 0);
            result = false;
        }
        else {
            if (alq <= this->parent.min_alq_ ) {
                // According to WLIFTOPT item 5:
                //   "If a positive value is specified, the well is
                //   allocated at least that amount of lift gas,
                //   unless the well is unable to flow with that rate
                //   of lift gas injection, or unless the well can
                //   already meet one of its own rate limits before
                //   receiving its minimum lift gas rate."
                //
                // - We already know that the well is flowing, (oil_rate > 0),
                //    since that was already checked in runOptimizeLoop_() by calling
                //    checkRatesViolated().
                // - We also know that the rate limit was not exceeded since that was
                //    checked by checkRatesViolated()
                assert( oil_rate >= 0);
                ss << "ALQ <= " << this->parent.min_alq_ << " (min limit), "
                       << "stopping iteration";
                result = true;
            }
            else {
                // NOTE: checking for an upper limit should not be necessary
                // when decreasing alq.. so this is just to catch an
                // illegal state at an early point.
                if (this->parent.checkALQequal_(alq, this->parent.max_alq_)) {
                    return false;
                }
                else if (alq > this->parent.max_alq_) {
                    warn_( "unexpected: alq above upper limit when trying to "
                        "decrease lift gas. aborting iteration.");
                    result = true;
                }
                else {
                    result = false;
                }
            }
        }
    }
    if (this->parent.debug) {
        const std::string msg = ss.str();
        if (!msg.empty())
            this->parent.displayDebugMessage_(msg);
    }
    return result;
}

bool
GasLiftSingleWellGeneric::
checkGroupALQrateExceeded(double delta_alq) const
{
    const auto &pairs =
        group_info_.getWellGroups(well_name_);
    for (const auto &[group_name, efficiency] : pairs) {
        auto max_alq_opt = group_info_.maxAlq(group_name);
        if (max_alq_opt) {
            double alq =
                group_info_.alqRate(group_name) + efficiency * delta_alq;
            if (alq > *max_alq_opt) {
                if (debug) {
                    const std::string msg = fmt::format(
                        "Group {} : alq {} exceeds max_alq {}. Stopping iteration",
                        group_name, alq, *max_alq_opt);
                    displayDebugMessage_(msg);
                }
                return true;
            }
        }
    }
    return false;
}

bool
GasLiftSingleWellGeneric::
checkGroupTotalRateExceeded(double delta_alq, double delta_gas_rate) const
{
    const auto &pairs =
        group_info_.getWellGroups(well_name_);
    for (const auto &[group_name, efficiency] : pairs) {
        auto max_total_rate_opt = group_info_.maxTotalGasRate(group_name);
        if (max_total_rate_opt) {
            double alq =
                group_info_.alqRate(group_name) + efficiency * delta_alq;
            double gas_rate =
                group_info_.gasRate(group_name) + efficiency * delta_gas_rate;

            if ( (alq + gas_rate) > *max_total_rate_opt) {
                if (debug) {
                    const std::string msg = fmt::format(
                        "Group {} : total gas rate {} exceeds max_total_gas_rate {}. Stopping iteration",
                        group_name, alq + gas_rate, *max_total_rate_opt);
                    displayDebugMessage_(msg);
                }
                return true;
            }
        }
    }
    return false;
}
//
// bool checkEcoGradient(double gradient)
//
//  - Determine if the gradient has reached the limit of the economic gradient.
//
//  - If we are increasing lift gas, returns true if the gradient is smaller
//    than or equal to the economic gradient,
//
//  - If we are decreasing lift gas, returns true if the gradient is greater
//    than or equal to the economic gradient. (I.e., we assume too much lift gas
//    is being used and the gradient has become too small. We try to decrease
//    lift gas until the gradient increases and reaches the economic gradient..)
//
bool
GasLiftSingleWellGeneric::OptimizeState::
checkEcoGradient(double gradient)
{
    std::ostringstream ss;
    bool result = false;

    if (this->parent.debug) {
        ss << "checking gradient: " << gradient;
    }
    if (this->increase) {
        if (this->parent.debug) ss << " <= " << this->parent.eco_grad_ << " --> ";
        if (gradient <= this->parent.eco_grad_) {
            if (this->parent.debug) ss << "yes, stopping";
            result = true;
        }
        else {
            if (this->parent.debug) ss << "no, continue";
        }
    }
    else {  // decreasing lift gas
        if (this->parent.debug) ss << " >= " << this->parent.eco_grad_ << " --> ";
        if (gradient >= this->parent.eco_grad_) {
            if (this->parent.debug) ss << "yes, stopping";
            result = true;
        }
        else {
            if (this->parent.debug) ss << "no, continue";
        }
    }
    if (this->parent.debug) this->parent.displayDebugMessage_(ss.str());
    return result;
}

bool
GasLiftSingleWellGeneric::OptimizeState::
checkRatesViolated(const LimitedRates& rates) const
{
    if (!this->increase) {
        if (rates.oil < 0) {
            // The well is not flowing, and it will(?) not help to reduce lift
            // gas further. Note that this assumes that the oil rates drops with
            // decreasing lift gas.
            this->parent.displayDebugMessage_(
                "Negative oil rate detected while descreasing "
                "lift gas. Stopping iteration.");
            return true;
        }
    }
    if (rates.limited()) {
        if (this->parent.debug) {
            const std::string well_or_group
                = rates.limit_type == LimitedRates::LimitType::well ? "well" : "group";
            std::string target_type;
            std::string rate_type;
            if (rates.oil_is_limited) {
                target_type = GasLiftGroupInfo::rateToString(
                    *(rates.oil_limiting_target));
                rate_type = "oil";
            }
            else if (rates.gas_is_limited) {
                target_type = "gas";
                rate_type = "gas";
            }
            else if (rates.water_is_limited) {
                target_type = GasLiftGroupInfo::rateToString(
                    *(rates.water_limiting_target));
                rate_type = "water";
            }
            const std::string msg = fmt::format(
                "iteration {} : {} rate was limited due to {} {} target. "
                "Stopping iteration",
                this->it, rate_type, well_or_group, target_type);
            this->parent.displayDebugMessage_(msg);
        }
        return true;
    }
    return false;
}

void
GasLiftSingleWellGeneric::OptimizeState::
debugShowIterationInfo(double alq)
{
    const std::string msg = fmt::format("iteration {}, ALQ = {}", this->it, alq);
    this->parent.displayDebugMessage_(msg);
}


//  NOTE: When calculating the gradient, determine what the well would produce if
//  the lift gas injection rate were increased by one increment. The
//  production rates are adjusted if necessary to obey
//  any rate or BHP limits that the well may be subject to. From this
//  information, calculate the well's "weighted incremental
//  gradient"
//
// TODO: What does it mean to "adjust the production rates" given a
//   BHP limit?
//
double
GasLiftSingleWellGeneric::OptimizeState::
getBhpWithLimit()
{
    auto [new_bhp, limited] = this->parent.getBhpWithLimit_(this->bhp);
    if (limited) {
        // TODO: is it possible that bhp falls below the limit when
        // adding lift gas? I.e. if this->increase == true..
        // TODO: we keep the current alq, but it should probably
        // be adjusted since we changed computed bhp. But how?

        // Stop iteration, but first check the economic gradient
        //   with the bhp_update. If the gradient looks OK (see the
        //   main optimize loop) we keep the current ALQ value.
        this->stop_iteration = true;
    }
    return new_bhp;
}

/****************************************
 * Methods declared in BasicRates
 ****************************************/

GasLiftSingleWellGeneric::BasicRates::
BasicRates(const LimitedRates& rates)
{
    oil = rates.oil;
    gas = rates.gas;
    water = rates.water;
    bhp_is_limited = rates.bhp_is_limited;
}


} // namespace Opm