/*
 * (C) Copyright 2025- ECMWF and individual contributors.
 *
 * This software is licensed under the terms of the Apache Licence Version 2.0
 * which can be obtained at http://www.apache.org/licenses/LICENSE-2.0.
 * In applying this licence, ECMWF does not waive the privileges and immunities
 * granted to it by virtue of its status as an intergovernmental organisation nor
 * does it submit to any jurisdiction.
 */

///
/// @file analysisOp.h
/// @brief Implementation of the GRIB `analysis` concept operation.
///
/// This header defines the applicability rules and execution logic for the
/// **analysis concept** within the mars2grib backend.
///
/// The concept is responsible for populating GRIB keys related to the
/// *Local Use Section* analysis metadata, based on information extracted
/// from MARS input dictionaries and validated against GRIB constraints.
///
/// The implementation follows the standard mars2grib concept model:
/// - Compile-time applicability via `analysisApplicable`
/// - Runtime validation and deduction
/// - Strict error handling with contextual concept exceptions
///
/// @note
/// The namespace name `concepts_` is intentionally used instead of `concepts`
/// to avoid ambiguity and potential conflicts with the C++20 `concept` language
/// feature and related standard headers.
///
/// This is a deliberate design choice and must not be changed.
///
/// @ingroup mars2grib_backend_concepts
///
#pragma once

// System includes
#include <optional>
#include <string>

// Core concept includes
#include "metkit/mars2grib/backend/compile-time-registry-engine/common.h"
#include "metkit/mars2grib/backend/concepts/analysis/analysisEnum.h"
#include "metkit/mars2grib/utils/generalUtils.h"

// Deductions
#include "metkit/mars2grib/backend/deductions/lengthOfTimeWindow.h"
#include "metkit/mars2grib/backend/deductions/offsetToEndOf4DvarWindow.h"

// Checks
#include "metkit/mars2grib/backend/checks/matchLocalDefinitionNumber.h"

// Utils
#include "metkit/config/LibMetkit.h"
#include "metkit/mars2grib/utils/logUtils.h"
#include "metkit/mars2grib/utils/mars2gribExceptions.h"

namespace metkit::mars2grib::backend::concepts_ {

using namespace metkit::mars2grib::backend::compile_time_registry_engine;

///
/// @brief Compile-time applicability predicate for the `analysis` concept.
///
/// This function determines whether the `analysis` concept is applicable
/// for a given combination of:
/// - encoding stage
/// - GRIB section
/// - concept variant
///
/// The applicability is evaluated entirely at compile time and is used
/// by the concept dispatcher to ensure that only valid concept invocations
/// are instantiated.
///
/// @tparam Stage   Encoding stage (compile-time constant)
/// @tparam Section GRIB section index (compile-time constant)
/// @tparam Variant Analysis concept variant
///
/// @return `true` if the concept is applicable for the given parameters,
/// `false` otherwise.
///
/// @note
/// The default applicability rule enables the concept only when:
/// - `Variant == AnalysisType::Default`
/// - `Stage == StagePreset`
/// - `Section == SecLocalUseSection`
///
/// Users may override or specialize this predicate to alter applicability.
///
template <std::size_t Stage, std::size_t Section, AnalysisType Variant>
constexpr bool analysisApplicable() {


    // Conditions to apply concept
    return ((Variant == AnalysisType::Default) && (Stage == StagePreset) && (Section == SecLocalUseSection));
}


///
/// @brief Execute the `analysis` concept operation.
///
/// This function implements the runtime logic of the GRIB `analysis` concept.
/// When applicable, it:
///
/// 1. Verifies GRIB preconditions for the Local Use Section.
/// 2. Deduces required analysis-related values from MARS and parameter dictionaries.
/// 3. Encodes the corresponding GRIB keys in the output dictionary.
///
/// If the concept is invoked when not applicable, a
/// `Mars2GribConceptException` is thrown.
///
/// @tparam Stage    Encoding stage (compile-time constant)
/// @tparam Section  GRIB section index (compile-time constant)
/// @tparam Variant  Analysis concept variant
/// @tparam MarsDict_t Type of the MARS input dictionary
/// @tparam ParDict_t  Type of the parameter dictionary
/// @tparam OptDict_t  Type of the options dictionary
/// @tparam OutDict_t  Type of the GRIB output dictionary
///
/// @param[in]  mars MARS input dictionary
/// @param[in]  par  Parameter dictionary
/// @param[in]  opt  Options dictionary
/// @param[out] out  Output GRIB dictionary to be populated
///
/// @throws metkit::mars2grib::utils::exceptions::Mars2GribConceptException
/// If:
/// - the concept is called when not applicable
/// - required GRIB preconditions are not satisfied
/// - any deduction or encoding step fails
///
/// @note
/// - All runtime errors are wrapped with full concept context
/// (concept name, variant, stage, section).
/// - This function does not rely on any pre-existing GRIB header state.
///
/// @see analysisApplicable
///
template <std::size_t Stage, std::size_t Section, AnalysisType Variant, class MarsDict_t, class ParDict_t,
          class OptDict_t, class OutDict_t>
void AnalysisOp(const MarsDict_t& mars, const ParDict_t& par, const OptDict_t& opt, OutDict_t& out) {

    using metkit::mars2grib::utils::dict_traits::set_or_throw;
    using metkit::mars2grib::utils::exceptions::Mars2GribConceptException;

    if constexpr (analysisApplicable<Stage, Section, Variant>()) {

        try {

            MARS2GRIB_LOG_CONCEPT(analysis);

            // Structural validation
            validation::match_LocalDefinitionNumber_or_throw(opt, out, {36L});

            // Deductions
            long offsetToEndOf4DvarWindowVal = deductions::resolve_offsetToEndOf4DvarWindow_or_throw(mars, par, opt);
            std::optional<long> lengthOfTimeWindowVal =
                deductions::resolve_LengthOfTimeWindowInSeconds_or_throw(mars, par, opt);

            // Encoding
            set_or_throw<long>(out, "offsetToEndOf4DvarWindow", offsetToEndOf4DvarWindowVal);
            if (lengthOfTimeWindowVal.has_value()) {
                set_or_throw<long>(out, "lengthOf4DvarWindow", lengthOfTimeWindowVal.value() / 3600);
            }
            else {
                long missingLengthOfTimeWindowInHours = 0xFFFF;  // Missing sentinel in hours
                set_or_throw<long>(out, "lengthOf4DvarWindow", missingLengthOfTimeWindowInHours);  // Missing
            }
        }
        catch (...) {

            MARS2GRIB_CONCEPT_RETHROW(analysis, "Unable to set `analysis` concept...");
        }

        return;
    }

    // Concept invoked outside its applicability domain
    MARS2GRIB_CONCEPT_THROW(analysis, "Concept called when not applicable...");

    // Remove compiler warning
    mars2gribUnreachable();
}

}  // namespace metkit::mars2grib::backend::concepts_
