/*
 * (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 derivedForecast.h
/// @brief Deduction of the GRIB `derivedForecast` key.
///
/// This header defines deduction utilities used by the mars2grib backend
/// to resolve the **GRIB derived forecast type** (GRIB2 Code Table 4.7).
///
/// The deduction supports both explicit user override and automatic
/// deduction from MARS metadata, following a strict precedence order.
///
/// Deductions are responsible for:
/// - extracting values from MARS, parameter, and option dictionaries
/// - applying explicit validation and mapping logic
/// - returning strongly typed GRIB table values to concept operations
///
/// Deductions:
/// - do NOT encode GRIB keys directly
/// - do NOT apply implicit defaults outside explicitly defined rules
/// - do NOT perform GRIB table validation beyond table lookups
///
/// Error handling follows a strict fail-fast strategy:
/// - missing or unsupported inputs cause immediate failure
/// - errors are reported using domain-specific deduction exceptions
/// - original errors are preserved via nested exception propagation
///
/// Logging follows the mars2grib deduction policy:
/// - RESOLVE: value derived via deduction logic from input dictionaries
/// - OVERRIDE: value provided by parameter dictionary overriding deduction logic
///
/// @section References
/// Concept:
/// - @ref derivedEncoding.h
///
/// Related deductions:
/// - @ref numberOfForecastsInEnsemble.h
///
/// @ingroup mars2grib_backend_deductions
///
#pragma once

// System includes
#include <string>

// Tables
#include "metkit/mars2grib/backend/tables/derivedForecast.h"
#include "metkit/mars2grib/utils/generalUtils.h"

// Core deduction includes
#include "metkit/config/LibMetkit.h"
#include "metkit/mars2grib/utils/logUtils.h"
#include "metkit/mars2grib/utils/mars2gribExceptions.h"

namespace metkit::mars2grib::backend::deductions {

///
/// @brief Resolve the GRIB `derivedForecast` key.
///
/// @section Deduction contract
/// - Reads:
/// - `par["derivedForecast"]` (if present),
/// - otherwise `mars["type"]`
/// - Writes: none
/// - Side effects: logging (RESOLVE or OVERRIDE)
/// - Failure mode: throws
///
/// This deduction resolves the GRIB `derivedForecast` value following a
/// strict precedence order.
///
/// If the parameter dictionary provides `derivedForecast`, the value is
/// treated as authoritative and validated via the GRIB code table.
/// Otherwise, the value is intended to be deduced from the MARS key
/// `type`.
///
/// @tparam MarsDict_t
/// Type of the MARS dictionary. Must provide `type` if automatic
/// deduction is required.
///
/// @tparam ParDict_t
/// Type of the parameter dictionary. May contain `derivedForecast`
/// as a numeric override.
///
/// @tparam OptDict_t
/// Type of the options dictionary (unused by this deduction).
///
/// @param[in] mars
/// MARS dictionary providing metadata for automatic deduction.
///
/// @param[in] par
/// Parameter dictionary optionally providing `derivedForecast`.
///
/// @param[in] opt
/// Options dictionary (unused).
///
/// @return
/// The resolved `tables::DerivedForecast` enumeration value.
///
/// @throws metkit::mars2grib::utils::exceptions::Mars2GribDeductionException
/// If an override value is invalid, if required MARS metadata is
/// missing, if automatic deduction is not supported, or if any
/// unexpected error occurs.
///
template <class MarsDict_t, class ParDict_t, class OptDict_t>
tables::DerivedForecast resolve_DerivedForecast_or_throw(const MarsDict_t& mars, const ParDict_t& par,
                                                         const OptDict_t& opt) {

    using metkit::mars2grib::utils::dict_traits::get_or_throw;
    using metkit::mars2grib::utils::dict_traits::has;
    using metkit::mars2grib::utils::exceptions::Mars2GribDeductionException;

    try {

        // Default to Missing
        tables::DerivedForecast derivedForecast = tables::DerivedForecast::Missing;

        if (has(par, "derivedForecast")) {
            // Retrieve override from parameter dictionary
            const auto derivedForecastVal = get_or_throw<long>(par, "derivedForecast");

            // Lookup and validate enum value
            derivedForecast = tables::long2enum_DerivedForecast_or_throw(derivedForecastVal);

            // Emit OVERRIDE log entry
            MARS2GRIB_LOG_OVERRIDE([&]() {
                std::string logMsg = "`derivedForecast` overridden from parameter dictionary: value='";
                logMsg += tables::enum2name_DerivedForecast_or_throw(derivedForecast);
                logMsg += "'";
                return logMsg;
            }());

            // Success exit point
            return derivedForecast;
        }
        else {
            const auto marsType = get_or_throw<std::string>(mars, "type");

            if (marsType == "em" || marsType == "taem") {
                derivedForecast = tables::DerivedForecast::UnweightedMeanAllMembers;
            }
            else if (marsType == "es" || marsType == "taes") {
                derivedForecast = tables::DerivedForecast::SpreadAllMembers;
            }
            else {
                throw Mars2GribDeductionException(
                    "Mapping from mars type " + marsType + " to derivedForecast is not implemented", Here());
            }

            // Emit RESOLVE log entry
            MARS2GRIB_LOG_RESOLVE([&]() {
                std::string logMsg = "`derivedForecast` resolved from input dictionaries: value='";
                logMsg += tables::enum2name_DerivedForecast_or_throw(derivedForecast);
                logMsg += "'";
                return logMsg;
            }());

            // Success exit point
            return derivedForecast;
        }
    }
    catch (...) {

        // Rethrow nested exceptions
        std::throw_with_nested(
            Mars2GribDeductionException("Failed to resolve `derivedForecast` from input dictionaries", Here()));
    };

    // Remove compiler warning
    mars2gribUnreachable();
};


}  // namespace metkit::mars2grib::backend::deductions
