FieldMapIO.h

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// SPDX-FileCopyrightText: 2026 CERN for the benefit of the SHiP Collaboration
//
// SPDX-License-Identifier: LGPL-3.0-or-later
#pragma once
 
// Reader and writer for the SHiP field-map format (docs/field_map_format.md),
// a ROOT RNTuple named "field_maps" with one entry per map. Part of the MapIO
// component (SHiP::FieldServiceMapIO), which depends on ROOT; the core
// library does not.
 
#include "SHiP/FieldService/FieldMap.h"
#include "SHiP/FieldService/IFieldSource.h"
 
#include <array>
#include <cstdint>
#include <memory>
#include <span>
#include <string>
#include <vector>
 
namespace SHiP {
 
inline constexpr std::uint16_t kFieldMapFormatMajor = 1;
inline constexpr std::uint16_t kFieldMapFormatMinor = 0;
 
inline constexpr char const* kFieldMapNTupleName = "field_maps";
 
struct FieldMapWriteOptions {
    unsigned truncated_bits = 0;
};
 
[[nodiscard]] std::vector<FieldMap> readFieldMaps(std::string const& path);
 
[[nodiscard]] FieldMap readFieldMap(std::string const& path, std::string const& name);
 
void writeFieldMaps(std::string const& path, std::span<FieldMap const> maps,
                    FieldMapWriteOptions const& options = {});
 
[[nodiscard]] std::shared_ptr<IFieldEvaluator> loadFieldMap(std::string const& file,
                                                            std::string const& map);
 
class FieldMapSource final : public IFieldSource {
   public:
    struct MagnetConfig {
        std::string name;
        std::string volume_pattern;
        std::string file;
        std::string map;
        std::array<double, 3> translation{};
    };
 
    explicit FieldMapSource(std::vector<MagnetConfig> magnets);
 
    [[nodiscard]] std::vector<FieldRegion> const& regions() const override { return regions_; }
 
   private:
    std::vector<FieldRegion> regions_;
};
 
inline constexpr int kPlacementsFormatVersion = 1;
 
struct FieldMapPlacements {
    std::string geometry_package;
    std::string geometry_version;
    std::vector<FieldMapSource::MagnetConfig> magnets;
};
 
[[nodiscard]] FieldMapPlacements readFieldMapPlacements(std::string const& path);
 
}  // namespace SHiP