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 #ifndef PODIO_RNTUPLEREADER_H
 #define PODIO_RNTUPLEREADER_H
 
 #include "podio/ROOTFrameData.h"
 #include "podio/podioVersion.h"
 #include "podio/utilities/DatamodelRegistryIOHelpers.h"
 #include "podio/utilities/RootHelpers.h"
 
 #include <string>
 #include <string_view>
 #include <unordered_map>
 #include <vector>
 
 #include <ROOT/RNTuple.hxx>
 #include <ROOT/RNTupleReader.hxx>
 #include <RVersion.h>
 
 namespace podio {
 
 /// Introduce a new namespace instead of potentially opening and polluting the
 /// ROOT namespace
 namespace root_compat {
 #if ROOT_VERSION_CODE < ROOT_VERSION(6, 35, 0)
   using RNTupleReader = ROOT::Experimental::RNTupleReader;
 #else
   using RNTupleReader = ROOT::RNTupleReader;
 #endif
 } // namespace root_compat
 
 /// The RNTupleReader can be used to read files that have been written with the
 /// RNTuple backend.
 ///
 /// The RNTupleReader provides the data as ROOTFrameData from which a podio::Frame
 /// can be constructed. It can be used to read files written by the RNTupleWriter.
 class RNTupleReader {
 
 public:
   /// Create a RNTupleReader
   RNTupleReader() = default;
   /// Destructor
   ~RNTupleReader() = default;
   /// The RNTupleReader is not copy-able
   RNTupleReader(const RNTupleReader&) = delete;
   /// The RNTupleReader is not copy-able
   RNTupleReader& operator=(const RNTupleReader&) = delete;
 
   /// Open a single file for reading.
   ///
   /// @param filename The name of the input file
   void openFile(const std::string& filename);
 
   /// Open multiple files for reading and then treat them as if they are one file
   ///
   /// @note All of the files are assumed to have the same structure. Specifically
   /// this means:
   /// - The same categories are available from all files
   /// - The collections that are contained in the individual categories are the
   ///   same across all files
   /// - This usually boils down to "the files have been written with the same
   ///   "settings", e.g. they are outputs of a batched process.
   ///
   /// @param filenames The filenames of all input files that should be read
   void openFiles(const std::vector<std::string>& filenames);
 
   /// Read the next data entry for a given category.
   ///
   /// @param name The category name for which to read the next entry
   /// @param collsToRead (optional) the collection names that should be read. If
   ///             not provided (or empty) all collections will be read
   ///
   /// @returns FrameData from which a podio::Frame can be constructed if the
   ///          category exists and if there are still entries left to read.
   ///          Otherwise a nullptr
   ///
   /// @throws std::invalid_argument in case collsToRead contains collection
   /// names that are not available
   std::unique_ptr<podio::ROOTFrameData> readNextEntry(const std::string& name,
                                                       const std::vector<std::string>& collsToRead = {});
 
   /// Read the desired data entry for a given category.
   ///
   /// @param name  The category name for which to read the next entry
   /// @param entry The entry number to read
   /// @param collsToRead (optional) the collection names that should be read. If
   ///             not provided (or empty) all collections will be read
   ///
   /// @returns FrameData from which a podio::Frame can be constructed if the
   ///          category and the desired entry exist. Otherwise a nullptr
   ///
   /// @throws std::invalid_argument in case collsToRead contains collection
   /// names that are not available
   std::unique_ptr<podio::ROOTFrameData> readEntry(const std::string& name, const unsigned entry,
                                                   const std::vector<std::string>& collsToRead = {});
 
   /// Get the names of all the available Frame categories in the current file(s).
   ///
   /// @returns The names of the available categores from the file
   std::vector<std::string_view> getAvailableCategories() const;
 
   /// Get the number of entries for the given name
   ///
   /// @param name The name of the category
   ///
   /// @returns The number of entries that are available for the category
   unsigned getEntries(const std::string& name) const;
 
   /// Get the build version of podio that has been used to write the current
   /// file
   ///
   /// @returns The podio build version
   podio::version::Version currentFileVersion() const {
     return m_fileVersion;
   }
 
   /// Get the (build) version of a datamodel that has been used to write the
   /// current file
   ///
   /// @param name The name of the datamodel
   ///
   /// @returns The (build) version of the datamodel if available or an empty
   ///          optional
   std::optional<podio::version::Version> currentFileVersion(const std::string& name) const {
     return m_datamodelHolder.getDatamodelVersion(name);
   }
 
   /// Get the datamodel definition for the given name
   ///
   /// @param name The name of the datamodel
   ///
   /// @returns The high level definition of the datamodel in JSON format
   const std::string_view getDatamodelDefinition(const std::string& name) const {
     return m_datamodelHolder.getDatamodelDefinition(name);
   }
 
   /// Get all names of the datamodels that are available from this reader
   ///
   /// @returns The names of the datamodels
   std::vector<std::string> getAvailableDatamodels() const {
     return m_datamodelHolder.getAvailableDatamodels();
   }
 
 private:
   /**
    * Initialize the given category by filling the maps with metadata information
    * that will be used later
    */
   bool initCategory(const std::string& category);
 
   /**
    * Read and reconstruct the generic parameters of the Frame
    */
   GenericParameters readEventMetaData(const std::string& name, const unsigned localEntry, const unsigned readerIndex);
 
   template <typename T>
   void readParams(const std::string& name, const unsigned entNum, const unsigned readerIndex,
                   GenericParameters& params);
 
   std::unique_ptr<root_compat::RNTupleReader> m_metadata{};
 
   podio::version::Version m_fileVersion{};
   DatamodelDefinitionHolder m_datamodelHolder{};
 
   std::unordered_map<std::string, std::vector<std::unique_ptr<root_compat::RNTupleReader>>> m_readers{};
   std::unordered_map<std::string, std::unique_ptr<root_compat::RNTupleReader>> m_metadata_readers{};
   std::vector<std::string> m_filenames{};
 
   std::unordered_map<std::string, unsigned> m_entries{};
   // Map category to a vector that contains at how many entries each reader starts
   // For example, if we have 3 readers and the first one has 10 entries, the second one 20 and the third one 30
   // then the vector will be {0, 10, 30}
   // 60 is not needed because anything after 30 will be in the last reader
   std::unordered_map<std::string, std::vector<unsigned>> m_readerEntries{};
   std::unordered_map<std::string, unsigned> m_totalEntries{};
 
   /// Map each category to the collections that have been written and are available
   std::unordered_map<std::string, std::vector<podio::root_utils::CollectionWriteInfo>> m_collectionInfo{};
 
   std::vector<std::string> m_availableCategories{};
 
   std::unordered_map<std::string, std::shared_ptr<podio::CollectionIDTable>> m_idTables{};
 };
 
 } // namespace podio
 
 #endif

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