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File indexing completed on 2026-09-16 09:20:01

 #ifndef PODIO_ROOTREADER_H
 #define PODIO_ROOTREADER_H
 
 #include "podio/ROOTFrameData.h"
 #include "podio/utilities/ReaderCommon.h"
 #include "podio/utilities/ReaderUtils.h"
 #include "podio/utilities/RootHelpers.h"
 
 #include "TChain.h"
 
 #include <memory>
 #include <optional>
 #include <string>
 #include <string_view>
 #include <tuple>
 #include <utility>
 #include <vector>
 
 // forward declarations
 class TClass;
 class TFile;
 class TTree;
 
 namespace podio {
 
 namespace detail {
   // Information about the collection class type, whether it is a subset, the
   // schema version on file and the index in the collection branches cache
   // vector
   using CollectionInfo = std::tuple<std::string, bool, SchemaVersionT, size_t>;
 
   struct NamedCollInfo {
     std::string name{};
     CollectionInfo info{};
   };
 } // namespace detail
 
 class CollectionBase;
 class CollectionIDTable;
 class GenericParameters;
 struct CollectionReadBuffers;
 
 /// This class has the function to read available data from disk in ROOTs TTree
 /// format.
 ///
 /// The ROOTReader provides the data as ROOTFrameData from which a podio::Frame
 /// can be constructed. It can be used to read files written by the ROOTWriter.
 class ROOTReader : public ReaderCommon {
 
 public:
   ROOTReader() = default;
   ~ROOTReader() = default;
 
   ROOTReader(const ROOTReader&) = delete;
   ROOTReader& operator=(const ROOTReader&) = delete;
   ROOTReader(ROOTReader&&) = default;
   ROOTReader& operator=(ROOTReader&&) = default;
 
   /// 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(std::string_view 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(std::string_view name, const unsigned entry,
                                                   const std::vector<std::string>& collsToRead = {});
 
   /// 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(std::string_view name) const;
 
   std::optional<std::map<std::string, SizeStats>> getSizeStats(std::string_view category);
 
 private:
   /// Helper struct to group together all the necessary state to read / process
   /// a given category. A "category" in this case describes all frames with the
   /// same name which are constrained by the ROOT file structure that we use to
   /// have the same contents. It encapsulates all state that is necessary for
   /// reading from a TTree / TChain (i.e. collection infos, branches, ...)
   struct CategoryInfo {
     /// constructor from chain for more convenient map insertion
     CategoryInfo(std::unique_ptr<TChain>&& c) : chain(std::move(c)) {
     }
     std::unique_ptr<TChain> chain{nullptr};                 ///< The TChain with the data
     unsigned entry{0};                                      ///< The next entry to read
     std::vector<detail::NamedCollInfo> storedClasses{};     ///< The stored collections in this
                                                             ///< category
     std::vector<root_utils::CollectionBranches> branches{}; ///< The branches for this category
     std::shared_ptr<CollectionIDTable> table{nullptr};      ///< The collection ID table for this category
   };
 
   /// Initialize the passed CategoryInfo by setting up the necessary branches,
   /// collection infos and all necessary meta data to be able to read entries
   /// with this name
   void initCategory(CategoryInfo& catInfo, std::string_view name);
 
   /// Get the category information for the given name. In case there is no TTree
   /// with contents for the given name this will return a CategoryInfo with an
   /// uninitialized chain (nullptr) member
   CategoryInfo& getCategoryInfo(std::string_view name);
 
   /// Read the parameters for the entry specified in the passed CategoryInfo
   GenericParameters readEntryParameters(CategoryInfo& catInfo, bool reloadBranches, unsigned int localEntry);
 
   template <typename T>
   static void readParams(CategoryInfo& catInfo, podio::GenericParameters& params, bool reloadBranches,
                          unsigned int localEntry);
 
   /// Read the data entry specified in the passed CategoryInfo, and increase the
   /// counter afterwards. In case the requested entry is larger than the
   /// available number of entries, return a nullptr.
   std::unique_ptr<podio::ROOTFrameData> readEntry(ROOTReader::CategoryInfo& catInfo,
                                                   const std::vector<std::string>& collsToRead);
 
   /// Get / read the buffers at index iColl in the passed category information
   std::optional<podio::CollectionReadBuffers> getCollectionBuffers(CategoryInfo& catInfo, size_t iColl,
                                                                    bool reloadBranches, unsigned int localEntry);
 
   std::unique_ptr<TChain> m_metaChain{nullptr};                      ///< The metadata tree
   std::unordered_map<std::string_view, CategoryInfo> m_categories{}; ///< All categories
 };
 
 } // namespace podio
 
 #endif // PODIO_ROOTREADER_H

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