text: #pragma once
  
  #include <map>
  #include <shared_mutex>
  #include <ext/shared_ptr_helper.h>
  
  #include <Poco/File.h>
  
  #include <Storages/IStorage.h>
  #include <Common/FileChecker.h>
  #include <Common/escapeForFileName.h>
  
  
  namespace DB
  {
  
  /** Implements simple table engine without support of indices.
    * The data is stored in a compressed form.
    */
  class StorageLog : public ext::shared_ptr_helper<StorageLog>, public IStorage
  {
  friend class LogBlockInputStream;
  friend class LogBlockOutputStream;
  friend struct ext::shared_ptr_helper<StorageLog>;
  
  public:
      std::string getName() const override { return "Log"; }
      std::string getTableName() const override { return table_name; }
      std::string getDatabaseName() const override { return database_name; }
  
      BlockInputStreams read(
          const Names & column_names,
          const SelectQueryInfo & query_info,
          const Context & context,
          QueryProcessingStage::Enum processed_stage,
          size_t max_block_size,
          unsigned num_streams) override;
  
      BlockOutputStreamPtr write(const ASTPtr & query, const Context & context) override;
  
      void rename(const String & new_path_to_table_data, const String & new_database_name, const String & new_table_name, TableStructureWriteLockHolder &) override;
  
      CheckResults checkData(const ASTPtr & /* query */, const Context & /* context */) override;
  
      void truncate(const ASTPtr &, const Context &, TableStructureWriteLockHolder &) override;
  
      std::string fullPath() const { return path; }
  
      Strings getDataPaths() const override { return {fullPath()}; }
  
  protected:
      /** Attach the table with the appropriate name, along the appropriate path (with / at the end),
        *  (the correctness of names and paths is not verified)
        *  consisting of the specified columns; Create files if they do not exist.
        */
      StorageLog(
          const std::string & relative_path_,
          const std::string & database_name_,
          const std::string & table_name_,
          const ColumnsDescription & columns_,
          const ConstraintsDescription & constraints_,
          size_t max_compress_block_size_,
          const Context & context_);
  
  private:
      String base_path;
      String path;
      String table_name;
      String database_name;
  
      mutable std::shared_mutex rwlock;
  
      /** Offsets to some row number in a file for column in table.
        * They are needed so that you can read the data in several threads.
        */
      struct Mark
      {
          size_t rows;    /// How many rows are before this offset including the block at this offset.
          size_t offset;  /// The offset in compressed file.
      };
  
      using Marks = std::vector<Mark>;
  
      /// Column data
      struct ColumnData
      {
          /// Specifies the column number in the marks file.
          /// Does not necessarily match the column number among the columns of the table: columns with lengths of arrays are also numbered here.
          size_t column_index;
  
          Poco::File data_file;
          Marks marks;
      };
      using Files_t = std::map<String, ColumnData>;
  
      Files_t files; /// name -> data
  
      Names column_names_by_idx; /// column_index -> name
  
      Poco::File marks_file;
  
      /// The order of adding files should not change: it corresponds to the order of the columns in the marks file.
      void addFiles(const String & column_name, const IDataType & type);
  
      bool loaded_marks = false;
  
      size_t max_compress_block_size;
      size_t file_count = 0;
  
      FileChecker file_checker;
  
      /// Read marks files if they are not already read.
      /// It is done lazily, so that with a large number of tables, the server starts quickly.
      /// You can not call with a write locked `rwlock`.
      void loadMarks();
  
      /// The order of adding files should not change: it corresponds to the order of the columns in the marks file.
      void addFile(const String & column_name, const IDataType & type, size_t level = 0);
  
      /** For normal columns, the number of rows in the block is specified in the marks.
        * For array columns and nested structures, there are more than one group of marks that correspond to different files
        *  - for elements (file name.bin) - the total number of array elements in the block is specified,
        *  - for array sizes (file name.size0.bin) - the number of rows (the whole arrays themselves) in the block is specified.
        *
        * Return the first group of marks that contain the number of rows, but not the internals of the arrays.
        */
      const Marks & getMarksWithRealRowCount() const;
  
      std::string getFullPath() const { return path; }
  };
  
  }
  