text: #pragma once
  #include <DataStreams/IBlockInputStream.h>
  #include <Storages/MergeTree/MergeTreeData.h>
  #include <Storages/MergeTree/IMergeTreeReader.h>
  #include <Storages/MergeTree/MarkRange.h>
  #include <memory>
  
  namespace DB
  {
  
  /// Lightweight (in terms of logic) stream for reading single part from MergeTree
  class MergeTreeSequentialBlockInputStream : public IBlockInputStream
  {
  public:
      MergeTreeSequentialBlockInputStream(
          const MergeTreeData & storage_,
          const MergeTreeData::DataPartPtr & data_part_,
          Names columns_to_read_,
          bool read_with_direct_io_,
          bool take_column_types_from_storage,
          bool quiet = false
      );
  
      ~MergeTreeSequentialBlockInputStream() override;
  
      String getName() const override { return "MergeTreeSequentialBlockInputStream"; }
  
      Block getHeader() const override;
  
      /// Closes readers and unlock part locks
      void finish();
  
      size_t getCurrentMark() const { return current_mark; }
  
      size_t getCurrentRow() const { return current_row; }
  
  protected:
      Block readImpl() override;
  
  private:
  
      const MergeTreeData & storage;
  
      Block header;
  
      /// Data part will not be removed if the pointer owns it
      MergeTreeData::DataPartPtr data_part;
  
      /// Forbids to change columns list of the part during reading
      std::shared_lock<std::shared_mutex> part_columns_lock;
  
      /// Columns we have to read (each Block from read will contain them)
      Names columns_to_read;
  
      /// Should read using direct IO
      bool read_with_direct_io;
  
      Logger * log = &Logger::get("MergeTreeSequentialBlockInputStream");
  
      std::shared_ptr<MarkCache> mark_cache;
      using MergeTreeReaderPtr = std::unique_ptr<IMergeTreeReader>;
      MergeTreeReaderPtr reader;
  
      /// current mark at which we stop reading
      size_t current_mark = 0;
  
      /// current row at which we stop reading
      size_t current_row = 0;
  
  private:
      void fixHeader(Block & header_block) const;
  
  };
  
  }
  