XLStreamWriter.hpp

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#ifndef OPENXLSX_XLSTREAMWRITER_HPP
#define OPENXLSX_XLSTREAMWRITER_HPP
 
#include "OpenXLSX-Exports.hpp"
#include "XLCellValue.hpp"
#include "XLStyles.hpp"
#include <cstddef>
#include <filesystem>
#include <fstream>
#include <optional>
#include <string>
#include <vector>
 
namespace OpenXLSX
{
 
    class XLWorksheet;
 
    class OPENXLSX_EXPORT XLStreamCell
    {
    public:
        explicit XLStreamCell(XLCellValue val) : value(std::move(val)), styleIndex(std::nullopt) {}
 
        XLStreamCell(XLCellValue val, XLStyleIndex style) : value(std::move(val)), styleIndex(style) {}
 
        XLCellValue                 value;
        std::optional<XLStyleIndex> styleIndex;
    };
 
    class OPENXLSX_EXPORT XLStreamWriter
    {
    public:
        XLStreamWriter()                                 = default;
        XLStreamWriter(const XLStreamWriter&)            = delete;
        XLStreamWriter& operator=(const XLStreamWriter&) = delete;
 
        XLStreamWriter(XLStreamWriter&& other) noexcept;
        XLStreamWriter& operator=(XLStreamWriter&& other) noexcept;
 
        ~XLStreamWriter();
 
        bool isStreamActive() const;
 
        void appendRow(const std::vector<XLCellValue>& values);
 
        void appendRow(const std::vector<XLStreamCell>& cells);
 
        std::string getTempFilePath() const;
        void        close();
 
    private:
        friend class XLWorksheet;
 
        explicit XLStreamWriter(XLWorksheet* worksheet);
 
        template<typename T>
        void appendRowImpl(const std::vector<T>& items);
 
        void flushWriteBuffer();
        void flushSheetDataClose();
 
        // Flush the in-memory write buffer to disk when it exceeds this threshold.
        // 256 KB gives a good balance between memory use and syscall frequency.
        static constexpr size_t kFlushThreshold = 256 * 1024;
 
        std::filesystem::path m_tempPath;
        std::ofstream         m_stream;
        uint32_t              m_currentRow{1};
        bool                  m_active{false};
        std::string           m_bottomHalf;
 
        // Write buffer — avoids one syscall per cell by coalescing multiple
        // small writes into a single fstream::write() call.
        std::string m_writeBuffer;
    };
 
}    // namespace OpenXLSX
#endif    // OPENXLSX_XLSTREAMWRITER_HPP