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  /*! \libinternal \file
   * \brief
   * Declares gmx::IFileOutputRedirector.
   *
   * \author Teemu Murtola <teemu.murtola@gmail.com>
   * \inlibraryapi
   * \ingroup module_utility
   */
  #ifndef GMX_UTILITY_FILEREDIRECTOR_H
  #define GMX_UTILITY_FILEREDIRECTOR_H
  
  #include <string>
  
  #include "gromacs/utility/path.h"
  #include "gromacs/utility/textstream.h"
  
  namespace gmx
  {
  
  /*! \libinternal \brief
   * Allows overriding file existence checks from code that supports it.
   *
   * The calling code should take in this interface and use the methods in it
   * all file system operations that need to support this redirection.
   *
   * This allows tests to override the file existence checks without actually
   * using the file system.  See IFileOutputRedirector for notes on
   * a typical usage pattern.
   *
   * With some further refactoring of the File class, this could also support
   * redirecting input files from in-memory buffers as well, but for now the
   * current capabilities are sufficient.
   *
   * \inlibraryapi
   * \ingroup module_utility
   */
  class IFileInputRedirector
  {
  public:
      virtual ~IFileInputRedirector();
  
      /*! \brief
       * Checks whether the provided path exists (and is a file).
       *
       * The \p onNotFound can be used to influence the behavior on error
       * conditions.  Functions to pass as this parameter are provided as
       * members of gmx::File.
       */
      virtual bool fileExists(const char* filename, File::NotFoundHandler onNotFound) const = 0;
  
      //! Convenience method to check file existence using an std::string path.
      bool fileExists(const std::string& filename, File::NotFoundHandler onNotFound) const
      {
          return fileExists(filename.c_str(), onNotFound);
      }
  };
  
  /*! \libinternal \brief
   * Allows capturing `stdout` and file output from code that supports it.
   *
   * The calling code should take in this interface and use the stream objects
   * it returns for all output that needs to support this redirection.
   *
   * Currently, the (nearly) only purpose for this interface is for unit tests to
   * capture the file output without duplicating the knowledge of which files are
   * actually produced.  The tests can also replace actual files with in-memory
   * streams (e.g., a StringOutputStream), and test the output without actually
   * accessing the file system and managing actual files.
   *
   * As the main user for non-default implementation of this interface is tests,
   * code using this interface generally uses a pattern where the redirector is
   * initialized to defaultFileOutputRedirector(), and a separate setter is
   * provided for tests to change the default.  This allows code outside the
   * tests (and outside the code actually calling the redirector) to be written
   * as if this interface did not exist (i.e., they do not need to pass the
   * default instance).
   *
   * Also, the interface only supports text files, but can be generalized if/when
   * there is a need for binary streams (see also TextOutputStream).
   *
   * \inlibraryapi
   * \ingroup module_utility
   */
  class IFileOutputRedirector
  {
  public:
      virtual ~IFileOutputRedirector();
  
      /*! \brief
       * Returns a stream to use for `stdout` output.
       */
      virtual TextOutputStream& standardOutput() = 0;
      /*! \brief
       * Returns a stream to use for output to a file at a given path.
       *
       * \param[in] filename  Requested file name.
       */
      virtual TextOutputStreamPointer openTextOutputFile(const char* filename) = 0;
  
      //! Convenience method to open a stream using an std::string path.
      TextOutputStreamPointer openTextOutputFile(const std::string& filename)
      {
          return openTextOutputFile(filename.c_str());
      }
  };
  
  //! \cond libapi
  /*! \brief
   * Returns default implementation for IFileInputRedirector.
   *
   * The returned implementation does not redirect anything, but just uses the
   * file system normally.
   *
   * Does not throw.
   *
   * \ingroup module_utility
   */
  IFileInputRedirector& defaultFileInputRedirector();
  /*! \brief
   * Returns default implementation for IFileOutputRedirector.
   *
   * The returned implementation does not redirect anything, but just opens the
   * files at requested locations.
   *
   * Does not throw.
   *
   * \ingroup module_utility
   */
  IFileOutputRedirector& defaultFileOutputRedirector();
  //! \endcond
  
  } // namespace gmx
  
  #endif
  