#pragma region CPL License
/*
Nuclex Native Framework
Copyright (C) 2002-2021 Nuclex Development Labs

This library is free software; you can redistribute it and/or
modify it under the terms of the IBM Common Public License as
published by the IBM Corporation; either version 1.0 of the
License, or (at your option) any later version.

This library is distributed in the hope that it will be useful,
but WITHOUT ANY WARRANTY; without even the implied warranty of
MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
IBM Common Public License for more details.

You should have received a copy of the IBM Common Public
License along with this library
*/
#pragma endregion // CPL License

#ifndef NUCLEX_STORAGE_FILESYSTEM_LINUX_LINUXFILE_H
#define NUCLEX_STORAGE_FILESYSTEM_LINUX_LINUXFILE_H

#include "Nuclex/Storage/Config.h"

#if defined(NUCLEX_STORAGE_LINUX)

#include "Nuclex/Storage/FileSystem/File.h"

#include <memory> // for std::shared_ptr
#include <atomic> // for std::atomic
#include <shared_mutex> // for std::shared_mutex

namespace Nuclex { namespace Storage { namespace FileSystem {

  // ------------------------------------------------------------------------------------------- //

  class FileManagerBackend;

  // ------------------------------------------------------------------------------------------- //

}}} // namespace Nuclex::Storage::FileSystem

namespace Nuclex { namespace Storage { namespace FileSystem { namespace Linux {

  // ------------------------------------------------------------------------------------------- //

  /// <summary>Accesses a real file on a mounted Linux file system</summary>
  class LinuxFile : public File { // use std::enable_shared_from_this?

    /// <summary>Initializes a new Windows file</summary>
    /// <param name="backend">Backend in which the open file will be tracked</param>
    /// <param name="absolutePath">Absolute path to the file</param>
    /// <param name="create">Whether the file should be created right away</param>
    /// <remarks>
    ///   If the file does not exist and <see cref="create" /> is false, an exception
    ///   is thrown. If <see cref="create" /> is true, the file will be created right
    ///   away to ensure it is reserved in the actual file system.
    /// </remarks>
    public: LinuxFile(
      std::shared_ptr<FileManagerBackend> backend,
      const std::string &absolutePath,
      bool create = false
    );

    /// <summary>Frees all resources owned by the instance</summary>
    public: virtual ~LinuxFile() override;

    /// <summary>Determines the size of the file</summary>
    /// <returns>The size of the file in bytes</returns>
    public: std::uint64_t GetSize() const override;

    /// <summary>Returns the name of the file</summary>
    /// <returns>The file's name</returns>
    public: const std::string &GetName() const override;

    /// <summary>Returns the path the file is stored at in the native format</summary>
    /// <returns>The file's absolute path in the native OS format</returns>
    public: virtual const std::string &GetNativePath() const override {
      return this->absolutePath;
    }

    /// <summary>Changes the name of the file</summary>
    /// <param name="name">New name the file will be known under</param>
    public: void Rename(const std::string &name) override;

    /// <summary>Retrieves the time at which the file has been last modified</summary>
    /// <returns>The since since the last modification of the file took place</returns>
    public: std::time_t GetLastModificationTime() const override;

    /// <summary>Reads raw data from the file</summary>
    /// <param name="location">Absolute file position data will be read from</param>
    /// <param name="buffer">Buffer into which data will be read</param>
    /// <param name="count">Number of bytes that will be read</param>
    public: void ReadAt(
      std::uint64_t location, void *buffer, std::size_t count
    ) const override;

    /// <summary>Writes raw data into the file</summary>
    /// <param name="location">Absolute file position data will be written to</param>
    /// <param name="buffer">Buffer from which data will be taken</param>
    /// <param name="count">Number of bytes that will be written</param>
    public: void WriteAt(
      std::uint64_t location, const void *buffer, std::size_t count
    ) override;

    /// <summary>Ensures changes to the file have been written to disk</summary>
    public: void Flush() override;

    /// <summary>Opens the file descriptor with shared read access</summary>
    /// <remarks>
    ///   This is called by the ReadAt() method if it detects that the file descriptor
    ///   is not valid (i.e. file not opened yet). It's moved into a separate method in
    ///   order to keep the hot code path inside ReadAt() short.
    /// </remarks>
    private: void openFileForReading() const;

    /// <summary>Opens the file descriptor with shared read access</summary>
    /// <remarks>
    ///   This is called by the WriteAt() method if it detects that the file descriptor
    ///   is not valid (i.e. file not opened yet). It's moved into a separate method in
    ///   order to keep the hot code path inside WriteAt() short.
    /// </remarks>
    private: void openFileForWriting() const;

    /// <summary>Backend that's keeping track of opened files</summary>
    private: std::shared_ptr<FileManagerBackend> backend;
    /// <summary>Absolute path of the file in the file system</summary>
    private: std::string absolutePath;
    /// <summary>Name of the file</summary>
    private: std::string name;

    // TODO: Move the fields below into a structure that is created on-demand
    //   to avoid having tons of mutexes around. Perhaps create this structure through
    //   the file manager backend so that it can close the least recently used files
    //   if too many are open?

    /// <summary>Reader/Writer lock mutex used for access + handle change</summary>
    /// <remarks>
    ///   Shared lock is used for accessing the file descriptor (including writes).
    ///   Exclusive lock is used to change (close, open, re-open) the file descriptor.
    /// </remarks>
    private: mutable std::shared_mutex readerWriterLock;
    /// <summary>Number of the opened file or -1 if not opened yet</summary>
    private: mutable std::atomic<int> fileDescriptor;
    /// <summary>Whether the file has been opened for writing</summary>
    private: mutable std::atomic<bool> isOpenedWritable;
    /// <summary>Current position of the file cursor</summary>
    private: mutable std::atomic<std::uint64_t> fileCursor;

  };

  // ------------------------------------------------------------------------------------------- //

}}}} // namespace Nuclex::Storage::FileSystem::Linux

#endif // defined(NUCLEX_STORAGE_LINUX)

#endif // NUCLEX_STORAGE_FILESYSTEM_LINUX_LINUXFILE_H