windows-user-space-emulator/src/windows-emulator/file_system.hpp

#pragma once
#include "std_include.hpp"
#include "windows_path.hpp"

class file_system
{
  public:
    file_system(const std::filesystem::path& root)
        : root_(canonical(root))
    {
    }

    static bool is_escaping_relative_path(const std::filesystem::path& p)
    {
        return p.empty() || *p.begin() == "..";
    }

    static bool is_subpath(const std::filesystem::path& normal_root, const std::filesystem::path& normal_target)
    {
        const auto relative_path = relative(normal_target, normal_root);
        return !is_escaping_relative_path(relative_path);
    }

    std::set<char> list_drives() const
    {
        std::set<char> drives{};

#ifdef OS_WINDOWS
        if (this->root_.empty())
        {
            const auto drive_bits = GetLogicalDrives();

            for (char drive = 'a'; drive <= 'z'; ++drive)
            {
                const auto drive_index = drive - 'a';
                if (drive_bits & (1 << drive_index))
                {
                    drives.insert(drive);
                }
            }

            return drives;
        }
#endif

        std::error_code ec{};
        for (const auto& file : std::filesystem::directory_iterator(this->root_, ec))
        {
            const auto filename = file.path().filename().string();
            if (filename.size() == 1)
            {
                drives.insert(utils::string::char_to_lower(filename.front()));
            }
        }

        return drives;
    }

    std::filesystem::path translate(const windows_path& win_path) const
    {
        if (!win_path.is_absolute())
        {
            throw std::runtime_error("Only absolute paths can be translated: " + win_path.string());
        }

        const auto mapping = this->mappings_.find(win_path);
        if (mapping != this->mappings_.end())
        {
            return mapping->second;
        }

#ifdef OS_WINDOWS
        if (this->root_.empty())
        {
            return win_path.u16string();
        }
#endif

        const std::array<char, 2> root_drive{win_path.get_drive().value_or('c'), 0};
        auto root = this->root_ / root_drive.data();

        auto path = this->root_ / win_path.to_portable_path();
        path = weakly_canonical(path);
        if (is_subpath(root, path))
        {
            return path;
        }

        return root;
    }

    template <typename F>
    void access_mapped_entries(const windows_path& win_path, const F& accessor) const
    {
        for (const auto& mapping : this->mappings_)
        {
            const auto& mapped_path = mapping.first;
            if (!mapped_path.empty() && mapped_path.parent() == win_path)
            {
                accessor(mapping);
            }
        }
    }

    windows_path local_to_windows_path(const std::filesystem::path& local_path) const
    {
        const auto absolute_local_path = weakly_canonical(absolute(local_path));
        const auto relative_path = relative(absolute_local_path, this->root_);

        if (is_escaping_relative_path(relative_path))
        {
            throw std::runtime_error("Path '" + local_path.string() + "' is not within the root filesystem!");
        }

        char drive{};
        std::list<std::u16string> folders{};

        for (auto i = relative_path.begin(); i != relative_path.end(); ++i)
        {
            if (i == relative_path.begin())
            {
                const auto str = i->string();
                assert(str.size() == 1);
                drive = str[0];
            }
            else
            {
                folders.push_back(i->u16string());
            }
        }

        return windows_path{drive, std::move(folders)};
    }

    void map(windows_path src, std::filesystem::path dest)
    {
        this->mappings_[std::move(src)] = std::move(dest);
    }

  private:
    std::filesystem::path root_{};
    std::unordered_map<windows_path, std::filesystem::path> mappings_{};
};