cache.hh

#ifndef VTESTBED_CACHE_CACHE_HH
#define VTESTBED_CACHE_CACHE_HH

#include <fstream>
#include <ios>
#include <sstream>
#include <string>

namespace vtb {

    namespace cache {

        std::string
        cache_directory();

        std::string
        cache_file(std::string key, std::string subkey);

        void
        make_directory(const std::string& dir);

        void
        print_cache(
            const std::string& tag,
            const std::string& filename,
            const std::string& subkey
        );

        template <class T>
        class cache_guard {

        private:
            T& _object;
            std::string _filename;
            std::string _subkey;
            std::ios::openmode _mode;
            bool _hit = false;

        public:

            inline explicit
            cache_guard(
                T& object,
                std::string key,
                std::string subkey,
                std::ios::openmode mode=std::ios::openmode{}
            ):
            _object{object},
            _filename{cache_file(key, subkey)},
            _subkey(subkey),
            _mode{mode} {
                std::ifstream in{this->_filename, this->_mode | std::ios::in};
                std::string tag = "miss";
                if (in.is_open()) {
                    tag = "hit";
                    this->_hit = true;
                    in >> _object;
                }
                print_cache(tag, this->_filename, subkey);
            }

            inline explicit
            cache_guard(std::streambuf* buf);

            inline
            ~cache_guard() {
                if (!this->_hit) {
                    std::ofstream{
                        this->_filename,
                        this->_mode | std::ios::out
                    } << this->_object;
                }
            }

            inline bool
            hit() const noexcept {
                return this->_hit;
            }

            inline void
            invalidate() {
                this->_hit = false;
                print_cache("invalidate", this->_filename, this->_subkey);
            }

        };

    }

}

#endif // vim:filetype=cpp