temp_file_path.hpp

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#ifndef BYTEME_TEMP_FILE_PATH_HPP
#define BYTEME_TEMP_FILE_PATH_HPP
 
#if __has_include(<filesystem>)
#include <filesystem>
namespace fs = std::filesystem;
#else
#include <experimental/filesystem>
namespace fs = std::experimental::filesystem;
#endif
 
#include <random>
#include <chrono>
#include <string>
#include <cstdint>
#include <fstream>
 
namespace byteme {
 
inline std::string temp_file_path(const std::string& prefix, const std::string& ext) {
    auto path = fs::temp_directory_path();
    path.append(prefix);
    
    // Hopefully, we create a new seed when the function re-runs.
    uint64_t seed;
    try {
        std::random_device rd;
        seed = rd();
    } catch (...) {
        auto now = std::chrono::system_clock::now();
        seed = std::chrono::duration_cast<std::chrono::seconds>(now.time_since_epoch()).count();
    }
 
    std::mt19937_64 rng(seed);
    while (1) {
        auto copy = path;
        copy += std::to_string(rng());
        copy += ext;
 
        if (!fs::exists(copy)) {
            path = std::move(copy);
            break;
        }
    }
 
    // Force the creation of the file. This is not entirely thread-safe
    // as the existence check is done separately, but there's no way to
    // guarantee safety without OS-level mechanics.
    std::ofstream dummy(path, std::ofstream::out);
    return path.string();
}
 
inline std::string temp_file_path(const std::string& prefix) {
    return temp_file_path(prefix, "");
}
 
}
 
#endif