Function getUniqueFileName

Core/MemoryFile.cpp:715–756

#endif

std::optional<MMKVPath_t> getUniqueFileName(const MMKVPath_t &folder, const MMKVPath_t &prefix) {
    fs::path folderPath(folder);
    fs::path prefixPath(prefix);

    // Ensure the directory exists
    std::error_code ec;
    if (!fs::exists(folderPath, ec)) {
        // Attempt to create it or fail if preferred.
        // GetTempFileName fails if dir doesn't exist, so we adhere to that.
        return std::nullopt;
    }

    // Behavior: Generate random unique filename, CREATE the file to reserve it.
    std::random_device rd;
    std::mt19937_64 gen(rd());
    std::uniform_int_distribution<uint64_t> dis;

    constexpr int maxAttempts = 64;
    for (int i = 0; i < maxAttempts; ++i) {
        uint64_t randomVal = dis(gen);
        MMKVPath_t suffix = to_string(randomVal);
        MMKVPath_t fileName = prefix + "." + suffix + ".tmp";
        fs::path candidatePath = folderPath / fileName;

        // Atomic check and create logic "mimic"
        // std::filesystem::exists is not atomic, but standard C++17 <fstream> doesn't
        // support O_EXCL (exclusive create) easily without platform headers.
        // We check existence first to avoid clobbering existing files.
        if (fs::exists(candidatePath, ec)) {
            continue; // Collision found, try next
        }

        // Try to create the file to "reserve" it
        File file(candidatePath.native(), OpenFlag::ReadWrite | OpenFlag::Create);
        if (file.isFileValid()) {
            return candidatePath.native();
        }
    }

    // Failed to find unique name after max attempts
    return std::nullopt;
}
} // namespace mmkv

#endif // !defined(MMKV_WIN32)