Спринт 12. Тернистые пути: работаем с файловой системой.

#include <cassert>
#include <filesystem>
#include <fstream>
#include <iostream>
#include <sstream>
#include <string>
#include <vector>
#include <algorithm>
#include <string_view>

using std::filesystem::path;

path operator""_p(const char* data, std::size_t sz) {
    return path(data, data + sz);
}

void PrintTree(std::ostream& dst, const std::filesystem::path& p, const std::filesystem::file_status& status, int offset) {

    if (status.type() == std::filesystem::file_type::regular) {
        dst << std::string (offset, ' ')
            << std::string(p.filename()) << std::endl;

    } else if (status.type() == std::filesystem::file_type::directory) {
        dst << std::string(offset, ' ')
            << std::string(p.filename()) << std::endl;

        std::vector<std::filesystem::path> vector_path;

        for (const std::filesystem::path& dir_entry : std::filesystem::directory_iterator(p)) {
            vector_path.push_back(dir_entry);
        }

        std::sort(vector_path.begin(),
                  vector_path.end(),
                  [](std::filesystem::path lhs, std::filesystem::path rhs) {
                     return std::lexicographical_compare(std::string(rhs.filename()).begin(),
                                                         std::string(rhs.filename()).end(),
                                                         std::string(lhs.filename()).begin(),
                                                         std::string(lhs.filename()).end());
                  });

        for (const std::filesystem::path& dir_entry : vector_path) {
            std::error_code err;
            auto new_status = std::filesystem::status(dir_entry, err);

            PrintTree(dst, dir_entry, new_status, offset + 2);
        }
    }
}

void PrintTree(std::ostream& dst, const path& p) {
    std::error_code err;
    auto status = std::filesystem::status(p,err);

    PrintTree(dst, p, status, 0);
}

int main() {
    using namespace std::literals;

    std::error_code err;
    std::filesystem::remove_all("test_dir", err);
    std::filesystem::create_directories("test_dir"_p / "a"_p, err);
    std::filesystem::create_directories("test_dir"_p / "b"_p, err);

    std::ofstream("test_dir"_p / "b"_p / "f1.txt"_p);
    std::ofstream("test_dir"_p / "b"_p / "f2.txt"_p);
    std::ofstream("test_dir"_p / "a"_p / "f3.txt"_p);

    std::ostringstream out;
    PrintTree(out, "test_dir"_p);
    assert(out.str() ==
        "test_dir\n"
        "  b\n"
        "    f2.txt\n"
        "    f1.txt\n"
        "  a\n"
        "    f3.txt\n"sv
    );
}