#include <iostream>
#include <iomanip>
#include <string>
#include <filesystem>
#include <type_traits>

namespace fs = std::filesystem;

auto operator<< (std::ostream& out, fs::file_type const type) -> std::ostream& {
    char c{'\0'};
    switch(type) {
    case fs::file_type::regular:   c = '-'; break;
    case fs::file_type::directory: c = 'd'; break;
    case fs::file_type::symlink:   c = 'l'; break;
    default: c = '?';
    }
    return out << c;
}

auto operator<< (std::ostream& out, fs::perms const permissions) -> std::ostream& {
    //
    char str[10] = "---------";

    // owner
    if ( ( permissions & fs::perms::owner_read  ) != fs::perms::none ) str[0] = 'r';
    if ( ( permissions & fs::perms::owner_write ) != fs::perms::none ) str[1] = 'w';
    if ( ( permissions & fs::perms::owner_exec  ) != fs::perms::none ) str[2] = 'x';

    // group
    if ( ( permissions & fs::perms::group_read  ) != fs::perms::none ) str[3] = 'r';
    if ( ( permissions & fs::perms::group_write ) != fs::perms::none ) str[4] = 'w';
    if ( ( permissions & fs::perms::group_exec  ) != fs::perms::none ) str[5] = 'x';

    // others
    if ( ( permissions & fs::perms::others_read  ) != fs::perms::none ) str[6] = 'r';
    if ( ( permissions & fs::perms::others_write ) != fs::perms::none ) str[7] = 'w';
    if ( ( permissions & fs::perms::others_exec  ) != fs::perms::none ) str[8] = 'x';

    //
    return out << str;
}

struct BeautifiedFileSize {
    std::uintmax_t size{0};
    std::uintmax_t multiplier{0};
};

auto beautify_file_size(std::uintmax_t const size) -> BeautifiedFileSize {
    BeautifiedFileSize bsize{size, 0};

    while( bsize.size > 1024 ) {
        bsize.size /= 1024;
        bsize.multiplier += 1;
    }

    return bsize;
}

auto byte_multiplier(std::size_t const index) -> char const* {
    static char const* BYTE_MULTIPLIER[] = {
        "_B", "kB", "MB", "GB", "TB"
    };
    return index < std::extent_v<decltype(BYTE_MULTIPLIER)>
         ? BYTE_MULTIPLIER[index]
         : "??"
         ;
}


auto main() -> int {
    fs::path pwd{"."};

    for(auto const& entry: fs::directory_iterator{pwd}) {
        //
        auto&& path = entry.path();
        auto&& filename = path.filename().string();
        auto&& status = fs::status(path);

        //
        auto&& bsize = beautify_file_size(fs::file_size(path));

        //
        std::cout
            << status.type()
            << status.permissions()
            << std::setw(6) << bsize.size << byte_multiplier(bsize.multiplier)
            << ' '
            << filename << "\n"
            ;
    }

    return 0;
}