#include <fstream>
#include <iterator>
#include <iostream>
#include <range/v3/all.hpp>
#include <vector>
#include <algorithm>
#include <string>

auto group() noexcept {
    return ranges::view::group_by([](auto&& lhs, auto&& rhs) {
            return std::isalpha(lhs) == std::isalpha(rhs);
        })
        | ranges::view::transform([](auto&& list) {
            return ranges::accumulate(list, std::string{});
        });
}

auto remove_separators() noexcept {
    return ranges::view::filter([](auto&& str) {
        return std::all_of(str.begin(), str.end(), [](auto&& c) {
            return std::isalpha(c);
        });
    });
}

auto restrict() noexcept {
    return ranges::view::filter([](auto&& str) {
        return str.length() >= 5 && std::all_of(str.begin(), str.end(), [](auto&& c) {
            return std::isalpha(c);
        });
    });
}

auto lowercase() noexcept {
    return ranges::view::transform([](auto str) {
        std::transform(str.begin(), str.end(), str.begin(), [](auto&& c) {
            return std::tolower(c);
        });
        return str;
    });
}

auto map() noexcept {
    return ranges::view::group_by([](auto&& lhs, auto&& rhs) {
            return lhs == rhs;
        })
        | ranges::view::transform([](auto&& list) {
            return std::pair(list | ranges::view::take(1), ranges::distance(list));
        });
}

int main(int argc, char* argv[]) noexcept {
    if (argc != 3) {
        std::cout << "Usage: ./" << argv[0] << " [file] [word-amount]n";
        return -1;
    }

    std::ifstream file{argv[1]};
    if (!file.is_open()) {
        std::cout << "Couldn't open file " << argv[1] << "!n";
        return -1;
    }

    auto amount = 0u;
    try {
        amount = std::stoi(argv[2]);
    }
    catch (const std::exception&) {
        std::cout << "Invalid number " << argv[2] << "!n";
    }

    std::vector<char> character_list;
    char character = '';
    while (file.read(&character, 1))
        character_list.push_back(character);

    auto words = character_list | group() | remove_separators()
        | restrict() | lowercase() | ranges::to_<std::vector>() | ranges::action::sort;

    auto highlights = words | map() | ranges::to_<std::vector>()
        | ranges::action::sort([](auto&& lhs, auto&& rhs) {
            return lhs.second > rhs.second;
        });

    for (auto&& word : highlights | ranges::view::take(amount))
        std::cout << word.first << ": " << word.second << 'n';
    return 0;
}