#include <fstream>
#include <iostream>
#include <string>
#include <vector>

// This file is incomplete and non-functional;
//  furthermore, it needs some separation into headers and source files.
// It is just a sketch of how to approach the task.

// class that contains the program state
class Stats {
public:
    Stats() : // initialize members...
        sum_(0),
        count_r_(0)
    {
        // do not "initialize" members here
    }

    // regular member function (method)
    void process_file(const std::string& filename) {
        std::ifstream file(filename);

        std::string line;

        while (std::getline(file, line)) {
            std::string_view line_view = line;
            while (process_word(line_view)) {

            }
        }
    }

    // static member function (does not depend on instance state)
    // takes a non-const reference -> modifies the argument
    static void skip_nonword(std::string_view& line_view) {
        size_t pos = 0;
        while (pos < line_view.size() && !std::isalnum(line_view[pos])) {
            ++pos;
        }

        line_view.remove_prefix(pos);
    }

    // takes a non-const reference -> modifies the argument
    bool process_word(std::string_view& line_view) {
        skip_nonword(line_view);

        if (line_view.empty()) {
            return false;
        }

        std::size_t pos = 0;

        while (pos < line_view.size() && std::isalnum(line_view[pos])) {
            ++pos;
        }

        // starting from here, this should be a separate function
        std::string_view word = line_view.substr(0, pos);

        if (is_number(word)) {
            // this should be a separate function
            for (char c : word) {
                sum_ += c - '0';
            }
        } else {
            // this should be a separate function
            for (char c : word) {
                if (c == 'r') {
                    ++count_r_;
                }
            }

            // todo: report the word in lowercase
        }

        return true;
    }

    // takes a copy of `std::string_view` -> does not actually copy the string data
    //  (`std::string_view` is a lightweight "view" of a string similar to a pointer)
    static bool is_number(std::string_view word) {
        for (char c : word) {
            if (!std::isdigit(c)) {
                return false;
            }
        }

        return true;
    }

private:
    // data members (state)
    int sum_;
    int count_r_;
};

void run_program(std::span<std::string> files) {
    Stats stats; // create an instance of the class (do not use `new`)

    for (auto&& file_name : files) {
        stats.process_file(file_name);

        // ...
    }

    // ...
}

int main(int argc, char* argv[]) {
    // starting point of the program

    std::vector<std::string> args(argv, argv + argc);
}