#include "series.h"

#include <algorithm>
#include <stdexcept>

namespace series {

using namespace std;


namespace {

inline int char_to_digit(char ch)
{
    if (!isdigit(ch))
        throw domain_error("not a digit");

    return ch - '0';
}

}


digits_t digits(const string &input)
{
    digits_t result(input.size());

    transform(input.cbegin(), input.cend(), result.begin(), char_to_digit);

    return result;
}

slice_t slice(const string &input, size_t size)
{
    if (size > input.size())
        throw domain_error("not enough digits to slice");

    if (size == 0)
        return slice_t();

    digits_t input_digits = digits(input);
    slice_t  result;

    auto begin = input_digits.cbegin();
    auto end   = begin + size - 1;

    while (end != input_digits.cend())
        result.push_back(digits_t(begin++, ++end));

    return result;
}


}