#ifndef UTIL_H
#define UTIL_H

#include <algorithm>
#include <cstring>
#include <stdexcept>
#include <string>
#include <string_view>

namespace util
{

namespace separators
{

constexpr char SPACE[] = " ";
constexpr char COLON[] = ":";
constexpr char SEMICOLON[] = ";";
constexpr char COMMA[] = ",";

}

/** @brief Trims a string view.
 *
 * @param the string view.
 */
inline void trim(std::string_view& view)
{
    std::string_view spaces{ " \f\r\n\t\v" };
    if (auto n = view.find_first_not_of(spaces); n != view.npos)
    {
        view.remove_prefix(n);
    }
    if (auto n = view.find_last_not_of(spaces); n != view.npos)
    {
        view.remove_suffix(view.size() - n - 1);
    }
}

/** @brief Split a string view according to a delimiter.
 *
 * This function applies a custom callable to all substring of a string
 * view generated by splitting it according to a delimiter.
 *
 * @tparam delim the delimiter to split the string view.
 * @tparam Accumulate a callable to call on each substring.
 * @param view the string view.
 * @param the callable object.
 */
template<const char* delim, typename Accumulate>
void accumulate(std::string_view& view, Accumulate acc)
{
    size_t from{}, to;
    std::string elem;

    while ((to = view.find(delim, from)) != std::string_view::npos) {
        auto sub = view.substr(from, to - from);
        trim(sub);
        acc(sub);
        from = to + std::strlen(delim);
    }
    auto sub = view.substr(from);
    if (not sub.empty())
    {
        trim(sub);
        acc(sub);
    }
}

/** @brief Discard element from stream by type.
 *
 * @tparam T the type of the element to discard.
 * @param stream the input stream.
 *
 * @return the input stream.
 */
template<typename T, typename CharT, typename Traits>
std::basic_istream<CharT, Traits>& skip(std::basic_istream<CharT, Traits>& stream)
{
    T discard;
    return stream >> discard;
}

/** @brief Skip token in stream.
 *
 * @tparam keyword the token to skip.
 * @param stream the input stream.
 *
 * @return the input stream.
 *
 * @note The token needs to be declared as a `const char[]`, but normally,
 * string literals are `const char*`.
 *
 * ```cpp
 * constexpr char RESULT[] = "Result:";
 *
 * int main(int argc, char* argv[])
 * {
 *     int res;
 *     std::istringstream in{ "Result: 42"}
 *     in >> skip<RESULT> >> res;
 *
 *     // ...
 *
 *     return 0
 * }
 * ```
 */
template<const char* keyword, typename CharT, typename Traits>
std::basic_istream<CharT, Traits>& skip(std::basic_istream<CharT, Traits>& stream)
{
    std::string word;
    stream >> word;
    if (word != keyword)
    {
        throw std::invalid_argument("Malformed input");
    }

    return stream;
}

} // namespace util

#endif //UTIL_H