cpp-argument-parser/include/program_args/utilities.h

#pragma once

#include <string>
#include <type_traits>
#include <vector>

namespace program::traits {
template <typename T, typename = void>
struct is_repeatable : std::false_type {};

template <typename F>
struct is_repeatable<F, std::enable_if_t<!std::is_void_v<
                            std::result_of_t<F(std::vector<std::string>)>>>>
    : std::true_type {};

template <typename T>
constexpr bool const is_repeatable_v = is_repeatable<T>::value;

template <typename T, typename = void> struct is_container : std::false_type {};
template <> struct is_container<std::string> : std::false_type {};
template <typename T>
struct is_container<T, std::void_t<typename T::value_type>> : std::true_type {};

template <typename T>
constexpr bool const is_container_v = is_container<T>::value;

template <typename T, typename = void> struct is_associative : std::false_type {};
template <typename T>
struct is_associative<T, std::void_t<typename T::mapped_type>> : std::true_type {};

template <typename T>
constexpr bool const is_associative_v = is_associative<T>::value;
}

namespace program {
inline std::string join(std::string const & tok,
                        std::vector<std::string> const & data) {
  std::string accum = data.empty() ? "" : data.front();
  for (size_t i = 1; i < data.size(); ++i) {
    accum += tok;
    accum += data[i];
  }
  return accum;
}

template <typename T, typename = void> struct conversion_helper;

/**
 * \brief Conversion method for positional arguments. Positional arguments are
 * always represented with a singular string.
 * \param name The name of the argument being parsed, for logging purposes
 * \param data A string containing the value to be processed.
 * \return An object of the given type
 */
template <typename T>
T convert(std::string const & name, std::string const & data) try {
  return conversion_helper<T>{}(data);
} catch (std::exception const & ex) {
  throw ArgumentStructureError(ex.what(), name);
}

template <typename T, typename V = typename T::mapped_type>
T convert_associative(std::string const & name, std::vector<std::string> const &args) {
  T rval;
  for (std::string const &arg : args) {
    size_t pos = arg.find('=');
    if (pos == std::string::npos) {
      throw ArgumentStructureError("expected argument of the form key=value, got " + arg,
                                   name);
    }
    rval.emplace(arg.substr(0, pos), convert<V>(name, arg.substr(pos + 1)));
  }
  return rval;
}

template <typename T, typename V = typename T::value_type>
T convert_container(std::string const & name, std::vector<std::string> const &args) {
  T rval;
  for (std::string const &arg : args) {
    rval.insert(rval.end(), convert<V>(name, arg));
  }
  return rval;
}

/**
 * \brief Conversion method for command-line options. Because some options are
 * repeatable, we need to pass in a vector of objects that might be used.
 * \param name The name of the option being parsed, for logging purposes
 * \param data A vector of arguments assigned to this option.
 * \invariant data.size() > 0
 * \return An object of the given type
 * \throws ArgumentStructureError if the argument has been repeated but is
 * not a repeatable type.
 */
template <typename T>
T convert(std::string const & name, std::vector<std::string> const & data) {
  if constexpr (traits::is_associative_v<T>) {
    return convert_associative<T>(name, data);
  } else if constexpr (traits::is_container_v<T> && !std::is_constructible_v<T, std::string>) {
    return convert_container<T>(name, data);
  } else if (data.size() == 1) {
    return convert<T>(name, data[0]);
  } else {
    throw ArgumentStructureError("Repeated option not allowed", name);
  }
}

template <typename T>
struct conversion_helper<
    T, std::enable_if_t<std::is_convertible_v<std::string, T>>> {
  T operator()(std::string const & str) const { return T(str); }
};

template <> struct conversion_helper<int> {
  int operator()(std::string const & str) const { return std::stoi(str); }
};

using std::to_string;
template <typename T> std::string to_string(T const &) { return "?"; }
inline std::string to_string(char const * str) { return str; }
inline std::string const & to_string(std::string const & str) { return str; }
}