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

#pragma once

#include <map>
#include <set>
#include <string>
#include <vector>

namespace program {

/**
 * @brief A string-literal object that requires input arguments to be two or more characters
 */
struct LongArg {
  template <size_t N> constexpr LongArg(char const (&str)[N]) : str(str) {
    static_assert(N > 1, "cannot create longargs with 0 or 1 character");
  }
  operator std::string const &() const { return str; }
  std::string str;
};

template <typename Impl> class Arguments {
private:
  using option_id = std::string;
  struct Action;
  struct Argument;
  struct Flag;
  struct Option;
  template <typename, typename> struct WithDefault;

public:
  Arguments() = default;
  Arguments(int argc, char const * const * const argv);

  std::vector<std::string> args() const {
    return {arguments.begin() + argument_names.size(), arguments.end()};
  }

protected:
  /**
   * @brief Define an "action"/"subcommand"/"verb" to be executed. An example of this pattern
   * would be how git visualizes sub-commands in its interface, even though in implementation
   * it appears different.
   * @invariant Will fail to compile if bound to something that isn't a subtype of Arguments
   * @param name A name of the action for usage messages
   * @param description An optional description object
   * @return A binding object that can implicitly cast to a subtype of Arguments
   *
   * @throws ArgumentMixingError if both argument() and action() have been invoked in this
   */
  auto action(LongArg name, std::string const &description = "");
  
  /**
   * @brief Define an argument to be passed in to this program
   *
   * @param index The 0-based index of this argument in the program args array.
   * @param name A name of the argument for usage messages
   * @param description An optional description object
   * @return A binding object that will write its data in to an object of arity 1
   *
   * @throws ArgumentMixingError if both argument() and action() have been invoked in this
   * @throws ArgumentStructureError if this argument is required, but a prior argument was optional
   * @throws IllegalPositionError if index is already in use in this
   * @throws IllegalPositionError if no argument is available at index
   */
  auto argument(size_t index, LongArg name,
                std::string const & description = "");
  /**
   * @brief Return all unbound arguments
   * @param name An optional name to describe these arguments
   * @param description An optional description object
   * @returns All unbound arguments in {@sa Arguments::arguments}

   * @throws ArgumentMixingError if both argument() and action() have been invoked in this
   * @throws ArgumentStructureError if rest is called with multiple names
   */
  std::vector<std::string> rest(LongArg name = "args",
                                std::string const & description = "");
  
  /**
   * @brief Define a flag (option with an arity of zero).
   * If a flag binds to a boolean and has a name, then t will be invertable with "--no-" prefix.
   * If a flag binds to an integer, then it increments the value with each repetition.
   * @invariant One or both of name and abbrev must be provided
   * @param name The name of the flag, to be parsed from the commandline with a "--" prefix
   * @param abbrev A single-character version of a flag, to be parsed from the commandline
   * with a '-' prefix
   * @param description An optional description object
   */
  auto flag(LongArg name, char abbrev, std::string const & description = "");
  auto flag(LongArg name, std::string const & description = "");
  auto flag(char abbrev, std::string const & description = "");
  
  /**
   * @brief Define an option. If an option is repeated, then it can be used to fill out multiple
   * entries in a map or vector.
   * @invariant One or both of name and abbrev must be provided
   * @param name The name of the option, to be parsed from the commandline with a "--" prefix
   * @param abbrev A single-character version of an option, to be parsed from the commandline
   * with a '-' prefix
   * @param description An optional description object
   */
  auto option(LongArg name, char abbrev,
              std::string const & description = "");
  auto option(LongArg name, std::string const & description = "");
  auto option(char abbrev, std::string const & description = "");

private:
  void usage() const;
  void add_options(std::string const & name, char abbrev,
                   std::string const & description,
                   std::vector<std::string> aliases = {});
  
  bool has_actions() const { return !action_descriptions.empty(); }
  bool has_arguments() const { return !(rest_name.empty() && argument_names.empty()); }
  
  option_id id(std::string const & arg) const;
  option_id id(char arg) const { return id({'-', arg}); }
  
  bool is_option(std::string const & arg) const;
  bool is_option(char arg) const { return is_option({'-', arg}); }
  
  bool is_flag(std::string const & arg) const;
  bool is_flag(char arg) const { return is_flag({'-', arg}); }

private:
  // A helper for what limited introspection is required for handling actions in test
  friend struct ArgumentTestHelper;
  friend int main(int, char const * const *);
  
private:
  using main_callback_t = std::function<int(Arguments const &)>;
  using make_hook_t = std::function<main_callback_t(size_t, char const * const *)>;
  // Metadata variables
  bool primed_{false};
  std::string rest_name;
  std::map<option_id, std::string> argument_descriptions;
  std::map<size_t, option_id> argument_names;
  std::map<option_id, std::string> option_descriptions;
  std::map<std::string, option_id> option_names;
  std::set<option_id> flag_names;
  std::map<std::string, make_hook_t> actions;
  std::map<std::string, std::string> action_descriptions;

  // Data/Output variables
  std::string program;
  main_callback_t main_callback{nullptr};
  constexpr static size_t const no_optional_args{~0ul};
  size_t optional_from{no_optional_args};
  std::vector<std::string> arguments;
  std::map<std::string, std::vector<std::string>> options;
  std::map<std::string, int> flags;
};

template <typename Impl> struct Arguments<Impl>::Action {
  Arguments<Impl> * self;
  std::string name;
  std::string description;

  template <typename T> operator T() const;
  bool primed() const;
  explicit operator bool() const;
};

template <typename Impl> struct Arguments<Impl>::Argument {
  Arguments<Impl> * self;
  size_t index;
  bool is_optional;
  std::string name;
  std::string description;

  template <typename T> auto operator=(T && value);
  template <typename T> operator T() const;
  bool primed() const;
  explicit operator bool() const;
};

template <typename Impl> struct Arguments<Impl>::Flag {
  Arguments<Impl> * self;
  std::string name;
  char abbrev;
  std::string description;
  bool default_value;

  auto operator=(bool && value);
  operator bool() const;
  template <typename T> operator T() const;
  bool primed(bool inv) const;
};

template <typename Impl> struct Arguments<Impl>::Option {
  Arguments<Impl> * self;
  std::string name;
  char abbrev;
  std::string description;

  template <typename T> auto operator=(std::initializer_list<T> value);
  template <typename T> auto operator=(T && value);
  template <typename T> operator T() const;
  bool primed() const;
  explicit operator bool() const;
};

template <typename Impl>
template <typename B, typename V>
struct Arguments<Impl>::WithDefault {
  B impl;
  V default_value;
  template <typename T> operator T() const {
    if (impl) { return impl; }
    if constexpr (std::is_invocable_r<T, V>{}) {
      return T(default_value());
    } else {
      return T{default_value};
    }
  }
};

}

#include "arguments_impl.hpp"


template <typename Args, typename Action>
int typed_main(Args const &, Action const &);

#define TYPED_MAIN(tname)                                                      \
  int typed_main(tname const & args);                                          \
  int main(int argc, char const * const * const argv) try {                    \
    tname args(argc, argv);                                                    \
    return (args.main_callback) ? args.main_callback(args) : typed_main(args); \
  } catch (program::ProgramArgumentsError const & pae) {                       \
    std::cerr << "Error in program argument handling: " << pae.what() << "\n"; \
  }                                                                            \
  int typed_main(tname const & args)

#define PROGRAM_DEFER(...) [this]() { return __VA_ARGS__; }