arg_handler.h

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*/
 
#ifndef HARNESS_ARG_HANDLER_INCLUDED
#define HARNESS_ARG_HANDLER_INCLUDED
 
/** @file
 * @brief Defining the commandline argument handler class CmdArgHandler
 *
 * This file defines the commandline argument handler class CmdArgHandler.
 */
 
#include "harness_export.h"
 
#include <cstdint>
#include <functional>
#include <map>
#include <memory>
#include <string>
#include <vector>
 
enum class CmdOptionValueReq {
  none = 0x01,
  required = 0x02,
  optional = 0x03,
};
 
/** @brief CmdOption stores information about command line options
 *
 * The CmdOption structure stores information about command line options.
 *
 */
struct CmdOption {
  using ActionFunc = std::function<void(const std::string &)>;
  using AtEndActionFunc = std::function<void(const std::string &)>;
  using OptionNames = std::vector<std::string>;
 
  OptionNames names;
  std::string description;
  CmdOptionValueReq value_req;
  std::string value;
  std::string metavar;
  ActionFunc action;
  AtEndActionFunc at_end_action;
  bool required{false};
 
  CmdOption(
      OptionNames names_, std::string description_,
      CmdOptionValueReq value_req_, const std::string metavar_,
      ActionFunc action_,
      AtEndActionFunc at_end_action_ = [](const std::string &) {})
      : names(names_),
        description(description_),
        value_req(value_req_),
        metavar(metavar_),
        action(action_),
        at_end_action(at_end_action_) {}
};
 
/** @brief Definition of a vector holding unique pointers to CmdOption
 * objects **/
using OptionContainer = std::vector<CmdOption>;
 
/** @class CmdArgHandler
 *  @brief Handles command line arguments
 *
 * The CmdArgHandler class handles command line arguments. It is a
 * replacement and supports most of the POSIX GNU getopt library.
 *
 * Command line options can have multiple aliases. For example, the
 * typical `--help` can be also called `-h`, or even `--help-me`. Long
 * names starting with one dash are not supported.
 *
 * Command line options are added through the `add_option()` method
 * and can be given 1 or more names and a description. It is also
 * possible to require the option to have a value, or make the value
 * optional.
 *
 * During processing of the command line arguments, actions will be
 * executed when the option (and it's potential value) was found.
 *
 * Usage example:
 *
 *     #include "arg_handler.h"
 *
 *     void MyApp::prepare_command_line_options() {
 *       // CmdArgHandler handler_;
 *       handler_.add_option(OptionNames({"-h", "--help", "--sos"}), "Show help
 * screen", CmdOptionValueReq::none, "", [this](const string &) {
 * this->show_help(); } handler_.add_option(OptionNames({"--config"}),
 * "Configuration file", CmdOptionValueReq::none, "", [this](const string
 * &value) { this->set_config_file(value); },
 *                          []{});
 *
 *     void MyApp::init(const vector<string> arguments) {
 *       prepare_command_line_options();
 *       handler_.process(arguments);
 *     }
 *
 *  All arguments which are not valid option names are are not values of options
 * are considered rest arguments. By default, rest arguments are not allowed and
 * will raise a std::invalid_argument exception. It is possible to allow them
 * through the constructor.
 *
 *  The CmdArgHandler class also provides functionality to help creating help
 *  screen or show how to use the the command line application. The method
 * `usage_lines()` produces a usage line showing all the option names, their
 * required or optional value with a meta variable. Similar, method
 * `option_descriptions()` will get all options and their descriptions. All this
 * is text wrapped at a configurable margin as well as, if needed, indented.
 *
 *  @internal
 *  The command line argument handling in CmdArgHandler is the bare minimum
 * needed for MySQL Router. It was needed to make sure that the application
 * would compile on system where the getopt library is not available.
 *  @endinternal
 *
 */
class HARNESS_EXPORT CmdArgHandler {
 public:
  /** @brief Constructor
   *
   * @param allow_rest_arguments_ whether we allow rest arguments or not
   * @param ignore_unknown_arguments_ whether we ignore unknown arguments or
   * give an error
   */
  explicit CmdArgHandler(bool allow_rest_arguments_,
                         bool ignore_unknown_arguments_ = false)
      : allow_rest_arguments(allow_rest_arguments_),
        ignore_unknown_arguments(ignore_unknown_arguments_) {}
 
  /** @brief Default constructor
   *
   * By default, rest arguments are not allowed and unknown arguments are not
   * ignored.
   */
  CmdArgHandler() : CmdArgHandler(false, false) {}
 
  /** @brief Adds a command line option
   *
   * Adds a command line option given names, description, value
   * requirement and optional action.
   *
   * `names` is a vector of strings which contains names starting
   * with either a single or double dash, `-` or `--`. It is possible
   * to add more than one name for an option.
   *
   * The description text will be used in the help output. Note that
   * this can be a very long as text will be wrapped (and optionally
   * indented). New lines in the description will be respected.
   *
   * The `metavar` argument is used in the usage text as a placeholder
   * for the (optional) value of the option, for example, when `metavar`
   * is set to `path`, the usage would show:
   *
   *     --config=<path>
   *
   * The value_req argument should be either:
   *
   * * `CmdOptionValueReq::none` : option has no value
   * * `CmdOptionValueReq::required` : option requires value
   * * `CmdOptionValueReq::optional` : option has optional value
   *
   * The `action` argument should be a `std::function` and is called
   * with the (optional) value of the option. The function should
   * accept only a `const std::string`.
   *
   * The `at_end_action` argument should be a `std::function`. This is optional
   * argument, if not provided then []{} is used as at_end_action. The
   * `at_end_action` is meant to be used for additional validation, if
   * particular set of options has to be used together, or if particular set of
   * options cannot be used together.
   *
   * Example usage:
   *
   *       handler_.add_option(OptionNames({"--config"}), "Configuration file",
   *                          CmdOptionValueReq::none, "",
   *                          [this](const string &value) {
   * this->set_config_file(value); },
   *                          []{});
   *
   * @internal
   * The `add_option` method will assert when `names` is empty,
   * one of the names is not valid or when a name was already used with
   * another option.
   * @endinternal
   *
   * @param names vector of string with option names, each starting with - or --
   * @param description descriptive text explaining the option
   * @param value_req value requirement of the option
   * @param metavar for formatting help text when option accepts a value
   * @param action action to perform when the option was found
   * @param at_end_action task to perform after all actions have been done
   */
  void add_option(
      const CmdOption::OptionNames &names, const std::string &description,
      const CmdOptionValueReq &value_req, const std::string &metavar,
      CmdOption::ActionFunc action,
      CmdOption::AtEndActionFunc at_end_action = [](const std::string &) {
      }) noexcept;
 
  void add_option(const CmdOption &other) noexcept;
 
  /** @brief Processes given command line arguments
   *
   * Processes given command line argument provided as a vector
   * of strings. It uses the stored option information added through the
   * `add_option()` method.
   *
   * Typically, the vector passed to process() are the argc and argv
   * arguments of the main() function:
   *
   *     process({argv + 1, argv + argc})
   *
   * When an option is found which requires an argument, optional or
   * not, process() will exit the application with an error message.
   *
   * If the option has an action defined, the function will be
   * executed with the (optional) value as argument.
   *
   * @param arguments vector of strings
   */
  void process(const std::vector<std::string> &arguments);
 
#ifndef NDEBUG
  bool debug_check_option_names(const CmdOption::OptionNames &names) const;
#endif
 
  /** @brief Checks whether given name is a valid option name
   *
   * Checks whether the given name is a valid option name.
   *
   * A valid option name should:
   *
   * * have at least consist of 2 characters
   * * start with a dash '-'
   * * match the reqular expression ^--[A-Za-z]{2}[A-Za-z_-]+$
   *
   * It is allowed to use the equal sign when giving value. Following options
   * are equal:
   *     --config /path/to/mysqlrouter.conf
   *     --config=/path/to/mysqlrouter.conf
   *
   * Throws std::invalid_argument when option name is not valid or
   * option was not registered.
   *
   * Examples of valid option names:
   *
   *     -h
   *     --with-ham
   *     --with_spam
   *
   * Example of invalid option names:
   *
   *     -help
   *     ---spam
   *     --x-ham
   *
   * @param name option name to check
   * @return true if name is valid; false otherwise
   */
  bool is_valid_option_name(const std::string &name) const noexcept;
 
  /** @brief Finds the option by name
   *
   * Finds the option by one of its name. The name should include the the dash
   * prefix.
   *
   * Example usage:
   *     // check if option name is already present
   *     assert(end() == find_option(name))
   *
   * @param name name of the option as string
   * @returns iterator object
   */
  OptionContainer::const_iterator find_option(
      const std::string &name) const noexcept;
 
  using UsagePredicate =
      std::function<std::pair<bool, CmdOption>(const CmdOption &)>;
 
  /** @brief Produces lines of text suitable to show usage
   *
   * Produces lines of text suitable to show usage of the command line
   * appliation. Each option is shown with all its names and with optional
   * or required value.
   *
   * The `prefix` argument can be used to add text, usually the name
   * of the command, in front of the options. The lines are indented
   * using the size of the prefix.
   *
   * The `rest_metavar` can be used to name non-options arguments.
   *
   * The `width` argument is used to set the maximum length of the lines.
   *
   * Example output when all lines are printed:
   *
   *     usage: mysqlrouter [-v|--version] [-h|--help] [-c|--config=<path>]
   *                        [-a=[<foo>]] [rest..]
   *
   *
   * @param prefix text in front of options (usually command name)
   * @param rest_metavar name of rest arguments (empty if not needed)
   * @param width maximum length of each line
   * @return vector of strings
   */
  std::vector<std::string> usage_lines(const std::string &prefix,
                                       const std::string &rest_metavar,
                                       size_t width) const noexcept {
    return usage_lines_if(
        prefix, rest_metavar, width,
        [](const CmdOption &opt) -> std::pair<bool, CmdOption> {
          return {true, opt};
        });
  }
 
  std::vector<std::string> usage_lines_if(
      const std::string &prefix, const std::string &rest_metavar, size_t width,
      UsagePredicate predicate) const noexcept;
 
  /** @brief Produces description of all options
   *
   * Produces description of all options. The result is typically shown
   * when the help screen is requested, for example when the `--help`
   * option is given.
   *
   * The `width` argument is used to set the maximum length of the lines. Text
   * is wrapped accordingly.
   *
   * Each description can be indented using space. The amount is given
   * by `indent` option.
   *
   * Example output when lines are printed:
   *
   *     -v, --version
   *           Show version
   *     -h, --help
   *           Show help
   *     -c <path>, --config <path>
   *           Path to the configuration file
   *
   * @param width maximum length of each line
   * @param indent how much the description should be indented.
   * @return vector of strings
   */
  std::vector<std::string> option_descriptions(
      const size_t width, const size_t indent) const noexcept;
 
  /** @brief Returns an iterator to first option
   *
   * Returns an iterator to the first option.
   *
   * @returns iterator
   */
  OptionContainer::const_iterator begin() { return options_.begin(); }
 
  /** @brief Returns an iterator to end of the option container
   *
   * Returns an iterator to the end of the option container.
   *
   * @returns iterator
   */
  OptionContainer::const_iterator end() { return options_.end(); }
 
  /** @brief Clears registered options
   *
   * Clears the registered options.
   *
   */
  void clear_options() { options_.clear(); }
 
  /** @brief Gets all registered options
   *
   * Returns as a reference to a vector of CmdOption objects.
   *
   * @return std::vector<CmdOption>
   */
  const std::vector<CmdOption> &get_options() const noexcept {
    return options_;
  }
 
  /** @brief Returns the rest arguments
   *
   * Returns the rest arguments.
   *
   * If rest arguments are not allow or there were no rest arguments,
   * an empty vector is returned.
   *
   * @return vector of strings
   */
  const std::vector<std::string> &get_rest_arguments() const noexcept {
    return rest_arguments_;
  }
 
  /** @brief Whether to allow rest arguments or not **/
  bool allow_rest_arguments;
 
  /** @brief Whether to ignore unknown arguments **/
  bool ignore_unknown_arguments;
 
  /** @brief The key is a section identificator (section name and optional
   * section key), the value is a map of all the overrides for a given section
   * (option/value pairs) **/
  using ConfigOverwrites = std::map<std::pair<std::string, std::string>,
                                    std::map<std::string, std::string>>;
  const ConfigOverwrites &get_config_overwrites() const noexcept {
    return config_overwrites_;
  }
 
 private:
  /** @brief Vector with registered options **/
  std::vector<CmdOption> options_;
  /** @brief Vector with arguments as strings not processed as options **/
  std::vector<std::string> rest_arguments_;
  /** @brief Keeps configuration options overwrites **/
  ConfigOverwrites config_overwrites_;
};
 
#endif  // HARNESS_ARG_HANDLER_INCLUDED