argh.hpp

#pragma once

#include <algorithm>
#include <sstream>
#include <string>
#include <vector>
#include <set>
#include <map>
#include <cassert>

namespace argh
{
   // Terminology:
   // A command line is composed of 2 types of args:
   // 1. Positional args, i.e. free standing values
   // 2. Options: args beginning with '-'. We identify two kinds:
   //    2.1: Flags: boolean options =>  (exist ? true : false)
   //    2.2: Parameters: a name followed by a non-option value

#if !defined(__GNUC__) || (__GNUC__ >= 5)
   using string_stream = std::istringstream;
#else
    // Until GCC 5, istringstream did not have a move constructor.
    // stringstream_proxy is used instead, as a workaround.
   class stringstream_proxy
   {
   public:
      stringstream_proxy() = default;

      // Construct with a value.
      stringstream_proxy(std::string const& value) :
         stream_(value)
      {}

      // Copy constructor.
      stringstream_proxy(const stringstream_proxy& other) :
         stream_(other.stream_.str())
      {
         stream_.setstate(other.stream_.rdstate());
      }

      void setstate(std::ios_base::iostate state) { stream_.setstate(state); }

      // Stream out the value of the parameter.
      // If the conversion was not possible, the stream will enter the fail state,
      // and operator bool will return false.
      template<typename T>
      stringstream_proxy& operator >> (T& thing)
      {
         stream_ >> thing;
         return *this;
      }


      // Get the string value.
      std::string str() const { return stream_.str(); }

      std::stringbuf* rdbuf() const { return stream_.rdbuf(); }

      // Check the state of the stream. 
      // False when the most recent stream operation failed
      operator bool() const { return !!stream_; }

      ~stringstream_proxy() = default;
   private:
      std::istringstream stream_;
   };
   using string_stream = stringstream_proxy;
#endif

   class parser
   {
   public:
      enum Mode { PREFER_FLAG_FOR_UNREG_OPTION = 1 << 0,
                  PREFER_PARAM_FOR_UNREG_OPTION = 1 << 1,
                  NO_SPLIT_ON_EQUALSIGN = 1 << 2,
                  SINGLE_DASH_IS_MULTIFLAG = 1 << 3,
                };

      parser() = default;
      parser(int argc, const char* const argv[], int mode = PREFER_FLAG_FOR_UNREG_OPTION)
      {
         parse(argc, argv, mode);
      }

      void add_param(std::string const& name);
      void parse(int argc, const char* const argv[], int mode = PREFER_FLAG_FOR_UNREG_OPTION);

      std::multiset<std::string>          const& flags()    const { return flags_; }
      std::map<std::string, std::string>  const& params()   const { return params_; }
      std::vector<std::string>            const& pos_args() const { return pos_args_; }

      //////////////////////////////////////////////////////////////////////////
      // Accessors

      // flag (boolean) accessors: return true if the flag appeared, otherwise false.
      bool operator[](std::string const& name);

      // returns positional arg string by order. Like argv[] but without the options
      std::string const& operator[](size_t ind);

      // returns a std::istream that can be used to convert a positional arg to a typed value.
      string_stream operator()(size_t ind);

      // same as above, but with a default value in case the arg is missing (index out of range).
      template<typename T>
      string_stream operator()(size_t ind, T&& def_val);

      // parameter accessors, give a name get an std::istream that can be used to convert to a typed value.
      // call .str() on result to get as string
      string_stream operator()(std::string const& name);

      // same as above, but with a default value in case the param was missing.
      // Non-string def_val types must have an operator<<() (output stream operator)
      // If T only has an input stream operator, pass the string version of the type as in "3" instead of 3.
      template<typename T>
      string_stream operator()(std::string const& name, T&& def_val);

   private:
      string_stream bad_stream() const;
      std::string trim_leading_dashes(std::string const& name);
      bool is_number(std::string const& arg);
      bool is_option(std::string const& arg);

   private:
      std::vector<std::string> args_;
      std::map<std::string, std::string> params_;
      std::vector<std::string> pos_args_;
      std::multiset<std::string> flags_;
      std::set<std::string> registeredParams_;
      std::string empty_;
   };


   //////////////////////////////////////////////////////////////////////////

   void parser::parse(int argc, const char* const argv[], int mode /*= PREFER_FLAG_FOR_UNREG_OPTION*/)
   {
      // convert to strings
      args_.resize(argc);
      std::transform(argv, argv + argc, args_.begin(), [](const char* const arg) { return arg;  });

      // parse line
      for (auto i = 0u; i < args_.size(); ++i)
      {
         if (!is_option(args_[i]))
         {
            pos_args_.emplace_back(args_[i]);
            continue;
         }

         auto name = trim_leading_dashes(args_[i]);

         if (!(mode & NO_SPLIT_ON_EQUALSIGN))
         {
            auto equalPos = name.find('=');
            if (equalPos != std::string::npos)
            {
               params_.insert({ name.substr(0, equalPos), name.substr(equalPos + 1) });
               continue;
            }
         }

         // if the option is unregistered and should be a multi-flag
         if (1 == (args_[i].size() - name.size()) &&                  // single dash
            argh::parser::SINGLE_DASH_IS_MULTIFLAG & mode &&         // multi-flag mode
            registeredParams_.find(name) == registeredParams_.end()) // unregistered
         {
            for (auto const& c : name)
            {
               flags_.emplace(std::string{ c });
            }
         }

         // any potential option will get as its value the next arg, unless that arg is an option too
         // in that case it will be determined a flag.
         if (i == args_.size() - 1 || is_option(args_[i + 1]))
         {
            flags_.emplace(name);
            continue;
         }

         // if 'name' is a pre-registered option, then the next arg cannot be a free parameter to it is skipped
         // otherwise we have 2 modes:
         // PREFER_FLAG_FOR_UNREG_OPTION: a non-registered 'name' is determined a flag. 
         //                               The following value (the next arg) will be a free parameter.
         //
         // PREFER_PARAM_FOR_UNREG_OPTION: a non-registered 'name' is determined a parameter, the next arg
         //                                will be the value of that option.

         if (registeredParams_.find(name) != registeredParams_.end() ||
            argh::parser::PREFER_PARAM_FOR_UNREG_OPTION & mode)
         {
            params_.insert({ name, args_[i + 1] });
            ++i; // skip next value, it is not a free parameter
            continue;
         }

         if (argh::parser::PREFER_FLAG_FOR_UNREG_OPTION & mode)
            flags_.emplace(name);
      };
   }

   //////////////////////////////////////////////////////////////////////////

   string_stream parser::bad_stream() const
   {
      string_stream bad;
      bad.setstate(std::ios_base::failbit);
      return bad;
   }

   //////////////////////////////////////////////////////////////////////////

   bool parser::is_number(std::string const& arg)
   {
      // inefficient but simple way to determine if a string is a number (which can start with a '-')
      std::istringstream istr(arg);
      double number;
      istr >> number;
      return !(istr.fail() || istr.bad());
   }

   //////////////////////////////////////////////////////////////////////////

   bool parser::is_option(std::string const& arg)
   {
      assert(0 != arg.size());
      if (is_number(arg))
         return false;
      return '-' == arg[0];
   }

   //////////////////////////////////////////////////////////////////////////

   std::string parser::trim_leading_dashes(std::string const& name)
   {
      auto pos = name.find_first_not_of('-');
      return name.substr(pos);
   }

   //////////////////////////////////////////////////////////////////////////

   bool parser::operator[](std::string const& name)
   {
      return flags_.end() != flags_.find(trim_leading_dashes(name));
   }

   //////////////////////////////////////////////////////////////////////////

   std::string const& parser::operator[](size_t ind)
   {
      if (ind < pos_args_.size())
         return pos_args_[ind];
      return empty_;
   }

   //////////////////////////////////////////////////////////////////////////

   string_stream parser::operator()(std::string const& name)
   {
      if (name.empty())
         return bad_stream();

      auto optIt = params_.find(trim_leading_dashes(name));
      if (params_.end() == optIt)
         return bad_stream();

      return string_stream(optIt->second);
   }

   //////////////////////////////////////////////////////////////////////////

   template<typename T>
   string_stream parser::operator()(std::string const& name, T&& def_val)
   {
      if (name.empty())
      {
         std::ostringstream ostr;
         ostr << def_val;
         return string_stream(ostr.str());
      }

      auto optIt = params_.find(trim_leading_dashes(name));
      if (params_.end() == optIt)
      {
         std::ostringstream ostr;
         ostr << def_val;
         return string_stream(ostr.str());
      }

      return string_stream(optIt->second);
   }

   //////////////////////////////////////////////////////////////////////////

   string_stream parser::operator()(size_t ind)
   {
      if (pos_args_.size() <= ind)
         return bad_stream();

      return string_stream(pos_args_[ind]);
   }

   //////////////////////////////////////////////////////////////////////////

   template<typename T>
   string_stream parser::operator()(size_t ind, T&& def_val)
   {
      if (pos_args_.size() <= ind)
      {
         std::ostringstream ostr;
         ostr << def_val;
         return string_stream(ostr.str());
      }

      return string_stream(pos_args_[ind]);
   }

   //////////////////////////////////////////////////////////////////////////

   void parser::add_param(std::string const& name)
   {
      registeredParams_.insert(trim_leading_dashes(name));
   }
}