SWI-cpp2-flags.h

/*  Part of SWI-Prolog

    Author:        Jan Wielemaker and Peter Ludemann
    E-mail:        J.Wielemaker@vu.nl
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*/

#ifndef _SWI_CPP2_FLAGS_H
#define _SWI_CPP2_FLAGS_H

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

#include "SWI-cpp2.h"

// TODO: add documentation to pl2cpp2.doc

/* WARNING: experimetal code, subject to change

   Class \ctype{PlOptionsFlag} contains utilities for translating between a
   list of strings and an flag of bits. The flag is designated as
   \ctopy{FlagT}, and typically is \ctype{int} or \ctype{unsigned}.

   \begin{description}
     \constructor{PlOptionsFlag}{string domain, vector<string,FlagT> str2flag} -
       \arg{domain} is used for exceptions; \arg{str2flag} maps
       strings to flag values. here may be multiple strings that map
       to the same flag; the first one is preferred by
       PlOptionsFlag::as_string().
     \cfunction{FlagT}{PlOptionsFlag::lookup_list}{PlTerm options, bool throw_not_found} -
       process \arg{options}, a list of strings or atoms, into a flag by looking
       up each itme and or-ing the flag values. If a lookup fails
       and \arg{throw_not_found} is \const{true} (the default),
       \ctype{PlDomainError} is thrown.
     \cfunction{FlagT}{PlOptionsFlag::lookup}{PlTerm e, bool throw_not_found}-
       process a single \arg{option}, returning its flag value.
       If a lookup fails
       and \arg{throw_not_found} is \const{true} (the default),
       \ctype{PlDomainError} is thrown, otherwise 0 is returned.
     \cfunction{string}PlOptionsFlag::as_string}{FlagT flags} -
       Return a string containing a comma-separated list of
       the preferred strings corresponding to the bits in \arg{flags}.
       If a bit value is found, "???" is added to the list
       TODO: with C++-20, std::format("{:x}")
   \end{description}

 */

template<typename FlagT>
class PlOptionsFlag {
public:
  explicit PlOptionsFlag() = delete;
  explicit PlOptionsFlag(const std::string& domain,
                         const std::vector<std::pair<std::string, FlagT>>& str2flag)
    : domain_(domain),
      str2flag_v_(str2flag)
  { for ( auto const& sf : str2flag )
    { str2flag_[sf.first] = sf.second;
    }
  }

  FlagT lookup_list(PlTerm options, bool throw_not_found = true) const
  { PlTerm_tail tail(options);
    PlTerm_var e;
    FlagT flags = 0;
    while (tail.next(e))
    { flags |= lookup(e, throw_not_found);
    }
    PlCheckFail(tail.unify_nil());
    return flags;
  }

  FlagT lookup(PlTerm option, bool throw_not_found = true) const
  { option.must_be_atom_or_string();
    auto const f = str2flag_.find(option.as_string());
    if ( f != str2flag_.end() )
      return f->second;
    if ( throw_not_found )
      throw PlDomainError(domain_, option);
    return 0;
  }

  std::string as_string(FlagT flags) const
  { std::string result;
    for ( auto const& f : str2flag_v_ )
    { if ( (flags & f.second) == f.second )
      { result += "," + f.first;
        flags &= ~f.second;
      }
    }
    if ( flags != 0 )
      result += ",???"; // TODO (C++-20): std::format("{:x}", flags)
    return result.empty() ? result : result.substr(1);
  }

private:
  std::string domain_;
  std::map<std::string, FlagT> str2flag_;
  std::vector<std::pair<std::string, FlagT>> str2flag_v_;
};

#endif /*_SWI_CPP2_FLAGS_H*/