#ifndef TOKEN_H
#define TOKEN_H

#include <iostream>
#include <string>
#include <set>

// A class to read strings from an istream just like std::string,
// but tokens are separated not only by space, but also by operators.

//// Tokens can be classified as integers, deciamls, identifiers or operators.
//
class Token
{
public:

  // interoperability with standard library (STL)
  using token_t = std::string;
  
  using value_type = token_t::value_type;
  using size_type = token_t::size_type;
  using pointer = token_t::pointer;
  using reference = token_t::reference;
  using iterator = token_t::const_iterator;

  iterator begin() const { return token.begin(); }
  iterator end() const { return token.end(); }
  size_type size() const { return token.size(); }
  size_type length() const { return token.length(); }
  value_type at(int i) const { return token.at(i); }

  // static constants for default values
  static std::set<std::string> const default_operators;
  static std::string const default_separators;

  // public members
  Token(std::set<std::string> const& operators = default_operators,
        std::string const& separators = default_separators);

  friend std::istream& operator>>(std::istream& iss, Token& t);
  
  friend std::ostream& operator<<(std::ostream& oss, Token const& t);

  operator std::string() const { return token; }

  bool operator==(std::string const& rhs) { return token == rhs; }
  bool operator!=(std::string const& rhs) { return token != rhs; }
  
  bool is_operator() const;
  bool is_integer() const;
  bool is_decimal() const;
  bool is_identifier() const;
  
private:

  // help functions
  bool is_delimeter(int c) const;
  bool is_separator(int c) const;

  bool is_candidate() const;

  void append(int c);
  void ignore_separators(std::istream& iss);
  
  std::istream& next(std::istream& iss);

  // data members
  std::set<std::string> const& operators;
  std::string const& separators;
  std::string token;

  friend class Token_Private_Tester;
};

#endif