#ifndef UTIL_EXCEPTION__
#define UTIL_EXCEPTION__

#include "util/string_piece.hh"

#include <exception>
#include <sstream>
#include <string>

namespace util {

template <class Except, class Data> typename Except::template ExceptionTag<Except&>::Identity operator<<(Except &e, const Data &data);

class Exception : public std::exception {
  public:
    Exception() throw();
    virtual ~Exception() throw();

    Exception(const Exception &from);
    Exception &operator=(const Exception &from);

    // Not threadsafe, but probably doesn't matter.  FWIW, Boost's exception guidance implies that what() isn't threadsafe.  
    const char *what() const throw();

  private:
    template <class Except, class Data> friend typename Except::template ExceptionTag<Except&>::Identity operator<<(Except &e, const Data &data);

    // This helps restrict operator<< defined below.  
    template <class T> struct ExceptionTag {
      typedef T Identity;
    };

    std::stringstream stream_;
    mutable std::string text_;
};

/* This implements the normal operator<< for Exception and all its children. 
 * SNIFAE means it only applies to Exception.  Think of this as an ersatz
 * boost::enable_if.  
 */
template <class Except, class Data> typename Except::template ExceptionTag<Except&>::Identity operator<<(Except &e, const Data &data) {
  e.stream_ << data;
  return e;
}

#define UTIL_THROW(Exception, Modify) { Exception UTIL_e; {UTIL_e << Modify;} throw UTIL_e; }

class ErrnoException : public Exception {
  public:
    ErrnoException() throw();

    virtual ~ErrnoException() throw();

    int Error() { return errno_; }

  private:
    int errno_;
};

} // namespace util

#endif // UTIL_EXCEPTION__