#ifndef ALPHANUM__HPP
#define ALPHANUM__HPP

/*
The Alphanum Algorithm is an improved sorting algorithm for strings
containing numbers.  Instead of sorting numbers in ASCII order like a
standard sort, this algorithm sorts numbers in numeric order.

The Alphanum Algorithm is discussed at http://www.DaveKoelle.com

This implementation is Copyright (c) 2008 Dirk Jagdmann <doj@cubic.org>.
It is a cleanroom implementation of the algorithm and not derived by
other's works. In contrast to the versions written by Dave Koelle this
source code is distributed with the libpng/zlib license.

This software is provided 'as-is', without any express or implied
warranty. In no event will the authors be held liable for any damages
arising from the use of this software.

Permission is granted to anyone to use this software for any purpose,
including commercial applications, and to alter it and redistribute it
freely, subject to the following restrictions:

    1. The origin of this software must not be misrepresented; you
       must not claim that you wrote the original software. If you use
       this software in a product, an acknowledgment in the product
       documentation would be appreciated but is not required.

    2. Altered source versions must be plainly marked as such, and
       must not be misrepresented as being the original software.

    3. This notice may not be removed or altered from any source
       distribution. */

/* $Header: /code/doj/alphanum.hpp,v 1.3 2008/01/28 23:06:47 doj Exp $ */

#include <cassert>
#include <functional>
#include <string>
#include <sstream>

namespace nc {

// anonymous namespace for functions we use internally. But if you
// are coding in C, you can use alphanum_impl() directly, since it
// uses not C++ features.
namespace {

bool alphanum_isdigit(const char c) { return c >= '0' && c <= '9'; }

/**
   compare l and r with strcmp() semantics, but using
   the "Alphanum Algorithm". This function is designed to read
   through the l and r strings only one time, for
   maximum performance. It does not allocate memory for
   substrings. It can either use the C-library functions isdigit()
   and atoi() to honour your locale settings, when recognizing
   digit characters when you "#define ALPHANUM_LOCALE=1" or use
   it's own digit character handling which only works with ASCII
   digit characters, but provides better performance.

   @param l NULL-terminated C-style string
   @param r NULL-terminated C-style string
   @return negative if l<r, 0 if l equals r, positive if l>r
 */
int alphanum_impl(const char* l, const char* r) {
  enum mode_t { STRING, NUMBER } mode = STRING;

  while (*l && *r) {
    if (mode == STRING) {
      char l_char, r_char;
      while ((l_char = *l) && (r_char = *r)) {
        // check if this are digit characters
        const bool l_digit = alphanum_isdigit(l_char),
                   r_digit = alphanum_isdigit(r_char);
        // if both characters are digits, we continue in NUMBER mode
        if (l_digit && r_digit) {
          mode = NUMBER;
          break;
        }
        // if only the left character is a digit, we have a result
        if (l_digit) return -1;
        // if only the right character is a digit, we have a result
        if (r_digit) return +1;
        // compute the difference of both characters
        const int diff = l_char - r_char;
        // if they differ we have a result
        if (diff != 0) return diff;
        // otherwise process the next characters
        ++l;
        ++r;
      }
    } else  // mode==NUMBER
    {
      // get the left number
      unsigned long l_int = 0;
      while (*l && alphanum_isdigit(*l)) {
        // TODO: this can overflow
        l_int = l_int * 10 + *l - '0';
        ++l;
      }

      // get the right number
      unsigned long r_int = 0;
      while (*r && alphanum_isdigit(*r)) {
        // TODO: this can overflow
        r_int = r_int * 10 + *r - '0';
        ++r;
      }

      // if the difference is not equal to zero, we have a comparison result
      const long diff = l_int - r_int;
      if (diff != 0) return diff;

      // otherwise we process the next substring in STRING mode
      mode = STRING;
    }
  }

  if (*r) return -1;
  if (*l) return +1;
  return 0;
}
}

/**
   Compare left and right with the same semantics as strcmp(), but with the
   "Alphanum Algorithm" which produces more human-friendly
   results. The classes lT and rT must implement "std::ostream
   operator<< (std::ostream&, const Ty&)".

   @return negative if left<right, 0 if left==right, positive if left>right.
*/
template <typename lT, typename rT>
int alphanum_comp(const lT& left, const rT& right) {
  std::ostringstream l;
  l << left;
  std::ostringstream r;
  r << right;
  return alphanum_impl(l.str().c_str(), r.str().c_str());
}

/**
   Compare l and r with the same semantics as strcmp(), but with
   the "Alphanum Algorithm" which produces more human-friendly
   results.

   @return negative if l<r, 0 if l==r, positive if l>r.
*/
template <>
int alphanum_comp<std::string>(const std::string& l, const std::string& r) {
  return alphanum_impl(l.c_str(), r.c_str());
}

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

// now follow a lot of overloaded alphanum_comp() functions to get a
// direct call to alphanum_impl() upon the various combinations of c
// and c++ strings.

/**
   Compare l and r with the same semantics as strcmp(), but with
   the "Alphanum Algorithm" which produces more human-friendly
   results.

   @return negative if l<r, 0 if l==r, positive if l>r.
*/
int alphanum_comp(char* l, char* r) {
  assert(l);
  assert(r);
  return alphanum_impl(l, r);
}

int alphanum_comp(const char* l, const char* r) {
  assert(l);
  assert(r);
  return alphanum_impl(l, r);
}

int alphanum_comp(char* l, const char* r) {
  assert(l);
  assert(r);
  return alphanum_impl(l, r);
}

int alphanum_comp(const char* l, char* r) {
  assert(l);
  assert(r);
  return alphanum_impl(l, r);
}

int alphanum_comp(const std::string& l, char* r) {
  assert(r);
  return alphanum_impl(l.c_str(), r);
}

int alphanum_comp(char* l, const std::string& r) {
  assert(l);
  return alphanum_impl(l, r.c_str());
}

int alphanum_comp(const std::string& l, const char* r) {
  assert(r);
  return alphanum_impl(l.c_str(), r);
}

int alphanum_comp(const char* l, const std::string& r) {
  assert(l);
  return alphanum_impl(l, r.c_str());
}

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

/**
   Functor class to compare two objects with the "Alphanum
   Algorithm". If the objects are no std::string, they must
   implement "std::ostream operator<< (std::ostream&, const Ty&)".
*/
template <class Ty>
struct alphanum_less : public std::binary_function<Ty, Ty, bool> {
  bool operator()(const Ty& left, const Ty& right) const {
    return alphanum_comp(left, right) < 0;
  }
};
}

#endif
