#ifndef UNITS_H			// -*- c++ -*-
#define UNITS_H
///
// Copyright (C) 2002 - 2004, Fredrik Arnerup & Rasmus Kaj, See COPYING
///
#include <map>
#include <vector>
#include <stdexcept>

class unknown_unit_error: public std::runtime_error {
public:
  unknown_unit_error(std::string msg) : std::runtime_error(msg) {}
};

template <class number, class identifier>
class Units {
public:
  Units(const identifier &_base_unit) : base_unit(_base_unit) {
    add_unit(base_unit, 1);
  }
  const identifier &get_base_unit() const {
    return base_unit;
  }
  void add_unit(identifier unit, number conv_factor) {
    units[unit] = conv_factor; 
  }
  bool has_unit(const identifier &unit) const {
    return find(unit) != units.end();
  }
  number get_factor(const identifier &unit) const {
    typename _Units::const_iterator i = find(unit);
    if(i == units.end())
      throw unknown_unit_error("Unit \"" + std::string(unit) 
                               + "\" is unknown");
    return i->second;
  }
  number to_base(number value, const identifier &unit) const {
    return value * get_factor(unit);
  }
  number from_base(number value, const identifier &unit) const {
    return value / get_factor(unit);
  }

  typedef std::vector<identifier> UnitList;
  UnitList list_units() const {
    UnitList list;
    for(typename _Units::const_iterator i = units.begin(); 
	i != units.end(); 
	i++)
      list.push_back(i->first);
    return list;
  }

private:
  identifier base_unit;
  typedef std::map<identifier, number> _Units;
  _Units units;

  /// map::find doesn't work with ustrings containing non-ascii chars
  /// for some reason
  typename _Units::const_iterator find(const identifier &unit) const {
    typename _Units::const_iterator i = units.begin();
    for(;i != units.end(); i++)
      if(i->first == unit)
        break;
    return i;
  }
};

#endif