dst_rules.hpp

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#ifndef DATE_TIME_DST_RULES_HPP__
#define DATE_TIME_DST_RULES_HPP__

/* Copyright (c) 2002,2003, 2007 CrystalClear Software, Inc.
 * Use, modification and distribution is subject to the 
 * Boost Software License, Version 1.0. (See accompanying
 * file LICENSE-1.0 or http://www.boost.org/LICENSE-1.0)
 * Author: Jeff Garland, Bart Garst
 * $Date: 2007/03/02 01:54:49 $
 */

/*! @file dst_rules.hpp
  Contains template class to provide static dst rule calculations
*/

#include "boost/date_time/date_generators.hpp"
#include "boost/date_time/period.hpp"
#include "boost/date_time/date_defs.hpp"
#include <stdexcept>

namespace boost {
  namespace date_time {

    enum time_is_dst_result {is_not_in_dst, is_in_dst, 
                             ambiguous, invalid_time_label};


    //! Dynamic class used to caluclate dst transition information
    template<class date_type_, 
             class time_duration_type_>
    class dst_calculator
    {
    public:
      typedef time_duration_type_ time_duration_type;
      typedef date_type_ date_type;

      //! Check the local time offset when on dst start day
      /*! On this dst transition, the time label between
       *  the transition boundary and the boudary + the offset
       *  are invalid times.  If before the boundary then still 
       *  not in dst.  
       *@param time_of_day Time offset in the day for the local time
       *@param dst_start_offset_minutes Local day offset for start of dst
       *@param dst_length_minutes Number of minutes to adjust clock forward
       *@retval status of time label w.r.t. dst
       */
      static time_is_dst_result 
      process_local_dst_start_day(const time_duration_type& time_of_day,
                                  unsigned int dst_start_offset_minutes,
                                  long dst_length_minutes)
      {
        //std::cout << "here" << std::endl;
        if (time_of_day < time_duration_type(0,dst_start_offset_minutes,0)) {
          return is_not_in_dst;
        }
        long offset = dst_start_offset_minutes + dst_length_minutes;
        if (time_of_day >= time_duration_type(0,offset,0)) {
          return is_in_dst;
        }
        return invalid_time_label; 
      }

      //! Check the local time offset when on the last day of dst
      /*! This is the calculation for the DST end day.  On that day times
       *  prior to the conversion time - dst_length (1 am in US) are still 
       *  in dst.  Times between the above and the switch time are 
       *  ambiguous.  Times after the start_offset are not in dst.
       *@param time_of_day Time offset in the day for the local time
       *@param dst_end_offset_minutes Local time of day for end of dst
       *@retval status of time label w.r.t. dst
       */
      static time_is_dst_result 
      process_local_dst_end_day(const time_duration_type& time_of_day,
                                unsigned int dst_end_offset_minutes,
                                long dst_length_minutes)
      {
        //in US this will be 60 so offset in day is 1,0,0
        int offset = dst_end_offset_minutes-dst_length_minutes;
        if (time_of_day < time_duration_type(0,offset,0)) {
          return is_in_dst;
        }
        if (time_of_day >= time_duration_type(0,dst_end_offset_minutes,0)) {
          return is_not_in_dst;
        }
        return ambiguous;
      }

      //! Calculates if the given local time is dst or not
      /*! Determines if the time is really in DST or not.  Also checks for 
       *  invalid and ambiguous.
       *  @param current_day The day to check for dst
       *  @param time_of_day Time offset within the day to check 
       *  @param dst_start_day  Starting day of dst for the given locality
       *  @param dst_start_offset Time offset within day for dst boundary
       *  @param dst_end_day    Ending day of dst for the given locality
       *  @param dst_end_offset Time offset within day given in dst for dst boundary
       *  @param dst_length lenght of dst adjusment
       *  @retval The time is either ambiguous, invalid, in dst, or not in dst
       */
      static time_is_dst_result 
      local_is_dst(const date_type& current_day,
                   const time_duration_type& time_of_day,
                   const date_type& dst_start_day,
                   const time_duration_type& dst_start_offset,
                   const date_type& dst_end_day,
                   const time_duration_type& dst_end_offset,
                   const time_duration_type& dst_length_minutes)
      {
        unsigned int start_minutes = 
          dst_start_offset.hours() * 60 + dst_start_offset.minutes();
        unsigned int end_minutes = 
          dst_end_offset.hours() * 60 + dst_end_offset.minutes();
        long length_minutes =  
          dst_length_minutes.hours() * 60 + dst_length_minutes.minutes();

        return local_is_dst(current_day, time_of_day,
                            dst_start_day, start_minutes,
                            dst_end_day, end_minutes,
                            length_minutes);
      }

      //! Calculates if the given local time is dst or not
      /*! Determines if the time is really in DST or not.  Also checks for 
       *  invalid and ambiguous.
       *  @param current_day The day to check for dst
       *  @param time_of_day Time offset within the day to check 
       *  @param dst_start_day  Starting day of dst for the given locality
       *  @param dst_start_offset_minutes Offset within day for dst 
       *         boundary (eg 120 for US which is 02:00:00)
       *  @param dst_end_day    Ending day of dst for the given locality
       *  @param dst_end_offset_minutes Offset within day given in dst for dst 
       *         boundary (eg 120 for US which is 02:00:00)
       *  @param dst_length_minutes Length of dst adjusment (eg: 60 for US)
       *  @retval The time is either ambiguous, invalid, in dst, or not in dst
       */
      static time_is_dst_result 
      local_is_dst(const date_type& current_day,
                   const time_duration_type& time_of_day,
                   const date_type& dst_start_day,
                   unsigned int dst_start_offset_minutes,
                   const date_type& dst_end_day,
                   unsigned int dst_end_offset_minutes,
                   long dst_length_minutes)
      {
        //in northern hemisphere dst is in the middle of the year
        if (dst_start_day < dst_end_day) {
          if ((current_day > dst_start_day) && (current_day < dst_end_day)) {
            return is_in_dst;
          }
          if ((current_day < dst_start_day) || (current_day > dst_end_day)) {
            return is_not_in_dst;
          }
        }
        else {//southern hemisphere dst is at begining /end of year
          if ((current_day < dst_start_day) && (current_day > dst_end_day)) {
            return is_not_in_dst;
          }
          if ((current_day > dst_start_day) || (current_day < dst_end_day)) {
            return is_in_dst;
          }
        }

        if (current_day == dst_start_day) {
          return process_local_dst_start_day(time_of_day,
                                             dst_start_offset_minutes,
                                             dst_length_minutes);
        }
      
        if (current_day == dst_end_day) {
          return process_local_dst_end_day(time_of_day,
                                           dst_end_offset_minutes,
                                           dst_length_minutes);
        }
        //you should never reach this statement
        return invalid_time_label;
      }

    };


    //! Compile-time configurable daylight savings time calculation engine
    /* This template provides the ability to configure a daylight savings
     * calculation at compile time covering all the cases.  Unfortunately
     * because of the number of dimensions related to daylight savings
     * calculation the number of parameters is high.  In addition, the
     * start and end transition rules are complex types that specify 
     * an algorithm for calculation of the starting day and ending
     * day of daylight savings time including the month and day 
     * specifications (eg: last sunday in October).
     *
     * @param date_type A type that represents dates, typically gregorian::date
     * @param time_duration_type Used for the offset in the day calculations
     * @param dst_traits A set of traits that define the rules of dst 
     *        calculation.  The dst_trait must include the following:
     * start_rule_functor - Rule to calculate the starting date of a
     *                      dst transition (eg: last_kday_of_month).