1 | #ifndef DATE_TIME_LOCAL_TIME_ADJUSTOR_HPP__ |
2 | #define DATE_TIME_LOCAL_TIME_ADJUSTOR_HPP__ |
3 | |
4 | /* Copyright (c) 2002,2003 CrystalClear Software, Inc. |
5 | * Use, modification and distribution is subject to the |
6 | * Boost Software License, Version 1.0. (See accompanying |
7 | * file LICENSE_1_0.txt or http://www.boost.org/LICENSE_1_0.txt) |
8 | * Author: Jeff Garland |
9 | * $Date$ |
10 | */ |
11 | |
12 | /*! @file local_time_adjustor.hpp |
13 | Time adjustment calculations for local times |
14 | */ |
15 | |
16 | #include <stdexcept> |
17 | #include <boost/throw_exception.hpp> |
18 | #include <boost/date_time/compiler_config.hpp> |
19 | #include <boost/date_time/date_generators.hpp> |
20 | #include <boost/date_time/dst_rules.hpp> |
21 | #include <boost/date_time/time_defs.hpp> // boost::date_time::dst_flags |
22 | #include <boost/date_time/special_defs.hpp> // not_a_date_time |
23 | |
24 | namespace boost { |
25 | namespace date_time { |
26 | |
27 | |
28 | //! Provides a base offset adjustment from utc |
29 | template<class time_duration_type, |
30 | short hours, unsigned short minutes = 0> |
31 | class utc_adjustment |
32 | { |
33 | public: |
34 | static time_duration_type local_to_utc_base_offset() |
35 | { |
36 | time_duration_type td(hours,minutes,0); |
37 | return td.invert_sign(); |
38 | } |
39 | static time_duration_type utc_to_local_base_offset() |
40 | { |
41 | return time_duration_type(hours,minutes,0); |
42 | } |
43 | }; |
44 | |
45 | |
46 | |
47 | //! Allow sliding utc adjustment with fixed dst rules |
48 | template<class time_type, class dst_rules> |
49 | class dynamic_local_time_adjustor : public dst_rules |
50 | { |
51 | public: |
52 | typedef typename time_type::time_duration_type time_duration_type; |
53 | typedef typename time_type::date_type date_type; |
54 | |
55 | dynamic_local_time_adjustor(time_duration_type utc_offset) : |
56 | utc_offset_(utc_offset) |
57 | {} |
58 | |
59 | //! Presumes local time |
60 | time_duration_type utc_offset(bool is_dst) |
61 | { |
62 | if (is_dst) { |
63 | return utc_offset_ + this->dst_offset(); |
64 | } |
65 | else { |
66 | return utc_offset_; |
67 | } |
68 | |
69 | } |
70 | private: |
71 | time_duration_type utc_offset_; |
72 | |
73 | }; |
74 | |
75 | |
76 | |
77 | //! Embed the rules for local time adjustments at compile time |
78 | template<class time_type, class dst_rules, class utc_offset_rules> |
79 | class static_local_time_adjustor: public dst_rules, public utc_offset_rules |
80 | { |
81 | public: |
82 | typedef typename time_type::time_duration_type time_duration_type; |
83 | typedef typename time_type::date_type date_type; |
84 | |
85 | //! Calculates the offset from a utc time to local based on dst and utc offset |
86 | /*! @param t UTC time to calculate offset to local time |
87 | * This adjustment depends on the following observations about the |
88 | * workings of the DST boundary offset. Since UTC time labels are |
89 | * monotonically increasing we can determine if a given local time |
90 | * is in DST or not and therefore adjust the offset appropriately. |
91 | * |
92 | * The logic is as follows. Starting with UTC time use the offset to |
93 | * create a label for an non-dst adjusted local time. Then call |
94 | * dst_rules::local_is_dst with the non adjust local time. The |
95 | * results of this function will either unabiguously decide that |
96 | * the initial local time is in dst or return an illegal or |
97 | * ambiguous result. An illegal result only occurs at the end |
98 | * of dst (where labels are skipped) and indicates that dst has |
99 | * ended. An ambiguous result means that we need to recheck by |
100 | * making a dst adjustment and then rechecking. If the dst offset |
101 | * is added to the utc time and the recheck proves non-ambiguous |
102 | * then we are past the boundary. If it is still ambiguous then |
103 | * we are ahead of the boundary and dst is still in effect. |
104 | * |
105 | * TODO -- check if all dst offsets are positive. If not then |
106 | * the algorithm needs to check for this and reverse the |
107 | * illegal/ambiguous logic. |
108 | */ |
109 | static time_duration_type utc_to_local_offset(const time_type& t) |
110 | { |
111 | //get initial local time guess by applying utc offset |
112 | time_type initial = t + utc_offset_rules::utc_to_local_base_offset(); |
113 | time_is_dst_result dst_flag = |
114 | dst_rules::local_is_dst(initial.date(), initial.time_of_day()); |
115 | switch(dst_flag) { |
116 | case is_in_dst: return utc_offset_rules::utc_to_local_base_offset() + dst_rules::dst_offset(); |
117 | case is_not_in_dst: return utc_offset_rules::utc_to_local_base_offset(); |
118 | case invalid_time_label:return utc_offset_rules::utc_to_local_base_offset() + dst_rules::dst_offset(); |
119 | case ambiguous: { |
120 | time_type retry = initial + dst_rules::dst_offset(); |
121 | dst_flag = dst_rules::local_is_dst(retry.date(), retry.time_of_day()); |
122 | //if still ambibuous then the utc time still translates to a dst time |
123 | if (dst_flag == ambiguous) { |
124 | return utc_offset_rules::utc_to_local_base_offset() + dst_rules::dst_offset(); |
125 | } |
126 | // we are past the dst boundary |
127 | else { |
128 | return utc_offset_rules::utc_to_local_base_offset(); |
129 | } |
130 | } |
131 | }//case |
132 | //TODO better exception type |
133 | boost::throw_exception(e: std::out_of_range("Unreachable case" )); |
134 | BOOST_DATE_TIME_UNREACHABLE_EXPRESSION(return time_duration_type(not_a_date_time)); // should never reach |
135 | } |
136 | |
137 | //! Get the offset to UTC given a local time |
138 | static time_duration_type local_to_utc_offset(const time_type& t, |
139 | date_time::dst_flags dst=date_time::calculate) |
140 | { |
141 | switch (dst) { |
142 | case is_dst: |
143 | return utc_offset_rules::local_to_utc_base_offset() - dst_rules::dst_offset(); |
144 | case not_dst: |
145 | return utc_offset_rules::local_to_utc_base_offset(); |
146 | case calculate: |
147 | time_is_dst_result res = |
148 | dst_rules::local_is_dst(t.date(), t.time_of_day()); |
149 | switch(res) { |
150 | case is_in_dst: return utc_offset_rules::local_to_utc_base_offset() - dst_rules::dst_offset(); |
151 | case is_not_in_dst: return utc_offset_rules::local_to_utc_base_offset(); |
152 | case ambiguous: return utc_offset_rules::local_to_utc_base_offset(); |
153 | case invalid_time_label: break; |
154 | } |
155 | } |
156 | boost::throw_exception(e: std::out_of_range("Time label invalid" )); |
157 | BOOST_DATE_TIME_UNREACHABLE_EXPRESSION(return time_duration_type(not_a_date_time)); // should never reach |
158 | } |
159 | |
160 | |
161 | private: |
162 | |
163 | }; |
164 | |
165 | void dummy_to_prevent_msvc6_ice(); //why ask why? |
166 | |
167 | //! Template that simplifies the creation of local time calculator |
168 | /*! Use this template to create the timezone to utc convertors as required. |
169 | * |
170 | * This class will also work for other regions that don't use dst and |
171 | * have a utc offset which is an integral number of hours. |
172 | * |
173 | * <b>Template Parameters</b> |
174 | * -time_type -- Time class to use |
175 | * -utc_offset -- Number hours local time is adjust from utc |
176 | * -use_dst -- true (default) if region uses dst, false otherwise |
177 | * For example: |
178 | * @code |
179 | * //eastern timezone is utc-5 |
180 | typedef date_time::local_adjustor<ptime, -5, us_dst> us_eastern; |
181 | typedef date_time::local_adjustor<ptime, -6, us_dst> us_central; |
182 | typedef date_time::local_adjustor<ptime, -7, us_dst> us_mountain; |
183 | typedef date_time::local_adjustor<ptime, -8, us_dst> us_pacific; |
184 | typedef date_time::local_adjustor<ptime, -7, no_dst> us_arizona; |
185 | @endcode |
186 | |
187 | */ |
188 | template<class time_type, short utc_offset, class dst_rule> |
189 | class local_adjustor |
190 | { |
191 | public: |
192 | typedef typename time_type::time_duration_type time_duration_type; |
193 | typedef typename time_type::date_type date_type; |
194 | typedef static_local_time_adjustor<time_type, |
195 | dst_rule, |
196 | utc_adjustment<time_duration_type, |
197 | utc_offset> > dst_adjustor; |
198 | //! Convert a utc time to local time |
199 | static time_type utc_to_local(const time_type& t) |
200 | { |
201 | time_duration_type td = dst_adjustor::utc_to_local_offset(t); |
202 | return t + td; |
203 | } |
204 | //! Convert a local time to utc |
205 | static time_type local_to_utc(const time_type& t, |
206 | date_time::dst_flags dst=date_time::calculate) |
207 | { |
208 | time_duration_type td = dst_adjustor::local_to_utc_offset(t, dst); |
209 | return t + td; |
210 | } |
211 | }; |
212 | |
213 | |
214 | } } //namespace date_time |
215 | |
216 | |
217 | |
218 | #endif |
219 | |