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Give tt_info objects a metatable; and document them
[etc/awesome.git] / luatz / tzinfo.lua
1 local gettime = require "luatz.gettime".gettime
2
3 local tz_info_methods = { }
4 local tz_info_mt = {
5         __index = tz_info_methods ;
6 }
7 local tt_info_mt = {
8 }
9
10 -- Binary search
11 local function _find_current ( tzinfo , target , i , j )
12         if i >= j then return j end
13
14         local half = math.ceil ( (j+i) / 2 )
15
16         if target >= tzinfo [ half ].transition_time then
17                 return _find_current ( tzinfo , target , half , j )
18         else
19                 return _find_current ( tzinfo , target , i , half-1 )
20         end
21 end
22
23 local function find_current_local ( tzinfo , ts_local )
24         -- Find two best possibilities by searching back and forward a day (assumes transition is never by more than 24 hours)
25         local tz_first = _find_current ( tzinfo , ts_local-86400 , 0 , #tzinfo )
26         local tz_last  = _find_current ( tzinfo , ts_local+86400 , 0 , #tzinfo )
27
28         local n_candidates = tz_last - tz_first + 1
29
30         if n_candidates == 1 then
31                 return tz_first
32         elseif n_candidates == 2 then
33                 local tz_first_ob = tzinfo [ tz_first ]
34                 local tz_last_ob  = tzinfo [ tz_last ]
35
36                 local first_gmtoffset = tz_first_ob.info.gmtoff
37                 local last_gmtoffset  = tz_last_ob .info.gmtoff
38
39                 local t_start = tz_last_ob.transition_time + first_gmtoffset
40                 local t_end   = tz_last_ob.transition_time + last_gmtoffset
41
42                 -- If timestamp is before start or after end
43                 if ts_local < t_start then
44                         return tz_first
45                 elseif ts_local > t_end then
46                         return tz_last
47                 end
48
49                 -- If we get this far, the local time is ambiguous
50                 return tz_first , tz_last
51         else
52                 error ( "Too many transitions in a 2 day period" )
53         end
54 end
55
56 function tz_info_methods:find_current ( current )
57         return self [ _find_current ( self , current , 0 , #self ) ].info
58 end
59
60 function tz_info_methods:localise ( utc_ts )
61         utc_ts = utc_ts or gettime ( )
62         return utc_ts + self:find_current ( utc_ts ).gmtoff
63 end
64 tz_info_methods.localize = tz_info_methods.localise
65
66 function tz_info_methods:utctime ( ts_local )
67         local tz1 , tz2 = find_current_local ( self , ts_local )
68         tz1 = self [ tz1 ].info
69         if tz2 == nil then
70                 return ts_local - tz1.gmtoff
71         else -- Local time is ambiguous
72                 tz2 = self [ tz2 ].info
73
74                 return ts_local - tz2.gmtoff , ts_local - tz2.gmtoff
75         end
76 end
77
78 return {
79         tz_info_mt = tz_info_mt ;
80         tt_info_mt = tt_info_mt ;
81 }