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11248adb34b11711372076447e2cfceaff49b4df
[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
8 -- Binary search
9 local function _find_current ( tzinfo , target , i , j )
10         if i >= j then return j end
11
12         local half = math.ceil ( (j+i) / 2 )
13
14         if target >= tzinfo [ half ].transition_time then
15                 return _find_current ( tzinfo , target , half , j )
16         else
17                 return _find_current ( tzinfo , target , i , half-1 )
18         end
19 end
20
21 local function find_current_local ( tzinfo , ts_local )
22         -- Find two best possibilities by searching back and forward a day (assumes transition is never by more than 24 hours)
23         local tz_first = _find_current ( tzinfo , ts_local-86400 , 0 , #tzinfo )
24         local tz_last  = _find_current ( tzinfo , ts_local+86400 , 0 , #tzinfo )
25
26         local n_candidates = tz_last - tz_first + 1
27
28         if n_candidates == 1 then
29                 return tz_first
30         elseif n_candidates == 2 then
31                 local tz_first_ob = tzinfo [ tz_first ]
32                 local tz_last_ob  = tzinfo [ tz_last ]
33
34                 local first_gmtoffset = tz_first_ob.info.gmtoff
35                 local last_gmtoffset  = tz_last_ob .info.gmtoff
36
37                 local t_start = tz_last_ob.transition_time + first_gmtoffset
38                 local t_end   = tz_last_ob.transition_time + last_gmtoffset
39
40                 -- If timestamp is before start or after end
41                 if ts_local < t_start then
42                         return tz_first
43                 elseif ts_local > t_end then
44                         return tz_last
45                 end
46
47                 -- If we get this far, the local time is ambiguous
48                 return tz_first , tz_last
49         else
50                 error ( "Too many transitions in a 2 day period" )
51         end
52 end
53
54 function tz_info_methods:find_current ( current )
55         return self [ _find_current ( self , current , 0 , #self ) ].info
56 end
57
58 function tz_info_methods:localise ( utc_ts )
59         utc_ts = utc_ts or gettime ( )
60         return utc_ts + self:find_current ( utc_ts ).gmtoff
61 end
62 tz_info_methods.localize = tz_info_methods.localise
63
64 function tz_info_methods:utctime ( ts_local )
65         local tz1 , tz2 = find_current_local ( self , ts_local )
66         tz1 = self [ tz1 ].info
67         if tz2 == nil then
68                 return ts_local - tz1.gmtoff
69         else -- Local time is ambiguous
70                 tz2 = self [ tz2 ].info
71
72                 return ts_local - tz2.gmtoff , ts_local - tz2.gmtoff
73         end
74 end
75
76 return {
77         tz_info_mt = tz_info_mt ;
78 }