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doc/timetable: spell check
[etc/awesome.git] / luatz / tzinfo.lua
1 local gettime = require "luatz.gettime".gettime
2 local timetable_mt = require "luatz.timetable".timetable_mt
3
4 local function to_timestamp ( o )
5         if type ( o ) == "number" then
6                 return o
7         elseif getmetatable ( o ) == timetable_mt then
8                 return o:timestamp ( )
9         end
10 end
11
12 local tz_info_methods = { }
13 local tz_info_mt = {
14         __index = tz_info_methods ;
15 }
16 local tt_info_mt = {
17         __tostring = function ( self )
18                 return string.format ( "tt_info:%s=%d" , self.abbr , self.gmtoff )
19         end ;
20 }
21
22 -- Binary search
23 local function _find_current ( tzinfo , target , i , j )
24         if i >= j then return j end
25
26         local half = math.ceil ( (j+i) / 2 )
27
28         if target >= tzinfo [ half ].transition_time then
29                 return _find_current ( tzinfo , target , half , j )
30         else
31                 return _find_current ( tzinfo , target , i , half-1 )
32         end
33 end
34
35 local function find_current_local ( tzinfo , ts_local )
36         -- Find two best possibilities by searching back and forward a day (assumes transition is never by more than 24 hours)
37         local tz_first = _find_current ( tzinfo , ts_local-86400 , 0 , #tzinfo )
38         local tz_last  = _find_current ( tzinfo , ts_local+86400 , 0 , #tzinfo )
39
40         local n_candidates = tz_last - tz_first + 1
41
42         if n_candidates == 1 then
43                 return tz_first
44         elseif n_candidates == 2 then
45                 local tz_first_ob = tzinfo [ tz_first ]
46                 local tz_last_ob  = tzinfo [ tz_last ]
47
48                 local first_gmtoffset = tz_first_ob.info.gmtoff
49                 local last_gmtoffset  = tz_last_ob .info.gmtoff
50
51                 local t_start = tz_last_ob.transition_time + first_gmtoffset
52                 local t_end   = tz_last_ob.transition_time + last_gmtoffset
53
54                 -- If timestamp is before start or after end
55                 if ts_local < t_start then
56                         return tz_first
57                 elseif ts_local > t_end then
58                         return tz_last
59                 end
60
61                 -- If we get this far, the local time is ambiguous
62                 return tz_first , tz_last
63         else
64                 error ( "Too many transitions in a 2 day period" )
65         end
66 end
67
68 function tz_info_methods:find_current ( current )
69         current = assert ( to_timestamp ( current ) , "invalid timestamp to :find_current" )
70         return self [ _find_current ( self , current , 0 , #self ) ].info
71 end
72
73 function tz_info_methods:localise ( utc_ts )
74         utc_ts = utc_ts or gettime ( )
75         return utc_ts + self:find_current ( utc_ts ).gmtoff
76 end
77 tz_info_methods.localize = tz_info_methods.localise
78
79 function tz_info_methods:utctime ( ts_local )
80         ts_local = assert ( to_timestamp ( ts_local ) , "invalid timestamp to :utctime" )
81         local tz1 , tz2 = find_current_local ( self , ts_local )
82         tz1 = self [ tz1 ].info
83         if tz2 == nil then
84                 return ts_local - tz1.gmtoff
85         else -- Local time is ambiguous
86                 tz2 = self [ tz2 ].info
87
88                 return ts_local - tz2.gmtoff , ts_local - tz2.gmtoff
89         end
90 end
91
92 return {
93         tz_info_mt = tz_info_mt ;
94         tt_info_mt = tt_info_mt ;
95 }