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         __name = "luatz.tz_info";
  15         __index = tz_info_methods;
  16 }
  17 local tt_info_mt = {
  18         __name = "luatz.tt_info";
  19         __tostring = function(self)
  20                 return string.format("tt_info:%s=%d", self.abbr, self.gmtoff)
  21         end;
  22 }
  23
  24 -- Binary search
  25 local function find_current(tzinfo, target, i, j)
  26         if i >= j then return j end
  27
  28         local half = math.ceil((j+i) / 2)
  29
  30         if target >= tzinfo[half].transition_time then
  31                 return find_current(tzinfo, target, half, j)
  32         else
  33                 return find_current(tzinfo, target, i, half-1)
  34         end
  35 end
  36
  37 local function find_current_local(tzinfo, ts_local)
  38         -- Find two best possibilities by searching back and forward a day (assumes transition is never by more than 24 hours)
  39         local tz_first = find_current(tzinfo, ts_local-86400, 0, #tzinfo)
  40         local tz_last  = find_current(tzinfo, ts_local+86400, 0, #tzinfo)
  41
  42         local n_candidates = tz_last - tz_first + 1
  43
  44         if n_candidates == 1 then
  45                 return tz_first
  46         elseif n_candidates == 2 then
  47                 local tz_first_ob = tzinfo[tz_first]
  48                 local tz_last_ob  = tzinfo[tz_last]
  49
  50                 local first_gmtoffset = tz_first_ob.info.gmtoff
  51                 local last_gmtoffset  = tz_last_ob .info.gmtoff
  52
  53                 local t_start = tz_last_ob.transition_time + first_gmtoffset
  54                 local t_end   = tz_last_ob.transition_time + last_gmtoffset
  55
  56                 -- If timestamp is before start or after end
  57                 if ts_local < t_start then
  58                         return tz_first
  59                 elseif ts_local > t_end then
  60                         return tz_last
  61                 end
  62
  63                 -- If we get this far, the local time is ambiguous
  64                 return tz_first, tz_last
  65         else
  66                 error("Too many transitions in a 2 day period")
  67         end
  68 end
  69
  70 function tz_info_methods:find_current(current)
  71         current = assert(to_timestamp(current), "invalid timestamp to :find_current")
  72         return self[find_current(self, current, 0, #self)].info
  73 end
  74
  75 function tz_info_methods:localise(utc_ts)
  76         utc_ts = utc_ts or gettime()
  77         return utc_ts + self:find_current(utc_ts).gmtoff
  78 end
  79 tz_info_methods.localize = tz_info_methods.localise
  80
  81 function tz_info_methods:utctime(ts_local)
  82         ts_local = assert(to_timestamp(ts_local), "invalid timestamp to :utctime")
  83         local tz1, tz2 = find_current_local(self, ts_local)
  84         tz1 = self[tz1].info
  85         if tz2 == nil then
  86                 return ts_local - tz1.gmtoff
  87         else -- Local time is ambiguous
  88                 tz2 = self[tz2].info
  89
  90                 return ts_local - tz2.gmtoff, ts_local - tz2.gmtoff
  91         end
  92 end
  93
  94 return {
  95         tz_info_mt = tz_info_mt;
  96         tt_info_mt = tt_info_mt;
  97 }