added posixtz.lua for parse functionality

The parse() function takes a POSIX TZ string and returns a table with TZ parameters.

1 files changed, 192 insertions, 0 deletions

diff --git a/posixtz.lua b/posixtz.lua
new file mode 100644
index 0000000..7eb92dd
--- /dev/null
+++ b/posixtz.lua
@@ -0,0 +1,192 @@
+-------------------------------------------------------------------------------
+-- POSIX TZ Parser for Lua
+-- Copyright (C) 2011 H. Andrew Latchman <aldevel@jamailca.com>
+--
+-- Performs some validation of TZ string
+-- based on fields to determine offset and dst settings
+--
+--   See http://pubs.opengroup.org/onlinepubs/9699919799/basedefs/V1_chap08.html
+--     TZ variable, with no leading colon
+--   Syntax: stdoffset[dst[offset][,start[/time],end[/time]]]
+--   Examples: 'GMT0' 'EST5EDT,M3.2.0,M11.1.0' '<GMT+5>5'
+-------------------------------------------------------------------------------
+
+-- Import Section
+--  declare everything this module needs from outside
+local error = error
+local string = string
+local tonumber = tonumber
+local pairs = pairs
+local ipairs = ipairs
+
+-- Rest of the code is part of module "posixtz"
+module('posixtz')
+
+function parse ( str )
+
+	-- create tz table for data to be returned
+	local tz = {}
+	-- create temp table for storing what is left to be parsed
+	local temp = {}
+
+	if not str then
+		error('Nothing to parse')
+	end
+
+
+	-- Check that values.device.timezone has required fields
+	--  (technically, std must be at least 3 chars, but we don't care)
+
+	-- Parse out 'std' and validate.
+	--  check for quoted format of std
+	tz.std, temp.afterstd = string.match(str, '^(<[%w+-]+>)(.*)')
+	if not tz.std then
+		-- try unquoted format of std
+		tz.std, temp.afterstd = string.match(str, '^(%a+)(.*)')
+	end
+
+	-- tz.std must be defined by now
+	if not tz.std then
+		error('Not a valid POSIX TZ. "std" invalid')
+	end
+
+
+	-- After 'std' there must be [+|-]hh[:mm[:ss]] as the offset
+	--    the following code simplifies to [+|-]hh[[:][mm[[:][ss]]
+	tz.offset = {}
+	tz.offset.sign, tz.offset.hour, tz.offset.min, tz.offset.sec, temp.afteroffset = string.match(temp.afterstd, '^([+-]?)(%d+):?(%d?%d?):?(%d?%d?)(.*)')
+
+	-- tz.offset.hour must be non-empty, the other vars may be '' if not present
+	if tz.offset.hour and ( tz.offset.hour ~= '' ) then
+
+		tz.offset.total = 3600 * tonumber(tz.offset.sign .. tz.offset.hour)
+
+		-- use tonumber to check that tz.offset[min|sec] are not ''
+		if tonumber(tz.offset.min) then
+			tz.offset.total = tz.offset.total + 60 * tonumber(tz.offset.sign .. tz.offset.min)
+		end
+		if tonumber(tz.offset.sec) then 
+			tz.offset.total = tz.offset.total + tonumber(tz.offset.sign .. tz.offset.sec)
+		end
+	
+	else
+		error('Not a valid POSIX TZ. "offset" invalid')
+	end
+	
+
+	-- The rest of the POSIX fields are optional
+	if ( temp.afteroffset == '' ) then
+		-- we are finished. no more data.
+		return tz
+	end
+
+
+	-- DST -- If we are here, then "dst" field is present
+
+	-- Parse out "dst" and validate
+	--  dst name comes after offset
+	tz.dst = {}
+	tz.dst.name, temp.afterdst = string.match(temp.afteroffset, '^(<[%w+-]+>)(.*)')
+	if not tz.dst.name then
+		-- try unquoted format of dst
+		tz.dst.name, temp.afterdst = string.match(temp.afteroffset, '^(%a+)(.*)')
+	end
+	if not tz.dst.name then
+		error('Not a valid POSIX TZ. "dst" present but not valid')
+	end
+
+	-- tz.dst.name is defined, so process "rule"
+	-- Parse out specifications from "rule"
+	temp.dststart, temp.dststop = string.match(temp.afterdst, '^,([^,]+),([^,]+)') 
+	if not temp.dststart then
+		error('Not a valid POSIX TZ. "dst" present but "rule" is not')
+	end
+
+
+	local function dstparse ( pos, spec )
+		local t = {}
+		tz.dst[pos] = t
+		
+	
+		-- Handle explicit hour for DST change
+		t.hour = string.match(spec, '/(%d+)')
+		-- TODO: Implement explicit min and sec
+
+	
+		local monkey = {}
+		monkey[1] = 31  -- January
+		monkey[2] = 28 
+		monkey[3] = 31
+		monkey[4] = 30
+		monkey[5] = 31
+		monkey[6] = 30
+		monkey[7] = 31
+		monkey[8] = 31
+		monkey[9] = 30
+		monkey[10] = 31
+		monkey[11] = 30
+		monkey[12] = 31
+	
+		local function whichmonth ( dayofyear )
+			-- assume day = 1 for '1 Jan'
+			-- uses monkey to determine month
+			local month, dayofmonth
+			local remaindays = tonumber(dayofyear)
+			for i, n in ipairs(monkey) do
+				if remaindays > n then
+					-- Jnday is not in this month
+					remaindays = remaindays - n
+				else
+					month = i
+					dayofmonth = remaindays
+					break
+				end
+			end
+			t.month = month
+			t.day = dayofmonth
+		end
+	
+		-- Jn format (Julian day, with [1 <= n <= 365], no Feb 29)
+		t.Jnday = string.match(spec, '^J(%d+)')
+		if t.Jnday then
+	
+			whichmonth(t.Jnday)
+	
+		end
+	
+		-- n format (zero-based Julian day, [0 <= n <= 364/5], counting Feb 29)
+		t.nday = string.match(spec, '^(%d+)')
+		if t.nday then
+	
+			monkey[2] = 29
+			whichmonth(t.nday + 1)
+
+		end
+	
+		-- Mm.w.d (day d of week w of month m)
+		--  m is between 1 and 12
+		--  w is between 1 and 5, where 1st,2nd..4th, and 5=last
+		--  d is between 0 (Sun) and 6 (Sat)
+		t.Mmonth, t.week, t.weekday = string.match(spec, 'M(%d+)%.(%d)%.(%d)')
+		if t.Mmonth then
+			t.month = t.Mmonth
+		end
+
+
+		-- Validation: t.month must be defined by now.
+		if not t.month then
+			error('Not a valid POSIX TZ. "rule" for DST "'..pos..'" is invalid')
+		end
+	end
+	
+	if temp.dststart and temp.dststop then	
+		-- Parse and validate dst rule specifications.
+		dstparse('start', temp.dststart)
+		dstparse('stop', temp.dststop)
+	end
+
+
+	return tz
+
+end
+