local new_timetable = require "luatz.timetable".new

--- Parse an RFC 3339 datetime at the given position
-- Returns a time table and the `tz_offset`
-- Return value is not normalised (this preserves a leap second)
-- If the timestamp is only partial (i.e. missing "Z" or time offset) then `tz_offset` will be nil
-- TODO: Validate components are within their boundarys (e.g. 1 <= month <= 12)
local function rfc_3339(str, init)
	local year, month, day, hour, min, sec, patt_end = str:match("^(%d%d%d%d)%-(%d%d)%-(%d%d)[Tt](%d%d%.?%d*):(%d%d):(%d%d)()", init) -- luacheck: ignore 631
	if not year then
		return nil, "Invalid RFC 3339 timestamp"
	end
	year  = tonumber(year)
	month = tonumber(month)
	day   = tonumber(day)
	hour  = tonumber(hour)
	min   = tonumber(min)
	sec   = tonumber(sec)

	local tt = new_timetable(year, month, day, hour, min, sec)

	local tz_offset
	if str:match("^[Zz]", patt_end) then
		tz_offset = 0
	else
		local hour_offset, min_offset = str:match("^([+-]%d%d):(%d%d)", patt_end)
		if hour_offset then
			tz_offset = tonumber(hour_offset) * 3600 + tonumber(min_offset) * 60
		else -- luacheck: ignore 542
			-- Invalid RFC 3339 timestamp offset (should be Z or (+/-)hour:min)
			-- tz_offset will be nil
		end
	end

	return tt, tz_offset
end

return {
	rfc_3339 = rfc_3339;
}