--[[
  The MIT License
  
  Copyright (c) 2011, Attractive Chaos <attractor@live.co.uk>
  
  Permission is hereby granted, free of charge, to any person obtaining a copy
  of this software and associated documentation files (the "Software"), to deal
  in the Software without restriction, including without limitation the rights
  to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
  copies of the Software, and to permit persons to whom the Software is
  furnished to do so, subject to the following conditions:
  
  The above copyright notice and this permission notice shall be included in
  all copies or substantial portions of the Software.
  
  THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
  IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
  FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
  AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
  LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
  OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
  SOFTWARE.
]]--


-- Description: getopt() translated from the BSD getopt(); compatible with the default Unix getopt()
--[[ Example:
	for o, a in os.getopt(arg, 'a:b') do
		print(o, a)
	end
]]--
-- The ':' after an option means it will search for an argument, the example
-- above is requiring an argument after 'a', but 'b' is just a flag
function os.getopt(args, ostr)
	local arg, place = nil, 0;
	return function ()
		if place == 0 then -- update scanning pointer
			place = 1
			if #args == 0 or args[1]:sub(1, 1) ~= '-' then place = 0; return nil end
			if #args[1] >= 2 then
				place = place + 1
				if args[1]:sub(2, 2) == '-' then -- found "--"
					place = 0
					table.remove(args, 1);
					return nil;
				end
			end
		end
		local optopt = args[1]:sub(place, place);
		place = place + 1;
		local oli = ostr:find(optopt);
		if optopt == ':' or oli == nil then -- unknown option
			if optopt == '-' then return nil end
			if place > #args[1] then
				table.remove(args, 1);
				place = 0;
			end
			return '?';
		end
		oli = oli + 1;
		if ostr:sub(oli, oli) ~= ':' then -- do not need argument
			arg = nil;
			if place > #args[1] then
				table.remove(args, 1);
				place = 0;
			end
		else -- need an argument
			if place <= #args[1] then  -- no white space
				arg = args[1]:sub(place);
			else
				table.remove(args, 1);
				if #args == 0 then -- an option requiring argument is the last one
					place = 0;
					if ostr:sub(1, 1) == ':' then return ':' end
					return '?';
				else arg = args[1] end
			end
			table.remove(args, 1);
			place = 0;
		end
		return optopt, arg;
	end
end