-- originally from http://lua-users.org/wiki/LuaXml
-- modified by me a bit

local function parseargs(s)
  local arg = {}
  string.gsub(s, "([%-%w]+)=([\"'])(.-)%2", function (w, _, a)
    arg[w] = a
  end)
  return arg
end

local function tag(x)
	return setmetatable(x, {__call=function(x, label)
		-- search for child with given label
		for _,c in ipairs(x) do
			if c.label == label then
				return c
			end
		end
		return nil
	end})
end

local psingle

local function pmulti(s, i, parent)
	::again::
	local nexti, child = psingle(s, i)
	if child.close and child.label == parent.label then
		return nexti, parent
	else
		table.insert(parent, child)
		i = nexti
		goto again
	end
end

psingle = function(s, i)
	i = i or 1
	local ts,j,c,label,xarg,empty = s:find("<(%/?)([%w:]+)(.-)(%/?)>", i)
	if not ts then
		local rest = s:sub(i)
		if rest:find("<",i) then
			error('ill formed (eof?)')
		elseif #rest == 0 then
			error('empty string')
		else
			return i+#rest, rest
		end
	end
	local nexti = j+1

	local pretext = s:sub(i, ts-1)
	if not pretext:find("^%s*$") then -- not entirely whitespace
		return ts, pretext
	end

	if empty == "/" then
		return nexti, tag{label=label, xarg=parseargs(xarg), empty=true}
	elseif c == "" then -- start tag
		return pmulti(s, nexti, tag{label=label, xarg=parseargs(xarg)})
	else -- end tag
		return nexti, tag{label=label, close=true}
	end
end

local wrap
do
	local _, cqa = pcall(require, 'cqueues.auxlib')
	wrap = cqa and cqa.wrap or coroutine.wrap
end
local function stanzae(getmore)
	return wrap(function()
		local buf = ''
		while true do
			local ok, ni, el = pcall(psingle, buf)
			if ok then
				coroutine.yield(el)
				buf = buf:sub(ni)
			else
				local more = getmore()
				buf = buf .. more
			end
		end
	end)
end


return { psingle = psingle, stanzae = stanzae, wrap=wrap }