local coroutine = coroutine;

local tonumber = tonumber;

local string = string;

local setmetatable, getmetatable = setmetatable, getmetatable;

local pairs = pairs;

local deadroutine = coroutine.create(function() end);

coroutine.resume(deadroutine);

module("lxp")

local entity_map = setmetatable({

	["amp"] = "&";

	["gt"] = ">";

	["lt"] = "<";

	["apos"] = "'";

	["quot"] = "\"";

}, {__index = function(_, s)

		if s:sub(1,1) == "#" then

			if s:sub(2,2) == "x" then

				return string.char(tonumber(s:sub(3), 16));

			else

				return string.char(tonumber(s:sub(2)));

			end

		end

	end

});

local function xml_unescape(str)

	return (str:gsub("&(.-);", entity_map));

end

local function parse_tag(s)

	local name,sattr=(s):gmatch("([^%s]+)(.*)")();

	local attr = {};

	for a,b in (sattr):gmatch("([^=%s]+)=['\"]([^'\"]*)['\"]") do attr[a] = xml_unescape(b); end

	return name, attr;

end

local function parser(data, handlers, ns_separator)

	local function read_until(str)

		local pos = data:find(str, nil, true);

		while not pos do

			data = data..coroutine.yield();

			pos = data:find(str, nil, true);

		end

		local r = data:sub(1, pos);

		data = data:sub(pos+1);

		return r;

	end

	local function read_before(str)

		local pos = data:find(str, nil, true);

		while not pos do

			data = data..coroutine.yield();

			pos = data:find(str, nil, true);

		end

		local r = data:sub(1, pos-1);

		data = data:sub(pos);

		return r;

	end

	local function peek()

		while #data == 0 do data = coroutine.yield(); end

		return data:sub(1,1);

	end

	local ns = { xml = "http://www.w3.org/XML/1998/namespace" };

	ns.__index = ns;

	local function apply_ns(name, dodefault)

		local prefix,n = name:match("^([^:]*):(.*)$");

		if prefix and ns[prefix] then

			return ns[prefix]..ns_separator..n;

		end

		if dodefault and ns[""] then

			return ns[""]..ns_separator..name;

		end

		return name;

	end

	local function push(tag, attr)

		ns = setmetatable({}, ns);

		for k,v in pairs(attr) do

			local xmlns = k == "xmlns" and "" or k:match("^xmlns:(.*)$");

			if xmlns then

				ns[xmlns] = v;

				attr[k] = nil;

			end

		end

		local newattr, n = {}, 0;

		for k,v in pairs(attr) do

			n = n+1;

			k = apply_ns(k);

			newattr[n] = k;

			newattr[k] = v;

		end

		tag = apply_ns(tag, true);

		ns[0] = tag;

		ns.__index = ns;

		return tag, newattr;

	end

	local function pop()

		local tag = ns[0];

		ns = getmetatable(ns);

		return tag;

	end

	while true do

		if peek() == "<" then

			local elem = read_until(">"):sub(2,-2);

			if elem:sub(1,1) == "!" or elem:sub(1,1) == "?" then -- neglect comments and processing-instructions

			elseif elem:sub(1,1) == "/" then -- end tag

				elem = elem:sub(2);

				local name = pop();

				handlers:EndElement(name); -- TODO check for start-end tag name match

			elseif elem:sub(-1,-1) == "/" then -- empty tag

				elem = elem:sub(1,-2);

				local name,attr = parse_tag(elem);

				name,attr = push(name,attr);

				handlers:StartElement(name,attr);

				name = pop();

				handlers:EndElement(name);

			else -- start tag

				local name,attr = parse_tag(elem);

				name,attr = push(name,attr);

				handlers:StartElement(name,attr);

			end

		else

			local text = read_before("<");

			handlers:CharacterData(xml_unescape(text));

		end

	end

end

function new(handlers, ns_separator)

	local co = coroutine.create(parser);

	return {

		parse = function(self, data)

			if not data then

				co = deadroutine;

				return true; -- eof

			end

			local success, result = coroutine.resume(co, data, handlers, ns_separator);

			if result then

				co = deadroutine;

				return nil, result; -- error

			end

			return true; -- success

		end;

	};

end

return _M;