local adns = require "net.adns";

local basic = require "net.resolvers.basic";

local methods = {};

local resolver_mt = { __index = methods };

-- Find the next target to connect to, and

-- pass it to cb()

function methods:next(cb)

	if self.targets then

		if #self.targets == 0 then

			cb(nil);

			return;

		end

		local next_target = table.remove(self.targets, 1);

		self.resolver = basic.new(unpack(next_target, 1, 4));

		self.resolver:next(function (...)

			if ... == nil then

				self:next(cb);

			else

				cb(...);

			end

		end);

		return;

	end

	local targets = {};

	local function ready()

		self.targets = targets;

		self:next(cb);

	end

	-- Resolve DNS to target list

	local dns_resolver = adns.resolver();

	dns_resolver:lookup(function (answer)

		if answer then

			if #answer == 0 then

				if self.extra and self.extra.default_port then

					table.insert(targets, { self.hostname, self.extra.default_port, self.conn_type, self.extra });

				end

				ready();

				return;

			end

			if #answer == 1 and answer[1].srv.target == "." then -- No service here

				ready();

				return;

			end

			table.sort(answer, function (a, b) return a.srv.priority < b.srv.priority end);

			for _, record in ipairs(answer) do

				table.insert(targets, { record.srv.target, record.srv.port, self.conn_type, self.extra });

			end

		end

		ready();

	end, "_" .. self.service .. "._" .. self.conn_type .. "." .. self.hostname, "SRV", "IN");

end

local function new(hostname, service, conn_type, extra)

	return setmetatable({

		service = service;

		conn_type = conn_type or "tcp";

		extra = extra;

	}, resolver_mt);

end

return {

	new = new;

};