local adns = require "net.adns";

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

local inet_pton = require "util.net".pton;

local idna_to_ascii = require "util.encodings".idna.to_ascii;

local unpack = table.unpack or unpack; -- luacheck: ignore 113

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 not self.resolver 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));

		end

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

			if self.resolver then

				self.last_error = self.resolver.last_error;

			end

			if ... == nil then

				self.resolver = nil;

				self:next(cb);

			else

				cb(...);

			end

		end);

		return;

	end

	if not self.hostname then

		self.last_error = "hostname failed IDNA";

		cb(nil);

		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, err)

		if not answer and not err then

			-- net.adns returns nil if there are zero records or nxdomain

			answer = {};

		end

		if answer then

			if self.extra and not answer.secure then

				self.extra.use_dane = false;

			elseif answer.bogus then

				self.last_error = "Validation error in SRV lookup";

				ready();

				return;

			end

			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 });

				else

					self.last_error = "zero SRV records found";

				end

				ready();

				return;

			end

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

				self.last_error = "service explicitly unavailable";

				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

		else

			self.last_error = err;

		end

		ready();

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

end

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

	local is_ip = inet_pton(hostname);

	if not is_ip and hostname:sub(1,1) == '[' then

		is_ip = inet_pton(hostname:sub(2,-2));

	end

	if is_ip and extra and extra.default_port then

		return basic.new(hostname, extra.default_port, conn_type, extra);

	end

	return setmetatable({

		hostname = idna_to_ascii(hostname);

		service = service;

		conn_type = conn_type or "tcp";

		extra = extra;

	}, resolver_mt);

end

return {

	new = new;

};