local component = require("component")
local serial = require("serialization")
local event = require("event")
local modem = component.modem
local fs = require("filesystem")
database = {}
local isRunning = false

--- message should be: either {data="ip", msg="REQUEST""} or {"DECLARE <addr> : <ip>"}
--- response will be : request_pass: {data="<addr>",msg="DOMAINNAME FOUND"}
                     --request_fail: {data="", msg="DOMAINNAME NON EXIST"}
                     --declare_pass: {data="true",msg="addr DECLARED <ip>"}
                     --declare_fail: {data="false", msg="UNABLE TO DECLARE ip"}
                     --generic_fail: {data="", msg="MALFORMED REQUEST"}

local function log(text)
	local f = io.open("/tmp/dns.log", "w")
	f:write(text .. "\n")
	f:close()
end

local function add_to_db(domain, addr)
	database[domain] = addr
	local f = io.open('/etc/dns/dns.db', 'w')
	f:write(serial.serialize(database))
	f:close()
end

local function get_dns(domainname)
	addr = database[domainname]

	if addr ~= nil then
		return addr
	end
	return nil,"DOMAINNAME NOT EXIST"
end

local function add_dns(addr, domainname)
	local _, err = get_dns(domainname)
	if err == "DOMAINNAME NOT EXIST" then
		add_to_db(domainname, addr)
		return addr, domainname
	else
		log("unable to declare " .. domainname .. " " .. addr)
		return nil,nil, "UNABLE TO DECLARE"
	end
end

local function handle_dns_request(_, _, from, port, dist, message)
	request = serial.unserialize(message)
	if request.msg == "DECLARE" then
		log(from .. " declares " .. request.data)
		local addr, dns, err = add_dns(from, request.data)
		if err then
			log(from .. " decleration fail")
			modem.send(from, port, serial.serialize({data="", msg="UNABLE TO DECLARE"}))
		else
			log(from .. " decleration success")
			modem.send(from, port, serial.serialize({data=from, msg=from .. " DECLARED " .. dns}))
		end

	elseif request.msg == "RESOLVE" then
		log(from .. " ask for resolve for " .. request.data)
		local addr,err = get_dns(request.data)
		if err ~= nil then
			log(from .. " resolve fail")
			modem.send(from, port, serial.serialize({data="",msg="DOMAINNAME NOT EXIST"}))
		else
			log(from .. " resolve pass")
			modem.send(from, port, serial.serialize({data=addr, msg="DOMAINNAME FOUND"}))
		end
	elseif request.msg == "EXIT" then
		event.ignore("modem_message", handle_dns_request)
	else
		modem.send(from, port, serial.serialize({data="",msg="MALFORMED REQUEST"}))
	end
end

function start()
	print("Starting DNS Service...")
	

	print("Checking config files...")
	if not fs.exists("/etc/dns/") then
		print("creating /etc/dns/")
		fs.makeDirectory("/etc/dns/")
	end
	print("> /etc/dns/dns.db")
	if not fs.exists("/etc/dns/dns.db") then
		print("creating dns.db")
		io.open("/etc/dns/dns.db", "w"):write("{}")
	end

	print("Loading existing DNS entries")
	f = io.open('/etc/dns/dns.db', 'r')
	database = serial.unserialize(f:read("*a"))
	f:close()

	if database ~= nil then
		for k,v in pairs(database) do
			print(k .. " : ".. v)
	end
	else
	    database = {}
	   end
	if not isRunning then
		modem.open(90)
		event.listen("modem_message", handle_dns_request)
		isRunning = true

		-- while true do
		-- 	local _,_,from,port,dist,mesg = event.pull("modem_message")
		-- 	handle_dns_request(_,_,from,port,dist,mesg)
		-- 	os.sleep(0.5)
		-- end
    end
end

function stop()
	print("Stopping DNS Serice...")
	event.ignore("modem_message", handle_dns_request)
	modem.close(90)
end

function status()
	if isRunning then
		status = "running"
	else
		status = "offline"
	end
	print("DNS Service status: " .. status)

end