-- DNS System for computercraft
--
-- The DNS System always listens on channel 0 and answers on channel 1.
--
-- PUT:
--
-- A programm can register itself by sending a "put" message to the DNS System
-- A "put" message has the following form:
-- {
--  type = "put",
--  name = "PUT_NAME_HERE"
-- }
--
-- This message will associate the channel the message was send on, with the
-- given name.
--
-- If a name was already given, it will be overwritten.
--
-- GET:
--
-- A programm can query the DNS for the channel of a programm.
-- A "get" message has the following form:
-- {
--  type = "get"
--  name = "PUT_NAME_HERE"
-- }
--
-- The System will send message of this form back:
--
-- {
--  type = "dns_response",
--  channel = NUM,
--  name = "SAME_NAME"
-- }
--
-- If no programm has previously associated the name with a channel, then
-- channel will be nil.
--
-- Reponse messages will be received by all clients listening on port 1.
-- A client should wait until a response message containing its own name
-- arrives.
--
local side_modem = "left"
local modem = nil
local query_channel = 0
local response_channel = 1

local db = {}
local next_channel = 2

local function run()
    modem = peripheral.wrap(side_modem)
    modem.open(query_channel)

    while true do
        a, b, c, msg, d = os.pullEvent("modem_message")

        print(a)
        print(b)
        print(c)
        print(msg)
        print(d)

        if msg.type == "get" then
            modem.transmit(response_channel, modem_channel, {type = "get", channel = db[msg.name]})
        elseif msg.type == "put" then
            db[msg.name] = next_channel
            next_channel = next_channel + 1
            modem.transmit(response_channel, modem_channel, {type = "put", channel = db[msg.name], name = msg.name})
        end
    end
end

run()