local emerald = {}
local path = "/usr/lib/emerald/"

local component = require("component")
local event = require("event")
local fs = require("filesystem")
local ser = require("serialization")
local modem = component.modem

local bPort = 20 -- Broadcast port
local ePort = 21 -- General transmision port

modem.open(bPort)

local localAddress = modem.address
local localAlias = ""
emerald.localAlias = ""
local router = ""

-- LOG FUNCTIONS --
local function log(f, m)
  event.push("emerald", f, m)
end

-- LEN FUNCTION -- (Gives the length of a table)
local function len(table)
  local count = 0
  for _, _ in pairs(table) do
    count = count + 1
  end
  return count
end

-- READ FUNCTION -- (Read the config file)
local function read()
  if fs.exists(path..".eConfig.cfg") then
    local file = io.open(path..".eConfig.cfg")
    local stream = file:read()
    file:close()
    return ser.unserialize(stream)
  else
    log("ERR", "No config file.")
    return "{}"
  end
end

-- WAIT FOR ACK FUNCTION -- (Wait 5 secs for a confirmation after send())
local function wait(expectedFrom)
  local _, _, addr, _, _, flag, from, to = event.pull(5, "modem_message")
  if flag == "ACK" then
    if from == expectedFrom then
      log("LOG", "ACK")
    else
      log("ERR", "Entangled packets. Expected from: "..expectedFrom.." but received from: "..from)
    end
  elseif flag == "PNF" then
    log("ERR", "Pair not found.")
  else
    log("ERR", "Pair seems to have crashed. Disconnecting pair.")
    modem.send(router, ePort, "DISCONNECT", "0", expectedFrom)
  end
end

-- HANDLER FUNCTION -- (Handle all incoming transmissions)
function handler(_, _, addr, _, _, flag, from, to, data)
  if flag == "MSG" then
    log("MSG", data)
    modem.send(router, ePort, "ACK", localAlias, from)
  end
end

-- WHO FUNCTION -- (Tries to discover all nearby routers)
function emerald.who()
  modem.broadcast(bPort, "WHO")
  local doSearch = true
  local routerList = {}
  while doSearch do
    _, _, addr, _, _, flag, alias = event.pull(1, "modem_message")
    if flag == nil then
      doSearch = false
      return routerList
    elseif flag == "WHO" then
      routerList[alias] = addr
    end
  end
  return routerList
end

-- CONNECT FUNCTION -- (Connect to the router)
function emerald.connect()
  if router == "" then
    data = read()
    localAlias = data["hostname"]
    emerald.localAlias = localAlias
    to = data["router"]

    modem.send(to, bPort, "CONNECT", localAddress, localAlias)
    _, _, addr, _, _, flag = event.pull(2, "modem_message")
    if addr == to then
      if flag == "CONNECT" then
        router = addr
        log("LOG", "CONNECT")
        modem.close(bPort)
        modem.open(ePort)
        messageListener = event.listen("modem_message", handler)
      elseif flag == "DPL" then
        log("ERR", flag)
      end
    end
  else
    log("ERR", "Already connected to router.")
  end
end

-- SEND FUNCTION -- (Send a message to another node)
function emerald.send(to, data)
  if router ~= "" then
    modem.send(router, ePort, "MSG", localAlias, to, data)
    wait(to)
  else
    log("ERR", "Not connected to router.")
  end
end

-- DISCONNECT FUNCTION -- (Disconnect from the router)
function emerald.disconnect()
  if router ~= "" then
    modem.send(router, ePort, "DISCONNECT", localAddress, localAlias)
    _, _, addr, _, _, flag = event.pull(2, "modem_message")
    if addr == router then
      if flag == "DISCONNECT" then
        router = ""
        log("LOG", "DISCONNECT")
        modem.close(ePort)
        modem.open(bPort)
      end
    end
  else
    log("ERR", "Not connected to a router.")
  end
end

return emerald