Detector

local P = peripheral.find("modem")
if P == nil then
  error("There is no router on this PC!")
end
print("Got the modem!")
P.open(15)
Whitelist = {"Famous5000"}
if fs.exists("Whitelist") then
  Whitelist = io.open("Whitelist","r")
  Whitelist = Whitelist:read()
  local W = {}
  for I = 1,#Whitelist do
    W = Whitelist[I]
  end
  Whitelist = W
end
while true do
  local _,_,Channel,_,Message = os.pullEvent("modem_message")
  if type(Message) == "table" then
    sleep(0.1)
    local Plr = Message[1]
    INVALID = false
    if Plr ~= "Famous5000" then
      INVALID = true
      for I = 1,#Whitelist do
        if Plr == Whitelist[I] then
          INVALID = false
        end
      end
      if INVALID == true then
        term.setTextColor(colors.red)
        print("A blocked attempt to access this system from "..Plr)
        term.setTextColor(colors.white)
      end
    end
    local Msg = Message[2]
    if INVALID == false then
      if Msg:lower() == "open" then
        redstone.setAnalogOutput("top",15)
        sleep(2)
        redstone.setAnalogOutput("top",0)
      end
      if Msg:lower() == "shutdown" then
        break
      end
      if Msg:lower():sub(0,3) == "add" then
        local P = Msg:sub(5)
        local C = 0
        for I = 1,#Whitelist do
          C = I + 1
        end
        C = tonumber(C)
        Whitelist[1] = P
      end
      if Msg:lower():sub(0,3) == "rem" then
        local P = Msg:sub(5)
        if P == "clr" then
          Whitelist = {"Famous5000"}
        else
          for I = 1,#Whitelist do
            if Whitelist[I]:lower():match(P:lower()) then
              table.remove(Whitelist,I)
            end
          end
        end
      end
      print("Recieved message from "..Plr)
    end
  end
end
local W = fs.open("Whitelist","w")
print("I have been told to shut down. Rebooting...")
sleep(3)
if W then
  for n,T in ipairs(Whitelist) do
    W.write(T.."\n")
  end
  W.close()
else
  print("Access denied. Please fix this")
end
sleep(10)
if not fs.exists("startup") then
  local R = fs.open("startup","w")
  Lines = {"shell.run(\"Detector\")",
  "os.reboot()"}
  if R then
    for n,T in ipairs(Lines) do
      R.write(T.."\n")
    end
  end
  R.close()
  os.reboot()
end