retreiver

-- Determine functions. variables, tables, etc.
local modem = nil
local channels = {}
local sides = {"front", "back", "left", "right", "top", "bottom"}
local default = 1
local id = tonumber(os.getComputerID())
local label = os.getComputerLabel()
local drive = false
local link = false
local spawn = false
local existance = false
local attempt = 1
local x, y
local function receive(timeout)
  local e, s, sC, rC, m, sD = nil
  local function rnEvent()
    e, s, sC, rC, m, sD = os.pullEvent("modem_message")
    if e ~= nil then returnValue = true end
  end
  parallel.waitForAny(function() sleep(timeout) end, rnEvent)
  if returnValue then return e, s, sC, rC, m, sd end
end

--Determine which side the modem/drive is located
for i=1, #sides do
  if peripheral.getType(sides[i]) == "modem" then
    modemSide = sides[i]
    modem = peripheral.wrap(sides[i])
  elseif peripheral.getType(sides[i]) == "drive" then
    drive = true
  end
end

--prevent script from continuing if errors
assert(label ~= nil, "Please label this computer as the spawner it will control. Ex: Creepers")

--if a drive is present
--copy the main channel
if drive then
  local f = io.open("disk/mobSpawnerChannels", "r")
  if fs.exists("disk/mobSpawnerChannels") then
    channels = textutils.unserialize(f:read("*a"))
  else
    channels = {}
  end

  if channels.main ~= nil then
    default = tonumber(channels.main)
  end

  for k,v in pairs(channels) do
    if tonumber(v) == tonumber(id) then
      existance = true
    end
  end

  if not existance then
    table.insert(channels, id)
  end

  local f = io.open("disk/mobSpawnerChannels", "w")
  f:write(textutils.serialize(channels))
  f:close()
  local f = io.open("mobSpawnerChannels", "w")
  f:write(channels.main)
  f:close()

else
  local f = io.open("mobSpawnerChannels")
  default = tonumber(f:read("*a"))
  f:close()
end

assert(modem ~= nil, "Please attach a wireless modem to any side.")

--Print some debug
  term.clear() term.setCursorPos(1,1)
  print("Spawner type: ".. label)
  print("Modem located on: ".. modemSide)
  print("Link: ".. tostring(link))

--Open channels to receive messages
  print("Opening channel: ".. id)
  modem.open(id)

--Begin loop
while true do

  --Look at spawn values and turn spawner on/off
  local signal = rs.getOutput("bottom")
  if spawn and signal then
    rs.setOutput("bottom", false)
    print("Turning spawner on")
  end
  if not spawn and not signal then
    rs.setOutput("bottom", true)
    print("Turning spawner off")
  end

  --Connect to main comp, if link is not there
  if not link then
    modem.transmit(id, id, "Spawner ".. label)
    spawn = false
    if attempt == 1 then
      x, y = term.getCursorPos()
    else term.setCursorPos(x,y)
    end
    term.clearLine()
    term.write("Attempting to ping main computer.".." Attempt: ".. attempt)
    attempt = attempt + 1
  end

  --receive a ping back or timeout after 10 sec
  local event, side, sChannel, rChannel, message, sDist = receive(5)

  --look at the received message, respond accordingly
  if sChannel == id then
    if message == "loop" then link = true
    elseif message == "true" then spawn = true
    elseif message == "false" then spawn = false
    elseif message == "ping" then link = false
    end
  end


end