FLOOR = 1

function rednet_or_redstone(protocol_filter, timeout)
  -- The parameters used to be ( nTimeout ), detect this case for backwards compatibility
  if type(protocol_filter) == "number" and timeout == nil then
      protocol_filter, timeout = nil, protocol_filter
  end
  expect(1, protocol_filter, "string", "nil")
  expect(2, timeout, "number", "nil")

  -- Start the timer
  local timer = nil
  if timeout then
      timer = os.startTimer(timeout)
  end

  -- Wait for events
  while true do
      local event, p1, p2, p3 = os.pullEvent()
      if event == "rednet_message" then
          -- Return the first matching rednet_message
          local sender_id, message, protocol = p1, p2, p3
          if protocol_filter == nil or protocol == protocol_filter then
              return "rednet_message", sender_id, message, protocol
          end
      elseif event == "timer" then
          -- Return nil if we timeout
          if p1 == timer then
              return nil
          end
      elseif event == "redstone" then
          return "redstone"
      end
  end
end

local monitor = peripheral.find("monitor")

monitor.setBackgroundColor(colors.white)
monitor.setTextColor(colors.black)
monitor.setTextScale(5)
monitor.clear()

function display_floor(floor)
  monitor.clear()
  monitor.setCursorPos(1, 1)
  monitor.write(floor)
end

peripheral.find("modem", rednet.open)

while true do
  local type, id, message = rednet_or_redstone()

  if type == "redstone" then
    if redstone.getInput("back") then
      local data = {
        event = "arrived",
        floor = FLOOR
      }

      rednet.broadcast(textutils.serialise(data))

      display_floor(FLOOR)
    end
  elseif type == "rednet_message" then
    local data = textutils.unserialise(message)
    local event = data["event"]

    if event == "arrived" then
      local floor = data["floor"]

      display_floor(floor)
    end
  end
end