Elevator client program

floor = 11
rednet.open("back")
serverID = 78
floortable = {[1]="2", [2]="1", [3]="0", [4]="-1", [5]="-2", [6]="-3", [7]="-4", [8]="-5", [9]="-6", [10]="-7", [11]="-8"}
banana = true

function gui()
 local w,h = term.getSize()
 local function printCentered(str, ypos)
  term.setCursorPos(w/2 - #str/2, ypos)
  term.write(str)
 end
 local function printRight(str, ypos)
  term.setCursorPos(w - #str, ypos)
  term.write(str)
 end

 function drawHeader()
  printCentered("ELEVATOR CONTROL", 1)
  printCentered(string.rep("-", w), 2)
  term.setCursorPos(1, 3)
  term.write("Current floor:   ")
  term.write(floor)
 end

 function drawMain()
  term.setCursorPos(1,4)
  term.write("|  2 : balcony")
  term.setCursorPos(1,5)
  term.write("|  1 : 1st floor")
  term.setCursorPos(1,6)
  term.write("|  0 : lobby")
  term.setCursorPos(1,7)
  term.write("| -1: ")
  term.setCursorPos(1,8)
  term.write("| -2: ")
  term.setCursorPos(1,9)
  term.write("| -3: ")
  term.setCursorPos(26,4)
  term.write("| -4: ")
  term.setCursorPos(26,5)
  term.write("| -5: Train station")
  term.setCursorPos(26,6)
  term.write("| -6: ")
  term.setCursorPos(26,7)
  term.write("| -7: ")
  term.setCursorPos(26,8)
  term.write("| -8: ")

 term.setCursorPos(4,11)
 term.write("Please enter destination floor: ")
 end
 drawHeader()
 drawMain()
 term.setCursorPos(42,11)
end

function listen()
 while true do
  local sendID, obj, distance = rednet.receive()
  if sendID == serverID then
   if obj >= floor then
    rs.setOutput("bottom", true)
   else
    rs.setOutput("bottom", false)
   end
  end
 end
end

function call()
 while true do
  if rs.getInput("left") == true then
   rednet.send(serverID, "call")
  end
 end
end

function input()
 while true do
  local input = read()
  if input == "quit" then
   banana = false
   shell.quit()
  end
  for k,v in pairs(floortable) do
   if v == input then
    rednet.send(serverID, k)
   else
    term.setCursorPos(4,12)
    term.write("Invalid floor number")
   end
  end
 end
end

function finish()
 if rs.getInput("right") == true then
  shell.exit()
 end
end

while banana == true do
 gui()
 parallel.waitForAny(listen, call, input, finish)
end