Auto refuel for turtles

-automatic refuel function for computercraft
--WIP


--clear screen and math functions
--for convenience
function cls()
 term.clear()
 term.setCursorPos(1,1)
end
function ceil(num)
 return math.ceil(num)
end
 function floor(num)
  return math.floor(num)
 end

 --checks if fueling is possible by
 --comparing the needed amount of items
 --with the amount of fuel in the turtle's
 --inventory
function canrefuel(items_needed)
 local actual_items=0
 for i=1,16 do
  turtle.select(i)
  if turtle.refuel(0) then
   actual_items=actual_items+turtle.getItemCount(i)
  end
 end
 if actual_items>=items_needed then
  return true
 else
  return false
 end
end


 --second refueling function
 --because it would be too confusing
 --to fit into the main function
function refuel_sub(items_needed,moves_needed)
 --for each spot in the inventory do
 for i=1,16 do
  turtle.select(i)
   if items_needed<=64 then
    if turtle.getItemCount(i)>=items_needed then
     --if there are more items than necessary then
     --refuel and return
     turtle.refuel(items_needed)
    else
     --else, subtract the amount of items needed
     --by the amount of items used, refuel
     -- and continue through
     items_needed=items_needed-turtle.getItemCount(i)
     turtle.refuel(items_needed)
    end
   else
    if floor(items_needed/64)>0 then
     items_needed=items_needed-64
     turtle.refuel(64)
    else
     turtle.refuel(items_needed%64)
    end
   end
 end
 if turtle.getFuelLevel()>=moves_needed then
  print("Finished!")
 else
  print("Something went wrong, try again.")
 end
end

--checks if refueling is possible
function refuel(moves_needed,items_needed)
 if canrefuel(items_needed) then
  cls()
  print("Refueling...")
  refuel_sub(items_needed,moves_needed)
 else
  print("Not enough coals, try again")
 end
end

 --Start of the program
cls()
print("Input amount of moves")
local moves_needed = tonumber(io.read())

 --custom prompts depending on the
 --amount of fuel needed
if moves_needed<=turtle.getFuelLevel() then
 print("You already have enough fuel")
else
 local items_needed=ceil((moves_needed-turtle.getFuelLevel())/80)
 local stacks_needed=floor(items_needed/64)
 local stacks_remainder=(items_needed%64)
 local inventory_space=stacks_needed+(stacks_remainder/stacks_remainder)
 if inventory_space<=16 then
  if items_needed==1 then
   print("Ok, put 1 unit of coal in the turtle's inventory")
  elseif items_needed>1 and items_needed<=64 then
   print("Ok, put ",items_needed," units of coals in the turtle's inventory")
  elseif stacks_remainder==0 and stacks_needed==1 then
   print("Ok, put 1 stack of coal in the turtle's inventory")
  elseif  stacks_remainder==1 and stacks_needed==1 then
   print("Ok, put 1 stack of coal and 1 unit of coal in the turtle's inventory")
  elseif stacks_remainder>1 and stacks_needed>1 then
   print("Ok, put ", stacks_needed , " stacks of coal and ", stacks_remainder, " units of coal in the turtle's inventory")
  elseif stacks_remainder>1 and stacks_needed==1 then
   print("Ok, put 1 stack of coal and ",stacks_remainder," units of coal in the turtle's inventory")
  end
 else
   print("There is not enough inventory space, try again")
 end
 print("<press enter to continue>")
 while true do
  local event,key = os.pullEvent("key")
  if key==28 then break end
 end
 refuel(moves_needed,items_needed)
end