platform

local blocks = turtle.getItemCount(2)

for slot=3,16 do
  if turtle.compareTo(2) then
    blocks = blocks + turtle.getItemCount(slot)
  end
end

size = math.floor(math.sqrt(blocks))
sizeStr = tostring(size)
print("Making a " .. sizeStr .. "x" .. sizeStr .. " platform")

function prevBlockSlot(curSlot)
  for slot=curSlot,2,-1 do
    turtle.select(slot)
    if turtle.compareTo(2) then
      return slot
    end
  end
end

function forward(curSlot)
  if turtle.getFuelLevel() < 1 then
    select(1)
    turtle.refuel(1)
    turtle.select(curSlot)
  end
  for i=1,10 do
    if turtle.detect() then
      turtle.dig()
    end
    if turtle.forward() then
      return true
    end
  end

  return nil
end

function placeDown(curSlot)
  if not turtle.compareTo(2) then
    curSlot = prevBlockSlot(curSlot)
  end
  turtle.placeDown()
  return curSlot
end

local curSlot = prevBlockSlot(16)

for row=1,size do
  for i=1,size-1 do
    curSlot = placeDown(curSlot)
    if not forward(curSlot) then
      print("Error: block in the way")
      return
    end
  end
  curSlot = placeDown(curSlot)
  if row%2 == 1 then
    turtle.turnRight()
    if not forward(curSlot) then
      print("Error: block in the way")
      return
    end
    turtle.turnRight()
  else
    turtle.turnLeft()
    if not forward(curSlot) then
      print("Error: block in the way")
      return
    end
    turtle.turnLeft()
  end
end