local slots = {
  seeds = 1,
  bonemeal = 2,
  fuel = 3
}
local waitTill
waitTill = function(condition, compare, callback)
  if compare == nil then
    compare = true
  end
  while condition() ~= compare do
    if callback then
      callback()
    end
    os.sleep(0.1)
  end
  return true
end
local fuel
fuel = function(amount)
  if amount == nil then
    amount = 100
  end
  local old = 1
  while turtle.getFuelLevel() < amount do
    print('Fuel level to low, put fuel in slot 16')
    turtle.select(slots.fuel)
    turtle.refuel()
    os.sleep(1)
  end
  return turtle.select(old)
end
local forward
forward = function(steps)
  if steps == nil then
    steps = 1
  end
  if steps < 1 then
    return true
  end
  fuel()
  waitTill(turtle.forward, true)
  return forward(steps - 1)
end
local up
up = function(steps)
  if steps == nil then
    steps = 1
  end
  if steps < 1 then
    return true
  end
  fuel()
  waitTill(turtle.up, true)
  return up(steps - 1)
end
local down
down = function(steps)
  if steps == nil then
    steps = 1
  end
  if steps < 1 then
    return true
  end
  fuel()
  waitTill(turtle.down, true)
  return down(steps - 1)
end
local emptyDown
emptyDown = function(first, last)
  if first == nil then
    first = 1
  end
  if last == nil then
    last = 16
  end
  for slot = first, last do
    turtle.select(slot)
    turtle.dropDown()
  end
end
local fertilize
fertilize = function()
  local initial = turtle.getItemCount(slots.bonemeal)
  if initial < 2 then
    return false
  end
  turtle.select(slots.bonemeal)
  turtle.placeDown()
  if initial ~= turtle.getItemCount(slots.bonemeal) then
    fertilize()
  end
  return true
end
turtle.step = function()
  while not fertilize() do
    os.sleep(0.5)
  end
  turtle.select(slots.seeds)
  turtle.digDown()
  return forward()
end
forward()
while turtle.detectDown() do
  step()
end