local saplings = 1 -- the slot where the saplings are
local log = 2
local fuel = 3

function getSaplings(slot)
    turtle.select(slot)
    local need = 64 - turtle.getItemCount()
    if (need >= 20) then
        turtle.turnRight()
        turtle.turnRight()
        turtle.forward()
        turtle.forward()
        turtle.forward()
        turtle.turnRight()
        turtle.forward()
        turtle.forward()
        turtle.suck(need)
        turtle.turnRight()
        turtle.turnRight()
        turtle.forward()
        turtle.forward()
        turtle.turnLeft()
        turtle.forward()
        turtle.forward()
        turtle.forward()
    end
end

function getFuel(slot)
    turtle.select(slot)
    local need = 64 - turtle.getItemCount()
    print("Need ",need," more fuel")
    if (need >= 20) then
        turtle.turnRight()
        turtle.turnRight()
        turtle.forward()
        turtle.forward()
        turtle.turnRight()
        turtle.forward()
        turtle.forward()
        turtle.suck(need)
        turtle.turnRight()
        turtle.turnRight()
        turtle.forward()
        turtle.forward()
        turtle.turnLeft()
        turtle.forward()
        turtle.forward()
    end
end

while turtle.getItemCount(saplings) > 0 do -- while more saplings in inventory
    if turtle.getFuelLevel() < 30 then
        turtle.select(fuel)
        turtle.refuel(2)
    end
    getFuel(fuel)
	for i = 1, 7 do -- plant 8 saplings in a row
        turtle.turnLeft()
        turtle.select(log)
        if turtle.compare() then
            turtle.dig()
        end
        turtle.select(saplings)
        turtle.place()
        turtle.turnRight()
        turtle.forward()
	end
	-- turn around and line up for next pass
    turtle.turnRight()
    turtle.turnRight()
    for i = 1, 7 do
        turtle.forward()
    end
    turtle.turnRight()
    turtle.turnRight()
    getSaplings(saplings)
	sleep(30) -- sleep for 30 seconds to allow trees to grow
end