chop

function chopTree()
  turtle.dig()
  turtle.forward()
  turtle.digDown()
  turtle.select(2)
  while turtle.compareUp() do
    turtle.digUp()
    turtle.up()
  end
  while turtle.detectDown() == false do
    turtle.down()
  end
end

function clearInv()
  for i = 2, 16 do
    turtle.select(i)
    turtle.dropDown()
  end
end

function checkLeft()
  turtle.turnLeft()
  if turtle.detect() then
    chopTree()
    turtle.up()
    turtle.select(1)
    turtle.placeDown()
    turtle.back()
  end
  turtle.turnRight()
end

turtle.select(1)
while true do
  turtle.forward()
  turtle.forward()
  turtle.forward()
  checkLeft()
  if turtle.detectDown() then
    if turtle.getFuelLevel() < 100 then
      turtle.select(2)
      turtle.refuel()
    end
    clearInv()
    turtle.select(1)
    turtle.turnRight()
    turtle.forward()
    turtle.turnRight()
    checkLeft()
  end
end