Feller Turtle

local function getFuel()
  if turtle.getFuelLevel() < 16 then
    while true do
      if turtle.getItemCount(16) > 0 then
        break
      else
        turtle.select(16)
        print("Fuel needed in slot 16")
        local events = {os.pullEvent()}
        if events[1] == "key" and events[2] == 28 then
          turtle.refuel()
          getFuel()
        end
      end
    end
  end
end

local function forward(dist)
  if not dist then dist = 1 end
  for i = 1, dist do
    getFuel()
    if not turtle.forward() then
      turtle.dig()
      turtle.forward()
    end
  end
end

local function back(dist)
  if not dist then dist = 1 end
  for i = 1, dist do
    getFuel()
    if not turtle.back() then
      turtle.turnRight()
      turtle.turnRight()
      turtle.dig()
      turtle.turnRight()
      turtle.turnRight()
    end
  end
end

function down(dist)
  if not dist then dist = 1 end
  for i = 1, dist do
    getFuel()
    if not turtle.down() then
      turtle.digDown()
      turtle.down()
    end
  end
end

function up(dist)
  getFuel()
  if not dist then dist = 1 end
  for i = 1,dist do
    if not turtle.up() then
      turtle.digUp()
      turtle.up()
    end
  end
end

local function plant()
  if turtle.getItemCount(1) >= 1 then
    turtle.select(1)
    turtle.forward()
    turtle.placeDown()
    turtle.back()
  else
    while true do
      print("Out of Saplings")
      print("Please place desired saplings in slot 1")
      local events = {os.pullEvent()}
      if events[1] == "key" and events[2] == 28 then
        if turtle.getItemCount(1) > 0 then
          turtle.select(1)
          turtle.forward()
          turtle.placeDown()
          turtle.back()
          break
        end
      end
    end
  end
end

local function fell()
  local height = 0
  forward()
  turtle.digDown()
  while turtle.detectUp() do
    up()
    for i = 1,4 do
      local branch = 0
      local bBranch = 0
      while turtle.detect() do
        forward()
        turtle.turnLeft()
        while turtle.detect() do
          forward()
          bBranch = bBranch + 1
        end
        if bBranch ~= 0 then
          repeat
            back()
            bBranch = bBranch - 1
          until bBranch == 0
        end
        turtle.turnRight()
        branch = branch + 1
      end
      if branch ~= 0 then
        repeat
          back()
          branch = branch - 1
        until branch == 0
      end
      turtle.turnLeft()
    end
    height = height + 1
  end
  repeat
    down()
    height = height - 1
  until height == 0
  back()
end

local trees = 0
while true do
  print("Fuel level: "..turtle.getFuelLevel())
  print("Planting")
  plant()
  print("Using redstone signal to grow sapling")
  turtle.turnRight()
  forward()
  down()
  rs.setOutput("back", true)
  sleep(1)
  rs.setOutput("back", false)
  up()
  back()
  turtle.turnLeft()
  print("Cutting down tree")
  fell()
  trees = trees + 1
  print("Cut down "..trees.." trees")
end