stripmine

local x = 0
local z = 0
local xdir = 0
local zdir = 1

local tryDig

local function forward()
  while not turtle.forward() do
    tryDig()
  end
  x = x + xdir
  z = z + zdir
end

local function turnLeft()
  turtle.turnLeft()
  xdir, zdir = -zdir, xdir
end

local function turnRight()
  turtle.turnRight()
  xdir, zdir = zdir, -xdir
end

local function goTo(xpos, zpos, xface, zface)
  if x < xpos then
    while xdir ~= 1 do
      turnRight()
    end
    while x < xpos do
      forward()
    end
  end
  if x > xpos then
    while xdir ~= -1 do
      turnRight()
    end
    while x > xpos do
      forward()
    end
  end
  if z > zpos then
    while zdir ~= -1 do
      turnRight()
    end
    while z > zpos do
      forward()
    end
  end
  if z < zpos then
    print("z is less than zero. Something is probably wrong!")
    while zdir ~= 1 do
      turnRight()
    end
    while z < zpos do
      forward()
    end
  end
  while xdir ~= xface or zdir ~= zface do
    turnRight()
  end
end

local function collect()
  local prevx, prevz, prevxd, prevzd = x, z, xdir, zdir
  local bUnload = false
  for c=1, 16 do
    select(c)
    if turtle.getItemCount() == 0 then
      bUnload = false
      return
    end
  end
  if bUnload == true then
    goTo(0, 0, 0, -1)
    for c=1, 16 do
         turtle.select(c)
         if turtle.getItemDetail() and turtle.getItemDetail().name == "minecraft:torch" or turtle.refuel(0) then
              break
         end
         turtle.drop()
    end
  goTo(prevx, prevz, prevxd, prevzd)
  end
end

function tryDig()
  while turtle.detect() do
    if turtle.dig() then
      sleep(0.1f)
        -- collect()
    else
      return false
    end
  end
  return true
end

local function tryDigUp()
  while turtle.detectUp() do
    if turtle.digUp() then
      sleep(0.1f)
        -- collect()
    else
      return false
    end
  end
  return true
end

local function tryDigDown()
  while turtle.detectDown() do
    if turtle.digDown() then
      sleep(0.1f)
      collect()
    else
      return false
    end
  end
  return true
end

local function fuelCheck()
  print("Fuel level at "..turtle.getFuelLevel())
  if turtle.getFuelLevel() < 1 then
    for n=1, 16 do
      turtle.select(n)
      if turtle.refuel() then
        turtle.select(1)
        return true
      end
    end
    print("Please Supply Fuel")
    return false
  end
  return true
end

local function refuel()
  while not fuelCheck() do
    os.pullEvent("turtle_inventory")
  end
end

local function dig()
  refuel()
  while not forward() do
    if turtle.detect() then
      tryDig()
      print("trydig loop!")
    end
  end
end

local function digUp()
  refuel()
  while not turtle.up() do
    if turtle.detectUp() then
      tryDigUp()
    end
  end
end

local function platform()
  for a=1, 16 do
    turtle.select(a)
    if turtle.getItemDetail() and turtle.getItemDetail().name == "minecraft:cobblestone" then
      turtle.placeDown()
      turtle.select(1)
      break
    end
  end
end

local function tunnel()
  print("Beginning tunnel!")
  for a=1, 32 do
    dig()
    platform()
    tryDigUp()
  end
end

local function returnTunnel()
  print("Ending tunnel!")
  local blockCount = 0
  for a=1, 32 do
    refuel()
    while not forward() do
      tryDig()
    end
    blockCount = blockCount + 1
    if blockCount == 8 then
      for a=1, 16 do
        turtle.select(a)
        if turtle.getItemDetail() and turtle.getItemDetail().name == "minecraft:torch" then
          if turtle.getItemCount() > 1 then
            blockCount = 0
            turnLeft()
            turnLeft()
            turtle.place()
            turnLeft()
            turnLeft()
            turtle.select(1)
            break
          end
        end
      end
    end
  end
end

for n=1, 16 do
  tryDigUp()
  turnLeft()
  tunnel()
  turnRight()
  turnRight()
  returnTunnel()
  tunnel()
  turnLeft()
  turnLeft()
  returnTunnel()
  turnRight()
  for a=1, 3 do
    dig()
    tryDigUp()
  end
end