Tree Farm

local lastTurn = 1 -- direction of last turn (0=left, 1=right)
local size = 11 -- square size of farm
local woodSlot = 16 -- slot comparison wood is kept
local maxStack = 4 -- maximum number of items to keep in slots
local sleepTimer = 300 -- time between farmings in seconds
local x,y,z = gps.locate(5) -- turtle position on startup
local hx,hy,hz = 306, 49, 130 -- turtle home position
local debugMessages = true -- print debug messages
local startTimer = 10 -- seconds to wait on startup before running

--debug print function
function db(mesg)
  if debugMessages then
    print(mesg)
  end
end

--check where home log is and then face south
function checkFacing()
  db("Checking facing")
  turtle.select(woodSlot)
  while not turtle.compare() do
    left()
  end
  db("Home log found")
  left()
end

function goHome()
  db("Going Home")
  x,y,z = gps.locate(5)
  db("hxyz="..hx..","..hy..","..hz)
  db(" xyz="..x..","..y..","..z)
  forward()
  nx,ny,nz = gps.locate(5)
  db("nxyz="..nx..","..ny..","..nz)
  --orient to west
  if nx > x then
    db("Looking east")
    left()
    left()
  elseif nz > z then
    db("Looking south")
    right()
  elseif nz < z then
    db("Looking north")
    left()
  end
  --go to home y level
  db("Going up")
  for i=1,hy-ny do
    up()
  end
  --go to home x position
  for i=1,nx-hx do
    forward()
  end
  right() --orient to north
  --go to home z position
  for i=1,nz-hz do
    forward()
  end
  --verify is home
  checkFacing()
end

function upperLayer()
  db("Running upperLayer")
  for i=1,size do
    for j=1,size-1 do
      forward()
      dig()
    end
    if i < size then
      gimbal()
    end
  end
  left()
  left()
  nextLayer()
end

function bottomLayer()
  db("Running bottomLayer")
  for i=1,size do
    for j=1,size-1 do
      forward()
      turtle.digUp()
      if turtle.compareDown() then
        plantSapling()
      end
    end
    if i < size then
      gimbal()
    end
  end
  dropExtras()
  --[[for i=1,6 do
    up()
  end
  right()
  for i=1,size-1 do
    forward()
    right()
    forward()
    left()
  end
  left()
  lastTurn = 1 ]]
  goHome()
end

-- turns the proper direction for next row
function gimbal()
  --db("Gimbaling")
  if lastTurn == 0 then
    right()
    forward()
    dig()
    right()
  else
    left()
    forward()
    dig()
    left()
  end
  lastTurn = math.abs(lastTurn-1)
  --db("Set lastTurn to "..lastTurn)
end

-- breaks the block below and places a random sapling
function plantSapling()
  db("Planting sapling")
  turtle.digDown()
  turtle.select(math.random(1,15))
  while turtle.placeDown() == false do
    turtle.select(math.random(1,15))
  end
  turtle.select(woodSlot)
end

-- drops excess inventory
function dropExtras()
  db("dropping excess inventory")
  for i=1,16 do
    turtle.select(i)
    while turtle.getItemCount(i) > maxStack do
      turtle.dropDown(math.ceil(maxStack/4))
    end
  end
end

function nextLayer()
  db("Going down to next layer")
  for i=1,3 do
    down()
  end
end

function forward()
  turtle.dig()
  turtle.forward()
end

function down()
  turtle.digDown()
  turtle.down()
end

function up()
  turtle.digUp()
  turtle.up()
end

function dig()
  turtle.digUp()
  turtle.digDown()
end

function right()
  turtle.turnRight()
end

function left()
  turtle.turnLeft()
end

-- main program
db("Waiting "..startTimer.." seconds to start")
for i=startTimer,1,-1 do
  sleep(1)
  db(i)
end
-- checks if in home position then checks facing or goes home
if x==hx and y==hy and z==hz then
  checkFacing()
else
  goHome()
end
while true do
  print("Fuel level: "..turtle.getFuelLevel())
  turtle.select(woodSlot)
  for i=1,2 do
    upperLayer()
  end
  bottomLayer()
  db("Sleeping for "..sleepTimer.."s")
  for i=math.ceil(sleepTimer/30),1,-1 do
    db(i*30)
    sleep(30)
  end
end