tree_harvest.lua

local GRID_X = 10
local GRID_Y = 10

local COMPARE_SLOT = 1
local FUEL_SLOT = 2
local SAPLING_SLOT = 3

local x_pos = 0
local y_pos = -1


local function force_move(num)
  print("Force moving ", num, " blocks")
  local i = 0
  while i < num do
    if turtle.detect() then
      turtle.dig()
    end
    local res = turtle.forward()
    if res then
      i = i + 1
    end
  end
end


local function move_to_column(column_num)
  local to_move = math.abs(column_num - x_pos)

  print("Moving ", to_move, " columns over")

  if column_num < x_pos then
    turtle.turnLeft()
    force_move(to_move)
    x_pos = x_pos - to_move
    turtle.turnRight()

  elseif column_num > x_pos then
    turtle.turnRight()
    force_move(to_move)
    x_pos = x_pos + to_move
    turtle.turnLeft()
  end
end


local function restock()
  move_to_column(0)
  -- Drop off everything collected first
  for i=1,16 do
    if((i ~= COMPARE_SLOT) and (i ~= FUEL_SLOT) and (i ~= SAPLING_SLOT)) then
      turtle.select(i)
      turtle.dropDown()
    end
  end

  -- drop off all but one of the comparison items
  turtle.select(COMPARE_SLOT)
  if turtle.getItemCount() > 1 then
    turtle.dropDown(turtle.getItemCount() - 1)
  end

  -- refuel
  turtle.turnRight()
  force_move(1)
  x_pos = x_pos + 1
  turtle.turnLeft()

  turtle.select(FUEL_SLOT)
  local slots_left = turtle.getItemSpace()
  turtle.suckDown(slots_left)
  if turtle.getItemCount() > 1 then
    turtle.refuel(turtle.getItemCount() - 1)
  end

  -- re-sapling
  turtle.turnRight()
  force_move(1)
  x_pos = x_pos + 1
  turtle.turnLeft()

  turtle.select(SAPLING_SLOT)
  slots_left = turtle.getItemSpace()
  turtle.suckDown(slots_left)

  turtle.turnLeft()
  force_move(2)
  x_pos = x_pos - 2
  turtle.turnRight()
end


local function place_sapling()
  turtle.select(SAPLING_SLOT)
  if not turtle.compareDown() then
    turtle.digDown()
  end
  turtle.placeDown()
end


local function harvest_move()
  local height_diff = 0
  turtle.select(COMPARE_SLOT)
  if turtle.compare() then
    print("Tree found, harvesting")
    turtle.dig()
    turtle.forward()
    turtle.digDown()
    while turtle.compareUp() do
      turtle.digUp()
      turtle.up()
      height_diff = height_diff + 1
    end
    while height_diff > 0 do
      turtle.digDown()
      local r = turtle.down()
      if r == true then
        height_diff = height_diff - 1
      end
    end

  else
    force_move(1)
  end
  place_sapling()
end


local function harvest_column(column_num)
  -- Harvests a single column of trees. Assumes it is right outside
  -- the grid below the "X axis". Travels to the row, faces it, and
  -- harvests the row
  move_to_column(column_num)
  -- Go down the column and harvest wood
  print("Harvesting down row")
  for y = 0, GRID_Y - 1 do
    harvest_move()
    y_pos = y_pos + 1
  end

  -- Go back the same way, harvest incase any tree grew
  turtle.turnRight()
  turtle.turnRight()
  print("Harvesting back row")
  for y = 0, GRID_Y - 2 do
    harvest_move()
    y_pos = y_pos - 1
  end
  force_move(1)
  y_pos = y_pos - 1

  turtle.turnRight()
  turtle.turnRight()
end


local function start_harvest_grid()
  turtle.select(FUEL_SLOT)
  turtle.refuel(turtle.getItemCount() - 1)
  while true do
    for x=0, GRID_X - 1 do
      print("harvesting column ", x)
      restock()
      harvest_column(x)
    end
  end
end



start_harvest_grid()