local location = {0,0,0}
local origin = {0,0,0}
local dir=1
local modX= {0,1,0,-1}
local modZ = {1,0,-1,0}
local max = {144,2,72}
turtle.select(1)

function turnLeft()
  turtle.turnLeft()
  dir = dir - 1
  if dir < 1 then dir = 4 end
end

function turnAround()
  turnLeft()
  turnLeft()
end

function turnRight()
  turtle.turnRight()
  dir = dir + 1
  if dir > 4 then dir = 1 end
end

function addLocStep()
  location[1] = location[1] + modX[dir]
  location[3] = location[3] + modZ[dir]
end

function subLocStep()
  location[1] = location[1] - modX[dir]
  location[3] = location[3] - modZ[dir]
end

function forward()
  local b = turtle.forward()
  if b then
    addLocStep()
    return true
  else
    return false
  end
end

function back()
  local b = turtle.back()
  if b then
    subLocStep()
	return true
  else
    return false
  end
end

function dig()
  c=0
  while turtle.detect() do
    turtle.dig()
	c = c+1
	if c > 10 then
	  sleep(0.1)
	  c=0
	end
  end
end

function digUp()
  while turtle.detectUp() do
    turtle.digUp()
	sleep(0)
  end
end

function digDown()
  while turtle.detectDown() do
    turtle.digDown()
  end
end

function digForward()
  while forward() == false do
    dig()
  end
end

function digBack()
  while back() == false do
    turnAround()
    dig()
	turnAround()
	sleep(0)
  end
end

function turnOriginLeft()
  while dir ~= 4 do
    turnLeft()
  end
end

function turnOriginRight()
  while dir ~= 2 do
    turnLeft()
  end
end

function turnOriginDown()
  while dir ~= 3 do
    turnLeft()
  end
end

function turnOriginUp()
  while dir ~= 1 do
    turnLeft()
  end
end


local input = ""
while input ~= "start" do
  input = read()
  sleep(0)
end

function checkInventory()
  if turtle.getItemCount(9) > 0 then
    return true
  else
    return false
  end
end

function getLocCopy()
  local copy = {}
  for i,n in ipairs(location) do
    copy[i] = n
  end
  return copy
end

function doDropOff(goBack)
  local orgDir = dir
  local orgPos = getLocCopy()
  moveToOrigin()
  turnOriginDown()
  forward()
  forward()
  dropAll()
  moveToOrigin()
  if goBack then
	moveTo(origin[1],orgPos[3])
	moveTo(orgPos[1],orgPos[3])
	while orgDir ~= dir do
		turnLeft()
		sleep(0)
	end
  end
end

function dropAll()
  for i=1,9,1 do
    turtle.select(i)
	if turtle.getItemCount(i) > 0 then
	  turtle.drop()
	end
  end
  turtle.select(1)
end

function moveToOrigin()
  moveTo(origin[1],location[3])
  moveTo(origin[1],origin[3])
end

function turnToX(x)
  if location[1] < x then
    turnOriginRight()
  elseif location[1] > x then
    turnOriginLeft()
  end
end

function turnToZ(z)
  if location[3] < z then
    turnOriginUp()
  elseif location[3] > z then
    turnOriginDown()
  end
end

function moveTo(x,z)
  turnToX(x)
  while location[1] ~= x do
    forward()
	sleep(0)
  end
  turnToZ(z)
  while location[3]~=z do
    forward()
	sleep(0)
  end
end

for x=1,max[1],1 do
  for z=1,max[3],1 do
    if x ~= 1 and z == 1 then
	else
    --print(tostring(x).."/"..tostring(z).."  /// " .. tostring(location[1]) .. "/"..tostring(location[2]).."/"..tostring(location[3]))

    digForward()
	digDown()
	if checkInventory() then
	  doDropOff(true)
	end
	end
  end
  if x < max[1] then
	turnOriginLeft()
	digForward()
	digDown()
	if x % 2 == 1 then
		turnOriginDown()
	else
		turnOriginUp()
	end
  end
  --turnOriginDown()
  --digBack()
end

doDropOff(false)