run

function move_dir( direction )
 local dir_char = direction:sub(1,1)
 if dir_char == "f" or dir_char == "" then
  return turtle.forward()
 elseif dir_char == "b" then
  return turtle.back()
 elseif dir_char == "u" then
  return turtle.up()
 elseif dir_char == "d" then
  return turtle.down()
 else
  print( "Invalid direction: "..direction )
  return false
 end
end

function move( direction )
 if not move_dir( direction ) then
  if turtle.getFuelLevel() == 0 then
   print( "Out of Fuel." )
   turtle.select( fuel_slot )
   if not turtle.refuel( 1 ) then
    print( "Cannot refuel." )
    print( "Waiting for fuel to continue." )
    while not turtle.refuel( 1 ) do
     sleep( 1 )
    end
   end
   print( "Refueled." )
   return move( direction )
  else
   print( "Path obstructed." )
   print( "Waiting to move." )
   while not move_dir( direction ) do
    sleep( 1 )
   end
  end
 end
 return true
end

fuel_slot = 1
log_slot = 2
sapling_slot = 3
break_slot = 4

turtle.select( sapling_slot )
turtle.suck()
turtle.select( 5 )
turtle.drop()
turtle.turnLeft()
turtle.select( 1 )

do_grid_loop = true
while do_grid_loop do

 do_row_loop = true
 while do_row_loop do

  if turtle.detect() then

   print( "Object found." )

   turtle.dig()
   move( "f" )

   turtle.select( log_slot )
   if turtle.compareUp() then

    print( "Tree found." )
    print( "Cutting down." )

    while turtle.compareUp() do
     turtle.digUp()
     move( "u" )
     turtle.select( log_slot )
    end

    while not turtle.detectDown() do
     move( "d" )
    end

   end

  else

   print( "Nothing found." )
   print( "Skipping." )

   move( "f" )

  end

  move( "f" )
  print( "Replanting sapling." )

  turtle.turnRight()
  turtle.turnRight()

  turtle.select( sapling_slot )
  turtle.place()

  turtle.turnRight()
  turtle.turnRight()

  print( "Advancing to either break loop or block." )
  turtle.select( break_slot )

  while ( not turtle.compareDown() ) and ( not turtle.detect() ) do
   move( "f" )
   turtle.select( break_slot )
  end

  if turtle.compareDown() then
   do_row_loop = false
  end
 end

 print( "Break loop found." )
 print( "Returning to start next row." )

 turtle.turnLeft()
 move( "f" )

 while not turtle.compareDown() do
  move( "f" )
  turtle.select( break_slot )
 end

 turtle.turnLeft()
 move( "f" )
 turtle.select( break_slot )

 while not turtle.compareDown() do
  move( "f" )
  turtle.select( break_slot )
 end

 turtle.turnRight()
 if turtle.detect() then
  do_grid_loop = false
 else

  move( "f" )
  turtle.select( break_slot )

  while ( not turtle.compareDown() ) or turtle.detect() do
   move( "f" )
   turtle.select( break_slot )
  end

  print( "Checking for next row." )

  if turtle.detect() then
   do_grid_loop = false
  end

 end

 turtle.turnRight()
end

print( "End of grid." )
print( "Returning to start/chest." )

turtle.turnRight()

while not turtle.detect() do
 move( "f" )
end

turtle.turnRight()

print( "Unloading chest." )

for slot = 1, 16, 1 do
 if slot ~= fuel_slot and slot ~= log_slot and slot ~= sapling_slot and slot ~= break_slot then
  turtle.select( slot )
  turtle.drop()
 elseif slot == log_slot then
  turtle.select( slot )
  turtle.drop( turtle.getItemCount( slot ) - 1 )
 end
end

turtle.turnLeft()

print( "Complete!" )