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 --[[
 
   Rectangular Quarry Program 1.2b
   by Adam Smith "shiphorns"
   March 7 2013
 
   1.0b -	Original public release
   1.1b -	Fixes bug with turtle using the wrong axis order when trying to return home after hitting
 			and undiggable block. I erroneously had it trying to do moveTo(0,0,0) instead of goHome()
 			which would result in the turtle trying to move in the x-direction first, and possibly
 			getting blocked by bedrock when trying to move home.
   1.2b -    Fix for turtle getting stuck if turtle simultaneous encounters bedrock in front and above it.
 
 --]]
 local tArgs = { ... }
 local sizeZ -- Quarry is this long in direction turtle is initially facing, including block turtle is on
 local sizeX -- Quarry is this wide to the right of where turtle is facing, including block turtle is on
 local sizeY -- Quarry removes this many layers of blocks including layer where turtle starts
 local bDebug= false
 
 local goUnload	-- Forward declaration
 
 if (#tArgs == 1) then
 	sizeZ,sizeX,sizeY = tonumber(tArgs[1]),tonumber(tArgs[1]),256
 elseif (#tArgs == 2) then
 	sizeZ,sizeX,sizeY = tonumber(tArgs[1]),tonumber(tArgs[2]),256
 elseif (#tArgs >= 3) then
 	sizeZ,sizeX,sizeY = tonumber(tArgs[1]),tonumber(tArgs[2]),tonumber(tArgs[3])
 	if (#tArgs > 3) then
 		bDebug = (tonumber(tArgs[4])==1)
 	end
 else
 	print( "Usage: quarry <sq. size> <optional width > <optional fixed depth> <optional 1 for debug mode>" )
 	return
 end
 
 -- Validate dimensions
 if (sizeX<2 or sizeZ<2 or sizeY<1) then
   print( "Dimensions given must be at least 2L x 2W x 1D. Efficiency is optimal if fixed depth is a multiple of 3." )
   return
 end
 
 local minFuel = math.ceil((math.ceil(sizeY/3)*(sizeX*sizeY)+(2*sizeY))/1200)
 local maxFuel = "TBD"
 
 print("Place fuel reserves in slot 1 (upper left) if desired and hit any key to start.")
 os.pullEvent("key")
 
 local tX,tZ,tY = 0,0,0    -- Place the turtle starts is considered block 0,0,0 in the turtle's local coordinate system
 local xDir,zDir = 0,1     -- Turtle is considered as initially facing positive z direction, regardless of global world facing direction
 local refuelSlot = 1      -- Turtle can fuel from any slot, but it will never dump this slot's contents so this is where fuel should be placed
 
 -- Notice that all coordinates formated as 0,0,0 are in X,Z,Y order, NOT alphabetical X,Y,Z order, where Y is up/down axis
 -- Y axis is always the minecraft world Y-axis, but X and Z in this turtle's local coordinate system won't necessarily match his
 -- orientation in the global world system (turtle's system is relative to how he is initially facing, +Z is his facing direction)
 
 local function checkFuel(bMovingAwayFromOrigin)
 	if bDebug then print("checkFuel()") end
 	-- This function returns true only if there is enough fuel left to move 1 block in any direction,
 	-- and still have enough left over for a return trip to 0,0,0 that might be needed for refuel or at
 	-- the end of the quarrying. This ensures the turtle is never stranded in the quarry.
 	local fuelLevel = turtle.getFuelLevel()
 
 	if (fuelLevel == "unlimited") then
 		-- Server has fuel requirement turned off in configs
 		return true
 	end
 
 	-- If the turtle is attempting to move away from its starting location, it is going to
 	-- consume the normal 1 fuel cost to move, but it will also add +1 to the cost of the
 	-- trip to return home to dump/refuel/finish. If we know the turtle is moving closer to
 	-- home, there is no extra cost since it is effectively part of the return trip.
 	local fuelNeeded = math.abs(tX)+math.abs(tY)+math.abs(tZ)
 	if (bMovingAwayFromOrigin == nil or bMovingAwayFromOrigin == true) then
 		-- Turtle is moving away from 0,0,0 or direction is unspecified (assume worst case), add 2 fuel
 		fuelNeeded = fuelNeeded + 2
 	end
 
 	if (fuelLevel >= fuelNeeded) then
 		-- Turtle has enough fuel to do the next 1-block movement, plus enough to
 		-- return home from there.
 		return true
 	end
 
 	-- If we get here, turtle does not have enough fuel for the move plus a return to base
 	-- First we will try to refuel from anything we find in the turtle's inventory. Failing that
 	-- We will return to home and prompt the user to add fuel
 
 	local slot = 1
 	turtle.select(slot)
 
 	if bDebug then print("Entering while true do in checkFuel") end
 	while true do
 		if turtle.refuel(1) then
 			-- Found fuel in current slot, consume 1, see if it's enough, if not loop again
 			if (turtle.getFuelLevel()>=fuelNeeded) then
 				print("Refueled from inventory, resuming quarrying...")
 				return true
 			end
 		else
 			-- Couldn't refuel from currently-selected slot, try next slot. If there are no more slots, ask for player help.
 			if (slot < 16) then
 				slot = slot + 1
 				turtle.select(slot)
 			else
 				-- There are no more slots to look in, reset selection so that we're ready to loop over all slots again, and so that the
 				-- player sees slot 1 highlighted (fastest for turtle to find fuel in). Return to 0,0,0 if we can (in case turtle is
 				-- under lava or otherwise inaccessible), prompt player to add fuel.
 
 				return goUnload(true)
 			end
 		end
 	end
 end
 
 local function turnLeft()
   turtle.turnLeft()
   xDir,zDir = -zDir,xDir
   return true
 end
 
 local function turnRight()
   turtle.turnRight()
   xDir,zDir = zDir,-xDir
   return true
 end
 
 local function goForward(bCheckFuel)
 	if bDebug then print("goForward()") end
 	-- Can't move without fuel. checkFuel() will wait on player if necessary.
 	if (bCheckFuel==true or bCheckFuel==nil) then
     checkFuel((xDir>0 and tX>=0) or (xDir<0 and tX<=0) or (zDir>0 and tZ>=0) or (zDir<0 and tZ<=0))	-- Passes boolean true if moving away from 0,0,0
   end
 
 	local tries = 3
 	while not turtle.forward() do
 		if bDebug then print("goForward: while not turtle.forward() do tries="..tries) end
 		if turtle.detect() then
 			if bDebug then print("goForward: detect") end
 			if not turtle.dig() then
 				print("Undiggable block encountered. Will retry in 5 seconds.")
 				-- Turtle is blocked. In case this is a temporary glitch, we try 3 times before conceding hard failure
 				tries = tries - 1
 				if (tries <= 0) then
 				  return false
 				else
 					if bDebug then print("goForward: sleep(5)") end
 					sleep(5) -- Wait 5 seconds, hope the problem resolves itself
 				end
 			end
 		elseif turtle.attack() then
 			if bDebug then print("goForward: attack") end
 			-- Had to attack player or mob. You can add additional code here such
 			-- as turtle.suck() if you want to collect killed mob loot. This is a quarry program
 			-- to collect ores, not rotten flesh and bones, so this block is empty.
 		else
 			-- Unknown obstruction, possibly a player in
 			-- peaceful or creative mode. Try again in 0.5 seconds and hope it's gone.
 			if bDebug then
 				print("goForward: sleep(0.5) else block")
 				print("Turtle fuel="..turtle.getFuelLevel())
 			end
 			sleep(0.5)
 		end
 	end
 
 	tX = tX + xDir  -- If we're moving in the xDir, this will change tX by + or - 1
 	tZ = tZ + zDir  -- If we're moving in the zDir, this will change tZ by + or - 1
 
 	return true -- Turtle moved successfully
 end
 
 local function goDown(bCheckFuel)
 	if bDebug then print("goDown()") end
 	-- Can't move without fuel. checkFuel() will wait on player if necessary.
 	if (bCheckFuel==true or bCheckFuel==nil) then
     checkFuel(tY<=0)	-- Passes boolean true if moving away from 0,0,0
   end
 
   local tries = 3
 	while not turtle.down() do
 		if bDebug then print("goDown: while not turtle.down() do tries="..tries) end
 		if turtle.detectDown() then
 			if bDebug then print("goDown: detectDown") end
 			if not turtle.digDown() then
 				print("Undiggable block encountered. Will retry in 5 seconds")
 				-- Turtle is blocked. In case this is a temporary glitch, we try 3 times before conceding hard failure
 				tries = tries - 1
 				if (tries <= 0) then
 				  return false
 				else
 					if bDebug then print("goDown: sleep(5)") end
 				  sleep(5) -- Wait 5 seconds, hope the problem resolves itself
 				end
 			end
 		elseif turtle.attackDown() then
 			if bDebug then print("goDown: attack") end
 			-- Had to attack player or mob. You can add additional code here such
 			-- as turtle.suck() if you want to collect killed mob loot. This is a quarry program
 			-- to collect ores, not rotten flesh and bones, so this block is empty.
 		else
 			-- Unknown obstruction, possibly a player in
 			-- peaceful or creative mode. Try again in 0.5 seconds and hope it's gone.
 			if bDebug then print("goDown: sleep(0.5)") end
 			sleep(0.5)
 		end
 	end
 
 	tY = tY - 1
 	return true -- Turtle moved successfully
 end
 
 local function goUp(bCheckFuel)
 	if bDebug then print("goUp()") end
 
   -- Can't move without fuel. checkFuel() will wait on player if necessary.
   if (bCheckFuel==true or bCheckFuel==nil) then
     checkFuel(tY>=0)	-- Passes boolean true if moving away from 0,0,0
   end
 
   local tries = 3
 	while not turtle.up() do
 		if bDebug then print("goUp: while not loop tries="..tries) end
 		if turtle.detectUp() then
 			if bDebug then print("goUp: detectUp") end
 			  if not turtle.digUp() then
 						print("Undiggable block encountered. Will retry in 5 seconds.")
 						-- Turtle is blocked. In case this is a temporary glitch, we try 3 times before conceding hard failure
 				tries = tries - 1
 				if (tries <= 0) then
 				  return false
 				else
 				  sleep(10) -- Wait 10 seconds, hope the problem resolves itself
 				end
 			end
 		elseif turtle.attackUp() then
 			if bDebug then print("goUp: attack") end
 			-- Had to attack player or mob. You can add additional code here such
 			-- as turtle.suck() if you want to collect killed mob loot. This is a quarry program
 			-- to collect ores, not rotten flesh and bones, so this block is empty.
 		else
 			-- Unknown obstruction, possibly a player in
 			-- peaceful or creative mode. Try again in 0.5 seconds and hope it's gone.
 			if bDebug then print("goUp: sleep(0.5)") end
 			sleep(0.5)
 		end
 	end
 
 	tY = tY + 1
 	return true -- Turtle moved successfully
 end
 
 local function orient(targetXdir, targetZdir)
 	-- One of the supplied directions should be -1 or +1, the other should be 0.
     if ((targetXdir ~= 0) and (targetZdir ~= 0)) or ((targetXdir==0) and (targetZdir==0)) then
         print("orient() given mutually exclusive values: "..targetXdir..", "..targetZdir)
         return false
     end
 
     if (((targetXdir ~= 0) and (math.abs(targetXdir) ~= 1)) or ((targetZdir ~= 0) and (math.abs(targetZdir) ~= 1))) then
         print("orient() given bad values: "..targetXdir..", "..targetZdir)
         return false
     end
 
     if (targetXdir ~= 0) and (targetXdir ~= xDir) then
         -- x axis alignment requested, and differs from current alignment
         if (xDir ~= 0) then
             -- Turtle is x-axis aligned 180 from target
             turnLeft()
             turnLeft()
         elseif (zDir == targetXdir) then
             turnRight()
         else
             turnLeft()
         end
      elseif (targetZdir ~= 0) and (targetZdir ~= zDir) then
          -- z axis alignment requested, and differs from current alignment
         if (zDir ~= 0) then
             -- Turtle is z-axis aligned 180 from target
             turnLeft()
             turnLeft()
         elseif (xDir == targetZdir) then
             turnLeft()
         else
             turnRight()
         end
     end
 
     return true
 end
 
 local function goHome()
   -- This is similar to moveTo(0,0,0) but axis ordering of movement is reversed, so that turtle takes
   -- the same path to and from home location and where it left off. Also, this function passes false to
   -- goDown, goUp and goForward to make them skip the per-move fuel check, because making that check
   -- could result in circular function calling: goHome()->goFoward()->checkFuel()->goHome()->goFoward()->checkFuel().. etc.
   -- This function is set up to move along Y-axis first, then X, then finally Z, unless bReverse is true
   -- Note: The order doesn't matter much when digging out a space, but can matter when building something
   -- so that you don't dig a tunnel through what you're building.
 
   local fuelNeeded = math.abs(tX)+math.abs(tY)+math.abs(tZ)
   if not (turtle.getFuelLevel()>=fuelNeeded) then
     print("Error: Turtle ended up in the unexpected state of not having enough fuel to return home.")
     return false
   end
 
 	while (tY<0) do
 		if bDebug then print("goHome while tY<0 tY="..tY) end
 		if not goUp(false) then
 			-- Critical movement fail, bail
 			return false
 		end
 	end
 
 	while (tY>0) do
 		if bDebug then print("goHome while tY>0 tY="..tY) end
 		if not goDown(false) then
 			-- Critical movement fail, bail
 			return false
 		end
 	end
 
 	-- If not at tX==targetX, move the right direction until tX==targetX
 	if (tX>0) then orient(-1,0) end
 	if (tX<0) then orient(1,0) end
 	while (tX~=0) do
 		if bDebug then print("goHome while tX~=0 tX="..tX) end
 		if not goForward(false) then
 		-- Critical movement fail, bail
 		return false
 		end
 	end
 
 	-- If not at tZ==targetZ, move the right direction until tZ==targetZ
 	if (tZ>0) then orient(0,-1) end
 	if (tZ<0) then orient(0,1) end
 	while (tZ~=0) do
 		if bDebug then print("goHome while tZ~=0 tZ="..tZ) end
 		if not goForward(false) then
 			-- Critical movement fail, bail
 			return false
 		end
 	end
 
 	return true
 end
 
 local function moveTo(targetX,targetZ,targetY)
 
 	local fuelNeeded = math.abs(tX-targetX)+math.abs(tY-targetY)+math.abs(tZ-targetZ)
   if not (turtle.getFuelLevel()>=fuelNeeded) then
     print("Error: Turtle ended up in the unexpected state of not having enough fuel to return home.")
     return false
   end
 
 	-- If not at tZ==targetZ, move the right direction until tZ==targetZ
 	if (tZ>targetZ) then orient(0,-1) end
 	if (tZ<targetZ) then orient(0,1) end
 	while (tZ~=targetZ) do
 		if bDebug then print("moveTo while tZ~=targetZ tZ="..tZ.." targetZ="..targetZ) end
 		if not goForward(false) then
 			-- Critical movement fail, bail
 			return false
 		end
 	end
 
   -- If not at tX==targetX, move the right direction until tX==targetX
 	if (tX>targetX) then orient(-1,0) end
 	if (tX<targetX) then orient(1,0) end
 	while (tX~=targetX) do
 		if bDebug then print("moveTo while tX~=targetX tX="..tX.." targetX="..targetX) end
 		if not goForward(false) then
 			-- Critical movement fail, bail
 			return false
 		end
 	end
 
 	while (tY<targetY) do
 		if bDebug then print("moveTo while tY<targetY tY="..tY.." targetY="..targetY) end
 		if not goUp(false) then
 			-- Critical movement fail, bail
 			return false
 		end
 	end
 
 	while (tY>targetY) do
 		if bDebug then print("moveTo while tY>targetY tY="..tY.." targetY="..targetY) end
 		if not goDown(false) then
 			-- Critical movement fail, bail
 			return false
 		end
 	end
 
   return true
 end
 
 function goUnload(bNeedsFuel)
 	if bDebug then print("goUnload()") end
 	-- Save position and orientation
 	local saveX = tX
 	local saveZ = tZ
 	local saveY = tY
 	local saveXdir = xDir
 	local saveZdir = zDir
 
 	if not goHome() then
 	-- Critical failure to move
 		return false
 	end
 
 	orient(0,-1)
 
 	-- Drop items. Turtle will not empty the slot designated as the refuel slot.
 	for i=1,16 do
 		if (i ~= refuelSlot) then
 		  turtle.select(i)
 		  turtle.drop()
 		end
 	end
 
 	orient(0,1)
 
 	-- Select first empty slot, might be a now-empty fuel slot, we don't really care
 	for i=1,16 do
 		if (turtle.getItemCount(i)==0) then
 		  turtle.select(i)
 		  break
 		end
 	end
 
 
 	-- Since we had to bring the turtle all the way home, calculate
 	-- the fuel needed to get back to where turtle left off mining, do at least one
 	-- full layer's worth of work, plus approximately enough to get back home again. It would be
 	-- silly to leave base with anything less than that, since the fuel would go nearly all to moving
 	-- the turtle through already-mined space doing no work...
 	local fuelNeeded = 2 * (math.abs(tX-saveX) + math.abs(tY-saveY) + math.abs(tZ-saveZ)) + (sizeX * sizeZ)
 
 	while (turtle.getFuelLevel() < fuelNeeded) do
 
 		if bDebug then print("Entering while true do in goUnload fuel check stage") end
 
 		-- Scan inventory for fuel
 		local slot = 1
 		turtle.select(slot)
 		local bRefueled = false
 
 		while true do
 			if turtle.refuel(1) then
 				-- Found fuel in current slot, consume 1, see if it's enough, if not loop again
 				print("Consuming fuel item from slot "..slot)
 				if (turtle.getFuelLevel()>=fuelNeeded) then
 					print("Refueled from inventory, resuming quarrying...")
 					bRefueled = true
 					break
 				end
 			else
 				-- Couldn't refuel from currently-selected slot, try next slot. If there are no more slots, ask for player help.
 				if (slot < 16) then
 					slot = slot + 1
 					turtle.select(slot)
 				else
 					-- There are no more slots to look in, reset selection so that we're ready to loop over all slots again, and so that the
 					slot = 1
 					break
 				end
 			end
 		end
 
 		if not bRefueled then
 			turtle.select(1)
 			print("Please add more fuel items to the turtle and press any key. Has:"..turtle.getFuelLevel().." Needs:"..fuelNeeded)
 			os.pullEvent("key")    -- suspend code execution awaiting user keypress
 		end
 	end
 
 	if not moveTo(saveX,saveZ,saveY) then
 		-- Critical failure to move
 		return false
 	end
 
 	orient(saveXdir,saveZdir)
 
 	return true
 end
 
 local function checkFreeSlot()
   -- This function will return true if the designated refuelSlot is empty, because if there is no fuel reserve there, there
   -- is no reason not to allow item collection into this slot.
 	for i=1,16 do
 		if turtle.getItemCount(i)==0 then
 		  return true
 		end
 	end
 
   -- Turtle does not have empty slot, goUnload
 	if not goUnload() then
 		return false
 	end
 
 	return true
 end
 
 --[[
 
   START OF THE MAIN PROGRAM
 
 --]]
 
 checkFreeSlot()
 
 local abort = false
 local traversal = 1 -- Counts x-z layers we're rasterizing. Used to determine turning directions at end of columns and layers
 local lowestY = 1-sizeY
 local bDigBelow, bDigAbove = false, false -- initially false
 while true do -- This loops digging layers
   print("Main loop traversal="..traversal.." tY="..tY.." lowestY="..lowestY)
 
   if (traversal==1) then --special case since turtle initially starts NOT on a layer that it just dug out.
 	if ((tY - lowestY) == 0) then
 		bDigBelow, bDigAbove = false, false
 	elseif ((tY - lowestY) == 1) then
 		bDigBelow, bDigAbove = true, false
 	elseif ((tY - lowestY) >= 2) then
 		bDigBelow, bDigAbove = true, true
 		if not goDown() then
           -- Turtle can't dig down, adjust lowestY because we can't go as deep as planned
 		  lowestY = tY - 1
 		end
 	else
 		-- Error: turtle is not in an expected place
 		print("Error: Turtle vertical position is not what we expect on 1st traversal. Aborting, please debug.")
 		abort = true
 		break
 	end
   else
 	-- Not our first traversal, and turtle should now be on the last layer it dug out.
 	if ((tY - lowestY) == 1) then
 		bDigBelow, bDigAbove = true, false
 	elseif ((tY - lowestY) == 2) then
 		bDigBelow, bDigAbove = true, false
 		if not goDown() then
           -- Turtle can't go down, adjust lowestY because we can't go as deep as planned
 		  lowestY = tY - 1
 		end
 	elseif ((tY - lowestY) >= 3) then
 		bDigBelow, bDigAbove = true, true
 		-- Try to descend 2, if either fails, adjust lowestY to just below where turtle is able to get to, and
 		-- cancel the need to digAbove
 		for j=1,2 do
 			if not goDown() then
 			  -- Turtle can't dig down, adjust lowestY because we can't go as deep as planned
 			  lowestY = tY - 1
 			  bDigAbove = false
 			end
 		end
 	else
 		-- Error: turtle is not in an expected place
 		print("Error: Turtle vertical position is not what we expect on traversal>1. Aborting, please debug.")
 		abort = true
 		break
 	end
   end
 
 
 
   for column=1,sizeX  do  -- This loops sizeX times digging out columns
     for block=1,(sizeZ-1) do -- this loops (sizeZ-1) times doing digDown and goForward to do all but the end of each column
 
       -- Since we're about to do a potentially ore-digging move, check for free space in inventory.
       -- hasFreeSlot() calls goUnload if necessary
       if not checkFreeSlot() then
         print("Error: checkFreeSlot failure.")
         abort = true
         break
       end
 
       if bDigBelow and turtle.detectDown() then
         if not turtle.digDown() then
           -- Turtle can't dig down, but we're not moving down so this is not a fatal error.
           -- It might be bedrock below turtle, but that's not a concern until turtle is level with it.
         end
       end
 
       if bDigAbove and turtle.detectUp() then
         if not turtle.digUp() then
           -- Turtle can't dig up. This is actually concerning since we don't want to get him trapped under bedrock.
           -- Because of the danger of entrapment, we're ending our quarrying here.
           print("Turtle below undiggable block, backing out and returning home.")
           turnRight()
           turnRight()
           if not goForward() then
             -- This failure we care about, because there is something blocking us that we
             -- can't dig, attack or otherwise resolve. Bust out of our digging loops and attempt to return home
             print("Fatal Error during column goForward tX="..tX.." tZ="..tZ.." tY="..tY)
           end
 		  abort = true
           break
         end
 		sleep(0.5) -- wait to see if anything falls on turtle from above (sand, gravel)
 
 		-- First dig up was successful, so we haven't got an undiggable block above, and undiggables can't fall, so we can
 		-- safely loop trying to dig up as long as something is falling on us (gravel, sand)
 		while turtle.detectUp() do
 			if bDebug then print("in while turtrle.detectUp() loop.") end
 			if not turtle.digUp() then
 				-- whatever is up there, we couldn't dig it, but it's not bedrock. Just move on...
 				break
 			end
 			sleep(0.5)
 		end
       end
 
       if not goForward() then
         -- This failure we care about, because there is something blocking us that we
         -- can't dig, attack or otherwise resolve. Bust out of our digging loops and attempt to return home
         -- after first checking to be sure the turtle is not under bedrock (if digging above)
         print("Fatal Error during column goForward tX="..tX.." tZ="..tZ.." tY="..tY)
         abort = true
         break
       end
     end -- end of block loop
 
     -- If movement failed while traversing column, escape out, backing out from under bedrock if needed
     if abort then
       if bDigAbove and turtle.detectUp() then
       	if not turtle.digUp() then
           -- Turtle can't dig up. This is actually concerning since we don't want to get him trapped under bedrock.
           -- Because of the danger of entrapment, we're ending our quarrying here.
           print("Turtle below undiggable block, backing out and returning home.")
           turnRight()
           turnRight()
           if not goForward() then
             -- This failure we care about, because there is something blocking us that we
             -- can't dig, attack or otherwise resolve. Bust out of our digging loops and attempt to return home
             print("Fatal Error during column goForward tX="..tX.." tZ="..tZ.." tY="..tY)
           end
         end
       end
 
       -- unwinding
       break
     end
 
     -- Dig out the last block of this column
     if bDigBelow and turtle.detectDown() then
       if not turtle.digDown() then
         -- Turtle can't dig down, but we're not moving down so this is not a fatal error.
         -- It might be bedrock below turtle, but that's not a concern until turtle is level with it.
       end
     end
 
     -- Do last digUp in this column, if required by bDigAbove
     if bDigAbove and turtle.detectUp() then
         if not turtle.digUp() then
           -- Turtle can't dig up. This is actually concerning since we don't want to get him trapped under bedrock.
           -- Because of the danger of entrapment, we're ending our quarrying here.
           print("Turtle below undiggable block, backing out and returning home.")
           turnRight()
           turnRight()
           if not goForward() then
             -- This failure we care about, because there is something blocking us that we
             -- can't dig, attack or otherwise resolve. Bust out of our digging loops and attempt to return home
             print("Fatal Error during column goForward tX="..tX.." tZ="..tZ.." tY="..tY)
           end
 		  abort = true
           break
         end
 		sleep(0.5) -- wait to see if anything falls on turtle from above (sand, gravel)
 
 		-- First dig up was successful, so we haven't got an undiggable block above, and undiggables can't fall, so we can
 		-- safely loop trying to dig up as long as something is falling on us (gravel, sand)
 		while turtle.detectUp() do
 			if bDebug then print("in while turtrle.detectUp() loop.") end
 			if not turtle.digUp() then
 				-- whatever is up there, we couldn't dig it, but it's not bedrock. Just move on...
 				break
 			end
 			sleep(0.5)
 		end
     end
 
     -- Turtle just finished the column, figure out if we need to advance to a new column, or
     -- if we've finished the layer. If we need to turn to start a new column, we have to figure out which
     -- direction to turn
     if (column<sizeX) then
       -- Turtle is at the end of a z column, but not the end of the whole x-z layer traversal
 
       -- FYI: These odd/even values are based on 1-based block, column, traversal numbers not 0-based tX, tZ, tY
       -- sorry if that's confusing, but Lua convention is to start loop indicies at 1
       local evenCol = ((column%2)==0)
       local evenWidth = ((sizeX%2)==0)
       local evenLayer = ((traversal%2)==0)
       local backtrackingLayer = (evenWidth and evenLayer)
 
       if ((not evenCol and not backtrackingLayer) or (evenCol and backtrackingLayer)) then
         turnRight() -- turn towards next row
         if not goForward() then
           print("Fatal Error during goForward from column "..column.." to column "..(column+1).." tX="..tX.." tZ="..tZ.." tY="..tY)
           abort = true
           break
         end
 
         -- Danger check to see if we've moved under an undiggable block
         if bDigAbove and turtle.detectUp() and not turtle.digUp() then
           print("Turtle below undiggable block, backing out 1 and returning home.")
           turnRight()
           turnRight()
           if not goForward() then
             -- This failure we care about, because there is something blocking us that we
             -- can't dig, attack or otherwise resolve. Bust out of our digging loops and attempt to return home
             print("Fatal Error during column goForward tX="..tX.." tZ="..tZ.." tY="..tY)
           end
           abort = true
           break
         end
 
         turnRight()
       else
         turnLeft()
         if not goForward() then
           print("Fatal Error during goForward from column "..column.." to column "..(column+1).." tX="..tX.." tZ="..tZ.." tY="..tY)
           abort = true
           break
         end
 
         -- Danger check to see if we've moved under an undiggable block
         if bDigAbove and turtle.detectUp() and not turtle.digUp() then
           print("Turtle below undiggable block, backing out 1 and returning home.")
           turnRight()
           turnRight()
           if not goForward() then
             -- This failure we care about, because there is something blocking us that we
             -- can't dig, attack or otherwise resolve. Bust out of our digging loops and attempt to return home
             print("Fatal Error during column goForward tX="..tX.." tZ="..tZ.." tY="..tY)
           end
           abort = true
           break
         end
 
         turnLeft()
       end
       -- Turtle is now ready to start the next column
     else
       -- Turtle is at the end of the layer, rotate 180
       turnRight()
       turnRight()
     end
   end -- end of column loop
 
   if abort then
 	print("Abort breaking out of while true loop.")
     -- abort in progress, unwinding out of loops
     break
   end
 
   -- See if we're done yet
   if ((tY - lowestY) == 0) or (((tY - lowestY) == 1) and (bDigBelow == true)) then
     -- We're done. We've finished digging our lowest layer either by digging forward or with digDown.
     done = true
     break
   end
 
   -- If we got past the last if-then, we are not done, so we need to descend in preparation for next layer traversal
   if bDigBelow then
     -- We were digging below us on the traversal we just finished, so we need to drop down 2 levels to be on an undug layer
     -- First we try to descend through the dug-down layer, but since that could have bedrock (we we skimming above it not caring)
     -- we need to test to see if we can descend into that layer at our current tX,tZ location
     if not goDown() then
       print("Turtle finished a traversal and was digging below. Turtle can't go further down, we're done quarrying.")
       abort = true
       break
     end
   end
 
   traversal = traversal + 1
 end -- end of while not done loop
 
 -- Quarrying ended, either normally or because of encountering undiggable block. Try to return to 0,0,0
 if not goHome(0,0,0) then
   -- Can't even get back home :-( Notify the user
   print("Turtle was not able to safely get back to starting location")
   abort = true
 else
 	orient(0,-1)
 
 	-- Drop everything
 	-- Drop items. Turtle will not empty the slot designated as the refuel slot.
   print("Unloading all contents...")
 	for i=1,16 do
 		turtle.select(i)
 		turtle.drop()
 	end
 	orient(0,1)
 end
 
 if abort then
   print("Quarrying ended due to encounter with undiggable block.")
 else
   print("Quarrying complete to desired depth.")
 end