targ = {
	nextColumnGenerator = function ()
		local curpos = {x=0, y=0, z=0, facing=3}
		local deph = 0
		while true do
			for i=0,deph do
				if deph == 0 then break end
				if deph%2 == 0 then
					curpos.z = curpos.z - 3
					curpos.x = curpos.x + 1
				else
					curpos.z = curpos.z + 3
					curpos.x = curpos.x - 1
				end
				coroutine.yield(curpos)
			end

			if deph%2 == 0 then
				curpos.z = curpos.z - 1
				curpos.x = curpos.x + 2
			else
				curpos.z = curpos.z + 2
				curpos.x = curpos.x + 1
			end
			deph = deph + 1
			coroutine.yield(curpos)
		end
	end
}

location = {
	lockd = false,

	x = 0,
	y = 0,
	z = 0,
	facing = 3,

	facingToAxis = {
		[0] = { axis = 'z', unit = 1 },
		[1] = { axis = 'x', unit = -1 },
		[2] = { axis = 'z', unit = -1 },
		[3] = { axis = 'x', unit = 1 }
	},

	lock = function()
		while location.lockd do
			sleep(1)
		end
	end,

	getAxisForFacing = function()
		return location.facingToAxis[location.facing]['axis'], location.facingToAxis[location.facing]['unit']
	end,

	turnLeft = function()
		location.lock()
		location.facing = (location.facing - 1) % 4
		turtle.turnLeft()
	end,

	turnRight = function()
		location.lock()
		location.facing = (location.facing + 1) % 4
		turtle.turnRight()
	end,

	moveForward = function()
		location.lock()
		if turtle.forward() then
			local axis, unit = location.getAxisForFacing()
			location[axis] = location[axis] + unit
			return true
		end
		return false
	end,

	moveBack = function()
		location.lock()
		if turtle.back() then
			local axis, unit = location.getAxisForFacing()
			location[axis] = location[axis] - unit
			return true
		end
		return false
	end,

	face = function(faceto)
		local dirdif = (faceto - location.facing) % 4
		if dirdif == 1 then
			location.turnRight()
		elseif dirdif == 2 then
			location.turnRight()
			location.turnRight()
		elseif dirdif == 3 then
			location.turnLeft()
		end
	end,

	movez = function(d)
		if d < location.z then location.face(2) elseif d > location.z then location.face(0) end
		return location.moveForward()
	end,

	movex = function(d)
		if d < location.x then location.face(1) elseif d > location.x then location.face(3) end
		return location.moveForward()
	end,

	movey = function(d)
		if d < location.y then
			return location.moveDown()
		end
		return location.moveUp()
	end,

	moveUp = function()
		location.lock()
		if turtle.up() then
			location.y = location.y + 1
			return true
		end
		return false
	end,

	moveDown = function()
		location.lock()
		if turtle.down() then
			location.y = location.y - 1
			return true
		end
		return false
	end,

	moveTo = function(x, y, z, facing)
		if y > location.y then
			while location.y < y do
				while not location.moveUp() do
					if turtle.detectUp() then
						turtle.select(1)
						turtle.digUp()
					else
						turtle.attackUp()
					end
				end
			end
		end
		while x ~= location.x do
			while not location.movex(x) do
				if turtle.detect() then
					turtle.select(1)
					turtle.dig()
				else
					turtle.attack()
				end
			end
		end
		while z ~= location.z do
			while not location.movez(z) do
				if turtle.detect() then
					turtle.select(1)
					turtle.dig()
				else
					turtle.attack()
				end
			end
		end
		if y < location.y then
			while location.y > y do
				while not location.moveDown() do
					if turtle.detectDown() then
						turtle.select(1)
						turtle.digDown()
					else
						turtle.attackDown()
					end
				end
			end
		end
		location.face(facing)
		return true
	end,

	moveToPos = function(pos)
		return location.moveTo(pos.x, pos.y, pos.z, pos.facing)
	end,

	distanceTo = function(x, y, z)
		return math.abs(x) - location.x + math.abs(y) - location.y + math.abs(z) - location.z
	end,

	distanceToPos = function(pos)
		return location.distanceTo(pos.x, pos.y, pos.z)
	end
}

mining = {
	-- returns false if bedrock
	down = function (h)
		while not location.movey(-1e10) do
			if turtle.detectDown() then
				turtle.digDown()
				if turtle.detectDown() then
					return false
				end
			else
				turtle.attackDown()
			end
		end
		return true
	end,

	checkForward = function()
		location.lock()
		local success, data = turtle.inspect()
		return success and not (data.name == "minecraft:stone" or data.name == "minecraft:dirt" or data.name == "minecraft:gravel")
	end,

	digHole = function ()
		while true do
			if not mining.down(0) then
				break
			end
			for j=1,4 do
				if mining.checkForward() then
					if not interface.space() then
						controls.returnToChest()
					end
					turtle.select(1)
					turtle.dig()
				end
				location.turnRight()
			end
		end
	end
}

interface = {
	refuel = function (ammount)
		if turtle.getFuelLevel() == "unlimited" then
			return true
		end
		local needed = ammount or location.distanceToPos({x=0, y=0, z=0, facing=1}) * 2 + 1
		if turtle.getFuelLevel() < needed then
			term.write("need more fuel. refueling\n")
			for n=1,16 do
				location.lock()
				if turtle.getItemCount(n) > 0 then
					turtle.select(n)
					if turtle.refuel(1) then
						while turtle.getItemCount(n) > 0 and turtle.getFuelLevel() < needed do
							turtle.refuel(1)
						end
						if turtle.getFuelLevel() >= needed then
							turtle.select(1)
							return true
						end
					end
				end
			end
			turtle.select(1)
			return false
		end
		return true
	end,

	unload = function ()
		for n=1,16 do
			location.lock()
			if turtle.getItemCount(n) > 0 then
				turtle.select(n)
				if n <= 0 then
					if (not false  and n == 1) or n > 1 then
						turtle.drop(turtle.getItemCount(n) - 1)
					end
				else
					turtle.drop()
				end
			end
		end
		turtle.select(1)
	end,

	space = function ()
		for n=1,16 do
			if turtle.getItemCount(n) == 0 then
				return true
			end
		end
		return false
	end
}

controls = {
	returnToChest = function()
		local returnPos = {x = location.x, y = location.y, z = location.z, facing = location.facing}
		local fuelNeeded = location.distanceToPos({x=0,y=0,z=0,facing=1}) * 2 + 1
		location.moveToPos({x=0,y=0,z=0,facing=1})
		location.face((location.facing + 2) % 4)
		if not interface.refuel(fuelNeeded) then
			interface.unload()
			while not interface.refuel(fuelNeeded) do
				location.lock()
				sleep(1)
			end
		else
			interface.unload()
		end
		location.moveToPos(returnPos)
	end,

	forward = function ()
		if not space() then
			controls.returnToChest()
		end
		while not location.moveForward() do
			if turtle.detect() then
				turtle.select(1)
				turtle.dig()
			else
				turtle.attack()
			end
		end
	end
}


function oreThread()
	local target = coroutine.create(targ.nextColumnGenerator)
	while true do
		if not interface.refuel() or not interface.space() then
			controls.returnToChest()
		end
		local error, shaft = coroutine.resume(target)
		term.write("mining shaft at x=" .. shaft.x .. " and z=" .. shaft.z .. "\n")
		location.moveToPos(shaft)
		mining.digHole()
	end
end

oreThread()