fabdrain

print("fabdrain: Rev 1.0")

beltSlot = 1
currentSlot = beltSlot
goForward = 0
goBackward = 1
direction = goForward
holeWidth = 3

-- The following 'face' directions are relative to the starting position of the turtle in this program
north = 0
west = 1
south = 2
east = 3

x = 0
y = 0
z = 0

currentFace = north

function setFace(f)
	if f == 0 then
	  if face == 0 then return end
	  if face == 1 then right() return end
	  if face == 2 then right() right() return end
	  if face == 3 then left() return end
	end

	if f == 1 then
	  if face == 0 then left() return end
	  if face == 1 then return end
	  if face == 2 then right() return end
	  if face == 3 then right() right() return end
	end

	if f == 2 then
	  if face == 0 then left() left() return end
	  if face == 1 then left() return end
	  if face == 2 then return end
	  if face == 3 then right() return end
	end

	if f == 3 then
	  if face == 0 then right() return end
	  if face == 1 then left() left() return end
	  if face == 2 then left() return end
	  if face == 3 then return end
	end
end

function left()
 if face == 0 then face = 1 turtle.turnLeft() return end
 if face == 1 then face = 2 turtle.turnLeft() return end
 if face == 2 then face = 3 turtle.turnLeft() return end
 if face == 3 then face = 0 turtle.turnLeft() return end
 print("function left\(\): Bad face value: ", face)
end

function right()
 if face == 0 then face = 3 turtle.turnRight() return end
 if face == 1 then face = 0 turtle.turnRight() return end
 if face == 2 then face = 1 turtle.turnRight() return end
 if face == 3 then face = 2 turtle.turnRight() return end
 print("function right\(\): Bad face value: ", face)
end

function aboutFace()
	if face == north then setFace(south) return end
	if face == south then setFace(north) return end
	if face == east then setFace(west) return end
	if face == west then setFace(east) return end
end

function reverseDirection()
	if direction == goForward then
		direction = goBackward
	else
		direction = goForward
	end
end

function moveForward(nBlocks)
	for i = 1, nBlocks do
		turtle.forward()
		if face == north then
			z = z + 1
		elseif face == south then
			z = z - 1
		elseif face == east then
			x = x + 1
		elseif face == west then
			x = x - 1
		end
	end

end

function moveBackward(nBlocks)
	for i = 1, nBlocks do
		turtle.back()
		if face == north then
			z = z - 1
		elseif face == south then
			z = z + 1
		elseif face == east then
			x = x - 1
		elseif face == west then
			x = x + 1
		end
	end
end

function home()
end

function xzHome()
	local X = gX
	local Z = gZ

	if x ~= X then
		if x < X then
			setFace(east)
			while x < X do
				turtle.forward()
				x = x + 1
			end
		else
			setFace(west)
			while x > X do
				turtle.forward()
				x = x - 1
			end
		end
	end

	if z ~= Z then
		if z < Z then
			setFace(north)
			while z < Z do
				turtle.forward()
				z = z + 1
			end
		else
			setFace(south)
			while z > Z do
				turtle.forward()
				z = z - 1
			end
		end
	end
end

function layBeltRow(direction, length)
	for j=1,5 do
		if turtle.getItemCount(currentSlot) < 1 then
			currentSlot = currentSlot + 1
			if turtle.getItemCount(currentSlot) < 1 then
				abort("No more belts in inventory.")
			end
			turtle.select(currentSlot)
		end
		turtle.placeDown()
		if j < 5 then
			if direction == goForward then
				moveForward(1)
			else
				moveBackward(1)
			end
		end
	end
end

rowHeading = west

function goToNextRow()
	currentFace = face
	if face == north or face == south then
		setFace(rowHeading)
		moveForward(1)
		setFace(currentFace)
	else
		setFace(rowHeading)
		moveForward(1)
		setFace(currentFace)
	end
end

function layBeltSection(length, width)
	moveBackward(length - 1)
	for i = 1,width do
		direction = goForward
		layBeltRow(direction, length)
		moveForward(holeWidth+1)
		aboutFace()
		direction = goBackward
		layBeltRow(direction, length)
		goToNextRow()
	end

	setFace(east)
	rowHeading = south
	direction = goBackwards
	segLength = length + 3 + length
	for i = 1, segLength do
		layBeltRow(direction, length)
		if i < segLength then
			goToNextRow()
			reverseDirection()
		end
	end

	setFace(east)
	moveForward(length + holeWidth)
	aboutFace()

	rowHeading = north
	direction = goBackwards
	for i = 1, segLength do
		layBeltRow(direction, length)
		if i < segLength then
			goToNextRow()
			reverseDirection()
		end
	end
end

function abort(message)
	print(message)
	error()
end

-- Main Program

turtle.up()
y = y + 1

turtle.select(1)
layBeltSection(5, holeWidth)

xzHome()
yHome()
setFace(north)