Computercraft Smart Farm

-- Place a turtle on top of a chest with a redstone input comming from the side.
-- On a straight line from that path, place redstone signals that can catch the turtle from below.
-- When the turtle finds a redstone signal, it will turn right and do the following:
-- > Go forward once, and read a single number in the disk file called "cropstage.txt", to know at which metadata to harvest the crop
-- > Go forward and farm until it hits a wall, setting the depth of the farm. Turn right and come back one tile over.
-- > Go back and forth, each time going one more tile to the right, until it hits another wall.
-- > Go back to the point of origin, pointing the oposite way as from the start
-- If nothing was harvested, the turtle will continue forward until it hits another torch.
-- If something was harvested, the turtle will go back home and drop its cargo in the chest.

local maxFarmSize = 20
local startInputSide = "left"
local neededFarmInputSide = "bottom"

local forward = 0
local returning = false

local function farmTile(cropStage)
	local success, detail = turtle.inspectDown()
	if (success) then
		if (detail.metadata == cropStage) then
			turtle.digDown()
			turtle.suckDown()
			if (turtle.getItemCount() > 1) then
				turtle.placeDown()
			end
			return true
		else
			turtle.suckDown()
		end
	else
		if (turtle.getItemCount() > 1) then
			turtle.placeDown()
		end
		turtle.suckDown()
	end
	return false
end

local function dropCargo()
	for i=1, 16 do
		turtle.select(i)
		turtle.dropDown()
	end
	turtle.select(1)
end

local function farmPass(cropStage)
	local depth = 0
	local width = 1
	local farmedSomething = false
	turtle.select(1)
	while true do
		if (depth == 0) then
			while turtle.forward() do
				depth = depth+1
				farmTile(cropStage)
			end
			depth = depth-1
		else
			for i=1, depth do
				turtle.forward()
				if (farmTile(cropStage)) then
					farmedSomething = true
				end
			end
		end
		turtle.turnRight()
		turtle.forward()
		if (farmTile(cropStage)) then
			farmedSomething = true
		end
		turtle.turnRight()
		for i=1, depth do
			turtle.forward()
			if (farmTile(cropStage)) then
				farmedSomething = true
			end
		end
		turtle.turnLeft()
		if (turtle.forward()) then
			if (farmTile(cropStage)) then
				farmedSomething = true
			end
			width = width+2
			turtle.turnLeft()
		else
			turtle.turnRight()
			turtle.turnRight()
			for i=1, width do
				turtle.forward()
			end
			turtle.turnLeft()
			turtle.forward()
			return farmedSomething
		end
	end
end

while true do
	forward = 0
	returning = false

	-- Wait for redstone signal to start
	while not rs.getInput(startInputSide) do
		os.pullEvent("redstone")
		print("Redstone update")
	end

	-- Go forward until...
	repeat
		turtle.forward()
		forward = forward+1

		-- ...it gets a redstone signal
		if (rs.getInput(neededFarmInputSide)) then
			turtle.turnRight()
			turtle.forward()
			local file = fs.open("disk/cropstage.txt", "r")
			local cropStage = file.readLine()
			file.close()
			returning = farmPass(tonumber(cropStage))
			turtle.forward()
			turtle.turnRight()
			if (returning) then
				break
			end
		end

	until turtle.detect() -- ...or you hit a wall

	turtle.up()
	for i=1, forward do
		turtle.back()
	end
	turtle.down()

	dropCargo()
end