Turtle Bubble Elevator

bubblevator.lua

depth = 0

slotFill = 1
slotKelp = 5
slotGate = 9
slotDirt = 10
slotSoul = 11
slotWater = 12

print("Builds a bubblevator. Face turtle at fence gate direction. Water ends up one block forward from turtle's current position.")
print("Slot 1-4: filler block")
print("Slot 5-8: kelp")
print("Slot 9: 2x fence gates")
print("Slot 10: dirt")
print("Slot 11: soul sand")
print("Slot 12: water bucket")

--get height
print("Bubblevator depth?: ")
depth = tonumber(read())

function selectFiller()
    if turtle.getItemCount(slotFill) == 0 then
        if slotFill == 4 then
            slotFill = 13 --out of filler blocks, use what is being dug up
        else
            slotFill = slotFill + 1
        end
    end
    turtle.select(slotFill)
end

function checkWalls()
    selectFiller()
    turtle.forward()
    turtle.turnLeft() selectFiller() turtle.place()
    turtle.turnRight() selectFiller() turtle.place()
    turtle.turnRight() selectFiller() turtle.place()
    turtle.turnLeft()
    turtle.back()
    turtle.turnLeft() selectFiller() turtle.place()
    turtle.turnLeft() selectFiller() turtle.place()
    turtle.turnLeft() selectFiller() turtle.place()
    turtle.turnLeft()
end

-- dig initial hole
for i = 1,depth do
    turtle.select(13)
    turtle.digDown()
    if not turtle.down() then --hit bedrock
        depth = i - 2 --adjust depth
        print("Hit bedrock, new depth is "..depth)
        turtle.up()
        break
    end
    turtle.dig()
    checkWalls()
end

-- move into water column spot and prep dirt for kelp
turtle.forward()
turtle.select(13)
turtle.digDown()
turtle.select(slotDirt)
turtle.placeDown()

-- place fence gates
for i = 1,depth do
    if i < 3 then
        turtle.dig()
        turtle.select(slotGate)
        turtle.place()
    end
    turtle.up()
end

--drop water
turtle.turnLeft()
turtle.turnLeft()
turtle.down()
turtle.select(slotWater)
turtle.placeDown()

-- move out of water
turtle.forward()
turtle.turnLeft()
turtle.turnLeft()

-- place kelp
for i = 1,depth-1 do
    turtle.down()
end 
for i = 1,depth do
    if turtle.getItemCount(slotKelp) == 0 and slotKelp ~= 8 then
        slotKelp = slotKelp + 1
    end
    turtle.select(slotKelp)
    turtle.place()
    turtle.up()
end

-- swap dirt for soul sand
for i = 1,depth do
    turtle.down()
end
turtle.digDown()
turtle.down()
turtle.select(13)
turtle.dig()
turtle.select(slotSoul) --soulsand
turtle.place()

-- backfill work column
selectFiller()
turtle.up()
turtle.placeDown()
for i = 1,depth do
    selectFiller()
    turtle.up()
    turtle.placeDown()
end