blocksMoved = 0
invSlot = 1
torchSlot = 16
length = 30

function placeBlocks()
    if blocksMoved >= 4 then
        turtle.placeDown()
        placeTorch()
        blocksMoved = 0
        turtle.select(invSlot)
    else
        turtle.placeDown()
        turtle.forward()
        blocksMoved = blocksMoved + 1
    end
end

function moveOver()
    turtle.turnRight()
    for i = 0, 5 do
        turtle.forward()
    end
    turtle.turnRight()
    turtle.forward()
end

function placeTorch()
    turtle.select(torchSlot)
    turtle.up()
    turtle.placeDown()
    turtle.forward()
    turtle.down()
end

function run()
    for i = 0, 1 do
        for i = 0, length do
            placeBlocks()

            if turtle.getItemCount(invSlot) < 1 then
                return
            else
                if turtle.getItemCount(invSlot + 1) < 1 and turtle.getItemCount(invSlot) < 1 then
                    return
                elseif turtle.getItemCount(invSlot) < 1 then
                    invSlot = invSlot + 1
                end

                turtle.select(invSlot)
            end
        end

        moveOver()
    end
end

run()