Autotunnel 2x2 - Izzobot

--[[
Autotunnel Program
Created by Izzobot

Mines out a 2x2 tunnel and surrounds tunnel with material in slots 2-16.
]]--

FUEL_SLOT = 1

-- Functions

function refuel()
    turtle.select(FUEL_SLOT)
    items = turtle.getItemCount(FUEL_SLOT)
    fuel = turtle.getFuelLevel(FUEL_SLOT)
    if fuel == 0 then   -- When no fuel
        if items ~= 0 then
            print("Refuelling...")
            turtle.refuel(FUEL_SLOT)
            print("Refueled!")
        else    -- If no fuel present
            print("Add more fuel to slot " .. FUEL_SLOT)
         error()
        end
    else
        print("Fuel level sufficient")
    end
end

function digForward()
    while turtle.detect() do
        turtle.dig()
    end
end

function moveForward()
    if turtle.getFuelLevel() == 0 then
        refuel()
    end

 while turtle.forward() == false do
    digForward()
    turtle.attack()
 end

end

function moveBack()
    if turtle.getFuelLevel() == 0 then
        refuel()
    end

 while turtle.back() == false do
    digForward()
    turtle.attack()
 end

end

function placeDown()
    changeSlot()
    turtle.placeDown()
end

function placeUp()
    changeSlot()
    turtle.placeUp()
end

function placeForward()
    changeSlot()
    turtle.place()
end

function moveUp()
    if turtle.getFuelLevel() == 0 then
        refuel()
    end

    while turtle.up() == false do
        turtle.digUp()
    end
end

function moveDown()
    if turtle.getFuelLevel() == 0 then
        refuel()
    end

    while turtle.down() == false do
        turtle.digDown()
    end
end

function enoughItems()
    total = 0
        for slot=2,16 do -- Count the number of blocks
        total = total + turtle.getItemCount(slot)
        end
    if total < l*8 then
        print("More blocks required.")
        if total ~= 0 then
            io.write("Continue? (y/n): ")
            answer = io.read()
            if answer == "y" then
                print("Continuing...")
            else
                print("Cancelled.")
                error()
            end
        else
            print("No blocks in inventory.")
            error()
        end
    end
end

function changeSlot()
    if turtle.getItemCount() == 0 then
        for i=2,16 do
            turtle.select(i)
            if turtle.getItemCount(i) ~= 0 then
                break
            end
        end
    end
end

-- Start of Code
turtle.select(2)
print(" ")
print("[Auto-tunnel]\n")
io.write("Length: ")
l = io.read()
print(" ")
enoughItems()
print("Building...")

for i=1,l do
    digForward()
    moveForward()
    placeDown()
    turtle.turnLeft()
    placeForward()
    moveUp()
    placeForward()
    placeUp()
    turtle.turnRight()
    turtle.turnRight()
    moveForward()
    placeUp()
    placeForward()
    moveDown()
    placeForward()
    turtle.turnLeft()
    placeDown()
    turtle.turnLeft()
    moveForward()
    turtle.turnRight()
end

print("Tunnel complete.")