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 (not turtle.forward()) do
        if (turtle.detect()) then
            turtle.dig()
        else
            turtle.attack()
        end
    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.")