steps.lua

if not turtle then
    printError("Requires a Turtle")
    return
end

local function tryDig()
    while turtle.detect() do
        if turtle.dig() then
            sleep(0.5)
        else
            return false
        end
    end
    return true
end

local function tryDigDown()
    while turtle.detectDown() do
        if turtle.digDown() then
            sleep(0.5)
        else
            return false
        end
    end
    return true
end

local function placeStep()
    local function tryBlock()
        for n = 1, 16 do
            if turtle.getItemCount(n) > 0 then
                turtle.select(n)
                if turtle.placeDown(1) then
                    turtle.select(1)
                    return true
                end
            end
        end
        turtle.select(1)
        return false
    end

    if not tryBlock() then
        print("Add more Blocks to continue.")
        while not tryBlock() do
            os.pullEvent("turtle_inventory")
        end
        print("Resuming Creation.")
    end
end

local function refuel()
    local fuelLevel = turtle.getFuelLevel()
    if fuelLevel == "unlimited" or fuelLevel > 0 then
        return
    end

    local function tryRefuel()
        for n = 1, 16 do
            if turtle.getItemCount(n) > 0 then
                turtle.select(n)
                if turtle.refuel(1) then
                    turtle.select(1)
                    return true
                end
            end
        end
        turtle.select(1)
        return false
    end

    if not tryRefuel() then
        print("Add more fuel to continue.")
        while not tryRefuel() do
            os.pullEvent("turtle_inventory")
        end
        print("Resuming Tunnel.")
    end
end

local function tryDown()
    refuel()
    while not turtle.down() do
        if turtle.detectDown() then
            if not tryDigDown() then
                return false
            end
        elseif turtle.attackDown() then
            collect()
        else
            sleep(0.5)
        end
    end
    return true
end


local function tryForward()
    refuel()
    while not turtle.forward() do
        if turtle.detect() then
            if not tryDig() then
                return false
            end
        elseif turtle.attack() then
            collect()
        else
            sleep(0.5)
        end
    end
    return true
end

while not turtle.detectDown() do
    refuel()
    placeStep()
    tryDig()
    tryForward()
    tryDigDown()
    tryDown()
end