U-Turn Tunnel

-- ******** PRE-INIT *********
--local tArgs = { ... }
--if #tArgs ~= 1 then
--  print( "Usage: mine <length>" )
--  return
--end
--
--local length = tonumber( tArgs[1] )

local length = 74

if length % 2 ~= 0 then
    length = length+1
end

-- ******** FUNCTIONS *********

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

local function tryDigUp()
    while turtle.detectUp() do
        if turtle.digUp() 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 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
            sleep(1)
        end
        print( "Resuming Tunnel." )
    end
end

local function tryUp()
    refuel()
    while not turtle.up() do
        if turtle.detectUp() then
            if not tryDigUp() then
                return false
            end
        elseif turtle.attackUp() then
        else
            sleep( 0.5 )
        end
    end
    return true
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
        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
        else
            sleep( 0.5 )
        end
    end
    return true
end

local function iteminSlot(Slot)
    if turtle.getItemCount(Slot) > 0 then
        return true
    else
        return false
    end
end

local function placeTorch()
    refuel()
    if iteminSlot(16) then
        turtle.select(16)
        if not turtle.place() then
            turtle.forward()
            tryDigDown()
            if not turtle.placeDown() then
                turtle.down()
                turtle.select(1)
                turtle.placeDown()
                turtle.select(16)
                turtle.up()
                turtle.placeDown()
            end
            turtle.back()
        end
    end
    turtle.select(1)
end

local function tunnel(length, torch)
    local nextTorch = 0
    if torch ~= false then
        nextTorch = torch
        torch = true
    end
    turtle.select(1)

    for n=1,length do
        turtle.placeDown()
        tryDigUp()
        turtle.turnLeft()
        tryDig()
        tryUp()
        tryDig()
        if torch == true and nextTorch == 0 then placeTorch() end
        turtle.turnRight()
        turtle.turnRight()
        tryDig()
        if torch == true and nextTorch == 0 then
            placeTorch()
            nextTorch = 9
        end
        tryDown()
        tryDig()
        turtle.turnLeft()

        if n<length then
            tryDig()
            if not tryForward() then
                return false
            end
             if torch == true then nextTorch = nextTorch -1 end
        else
            return true
        end
    end
end


-- ******** MAIN *********

if not tunnel(length/2, 0) then
    print( "Aborting Mining." )
    return false
end
tryDig()
tryForward()
tunnel(2, false)
turtle.turnRight()
tunnel(7, 3)
turtle.turnRight()
if not tunnel(length/2+2, 2) then
    print( "Aborting Mining." )
    return false
end