ComputerCraft Turtle - Excavator

local version = 3
print ("## Nick's chunk excavator v" .. version)

local testing = false
local size = { x = 4, y = 4, z = 4 }
local turns = 0

if testing then print ("## (operating in test mode!)") end
print ("## (size: " .. size.x .. "x" .. size.y .. ")")

-- Main loop
function Excavate ()
    while Refuel() == false do end
    GoForward (1)
    GoDown (1)
    -- Left/right
    local a, b, c = 1, 1, 1
    while a <= size.x do
        -- Up/down
        b = 1
        while b <= size.y do
            -- Forward/backward
            c = size.z
            GoForward (c)
            if b ~= size.y then
                GoDown (1)
                turtle.turnRight()
                turtle.turnRight()
            end
            turns = turns + 2
            b = b + 1
        end
        if b % 2 == 0 then
            TurnToward (2)
            GoForward (c)
        end
        GoUp (b - 2)
        if a ~= size.x then
            if turns % 2 == 0 then
                GoLeft()
                turtle.turnLeft()
                turns = turns - 1
            else
                GoRight()
                turtle.turnRight()
                turns = turns + 1
            end
        end
        a = a + 1
    end

    -- Return home
    if a % 2 == 0 then
        TurnToward (2)
        GoForward (c - 2)
    end
    TurnToward (3)
    GoForward (a - 2)
    GoUp (1)
    GoLeft()
end

-- Methods

function Refuel ()
    for i = 1, 16 do
        turtle.select (i)
        if turtle.refuel (0) then
            turtle.refuel (1)
            return true
        end
    end
    return false
end

function TurnToward (direction)
    while turns % 4 ~= direction do
        if turns % 4 > direction then
            turtle.turnLeft()
            turns = turns - 1
        else
            turtle.turnRight()
            turns = turns + 1
        end
    end
end

function GoForward (meters)
    for m = 1, meters do
        while turtle.detect() do
            if not testing then turtle.dig() end
            os.sleep (0.5)
        end
        if turtle.getFuelLevel() ~= "unlimited" and turtle.getFuelLevel() < 1 then
            Refuel()
        end
        turtle.forward()
    end
end

function GoUp (meters)
    for m = 1, meters do
        while turtle.detectUp() do
            if not testing then turtle.digUp() end
            os.sleep (0.5)
        end
        if turtle.getFuelLevel() ~= "unlimited" and turtle.getFuelLevel() < 1 then
            Refuel()
        end
        turtle.up()
    end
end

function GoDown (meters)
    for m = 1, meters do
        while turtle.detectDown() do
            if not testing then turtle.digDown() end
            os.sleep (0.5)
        end
        if turtle.getFuelLevel() ~= "unlimited" and turtle.getFuelLevel() < 1 then
            Refuel()
        end
        turtle.down()
    end
end

function GoLeft ()
    turtle.turnLeft()
    turns = turns - 1
    GoForward (1)
end

function GoRight ()
    turtle.turnRight()
    turns = turns + 1
    GoForward (1)
end

-- Here we go
Excavate()