Excav2

    local tArgs = { ... }
    if #tArgs ~= 3 then
            print( "Usage: excavate <diameter> <depth> <bResume 1|0>" )
            return
    end

    -- Mine in a quarry pattern until we hit something we can't dig
    local size = tonumber( tArgs[1] )
    if size < 1 then
            print( "Excavate diameter must be positive" )
            return
    end

    local targetDepth = tonumber( tArgs[2] )
    if targetDepth < 1 then
            print( "Excavate depth must be positive" )
            return
    end

    local bResume = ( tArgs[3] )
if not bResume == '1' and not bResume == '0' then
print("bResume must be either 0 or 1")
return
end

    local depth = 0
    local unloaded = 0
    local collected = 0

    local xPos,zPos = 0,0
    local xDir,zDir = 0,1

    local goTo -- Filled in further down
    local refuel -- Filled in further down

    local function unload( _bKeepOneFuelStack )
            print( "Unloading items..." )
            for n=1,16 do
                    local nCount = turtle.getItemCount(n)
                    if nCount > 0 then
                            turtle.select(n)
                            local bDrop = true
                            if _bKeepOneFuelStack and turtle.refuel(0) then
                                    bDrop = false
                                    _bKeepOneFuelStack = false
                            end
                            if bDrop then
                                    turtle.drop()
                                    unloaded = unloaded + nCount
                            end
                    end
            end
            collected = 0
            turtle.select(1)
    end

    local function returnSupplies()
            local x,y,z,xd,zd = xPos,depth,zPos,xDir,zDir
            print( "Returning to surface..." )
            goTo( 0,0,0,0,-1 )

            local fuelNeeded = 2*(x+y+z) + 1
            if not refuel( fuelNeeded ) then
                    unload( true )
                    print( "Waiting for fuel" )
                    while not refuel( fuelNeeded ) do
                            sleep(1)
                    end
            else
                    unload( true )
            end

            print( "Resuming mining..." )
            goTo( x,y,z,xd,zd )
    end

    local function collect()
            local bFull = true
            local nTotalItems = 0
            for n=1,16 do
                    local nCount = turtle.getItemCount(n)
                    if nCount == 0 then
                            bFull = false
                    end
                    nTotalItems = nTotalItems + nCount
            end

            if nTotalItems > collected then
                    collected = nTotalItems
                    if math.fmod(collected + unloaded, 50) == 0 then
                            print( "Mined "..(collected + unloaded).." items." )
                    end
            end

            if bFull then
                    print( "No empty slots left." )
                    return false
            end
            return true
    end

    function refuel( ammount )
            local fuelLevel = turtle.getFuelLevel()
            if fuelLevel == "unlimited" then
                    return true
            end

            local needed = ammount or (xPos + zPos + depth + 2)
            if turtle.getFuelLevel() < needed then
                    local fueled = false
                    for n=1,16 do
                            if turtle.getItemCount(n) > 0 then
                                    turtle.select(n)
                                    if turtle.refuel(1) then
                                            while turtle.getItemCount(n) > 0 and turtle.getFuelLevel() < needed do
                                                    turtle.refuel(1)
                                            end
                                            if turtle.getFuelLevel() >= needed then
                                                    turtle.select(1)
                                                    return true
                                            end
                                    end
                            end
                    end
                    turtle.select(1)
                    return false
            end

            return true
    end

    local function tryForwards()
            if not refuel() then
                    print( "Not enough Fuel" )
                    returnSupplies()
            end

            while not turtle.forward() do
                    if turtle.detect() then
                            if turtle.dig() then
                                    if not collect() then
                                            returnSupplies()
                                    end
                            else
                                    return false
                            end
                    elseif turtle.attack() then
                            if not collect() then
                                    returnSupplies()
                            end
                    else
                            sleep( 0.5 )
                    end
            end

            xPos = xPos + xDir
            zPos = zPos + zDir
            return true
    end

    local function tryDown()
            if not refuel() then
                    print( "Not enough Fuel" )
                    returnSupplies()
            end

            while not turtle.down() do
                    if turtle.detectDown() then
                            if turtle.digDown() then
                                    if not collect() then
                                            returnSupplies()
                                    end
                            else
                                    return false
                            end
                    elseif turtle.attackDown() then
                            if not collect() then
                                    returnSupplies()
                            end
                    else
                            sleep( 0.5 )
                    end
            end

            depth = depth + 1
            if math.fmod( depth, 10 ) == 0 then
                    print( "Descended "..depth.." metres." )
            end

            return true
    end

    local function turnLeft()
            turtle.turnLeft()
            xDir, zDir = -zDir, xDir
    end

    local function turnRight()
            turtle.turnRight()
            xDir, zDir = zDir, -xDir
    end

    function goTo( x, y, z, xd, zd )
            while depth > y do
                    if turtle.up() then
                            depth = depth - 1
                    elseif turtle.digUp() or turtle.attackUp() then
                            collect()
                    else
                            sleep( 0.5 )
                    end
            end

            if xPos > x then
                    while xDir ~= -1 do
                            turnLeft()
                    end
                    while xPos > x do
                            if turtle.forward() then
                                    xPos = xPos - 1
                            elseif turtle.dig() or turtle.attack() then
                                    collect()
                            else
                                    sleep( 0.5 )
                            end
                    end
            elseif xPos < x then
                    while xDir ~= 1 do
                            turnLeft()
                    end
                    while xPos < x do
                            if turtle.forward() then
                                    xPos = xPos + 1
                            elseif turtle.dig() or turtle.attack() then
                                    collect()
                            else
                                    sleep( 0.5 )
                            end
                    end
            end

            if zPos > z then
                    while zDir ~= -1 do
                            turnLeft()
                    end
                    while zPos > z do
                            if turtle.forward() then
                                    zPos = zPos - 1
                            elseif turtle.dig() or turtle.attack() then
                                    collect()
                            else
                                    sleep( 0.5 )
                            end
                    end
            elseif zPos < z then
                    while zDir ~= 1 do
                            turnLeft()
                    end
                    while zPos < z do
                            if turtle.forward() then
                                    zPos = zPos + 1
                            elseif turtle.dig() or turtle.attack() then
                                    collect()
                            else
                                    sleep( 0.5 )
                            end
                    end
            end

            while depth < y do
                    if turtle.down() then
                            depth = depth + 1
                    elseif turtle.digDown() or turtle.attackDown() then
                            collect()
                    else
                            sleep( 0.5 )
                    end
            end

            while zDir ~= zd or xDir ~= xd do
                    turnLeft()
            end
    end

    if not refuel() then
            print( "Out of Fuel" )
            return
    end

    print( "Excavating..." )

    local reseal = false
    turtle.select(1)
    if turtle.digDown() then
            reseal = true
    end


    if bResume == '1' then
        print("Resuming...")
        while turtle.down() do
            depth = depth + 1
        end
    end

    local alternate = 0
    local done = false
    while not done do
            for n=1,size do
                    for m=1,size-1 do
                            if not tryForwards() then
                                    done = true
                                    break
                            end
                    end
                    if done then
                            break
                    end
                    if n<size then
                            if math.fmod(n + alternate,2) == 0 then
                                    turnLeft()
                                    if not tryForwards() then
                                            done = true
                                            break
                                    end
                                    turnLeft()
                            else
                                    turnRight()
                                    if not tryForwards() then
                                            done = true
                                            break
                                    end
                                    turnRight()
                            end
                    end
            end
            if done then
                    break
            end

            if size > 1 then
                    if math.fmod(size,2) == 0 then
                            turnRight()
                    else
                            if alternate == 0 then
                                    turnLeft()
                            else
                                    turnRight()
                            end
                            alternate = 1 - alternate
                    end
            end

            if not tryDown() or depth + 1 > targetDepth then
                    done = true
                    break
            end
    end

    print( "Returning to surface..." )

    -- Return to where we started
    goTo( 0,0,0,0,-1 )
    unload( false )
    goTo( 0,0,0,0,1 )

    -- Seal the hole
    if reseal then
            turtle.placeDown()
    end

    print( "Mined "..(collected + unloaded).." items total." )