Ender Turtle

local S_MINING = "MINING"
local S_FINISH  = "FINISH"
local S_ADVANCE = "ADVANCE"

local chestIndex = 1
local CHEST = "Ender"

local DepthTarget = 130

local status = {}
local statusFileName = "enderstatus"

local function loadTable(name)
        local file = fs.open(name,"r")
        if file == nil then
            return
        end
        local data = file.readAll()
        file.close()
        return textutils.unserialize(data)
end

local function saveTable(table,name)
        local file = fs.open(name,"w")
        file.write(textutils.serialize(table))
        file.close()
end

local function saveStatus()
    saveTable(status, statusFileName)
end

local function loadStatus()
    status = loadTable(statusFileName)
end

local function CheckRefuel()
    if turtle.getFuelLevel() > 4000 then
        return
    end

    for i=2,16 do
        turtle.select(i)
        turtle.refuel(64)
    end
end

local function ReturnBack()

    for i=1,DepthTarget do
        turtle.up()
    end
end

local function DepositChest()

    if turtle.detectUp() == true then
        turtle.down()
    end

    turtle.select(1)
    turtle.placeUp()

    for i = 2,16 do
            turtle.select(i)
            turtle.dropUp()
    end

    turtle.select(1)
    turtle.digUp()
    turtle.select(2)
    turtle.up()
end

local function InventoryFull()
    -- check 2-16, backwards for efficiency
    for i=1,15 do
            if turtle.getItemCount(16-i) == 0 then
                    return false
            end
    end

    return true
end

local function CheckInventory()

    if InventoryFull() then
        CheckRefuel()
        DepositChest()
    end
end

local function Harvest()

    if not turtle.detectDown() then
        return
    end

    while turtle.suckDown() == true do
        CheckInventory()
    end

    turtle.digDown()
    CheckInventory()
end

local function Finish()

    DepositChest()
    ReturnBack()
    status.status = S_ADVANCE
end

local function NextColumn()

    for i=1,4 do
        if turtle.detect() then
            turtle.dig()
        end
        turtle.forward()
    end

    status.status = S_MINING
end


local function StartMining()

    for i=1,DepthTarget do
        turtle.attackDown()
        Harvest()
        turtle.down()
    end

    status.status = S_FINISH
end


function Main()

    while status.status ~= S_STOP do
        saveStatus()
        sleep(1)

        if status.status == S_MINING then
            StartMining()

        elseif status.status == S_FINISH then
            Finish()

        elseif status.status == S_ADVANCE then
            NextColumn()

        else
            print("Unknown status: "..status.status)
            status.status = S_STOP
        end
    end
    ReturnBack()
end

-- ON LAUNCH
loadStatus()

if status == nil then
    status = { }
   status.status = S_MINING
end

Main()