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

function load(name)
    local file = fs.open(name, "r")
    if not file then
        if name == "open_positions" then
            save({{x=-5,y=2,z=-5}}, name)
        else
            save({}, name)
        end
        return load(name)
    else
        local data = file.readAll()
        file.close()
        return textutils.unserialize(data)
    end
end

function go_to(target)
    if me.y ~= target.y then
        go_to({x = 0, y = me.y, z = 0})
        while me.y < target.y do
            if turtle.up() then me.y = me.y + 1 end
        end
        while me.y > target.y do
            if turtle.down() then me.y = me.y - 1 end
        end
    end
    if me.x < target.x then
        turtle.turnRight()
        while me.x < target.x do
            if turtle.forward() then me.x = me.x + 1 end
        end
        turtle.turnLeft()
    end
    if me.x > target.x then
        turtle.turnLeft()
        while me.x > target.x do
            if turtle.forward() then me.x = me.x - 1 end
        end
        turtle.turnRight()
    end
    while me.z < target.z do
        if turtle.forward() then me.z = me.z + 1 end
    end
    while me.z > target.z do
        if turtle.back() then me.z = me.z - 1 end
    end
end

function next_position(position)
    local new_position = {x = position.x, y = position.y, z = position.z, side = position.side}
    if position.side == "down" then
        new_position.side = "up"
    else
        new_position.side = "down"
        if position.x == 5 then
            new_position.x = -5
            if position.z == 5 then
                new_position.z = -5
                new_position.y = position.y + 3
            else
                new_position.z = position.z + 1
            end
        else
            if position.x == -1 and position.z == 0 then
                new_position.x = position.x + 2
            else
                new_position.x = position.x + 1
            end
        end
    end
    return new_position
end

function get_enderchest(group)
    turtle.select(16)
    turtle.placeDown()
end

function safe_string(text)
    local new_text = {}
    for i = 1, #text do
        local val = string.byte(text, i)
        new_text[i] = (val > 31 and val < 127) and val or 32
    end
    return string.char(unpack(new_text))
end

function earliest_order(position_1, position_2)
    if position_1.y > position_2.y then
        return true
    elseif position_1.y == position_2.y then
        if position_1.z > position_2.z then
            return true
        elseif position_1.z == position_2.z then
            if position_1.x > position_2.x then
                return true
            elseif position_1.x == position_2.x then
                if position_1.side == "up" then
                    return true
                end
            end
        end
    end
end

function next_open_position()
    if #open_positions > 1 then
        table.sort(open_positions, earliest_order)
        return table.remove(open_positions)
    else
        local position = table.remove(open_positions)
        table.insert(next_position(position))
        return position
    end
end

function register(stack)
    local item = nil
    stack.string_id = safe_string(stack.id..stack.dmg..stack.raw_name..stack.display_name)
    for _, existing_item in ipairs(items) do
        if existing_item.string_id == stack.string_id then
            item = existing_item
            break
        end
    end
    if not item then
        item = {}
        item.string_id = stack.string_id
        item.damage = stack.dmg
        item.max_damage = stack.max_dmg
        item.max_stack = stack.max_size
        item.recipes = {}
        item.quantity = 0
        item.position = next_open_position()
        item.slot = nil
        table.insert(items, item)
    end
    if item.position == nil then
        item.position = next_open_position()
    end
    save(open_positions, "open_positions")
end

function check_inventory()
    local items_to_sort = {}
    local inventory_items = inventory.getAllStacks()
    for i = 1, #inventory_items - 1 do
        table.insert(items_to_sort, register(inventory_items[i].basic()))
    end
    return items_to_sort
end

function distance_away(position)
    local distance = math.abs(position.y - me.y)
    distance = distance + math.abs(me.x) + math.abs(me.z)
    distance = distance + math.abs(position.x) + math.abs(position.z)
    return distance
end

function closest_order(item_1, item_2)
    return distance_away(item_1.position) > distance_away(item_2.position)
end

function give_item_slots(items_to_sort)
    for i = 1, #items_to_sort do
        items_to_sort[i].slot = i
    end
end

function deposit_item(item)
    go_to(item.position)
    local amount = inventory.push(item.position.side, item.slot)
    item.quantity = item.quantity + amount
    save(items, "items")
end

function sort_items(items_to_sort)
    give_item_slots(items_to_sort)
    while #items_to_sort > 0 do
        local closest_item = table.sort(items_to_sort, closest_order)[#items_to_sort]
        deposit_item(closest_item)
        table.remove(items_to_sort)
    end
end

function condense_inventory()
    inventory.condenseItems()
    inventory.swapStacks(#inventory.getAllStacks(), 16)
end

function begin_depositing()
    go_to({x=0, y=me.y, z=0})
    local at_home = turtle.detectDown()
    condense_inventory()
    if not at_home then
        get_enderchest("deposit")
    end
    turtle.select(1)
    while turtle.suckDown() do end
    chest.condenseItems()
    if #chest.getAllStacks() > 0 then
        table.insert(queue, 2, begin_depositing)
    end
    if not at_home then
        turtle.digDown()
    end
    local items_to_sort = check_inventory()
    sort_items(items_to_sort)
end

function start()
    me = {x=0,y=0,z=0}
    queue = {}
    while not chest do
        chest = peripheral.wrap("bottom")
        sleep(3)
    end
    inventory = peripheral.wrap("right")
    items = load("items")
    open_positions = load("open_positions")
end

function do_queue()
    local i = 1
    while i <= #queue do
        queue[i]()
        i = i + 1
    end
end

start()

while true do
    command = io.read()
    if command == ">" then
        table.insert(queue, begin_depositing)
    elseif command == "" then
        do_queue()
    end
end