diff --git a/cargo-elevator.lua b/cargo-elevator.lua
index 1717d56..3a850ea 100644
--- a/cargo-elevator.lua
+++ b/cargo-elevator.lua
@@ -21,41 +21,89 @@ local FLOORS = {
 
 local SLEEP_T = 5
 
-local PKG_STACK = {
-    transfer_all = function (self, src, dest)
-        -- TODO
-    end,
-    transfer_matching = function (self, src, dest, match_f)
-        -- TODO
-    end,
-    get_next_floor = function (self)
-        -- TODO
-    end
-    stack = {},
-}
-
-function run (floors, stack)
-    local next_addr = nil
-    for _, floor in pairs(floors) do
-        if floor.detect() then
-            stack:transfer_all(floor.storage, floor.elevator_storage)
-            stack:transfer_matching(
-                floor.elevator_storage, floor.storage, floor.match
-            )
-            next_addr = stack:get_next_floor()
+local PKG_QUEUE = {
+    insert = function (self, floor_i)
+        local is_in = function (item, list)
+            for _, l_item in ipairs(list) do
+                if l_item == item then return true end
+            end
+            return false
         end
-    end
-    if next_addr ~= nil then
-        for _, floor in pairs(floors) do
-            if floor.match(next_addr) then
-                floor.call()
-                break
+        if not is_in(floor_i, self.queue) then
+            table.insert(self.queue, floor_i)
+        end
+    end,
+    check_floors = function (self, floors)
+        for i, floor in pairs(floors) do
+            if #(peripheral.call(floor.storage, "list")) > 0 then
+                self:insert(i)
+            end
+        end
+    end,
+    check_cargo = function (self, inv, floors)
+        for slot, item in pairs(peripheral.call(inv, "list")) do
+            local item_detail = peripheral.call(src, "getItemDetail", slot)
+            for i, floor in ipairs(floors) do
+                if item_detail.package ~= nil and
+                    floor.match(item_detail.package.getAddress()) then
+                    self:insert(i)
+                    break
+                end
             end
         end
     end
+    transfer_all = function (self, src, dest, floors)
+        -- assumption: this always transfers into the cargo box
+        for slot, item in pairs(peripheral.call(src, "list")) do
+            local item_detail = peripheral.call(src, "getItemDetail", slot)
+            for i, floor in ipairs(floors) do
+                if item_detail.package ~= nil and
+                    floor.match(item_detail.package.getAddress()) then
+                    self:insert(i)
+                    peripheral.call(src, "pushItems", dest, slot)
+                    break
+                end
+            end
+        end
+    end,
+    transfer_matching = function (self, src, dest, match_f)
+        -- assumption: this always transfers out of the cargo box
+        for slot, item in pairs(peripheral.call(src, "list")) do
+            local item_detail = peripheral.call(src, "getItemDetail", slot)
+            if item_detail.package ~= nil and
+                match_f(item_detail.package.getAddress()) then
+                peripheral.call(src, "pushItems", dest, slot)
+            end
+        end
+    end,
+    get_next_floor = function (self)
+        return table.remove(self.queue, 1)
+    end
+    queue = {},
+}
+
+function run (floors, queue, first_run)
+    local next_floor = nil
+    queue:check_floors(floors)
+    for i, floor in pairs(floors) do
+        if floor.detect() then
+            if first_run then
+                queue:check_cargo(floor.elevator_storage, floors)
+            end
+            queue:transfer_all(floor.storage, floor.elevator_storage, floors)
+            queue:transfer_matching(
+                floor.elevator_storage, floor.storage, floor.match
+            )
+            next_floor = queue:get_next_floor()
+        end
+    end
+    if next_floor ~= nil then
+        floors[next_floor].call()
+    end
+    os.sleep(SLEEP_T)
+    return run(floors, queue, false)
 end
 
-while true do
-    run(FLOORS)
-    os.sleep(SLEEP_T)
+if arg ~= nil and arg[1] == "run" then
+    run(FLOORS, queue, true)
 end