Refactor of commands

utils/queue.lua

@@ -0,0 +1,34 @@
+local Queue = {}
+
+function Queue.new()
+    local queue = {_head = 0, _tail = 0}
+    return queue
+end
+
+function Queue.size(queue)
+    return queue._tail - queue._head
+end
+
+function Queue.push(queue, element)
+    local index = queue._head
+    queue[index] = element
+    queue._head = index - 1
+end
+
+function Queue.peek(queue)
+    return queue[queue._tail]
+end
+
+function Queue.pop(queue)
+    local index = queue._tail
+
+    local element = queue[index]
+    queue[index] = nil
+
+    if element then
+        queue._tail = index - 1
+    end
+    return element
+end
+
+return Queue