Add stripping HTML attributes

lib/outlook/internal_tree/html.ex

@@ -3,6 +3,25 @@ defmodule Outlook.InternalTree.Html do
   alias Outlook.InternalTree.InternalNode
   alias Outlook.InternalTree.TranslationUnit
 
+  @desirable_atts %{"a" => [:href], "img" => [:src]}
+
+  def strip_attributes([%InternalNode{type: :element} = node | rest]) do
+    d_atts = Map.get(@desirable_atts, node.name, [])
+    atts = Map.reject(node.attributes, fn {k,_} -> k not in d_atts end)
+    [ %{node |
+        attributes: atts,
+        content: strip_attributes(node.content)
+      }
+      | strip_attributes(rest) ]
+  end
+
+  def strip_attributes([node | rest]) do
+    [ node | strip_attributes(rest)]
+  end
+
+  def strip_attributes([]), do: []
+
+
   def to_html([ %InternalNode{type: :element} = node | rest]) do
     attr_string = Map.put(node.attributes, :uuid, node.uuid)
     |> Enum.map_join(" ", fn {k,v} -> "#{k}=\"#{v}\"" end)