Merge branch 'fetch-posts-on-first-federation' into 'develop'

Fetch user's outbox posts on first federation with that user

Closes #131

See merge request pleroma/pleroma!907

lib/pleroma/web/activity_pub/utils.ex

@@ -633,4 +633,43 @@ defmodule Pleroma.Web.ActivityPub.Utils do
     }
     |> Map.merge(additional)
   end
+
+  @doc """
+  Fetches the OrderedCollection/OrderedCollectionPage from `from`, limiting the amount of pages fetched after
+  the first one to `pages_left` pages.
+  If the amount of pages is higher than the collection has, it returns whatever was there.
+  """
+  def fetch_ordered_collection(from, pages_left, acc \\ []) do
+    with {:ok, response} <- Tesla.get(from),
+         {:ok, collection} <- Poison.decode(response.body) do
+      case collection["type"] do
+        "OrderedCollection" ->
+          # If we've encountered the OrderedCollection and not the page,
+          # just call the same function on the page address
+          fetch_ordered_collection(collection["first"], pages_left)
+
+        "OrderedCollectionPage" ->
+          if pages_left > 0 do
+            # There are still more pages
+            if Map.has_key?(collection, "next") do
+              # There are still more pages, go deeper saving what we have into the accumulator
+              fetch_ordered_collection(
+                collection["next"],
+                pages_left - 1,
+                acc ++ collection["orderedItems"]
+              )
+            else
+              # No more pages left, just return whatever we already have
+              acc ++ collection["orderedItems"]
+            end
+          else
+            # Got the amount of pages needed, add them all to the accumulator
+            acc ++ collection["orderedItems"]
+          end
+
+        _ ->
+          {:error, "Not an OrderedCollection or OrderedCollectionPage"}
+      end
+    end
+  end
 end