Fix hashtags casing

Signed-off-by: marcin mikołajczak <git@mkljczk.pl>

lib/pleroma/formatter.ex

@@ -67,7 +67,6 @@ def mention_from_user(%User{id: id} = user, opts \\ %{mentions_format: :full}) d
   end
 
   def hashtag_handler("#" <> tag = tag_text, _buffer, _opts, acc) do
-    tag = String.downcase(tag)
     url = "#{Pleroma.Web.Endpoint.url()}/tag/#{tag}"
 
     link =
@@ -83,11 +82,11 @@ def hashtag_handler("#" <> tag = tag_text, _buffer, _opts, acc) do
   end
 
   def doublehashtag_handler("##" <> tag = tag_text, _buffer, _opts, acc) do
-    {tag, %{acc | tags: MapSet.put(acc.tags, {tag_text, tag |> String.downcase()})}}
+    {tag, %{acc | tags: MapSet.put(acc.tags, {tag_text, tag})}}
   end
 
   def triplehashtag_handler("###" <> tag = tag_text, _buffer, _opts, acc) do
-    {"", %{acc | tags: MapSet.put(acc.tags, {tag_text, tag |> String.downcase()})}}
+    {"", %{acc | tags: MapSet.put(acc.tags, {tag_text, tag})}}
   end
 
   @doc """

lib/pleroma/hashtag.ex

@@ -40,7 +40,8 @@ def get_or_create_by_name(name) do
   end
 
   def get_or_create_by_names(names) when is_list(names) do
-    names = Enum.map(names, &normalize_name/1)
+    lowercase_names = names |> Enum.map(&normalize_name/1)
+
     timestamp = NaiveDateTime.truncate(NaiveDateTime.utc_now(), :second)
 
     structs =
@@ -59,7 +60,7 @@ def get_or_create_by_names(names) when is_list(names) do
                conflict_target: :name
              )
              |> Multi.run(:query_op, fn _repo, _changes ->
-               {:ok, Repo.all(from(ht in Hashtag, where: ht.name in ^names))}
+               {:ok, Repo.all(from(ht in Hashtag, where: ht.name in ^lowercase_names))}
              end)
              |> Repo.transaction() do
         {:ok, hashtags}

lib/pleroma/object.ex

@@ -464,17 +464,28 @@ def object_data_hashtags(%{"tag" => tags}) when is_list(tags) do
       _ -> false
     end)
     |> Enum.map(fn
-      %{"name" => "#" <> hashtag} -> String.downcase(hashtag)
-      %{"name" => hashtag} -> String.downcase(hashtag)
-      hashtag when is_bitstring(hashtag) -> String.downcase(hashtag)
+      %{"name" => "#" <> hashtag} -> hashtag
+      %{"name" => hashtag} -> hashtag
+      hashtag when is_bitstring(hashtag) -> hashtag
     end)
-    |> Enum.uniq()
+    |> uniq_case_insensitive()
     # Note: "" elements (plain text) might occur in `data.tag` for incoming objects
     |> Enum.filter(&(&1 not in [nil, ""]))
   end
 
   def object_data_hashtags(_), do: []
 
+  defp uniq_case_insensitive(strings) do
+    strings
+    |> Enum.map(&String.downcase/1)
+    |> Enum.uniq()
+    |> Enum.map(&find_original_case(&1, strings))
+  end
+
+  defp find_original_case(string, strings) do
+    Enum.find(strings, &String.downcase(&1) == string)
+  end
+
   def get_emoji_reactions(object) do
     reactions = object.data["reactions"]