Refactor Mobilizon.Federation.ActivityPub and add typespecs

Signed-off-by: Thomas Citharel <tcit@tcit.fr>

lib/web/plugs/detect_locale_plug.ex

@@ -11,19 +11,23 @@ defmodule Mobilizon.Web.Plugs.DetectLocalePlug do
   import Plug.Conn, only: [get_req_header: 2, assign: 3]
   alias Mobilizon.Web.Gettext, as: GettextBackend
 
+  @spec init(any()) :: any()
   def init(_), do: nil
 
+  @spec call(Plug.Conn.t(), Keyword.t()) :: Plug.Conn.t()
   def call(conn, _) do
     locale = get_locale_from_header(conn)
     assign(conn, :detected_locale, locale)
   end
 
+  @spec get_locale_from_header(Plug.Conn.t()) :: String.t()
   defp get_locale_from_header(conn) do
     conn
     |> extract_accept_language()
     |> Enum.find(&supported_locale?/1)
   end
 
+  @spec extract_accept_language(Plug.Conn.t()) :: list(String.t())
   defp extract_accept_language(conn) do
     case get_req_header(conn, "accept-language") do
       [value | _] ->
@@ -40,12 +44,14 @@ defmodule Mobilizon.Web.Plugs.DetectLocalePlug do
     end
   end
 
+  @spec supported_locale?(String.t()) :: boolean()
   defp supported_locale?(locale) do
     GettextBackend
     |> Gettext.known_locales()
     |> Enum.member?(locale)
   end
 
+  @spec parse_language_option(String.t()) :: %{tag: String.t(), quality: float()}
   defp parse_language_option(string) do
     captures = Regex.named_captures(~r/^\s?(?<tag>[\w\-]+)(?:;q=(?<quality>[\d\.]+))?$/i, string)
 
@@ -58,6 +64,7 @@ defmodule Mobilizon.Web.Plugs.DetectLocalePlug do
     %{tag: captures["tag"], quality: quality}
   end
 
+  @spec ensure_language_fallbacks(list(String.t())) :: list(String.t())
   defp ensure_language_fallbacks(tags) do
     Enum.flat_map(tags, fn tag ->
       [language | _] = String.split(tag, "-")