Refactor Core things, including Ecto handling, ActivityPub & Transmogrifier modules

* Data doesn't need anymore to be converted to ActivityStream format to
be saved (this was taken from Pleroma and not at all a good idea here)
* Everything saved when creating an event is inserted into PostgreSQL in
a single transaction

lib/service/activity_pub/converter/utils.ex

@@ -0,0 +1,100 @@
+defmodule Mobilizon.Service.ActivityPub.Converter.Utils do
+  @moduledoc """
+  Various utils for converters
+  """
+
+  alias Mobilizon.Actors.Actor
+  alias Mobilizon.Events.Tag
+  alias Mobilizon.Mention
+  alias Mobilizon.Service.ActivityPub
+  alias Mobilizon.Storage.Repo
+  require Logger
+
+  @spec fetch_tags([String.t()]) :: [Tag.t()]
+  def fetch_tags(tags) when is_list(tags) do
+    Logger.debug("fetching tags")
+
+    Enum.reduce(tags, [], &fetch_tag/2)
+  end
+
+  @spec fetch_mentions([map()]) :: [map()]
+  def fetch_mentions(mentions) when is_list(mentions) do
+    Logger.debug("fetching mentions")
+
+    Enum.reduce(mentions, [], fn mention, acc -> create_mention(mention, acc) end)
+  end
+
+  def fetch_address(%{id: id}) do
+    with {id, ""} <- Integer.parse(id) do
+      %{id: id}
+    end
+  end
+
+  def fetch_address(address) when is_map(address) do
+    address
+  end
+
+  @spec build_tags([Tag.t()]) :: [Map.t()]
+  def build_tags(tags) do
+    Enum.map(tags, fn %Tag{} = tag ->
+      %{
+        "href" => MobilizonWeb.Endpoint.url() <> "/tags/#{tag.slug}",
+        "name" => "##{tag.title}",
+        "type" => "Hashtag"
+      }
+    end)
+  end
+
+  def build_mentions(mentions) do
+    Enum.map(mentions, fn %Mention{} = mention ->
+      if Ecto.assoc_loaded?(mention.actor) do
+        build_mention(mention.actor)
+      else
+        build_mention(Repo.preload(mention, [:actor]).actor)
+      end
+    end)
+  end
+
+  defp build_mention(%Actor{} = actor) do
+    %{
+      "href" => actor.url,
+      "name" => "@#{Mobilizon.Actors.Actor.preferred_username_and_domain(actor)}",
+      "type" => "Mention"
+    }
+  end
+
+  defp fetch_tag(tag, acc) when is_map(tag) do
+    case tag["type"] do
+      "Hashtag" ->
+        acc ++ [%{title: tag}]
+
+      _err ->
+        acc
+    end
+  end
+
+  defp fetch_tag(tag, acc) when is_bitstring(tag) do
+    acc ++ [%{title: tag}]
+  end
+
+  @spec create_mention(map(), list()) :: list()
+  defp create_mention(%Actor{id: actor_id} = _mention, acc) do
+    acc ++ [%{actor_id: actor_id}]
+  end
+
+  @spec create_mention(map(), list()) :: list()
+  defp create_mention(mention, acc) when is_map(mention) do
+    with true <- mention["type"] == "Mention",
+         {:ok, %Actor{id: actor_id}} <- ActivityPub.get_or_fetch_actor_by_url(mention["href"]) do
+      acc ++ [%{actor_id: actor_id}]
+    else
+      _err ->
+        acc
+    end
+  end
+
+  @spec create_mention({String.t(), map()}, list()) :: list()
+  defp create_mention({_, mention}, acc) when is_map(mention) do
+    create_mention(mention, acc)
+  end
+end