add tag alias validations

lib/philomena/tags.ex

@@ -180,11 +180,26 @@ defmodule Philomena.Tags do
   end
 
   def alias_tag(%Tag{} = tag, attrs) do
-    target_tag = Repo.get_by!(Tag, name: attrs["target_tag"])
+    target_tag = Repo.get_by(Tag, name: String.downcase(attrs["target_tag"]))
 
-    if tag.id == target_tag.id do
     tag
-    else
+    |> Repo.preload(:aliased_tag)
+    |> Tag.alias_changeset(target_tag)
+    |> Repo.update()
+    |> case do
+      {:ok, tag} ->
+        spawn(fn ->
+          perform_alias(tag, target_tag)
+        end)
+
+        {:ok, tag}
+
+      error ->
+        error
+    end
+  end
+
+  defp perform_alias(tag, target_tag) do
     filters_hidden =
       where(Filter, [f], fragment("? @> ARRAY[?]::integer[]", f.hidden_tag_ids, ^tag.id))
 
@@ -236,7 +251,6 @@ defmodule Philomena.Tags do
     reindex_tag_images(target_tag)
     reindex_tags([tag, target_tag])
   end
-  end
 
   def reindex_tag_images(%Tag{} = tag) do
     # First recount the tag

lib/philomena/tags/tag.ex

@@ -1,12 +1,14 @@
 defmodule Philomena.Tags.Tag do
   use Ecto.Schema
   import Ecto.Changeset
+  import Ecto.Query
 
   alias Philomena.Channels.Channel
   alias Philomena.DnpEntries.DnpEntry
   alias Philomena.UserLinks.UserLink
   alias Philomena.Tags.Tag
   alias Philomena.Slug
+  alias Philomena.Repo
 
   @namespaces [
     "artist",
@@ -111,6 +113,15 @@ defmodule Philomena.Tags.Tag do
     |> put_change(:image, nil)
   end
 
+  def alias_changeset(tag, target_tag) do
+    change(tag)
+    |> put_assoc(:aliased_tag, target_tag)
+    |> validate_required([:aliased_tag])
+    |> validate_not_aliased_to_self()
+    |> validate_alias_not_transitive()
+    |> validate_incoming_aliases()
+  end
+
   def unalias_changeset(tag) do
     change(tag, aliased_tag_id: nil)
   end
@@ -245,4 +256,46 @@ defmodule Philomena.Tags.Tag do
       category -> change(changeset, category: category)
     end
   end
+
+  defp validate_not_aliased_to_self(changeset) do
+    aliased_tag = get_field(changeset, :aliased_tag)
+    id = get_field(changeset, :id)
+
+    case aliased_tag do
+      %{id: ^id} ->
+        add_error(changeset, :aliased_tag, "is the same tag as the source")
+
+      _tag ->
+        changeset
+    end
+  end
+
+  defp validate_alias_not_transitive(changeset) do
+    case get_field(changeset, :aliased_tag) do
+      %{aliased_tag_id: tag} when not is_nil(tag) ->
+        add_error(
+          changeset,
+          :aliased_tag,
+          "is itself aliased and would create a transitive alias"
+        )
+
+      _tag ->
+        changeset
+    end
+  end
+
+  defp validate_incoming_aliases(changeset) do
+    id = get_field(changeset, :id)
+
+    count =
+      Tag
+      |> where(aliased_tag_id: ^id)
+      |> Repo.aggregate(:count, :id)
+
+    if count > 0 do
+      add_error(changeset, :tag, "has incoming aliases and cannot be aliased")
+    else
+      changeset
+    end
+  end
 end

lib/philomena_web/controllers/tag/alias_controller.ex

@@ -19,13 +19,15 @@ defmodule PhilomenaWeb.Tag.AliasController do
   end
 
   def update(conn, %{"tag" => tag_params}) do
-    spawn(fn ->
-      Tags.alias_tag(conn.assigns.tag, tag_params)
-    end)
-
+    case Tags.alias_tag(conn.assigns.tag, tag_params) do
+      {:ok, tag} ->
         conn
         |> put_flash(:info, "Tag alias queued.")
-    |> redirect(to: Routes.tag_alias_path(conn, :edit, conn.assigns.tag))
+        |> redirect(to: Routes.tag_alias_path(conn, :edit, tag))
+
+      {:error, changeset} ->
+        render(conn, "edit.html", changeset: changeset)
+    end
   end
 
   def delete(conn, _params) do

lib/philomena_web/templates/tag/alias/edit.html.slime

@@ -10,6 +10,8 @@ h1
   .field
     => label f, "Alias target:"
     = text_input f, :target_tag, value: alias_target(@tag), class: "input"
+    = error_tag f, :tag
+    = error_tag f, :aliased_tag
 
   .field
     => submit "Alias tag", class: "button"