add api tag controller

lib/philomena_web/controllers/api/json/tag_controller.ex

@@ -0,0 +1,44 @@
+defmodule PhilomenaWeb.Api.Json.TagController do
+  use PhilomenaWeb, :controller
+
+  alias Philomena.Tags.Tag
+
+  plug :load_resource, model: Tag, id_field: "slug", persisted: true, preload: [:aliased_tag, :aliases, :implied_tags, :implied_by_tags, :dnp_entries]
+
+  def show(conn, _params) do
+    json(conn, %{tag: tag_json(conn.assigns.tag)})
+  end
+
+  defp tag_json(tag) do
+    %{
+      id: tag.id,
+      name: tag.name,
+      slug: tag.slug,
+      description: tag.description,
+      short_description: tag.short_description,
+      images: tag.images_count,
+      spoiler_image_uri: tag_image(tag),
+      namespace: tag.namespace,
+      name_in_namespace: tag.name_in_namespace,
+      category: tag.category,
+      aliased_tag: aliased_tag(tag),
+      aliases: Enum.map(tag.aliases, & &1.slug),
+      implied_tags: Enum.map(tag.implied_tags, & &1.slug),
+      implied_by_tags: Enum.map(tag.implied_by_tags, & &1.slug),
+      dnp_entries: Enum.map(tag.dnp_entries, &%{conditions: &1.conditions})
+    }
+  end
+
+  defp aliased_tag(%{aliased_tag: nil}), do: nil
+  defp aliased_tag(%{aliased_tag: t}), do: t.slug
+
+  # TODO: copied from Tag.Fetch
+  defp tag_image(%{image: image}) when image not in [nil, ""],
+    do: tag_url_root() <> "/" <> image
+  defp tag_image(_other),
+    do: nil
+
+  defp tag_url_root do
+    Application.get_env(:philomena, :tag_url_root)
+  end
+end

lib/philomena_web/router.ex

@@ -83,6 +83,7 @@ defmodule PhilomenaWeb.Router do
     end
     resources "/search", SearchController, only: [:index]
     resources "/oembed", OembedController, only: [:index]
+    resources "/tags", TagController, only: [:show]
   end
 
   scope "/", PhilomenaWeb do