feat: tag discovery from posts

lib/bds/tags.ex

@@ -47,6 +47,52 @@ defmodule BDS.Tags do
     :ok
   end
 
+  def sync_tags_from_posts(project_id) do
+    Repo.transaction(fn ->
+      existing_names =
+        project_id
+        |> list_tags()
+        |> Enum.map(&String.downcase(&1.name))
+        |> MapSet.new()
+
+      missing_names =
+        project_id
+        |> post_tag_names()
+        |> Enum.reduce({existing_names, []}, fn tag_name, {seen_names, acc} ->
+          normalized = String.downcase(tag_name)
+
+          if MapSet.member?(seen_names, normalized) do
+            {seen_names, acc}
+          else
+            {MapSet.put(seen_names, normalized), [tag_name | acc]}
+          end
+        end)
+        |> elem(1)
+        |> Enum.reverse()
+
+      now = System.system_time(:second)
+
+      Enum.each(missing_names, fn name ->
+        %Tag{}
+        |> Tag.changeset(%{
+          id: Ecto.UUID.generate(),
+          project_id: project_id,
+          name: name,
+          created_at: now,
+          updated_at: now
+        })
+        |> Repo.insert!()
+      end)
+
+      write_tags_json(project_id)
+      list_tags(project_id)
+    end)
+    |> case do
+      {:ok, tags} -> {:ok, tags}
+      {:error, reason} -> {:error, reason}
+    end
+  end
+
   def update_tag(tag_id, attrs) do
     case Repo.get(Tag, tag_id) do
       nil ->
@@ -212,6 +258,16 @@ defmodule BDS.Tags do
     |> Enum.filter(fn post -> Enum.any?(post.tags || [], &(&1 in tag_names)) end)
   end
 
+  defp post_tag_names(project_id) do
+    Repo.all(from post in Post, where: post.project_id == ^project_id)
+    |> Enum.flat_map(fn post ->
+      post.tags
+      |> Kernel.||([])
+      |> Enum.map(&String.trim/1)
+      |> Enum.reject(&(&1 == ""))
+    end)
+  end
+
   defp replace_tag(tags, old_name, new_name) do
     tags
     |> Enum.map(fn tag -> if tag == old_name, do: new_name, else: tag end)

test/bds/tags_test.exs

@@ -145,6 +145,50 @@ defmodule BDS.TagsTest do
     assert %{"tags" => [%{"name" => "Beta"}]} = Jason.decode!(File.read!(tags_path))
   end
 
+  test "sync_tags_from_posts creates missing tags from post tag arrays and refreshes tags.json", %{project: project, temp_dir: temp_dir} do
+    assert {:ok, existing} =
+             BDS.Tags.create_tag(%{
+               project_id: project.id,
+               name: "Existing",
+               color: "#112233",
+               post_template_slug: "feature-view"
+             })
+
+    assert {:ok, _post_a} =
+             BDS.Posts.create_post(%{
+               project_id: project.id,
+               title: "First",
+               content: "Body",
+               tags: ["Existing", "Missing", "Missing"]
+             })
+
+    assert {:ok, _post_b} =
+             BDS.Posts.create_post(%{
+               project_id: project.id,
+               title: "Second",
+               content: "Body",
+               tags: ["Another", "Missing"]
+             })
+
+    assert {:ok, synced_tags} = BDS.Tags.sync_tags_from_posts(project.id)
+
+    assert Enum.map(synced_tags, & &1.name) == ["Another", "Existing", "Missing"]
+
+    reloaded_existing = Repo.get!(BDS.Tags.Tag, existing.id)
+    assert reloaded_existing.color == "#112233"
+    assert reloaded_existing.post_template_slug == "feature-view"
+
+    tags_path = Path.join([temp_dir, "meta", "tags.json"])
+
+    assert %{
+             "tags" => [
+               %{"name" => "Another"},
+               %{"name" => "Existing", "color" => "#112233", "post_template_slug" => "feature-view"},
+               %{"name" => "Missing"}
+             ]
+           } = Jason.decode!(File.read!(tags_path))
+  end
+
   defp errors_on(changeset) do
     Ecto.Changeset.traverse_errors(changeset, fn {message, opts} ->
       Regex.replace(~r"%{(\w+)}", message, fn _, key ->