From a0f1d0c4c33c57bacd51da22343c3da5251a6f7c Mon Sep 17 00:00:00 2001
From: miteruzo <miteruzo@naver.com>
Date: Thu, 24 Sep 2026 12:48:29 +0900
Subject: [PATCH] #419

---
 .../app/controllers/nico_tags_controller.rb   |  6 +++++
 backend/config/routes.rb                      |  2 +-
 backend/spec/requests/nico_tags_spec.rb       | 26 +++++++++++++++++++
 3 files changed, 33 insertions(+), 1 deletion(-)

diff --git a/backend/app/controllers/nico_tags_controller.rb b/backend/app/controllers/nico_tags_controller.rb
index ea02a12..6f97dbc 100644
--- a/backend/app/controllers/nico_tags_controller.rb
+++ b/backend/app/controllers/nico_tags_controller.rb
@@ -71,6 +71,12 @@ class NicoTagsController < ApplicationController
     }, count: }
   end
 
+  def show
+    tag = ExternalTag.find(params[:id])
+
+    render json: external_tag_json(tag)
+  end
+
   def update
     return head :unauthorized unless current_user
     return head :forbidden unless current_user.gte_member?
diff --git a/backend/config/routes.rb b/backend/config/routes.rb
index 00fc425..0f721d1 100644
--- a/backend/config/routes.rb
+++ b/backend/config/routes.rb
@@ -1,5 +1,5 @@
 Rails.application.routes.draw do
-  resources :nico_tags, path: 'tags/nico', only: [:index, :update]
+  resources :nico_tags, path: 'tags/nico', only: [:index, :show, :update]
 
   scope 'tags/:parent_id/children', controller: :tag_children do
     post ':child_id', action: :create
diff --git a/backend/spec/requests/nico_tags_spec.rb b/backend/spec/requests/nico_tags_spec.rb
index b1572dd..243cbd3 100644
--- a/backend/spec/requests/nico_tags_spec.rb
+++ b/backend/spec/requests/nico_tags_spec.rb
@@ -106,6 +106,32 @@ RSpec.describe 'NicoTags', type: :request do
     end
   end
 
+  describe 'GET /tags/nico/:id' do
+    it 'returns the external tag even when an internal tag has the same id' do
+      internal = create(:tag)
+      external = create(
+          :external_tag,
+          id: internal.id,
+          name: 'external_detail')
+
+      get "/tags/nico/#{ external.id }"
+
+      expect(response).to have_http_status(:ok)
+      expect(json).to include(
+          'id' => external.id,
+          'name' => 'nico:external_detail',
+          'category' => 'nico')
+    end
+
+    it 'returns 404 when the external tag does not exist' do
+      internal = create(:tag)
+
+      get "/tags/nico/#{ internal.id }"
+
+      expect(response).to have_http_status(:not_found)
+    end
+  end
+
   describe 'PATCH /tags/nico/:id' do
     let(:member) { create(:user, :member) }
     let(:admin) { create(:user, :admin) }