From 2cd9c603688e0dc92f21a236454a82a0dff64880 Mon Sep 17 00:00:00 2001
From: miteruzo <miteruzo@naver.com>
Date: Mon, 22 Jun 2026 06:18:10 +0900
Subject: [PATCH] #378

---
 backend/app/controllers/tags_controller.rb | 124 ++++++++++++++++-----
 1 file changed, 94 insertions(+), 30 deletions(-)

diff --git a/backend/app/controllers/tags_controller.rb b/backend/app/controllers/tags_controller.rb
index b9fadb9..c9e585e 100644
--- a/backend/app/controllers/tags_controller.rb
+++ b/backend/app/controllers/tags_controller.rb
@@ -1,5 +1,6 @@
 require 'net/http'
 require 'uri'
+require 'set'
 
 
 class TagsController < ApplicationController
@@ -82,51 +83,27 @@ class TagsController < ApplicationController
     parent_tag_id = params[:parent].to_i
     parent_tag_id = nil if parent_tag_id <= 0
 
+    graph = build_with_depth_graph
+
     tag_ids =
         if parent_tag_id
-          TagImplication.joins(:tag)
-                        .where(parent_tag_id:)
-                        .where(tags: { deprecated_at: nil })
-                        .select(:tag_id)
+          visible_child_tag_ids(parent_tag_id, graph)
         else
-          Tag.where(deprecated_at: nil)
-             .where.not(id: TagImplication
-                              .joins(<<~SQL.squish)
-                                INNER JOIN
-                                  tags parent_tags
-                                  ON parent_tags.id = tag_implications.parent_tag_id
-                              SQL
-                              .where('parent_tags.deprecated_at IS NULL')
-                              .select(:tag_id))
-             .select(:id)
+          visible_root_tag_ids(graph)
         end
 
     tags =
         Tag
         .joins(:tag_name)
         .includes(:tag_name, :materials, tag_name: :wiki_page)
-        .where(category: [:meme, :character, :material])
-        .where(deprecated_at: nil)
         .where(id: tag_ids)
         .order('tag_names.name')
         .distinct
         .to_a
 
-    has_children_tag_ids =
-        if tags.empty?
-          []
-        else
-          TagImplication
-              .joins(:tag)
-              .where(parent_tag_id: tags.map(&:id),
-                     tags: { category: [:meme, :character, :material],
-                             deprecated_at: nil })
-              .distinct
-              .pluck(:parent_tag_id)
-        end
-
     render json: tags.map { |tag|
-      TagRepr.base(tag).merge(has_children: has_children_tag_ids.include?(tag.id), children: [])
+      TagRepr.base(tag).merge(has_children: visible_child_tag_ids(tag.id, graph).present?,
+                              children: [])
     }
   end
 
@@ -371,6 +348,93 @@ class TagsController < ApplicationController
 
   private
 
+  def build_with_depth_graph
+    children_by_parent_id = Hash.new { |h, k| h[k] = [] }
+    parent_ids_by_child_id = Hash.new { |h, k| h[k] = [] }
+
+    TagImplication.pluck(:parent_tag_id, :tag_id).each do |parent_id, child_id|
+      children_by_parent_id[parent_id] << child_id
+      parent_ids_by_child_id[child_id] << parent_id
+    end
+
+    tag_ids = (children_by_parent_id.keys +
+               parent_ids_by_child_id.keys +
+               Tag.where(category: ['meme', 'character', 'material']).pluck(:id)).uniq
+
+    tags_by_id = Tag.where(id: tag_ids)
+                    .pluck(:id, :category, :deprecated_at)
+                    .each_with_object({ }) do |(id, category, deprecated_at), h|
+      h[id] = { category:, deprecated: deprecated_at.present? }
+    end
+
+    { children_by_parent_id:, parent_ids_by_child_id:, tags_by_id:,
+      visible_child_tag_ids_by_parent_id: { } }
+  end
+
+  def visible_root_tag_ids graph
+    graph[:tags_by_id].filter_map do |tag_id, attrs|
+      next unless with_depth_visible_tag?(attrs)
+      next unless visible_root_tag?(tag_id, graph)
+
+      tag_id
+    end
+  end
+
+  def visible_root_tag? tag_id, graph
+    seen = Set.new([tag_id])
+    stack = graph[:parent_ids_by_child_id][tag_id].dup
+
+    until stack.empty?
+      parent_id = stack.pop
+      next if seen.include?(parent_id)
+
+      seen << parent_id
+
+      parent = graph[:tags_by_id][parent_id]
+      next unless parent
+
+      return false unless parent[:deprecated]
+
+      stack.concat(graph[:parent_ids_by_child_id][parent_id])
+    end
+
+    true
+  end
+
+  def visible_child_tag_ids parent_tag_id, graph
+    cache = graph[:visible_child_tag_ids_by_parent_id]
+    return cache[parent_tag_id] if cache.key?(parent_tag_id)
+
+    visible_ids = Set.new
+
+    graph[:children_by_parent_id][parent_tag_id].each do |child_tag_id|
+      collect_visible_child_tag_ids(child_tag_id, graph, visible_ids, Set.new([parent_tag_id]))
+    end
+
+    cache[parent_tag_id] = visible_ids.to_a
+  end
+
+  def collect_visible_child_tag_ids tag_id, graph, visible_ids, seen
+    return if seen.include?(tag_id)
+
+    seen = seen.dup << tag_id
+    tag = graph[:tags_by_id][tag_id]
+    return unless tag
+
+    if tag[:deprecated]
+      graph[:children_by_parent_id][tag_id].each do |child_tag_id|
+        collect_visible_child_tag_ids(child_tag_id, graph, visible_ids, seen)
+      end
+      return
+    end
+
+    visible_ids << tag_id if with_depth_visible_tag?(tag)
+  end
+
+  def with_depth_visible_tag? tag
+    tag[:category].in?(['meme', 'character', 'material']) && !tag[:deprecated]
+  end
+
   def build_tag_children tag
     material = tag.materials.first
     file = nil