AI: address review on PR #469

backend/app/models/post_implication.rb

@@ -8,6 +8,7 @@ class PostImplication < ApplicationRecord
   validates :parent_post_id, presence: true
 
   validate :parent_post_mustnt_be_itself
+  validate :parent_post_mustnt_create_cycle
 
   private
 
@@ -16,4 +17,24 @@ class PostImplication < ApplicationRecord
       errors.add :parent_post_id, '親投稿に同じ投稿を設定することはできません．'
     end
   end
+
+  def parent_post_mustnt_create_cycle
+    return if post_id.blank? || parent_post_id.blank?
+    return if errors[:parent_post_id].present?
+
+    ancestor_ids = Set.new
+    frontier_ids = [parent_post_id]
+
+    until frontier_ids.empty?
+      if frontier_ids.include?(post_id)
+        errors.add :parent_post_id, :invalid
+        return
+      end
+
+      ancestor_ids.merge(frontier_ids)
+      frontier_ids = PostImplication.where(post_id: frontier_ids)
+          .distinct.pluck(:parent_post_id)
+          .reject { ancestor_ids.include?(_1) }
+    end
+  end
 end

backend/spec/models/post_implication_spec.rb

@@ -48,4 +48,47 @@ RSpec.describe PostImplication, type: :model do
     expect(duplicate).not_to be_valid
     expect(duplicate.errors[:post_id]).to be_present
   end
+
+  it 'rejects a parent that would create a two-post cycle' do
+    described_class.create!(post: post_record, parent_post:)
+
+    implication = described_class.new(
+        post: parent_post, parent_post: post_record)
+
+    expect(implication).not_to be_valid
+    expect(implication.errors.of_kind?(:parent_post_id, :invalid)).to be true
+  end
+
+  it 'rejects a parent that would create a three-post cycle' do
+    ancestor_post = create(:post)
+    described_class.create!(post: post_record, parent_post:)
+    described_class.create!(post: parent_post, parent_post: ancestor_post)
+
+    implication = described_class.new(
+        post: ancestor_post, parent_post: post_record)
+
+    expect(implication).not_to be_valid
+    expect(implication.errors.of_kind?(:parent_post_id, :invalid)).to be true
+  end
+
+  it 'allows a parent with an ancestor when no cycle would result' do
+    ancestor_post = create(:post)
+    described_class.create!(post: parent_post, parent_post: ancestor_post)
+
+    implication = described_class.new(post: post_record, parent_post:)
+
+    expect(implication).to be_valid
+  end
+
+  it 'terminates when existing ancestors already contain a cycle' do
+    ancestor_post = create(:post)
+    described_class.create!(post: parent_post, parent_post: ancestor_post)
+    legacy_implication = described_class.new(
+        post: ancestor_post, parent_post:)
+    legacy_implication.save!(validate: false)
+
+    implication = described_class.new(post: post_record, parent_post:)
+
+    expect(implication).to be_valid
+  end
 end

frontend/src/components/PostEmbed.tsx

@@ -177,39 +177,6 @@ const PostEmbed: FC<Props> = (
 	      onError={onError}/>)
     }
 
-  case 'pixiv.net':
-    {
-      if (url.hostname !== 'pixiv.net' && url.hostname !== 'www.pixiv.net')
-	break
-
-      const artworkId =
-	  url.pathname === '/member_illust.php'
-	  ? url.searchParams.get ('illust_id')
-	  : url.pathname.match (
-	      /^\/(?:[a-z]{2}(?:-[A-Za-z]{2})?\/)?artworks\/(\d+)\/?$/)?.[1]
-
-      if (!(artworkId) || !(/^\d+$/.test (artworkId)))
-	break
-
-      if (embedAutoLoadMode === 'off')
-	return externalLink
-      if (shouldLoadEmbed === false)
-	return manualLoadControl
-
-      const embedUrl =
-	  `https://embed.pixiv.net/oembed_iframe.php?type=illust&id=${ artworkId }`
-
-      return (
-	  <iframe
-	      src={embedUrl}
-	      title={post.title || post.url}
-	      width={600}
-	      height={315}
-	      style={{ border: 0 }}
-	      loading="lazy"
-	      className="max-w-full"/>)
-    }
-
   case 'twitter.com':
   case 'x.com':
     {