Limit mentions in posts (#13259)

* Limit mentions in articles

* Bump MAX_USER_MENTION_LIVE_AT to April 7th, 2021 UTC time

* Use stubbed constants in article and comment specs

* Add TODOs around extracting MAX_USER_MENTIONS into constant

app/models/article.rb

@@ -30,6 +30,12 @@ class Article < ApplicationRecord
   counter_culture :user
   counter_culture :organization
 
+  # TODO: Vaidehi Joshi - Extract this into a constant or SiteConfig variable
+  # after https://github.com/forem/rfcs/pull/22 has been completed?
+  MAX_USER_MENTIONS = 7 # Explicitly set to 7 to accommodate DEV Top 7 Posts
+  # The date that we began limiting the number of user mentions in an article.
+  MAX_USER_MENTION_LIVE_AT = Time.utc(2021, 4, 7).freeze
+
   has_many :comments, as: :commentable, inverse_of: :commentable, dependent: :nullify
   has_many :html_variant_successes, dependent: :nullify
   has_many :html_variant_trials, dependent: :nullify
@@ -80,6 +86,7 @@ class Article < ApplicationRecord
   validate :validate_collection_permission
   validate :validate_tag
   validate :validate_video
+  validate :user_mentions_in_markdown
   validate :validate_co_authors, unless: -> { co_author_ids.blank? }
   validate :validate_co_authors_must_not_be_the_same, unless: -> { co_author_ids.blank? }
   validate :validate_co_authors_exist, unless: -> { co_author_ids.blank? }
@@ -629,6 +636,16 @@ class Article < ApplicationRecord
     errors.add(:canonical_url, "must not have spaces")
   end
 
+  def user_mentions_in_markdown
+    return if created_at.present? && created_at.before?(MAX_USER_MENTION_LIVE_AT)
+
+    # The "comment-mentioned-user" css is added by Html::Parser#user_link_if_exists
+    mentions_count = Nokogiri::HTML(processed_html).css(".comment-mentioned-user").size
+    return if mentions_count <= MAX_USER_MENTIONS
+
+    errors.add(:base, "You cannot mention more than #{MAX_USER_MENTIONS} users in a post!")
+  end
+
   def create_slug
     if slug.blank? && title.present? && !published
       self.slug = title_to_slug + "-temp-slug-#{rand(10_000_000)}"

app/models/comment.rb

@@ -12,6 +12,9 @@ class Comment < ApplicationRecord
   COMMENTABLE_TYPES = %w[Article PodcastEpisode].freeze
   TITLE_DELETED = "[deleted]".freeze
   TITLE_HIDDEN = "[hidden by post author]".freeze
+
+  # TODO: Vaidehi Joshi - Extract this into a constant or SiteConfig variable
+  # after https://github.com/forem/rfcs/pull/22 has been completed?
   MAX_USER_MENTIONS = 7 # Explicitly set to 7 to accommodate DEV Top 7 Posts
   # The date that we began limiting the number of user mentions in a comment.
   MAX_USER_MENTION_LIVE_AT = Time.utc(2021, 3, 12).freeze

spec/models/article_spec.rb

@@ -1091,6 +1091,33 @@ RSpec.describe Article, type: :model do
     end
   end
 
+  describe "#user_mentions_in_markdown" do
+    before do
+      stub_const("Article::MAX_USER_MENTIONS", 7)
+      stub_const("Article::MAX_USER_MENTION_LIVE_AT", 1.day.ago) # Set live_at date to a time in the past
+    end
+
+    it "is valid with any number of mentions if created before MAX_USER_MENTION_LIVE_AT date" do
+      # Explicitly set created_at date to a time before MAX_USER_MENTION_LIVE_AT
+      article = create(:article, created_at: 3.days.ago)
+
+      article.body_markdown = "hi @#{user.username}! " * (Article::MAX_USER_MENTIONS + 1)
+      expect(article).to be_valid
+    end
+
+    it "is valid with seven or fewer mentions if created after MAX_USER_MENTION_LIVE_AT date" do
+      article.body_markdown = "hi @#{user.username}! " * Article::MAX_USER_MENTIONS
+      expect(article).to be_valid
+    end
+
+    it "is invalid with more than seven mentions if created after MAX_USER_MENTION_LIVE_AT date" do
+      article.body_markdown = "hi @#{user.username}! " * (Article::MAX_USER_MENTIONS + 1)
+      expect(article).not_to be_valid
+      expect(article.errors[:base])
+        .to include("You cannot mention more than #{Article::MAX_USER_MENTIONS} users in a post!")
+    end
+  end
+
   describe "#update_score" do
     it "stably sets the correct blackbox values" do
       create(:reaction, reactable: article, points: 1)

spec/models/comment_spec.rb

@@ -85,7 +85,7 @@ RSpec.describe Comment, type: :model do
       end
     end
 
-    describe "#mention_total" do
+    describe "#user_mentions_in_markdown" do
       before do
         stub_const("Comment::MAX_USER_MENTIONS", 7)
         stub_const("Comment::MAX_USER_MENTION_LIVE_AT", 1.day.ago) # Set live_at date to a time in the past
@@ -96,24 +96,24 @@ RSpec.describe Comment, type: :model do
         subject.created_at = 3.days.ago
         subject.commentable_type = "Article"
 
-        subject.body_markdown = "hi @#{user.username}! " * 8
+        subject.body_markdown = "hi @#{user.username}! " * (Comment::MAX_USER_MENTIONS + 1)
         expect(subject).to be_valid
       end
 
       it "is valid with seven or fewer mentions if created after MAX_USER_MENTION_LIVE_AT date" do
         subject.commentable_type = "Article"
 
-        subject.body_markdown = "hi @#{user.username}! " * 7
+        subject.body_markdown = "hi @#{user.username}! " * Comment::MAX_USER_MENTIONS
         expect(subject).to be_valid
       end
 
       it "is invalid with more than seven mentions if created after MAX_USER_MENTION_LIVE_AT date" do
         subject.commentable_type = "Article"
 
-        subject.body_markdown = "hi @#{user.username}! " * 8
+        subject.body_markdown = "hi @#{user.username}! " * (Comment::MAX_USER_MENTIONS + 1)
         expect(subject).not_to be_valid
         expect(subject.errors[:base])
-          .to include("You cannot mention more than 7 users in a comment!")
+          .to include("You cannot mention more than #{Comment::MAX_USER_MENTIONS} users in a comment!")
       end
     end
     # rubocop:enable RSpec/NamedSubject