12 files changed, 198 insertions, 23 deletions
diff --git a/app/models/broadcast_message.rb b/app/models/broadcast_message.rb
index 9c2ae92071d..b3d72ebdcf3 100644
--- a/app/models/broadcast_message.rb
+++ b/app/models/broadcast_message.rb
@@ -9,6 +9,7 @@ class BroadcastMessage < ApplicationRecord
   validates :message,   presence: true
   validates :starts_at, presence: true
   validates :ends_at,   presence: true
+  validates :broadcast_type, presence: true
 
   validates :color, allow_blank: true, color: true
   validates :font,  allow_blank: true, color: true
@@ -17,35 +18,62 @@ class BroadcastMessage < ApplicationRecord
   default_value_for :font,  '#FFFFFF'
 
   CACHE_KEY = 'broadcast_message_current_json'
+  BANNER_CACHE_KEY = 'broadcast_message_current_banner_json'
+  NOTIFICATION_CACHE_KEY = 'broadcast_message_current_notification_json'
 
   after_commit :flush_redis_cache
 
-  def self.current(current_path = nil)
-    messages = cache.fetch(CACHE_KEY, as: BroadcastMessage, expires_in: cache_expires_in) do
-      current_and_future_messages
+  enum broadcast_type: {
+    banner: 1,
+    notification: 2
+  }
+
+  class << self
+    def current_banner_messages(current_path = nil)
+      fetch_messages BANNER_CACHE_KEY, current_path do
+        current_and_future_messages.banner
+      end
     end
 
-    return [] unless messages&.present?
+    def current_notification_messages(current_path = nil)
+      fetch_messages NOTIFICATION_CACHE_KEY, current_path do
+        current_and_future_messages.notification
+      end
+    end
 
-    now_or_future = messages.select(&:now_or_future?)
+    def current(current_path = nil)
+      fetch_messages CACHE_KEY, current_path do
+        current_and_future_messages
+      end
+    end
 
-    # If there are cached entries but none are to be displayed we'll purge the
-    # cache so we don't keep running this code all the time.
-    cache.expire(CACHE_KEY) if now_or_future.empty?
+    def current_and_future_messages
+      where('ends_at > :now', now: Time.current).order_id_asc
+    end
 
-    now_or_future.select(&:now?).select { |message| message.matches_current_path(current_path) }
-  end
+    def cache
+      Gitlab::JsonCache.new(cache_key_with_version: false)
+    end
 
-  def self.current_and_future_messages
-    where('ends_at > :now', now: Time.zone.now).order_id_asc
-  end
+    def cache_expires_in
+      2.weeks
+    end
 
-  def self.cache
-    Gitlab::JsonCache.new(cache_key_with_version: false)
-  end
+    private
+
+    def fetch_messages(cache_key, current_path)
+      messages = cache.fetch(cache_key, as: BroadcastMessage, expires_in: cache_expires_in) do
+        yield
+      end
+
+      now_or_future = messages.select(&:now_or_future?)
 
-  def self.cache_expires_in
-    2.weeks
+      # If there are cached entries but none are to be displayed we'll purge the
+      # cache so we don't keep running this code all the time.
+      cache.expire(cache_key) if now_or_future.empty?
+
+      now_or_future.select(&:now?).select { |message| message.matches_current_path(current_path) }
+    end
   end
 
   def active?
@@ -53,19 +81,19 @@ class BroadcastMessage < ApplicationRecord
   end
 
   def started?
-    Time.zone.now >= starts_at
+    Time.current >= starts_at
   end
 
   def ended?
-    ends_at < Time.zone.now
+    ends_at < Time.current
   end
 
   def now?
-    (starts_at..ends_at).cover?(Time.zone.now)
+    (starts_at..ends_at).cover?(Time.current)
   end
 
   def future?
-    starts_at > Time.zone.now
+    starts_at > Time.current
   end
 
   def now_or_future?
@@ -79,7 +107,9 @@ class BroadcastMessage < ApplicationRecord
   end
 
   def flush_redis_cache
-    self.class.cache.expire(CACHE_KEY)
+    [CACHE_KEY, BANNER_CACHE_KEY, NOTIFICATION_CACHE_KEY].each do |key|
+      self.class.cache.expire(key)
+    end
   end
 end
 
diff --git a/app/models/commit.rb b/app/models/commit.rb
index c683a9aeb76..01c7991ba2f 100644
--- a/app/models/commit.rb
+++ b/app/models/commit.rb
@@ -281,6 +281,10 @@ class Commit
     project.notes.for_commit_id(self.id)
   end
 
+  def user_mentions
+    CommitUserMention.where(commit_id: self.id)
+  end
+
   def discussion_notes
     notes.non_diff_notes
   end
diff --git a/app/models/commit_user_mention.rb b/app/models/commit_user_mention.rb
new file mode 100644
index 00000000000..680d20b61cf
--- /dev/null
+++ b/app/models/commit_user_mention.rb
@@ -0,0 +1,5 @@
+# frozen_string_literal: true
+
+class CommitUserMention < UserMention
+  belongs_to :note
+end
diff --git a/app/models/concerns/mentionable.rb b/app/models/concerns/mentionable.rb
index 9b6c57261d8..b43b91699ab 100644
--- a/app/models/concerns/mentionable.rb
+++ b/app/models/concerns/mentionable.rb
@@ -80,6 +80,66 @@ module Mentionable
     all_references(current_user).users
   end
 
+  def store_mentions!
+    # if store_mentioned_users_to_db feature flag is not enabled then consider storing operation as succeeded
+    # because we wrap this method in transaction with with_transaction_returning_status, and we need the status to be
+    # successful if mentionable.save is successful.
+    #
+    # This line will get removed when we remove the feature flag.
+    return true unless store_mentioned_users_to_db_enabled?
+
+    refs = all_references(self.author)
+
+    references = {}
+    references[:mentioned_users_ids] = refs.mentioned_users&.pluck(:id).presence
+    references[:mentioned_groups_ids] = refs.mentioned_groups&.pluck(:id).presence
+    references[:mentioned_projects_ids] = refs.mentioned_projects&.pluck(:id).presence
+
+    # One retry should be enough as next time `model_user_mention` should return the existing mention record, that
+    # threw the `ActiveRecord::RecordNotUnique` exception in first place.
+    self.class.safe_ensure_unique(retries: 1) do
+      user_mention = model_user_mention
+      user_mention.mentioned_users_ids = references[:mentioned_users_ids]
+      user_mention.mentioned_groups_ids = references[:mentioned_groups_ids]
+      user_mention.mentioned_projects_ids = references[:mentioned_projects_ids]
+
+      if user_mention.has_mentions?
+        user_mention.save!
+      elsif user_mention.persisted?
+        user_mention.destroy!
+      end
+
+      true
+    end
+  end
+
+  def referenced_users
+    User.where(id: user_mentions.select("unnest(mentioned_users_ids)"))
+  end
+
+  def referenced_projects(current_user = nil)
+    Project.where(id: user_mentions.select("unnest(mentioned_projects_ids)")).public_or_visible_to_user(current_user)
+  end
+
+  def referenced_project_users(current_user = nil)
+    User.joins(:project_members).where(members: { source_id: referenced_projects(current_user) }).distinct
+  end
+
+  def referenced_groups(current_user = nil)
+    # TODO: IMPORTANT: Revisit before using it.
+    # Check DB data for max mentioned groups per mentionable:
+    #
+    # select issue_id, count(mentions_count.men_gr_id) gr_count from
+    # (select DISTINCT unnest(mentioned_groups_ids) as men_gr_id, issue_id
+    # from issue_user_mentions group by issue_id, mentioned_groups_ids) as mentions_count
+    # group by mentions_count.issue_id order by gr_count desc limit 10
+    Group.where(id: user_mentions.select("unnest(mentioned_groups_ids)")).public_or_visible_to_user(current_user)
+  end
+
+  def referenced_group_users(current_user = nil)
+    User.joins(:group_members).where(members: { source_id: referenced_groups }).distinct
+  end
+
   def directly_addressed_users(current_user = nil)
     all_references(current_user).directly_addressed_users
   end
@@ -171,6 +231,26 @@ module Mentionable
   def mentionable_params
     {}
   end
+
+  # User mention that is parsed from model description rather then its related notes.
+  # Models that have a descriprion attribute like Issue, MergeRequest, Epic, Snippet may have such a user mention.
+  # Other mentionable models like Commit, DesignManagement::Design, will never have such record as those do not have
+  # a description attribute.
+  #
+  # Using this method followed by a call to *save* may result in *ActiveRecord::RecordNotUnique* exception
+  # in a multithreaded environment. Make sure to use it within a *safe_ensure_unique* block.
+  def model_user_mention
+    user_mentions.where(note_id: nil).first_or_initialize
+  end
+
+  # We need this method to be checking that store_mentioned_users_to_db feature flag is enabled at the group level
+  # and not the project level as epics are defined at group level and we want to have epics store user mentions as well
+  # for the test period.
+  # During the test period the flag should be enabled at the group level.
+  def store_mentioned_users_to_db_enabled?
+    return Feature.enabled?(:store_mentioned_users_to_db, self.project&.group) if self.respond_to?(:project)
+    return Feature.enabled?(:store_mentioned_users_to_db, self.group) if self.respond_to?(:group)
+  end
 end
 
 Mentionable.prepend_if_ee('EE::Mentionable')
diff --git a/app/models/issue.rb b/app/models/issue.rb
index 2f8d6cb0c06..d49f3c28000 100644
--- a/app/models/issue.rb
+++ b/app/models/issue.rb
@@ -42,6 +42,7 @@ class Issue < ApplicationRecord
   has_many :issue_assignees
   has_many :assignees, class_name: "User", through: :issue_assignees
   has_many :zoom_meetings
+  has_many :user_mentions, class_name: "IssueUserMention"
   has_one :sentry_issue
 
   validates :project, presence: true
diff --git a/app/models/issue_user_mention.rb b/app/models/issue_user_mention.rb
new file mode 100644
index 00000000000..3eadd580f7f
--- /dev/null
+++ b/app/models/issue_user_mention.rb
@@ -0,0 +1,6 @@
+# frozen_string_literal: true
+
+class IssueUserMention < UserMention
+  belongs_to :issue
+  belongs_to :note
+end
diff --git a/app/models/merge_request.rb b/app/models/merge_request.rb
index f4dfd9128fa..240c143abba 100644
--- a/app/models/merge_request.rb
+++ b/app/models/merge_request.rb
@@ -71,6 +71,7 @@ class MergeRequest < ApplicationRecord
 
   has_many :merge_request_assignees
   has_many :assignees, class_name: "User", through: :merge_request_assignees
+  has_many :user_mentions, class_name: "MergeRequestUserMention"
 
   has_many :deployment_merge_requests
 
diff --git a/app/models/merge_request_user_mention.rb b/app/models/merge_request_user_mention.rb
new file mode 100644
index 00000000000..222d9c1aa8c
--- /dev/null
+++ b/app/models/merge_request_user_mention.rb
@@ -0,0 +1,6 @@
+# frozen_string_literal: true
+
+class MergeRequestUserMention < UserMention
+  belongs_to :merge_request
+  belongs_to :note
+end
diff --git a/app/models/note.rb b/app/models/note.rb
index f5f6ecf6336..cfa7ba98081 100644
--- a/app/models/note.rb
+++ b/app/models/note.rb
@@ -499,8 +499,18 @@ class Note < ApplicationRecord
     project
   end
 
+  def user_mentions
+    noteable.user_mentions.where(note: self)
+  end
+
   private
 
+  # Using this method followed by a call to `save` may result in ActiveRecord::RecordNotUnique exception
+  # in a multithreaded environment. Make sure to use it within a `safe_ensure_unique` block.
+  def model_user_mention
+    user_mentions.first_or_initialize
+  end
+
   def system_note_viewable_by?(user)
     return true unless system_note_metadata
 
diff --git a/app/models/snippet.rb b/app/models/snippet.rb
index b802ea2fd59..92746d28f05 100644
--- a/app/models/snippet.rb
+++ b/app/models/snippet.rb
@@ -37,6 +37,7 @@ class Snippet < ApplicationRecord
   belongs_to :project
 
   has_many :notes, as: :noteable, dependent: :destroy # rubocop:disable Cop/ActiveRecordDependent
+  has_many :user_mentions, class_name: "SnippetUserMention"
 
   delegate :name, :email, to: :author, prefix: true, allow_nil: true
 
@@ -69,6 +70,8 @@ class Snippet < ApplicationRecord
   scope :inc_author, -> { includes(:author) }
   scope :inc_relations_for_view, -> { includes(author: :status) }
 
+  attr_mentionable :description
+
   participant :author
   participant :notes_with_associations
 
diff --git a/app/models/snippet_user_mention.rb b/app/models/snippet_user_mention.rb
new file mode 100644
index 00000000000..87ce77a5787
--- /dev/null
+++ b/app/models/snippet_user_mention.rb
@@ -0,0 +1,6 @@
+# frozen_string_literal: true
+
+class SnippetUserMention < UserMention
+  belongs_to :snippet
+  belongs_to :note
+end
diff --git a/app/models/user_mention.rb b/app/models/user_mention.rb
new file mode 100644
index 00000000000..a85c6168cea
--- /dev/null
+++ b/app/models/user_mention.rb
@@ -0,0 +1,23 @@
+# frozen_string_literal: true
+
+class UserMention < ApplicationRecord
+  self.abstract_class = true
+
+  def has_mentions?
+    mentioned_users_ids.present? || mentioned_groups_ids.present? || mentioned_projects_ids.present?
+  end
+
+  private
+
+  def mentioned_users
+    User.where(id: mentioned_users_ids)
+  end
+
+  def mentioned_groups
+    Group.where(id: mentioned_groups_ids)
+  end
+
+  def mentioned_projects
+    Project.where(id: mentioned_projects_ids)
+  end
+end