Add trending links (#16917)

* Add trending links

* Add overriding specific links trendability

* Add link type to preview cards and only trend articles

Change trends review notifications from being sent every 5 minutes to being sent every 2 hours

Change threshold from 5 unique accounts to 15 unique accounts

* Fix tests

app/models/preview_card_provider.rb

@@ -0,0 +1,57 @@
+# frozen_string_literal: true
+# == Schema Information
+#
+# Table name: preview_card_providers
+#
+#  id                  :bigint(8)        not null, primary key
+#  domain              :string           default(""), not null
+#  icon_file_name      :string
+#  icon_content_type   :string
+#  icon_file_size      :bigint(8)
+#  icon_updated_at     :datetime
+#  trendable           :boolean
+#  reviewed_at         :datetime
+#  requested_review_at :datetime
+#  created_at          :datetime         not null
+#  updated_at          :datetime         not null
+#
+
+class PreviewCardProvider < ApplicationRecord
+  include DomainNormalizable
+  include Attachmentable
+
+  ICON_MIME_TYPES = %w(image/x-icon image/vnd.microsoft.icon image/png).freeze
+  LIMIT = 1.megabyte
+
+  validates :domain, presence: true, uniqueness: true, domain: true
+
+  has_attached_file :icon, styles: { static: { format: 'png', convert_options: '-coalesce -strip' } }, validate_media_type: false
+  validates_attachment :icon, content_type: { content_type: ICON_MIME_TYPES }, size: { less_than: LIMIT }
+  remotable_attachment :icon, LIMIT
+
+  scope :trendable, -> { where(trendable: true) }
+  scope :not_trendable, -> { where(trendable: false) }
+  scope :reviewed, -> { where.not(reviewed_at: nil) }
+  scope :pending_review, -> { where(reviewed_at: nil) }
+
+  def requires_review?
+    reviewed_at.nil?
+  end
+
+  def reviewed?
+    reviewed_at.present?
+  end
+
+  def requested_review?
+    requested_review_at.present?
+  end
+
+  def requires_review_notification?
+    requires_review? && !requested_review?
+  end
+
+  def self.matching_domain(domain)
+    segments = domain.split('.')
+    where(domain: segments.map.with_index { |_, i| segments[i..-1].join('.') }).order(Arel.sql('char_length(domain) desc')).first
+  end
+end