1 files changed, 164 insertions, 0 deletions
diff --git a/app/models/concerns/has_wiki_page_meta_attributes.rb b/app/models/concerns/has_wiki_page_meta_attributes.rb
new file mode 100644
index 00000000000..136f2d00ce3
--- /dev/null
+++ b/app/models/concerns/has_wiki_page_meta_attributes.rb
@@ -0,0 +1,164 @@
+# frozen_string_literal: true
+
+module HasWikiPageMetaAttributes
+  extend ActiveSupport::Concern
+  include Gitlab::Utils::StrongMemoize
+
+  CanonicalSlugConflictError = Class.new(ActiveRecord::RecordInvalid)
+  WikiPageInvalid = Class.new(ArgumentError)
+
+  included do
+    has_many :events, as: :target, dependent: :delete_all # rubocop:disable Cop/ActiveRecordDependent
+
+    validates :title, length: { maximum: 255 }, allow_nil: false
+    validate :no_two_metarecords_in_same_container_can_have_same_canonical_slug
+
+    scope :with_canonical_slug, ->(slug) do
+      slug_table_name = klass.reflect_on_association(:slugs).table_name
+
+      joins(:slugs).where(slug_table_name => { canonical: true, slug: slug })
+    end
+  end
+
+  class_methods do
+    # Return the (updated) WikiPage::Meta record for a given wiki page
+    #
+    # If none is found, then a new record is created, and its fields are set
+    # to reflect the wiki_page passed.
+    #
+    # @param [String] last_known_slug
+    # @param [WikiPage] wiki_page
+    #
+    # This method raises errors on validation issues.
+    def find_or_create(last_known_slug, wiki_page)
+      raise WikiPageInvalid unless wiki_page.valid?
+
+      container = wiki_page.wiki.container
+      known_slugs = [last_known_slug, wiki_page.slug].compact.uniq
+      raise 'No slugs found! This should not be possible.' if known_slugs.empty?
+
+      transaction do
+        updates = wiki_page_updates(wiki_page)
+        found = find_by_canonical_slug(known_slugs, container)
+        meta = found || create!(updates.merge(container_attrs(container)))
+
+        meta.update_state(found.nil?, known_slugs, wiki_page, updates)
+
+        # We don't need to run validations here, since find_by_canonical_slug
+        # guarantees that there is no conflict in canonical_slug, and DB
+        # constraints on title and project_id/group_id enforce our other invariants
+        # This saves us a query.
+        meta
+      end
+    end
+
+    def find_by_canonical_slug(canonical_slug, container)
+      meta, conflict = with_canonical_slug(canonical_slug)
+        .where(container_attrs(container))
+        .limit(2)
+
+      if conflict.present?
+        meta.errors.add(:canonical_slug, 'Duplicate value found')
+        raise CanonicalSlugConflictError.new(meta)
+      end
+
+      meta
+    end
+
+    private
+
+    def wiki_page_updates(wiki_page)
+      last_commit_date = wiki_page.version_commit_timestamp || Time.now.utc
+
+      {
+        title: wiki_page.title,
+        created_at: last_commit_date,
+        updated_at: last_commit_date
+      }
+    end
+
+    def container_key
+      raise NotImplementedError
+    end
+
+    def container_attrs(container)
+      { container_key => container.id }
+    end
+  end
+
+  def canonical_slug
+    strong_memoize(:canonical_slug) { slugs.canonical.take&.slug }
+  end
+
+  # rubocop:disable Gitlab/ModuleWithInstanceVariables
+  def canonical_slug=(slug)
+    return if @canonical_slug == slug
+
+    if persisted?
+      transaction do
+        slugs.canonical.update_all(canonical: false)
+        page_slug = slugs.create_with(canonical: true).find_or_create_by(slug: slug)
+        page_slug.update_columns(canonical: true) unless page_slug.canonical?
+      end
+    else
+      slugs.new(slug: slug, canonical: true)
+    end
+
+    @canonical_slug = slug
+  end
+  # rubocop:enable Gitlab/ModuleWithInstanceVariables
+
+  def update_state(created, known_slugs, wiki_page, updates)
+    update_wiki_page_attributes(updates)
+    insert_slugs(known_slugs, created, wiki_page.slug)
+    self.canonical_slug = wiki_page.slug
+  end
+
+  private
+
+  def update_wiki_page_attributes(updates)
+    # Remove all unnecessary updates:
+    updates.delete(:updated_at) if updated_at == updates[:updated_at]
+    updates.delete(:created_at) if created_at <= updates[:created_at]
+    updates.delete(:title) if title == updates[:title]
+
+    update_columns(updates) unless updates.empty?
+  end
+
+  def insert_slugs(strings, is_new, canonical_slug)
+    creation = Time.current.utc
+
+    slug_attrs = strings.map do |slug|
+      slug_attributes(slug, canonical_slug, is_new, creation)
+    end
+    slugs.insert_all(slug_attrs) unless !is_new && slug_attrs.size == 1
+
+    @canonical_slug = canonical_slug if is_new || strings.size == 1 # rubocop:disable Gitlab/ModuleWithInstanceVariables
+  end
+
+  def slug_attributes(slug, canonical_slug, is_new, creation)
+    {
+      slug: slug,
+      canonical: (is_new && slug == canonical_slug),
+      created_at: creation,
+      updated_at: creation
+    }.merge(slug_meta_attributes)
+  end
+
+  def slug_meta_attributes
+    { self.association(:slugs).reflection.foreign_key => id }
+  end
+
+  def no_two_metarecords_in_same_container_can_have_same_canonical_slug
+    container_id = attributes[self.class.container_key.to_s]
+
+    return unless container_id.present? && canonical_slug.present?
+
+    offending = self.class.with_canonical_slug(canonical_slug).where(self.class.container_key => container_id)
+    offending = offending.where.not(id: id) if persisted?
+
+    if offending.exists?
+      errors.add(:canonical_slug, 'each page in a wiki must have a distinct canonical slug')
+    end
+  end
+end