1 files changed, 136 insertions, 0 deletions
diff --git a/app/models/wiki_page/meta.rb b/app/models/wiki_page/meta.rb
new file mode 100644
index 00000000000..2af7d86ebcc
--- /dev/null
+++ b/app/models/wiki_page/meta.rb
@@ -0,0 +1,136 @@
+# frozen_string_literal: true
+
+class WikiPage
+  class Meta < ApplicationRecord
+    include Gitlab::Utils::StrongMemoize
+
+    CanonicalSlugConflictError = Class.new(ActiveRecord::RecordInvalid)
+
+    self.table_name = 'wiki_page_meta'
+
+    belongs_to :project
+
+    has_many :slugs, class_name: 'WikiPage::Slug', foreign_key: 'wiki_page_meta_id', inverse_of: :wiki_page_meta
+    has_many :events, as: :target, dependent: :delete_all # rubocop:disable Cop/ActiveRecordDependent
+
+    validates :title, presence: true
+    validates :project_id, presence: true
+    validate :no_two_metarecords_in_same_project_can_have_same_canonical_slug
+
+    scope :with_canonical_slug, ->(slug) do
+      joins(:slugs).where(wiki_page_slugs: { canonical: true, slug: slug })
+    end
+
+    alias_method :resource_parent, :project
+
+    # 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
+    #
+    # As with all `find_or_create` methods, this one raises errors on
+    # validation issues.
+    def self.find_or_create(last_known_slug, wiki_page)
+      project = wiki_page.wiki.project
+      known_slugs = [last_known_slug, wiki_page.slug].compact.uniq
+      raise 'no slugs!' if known_slugs.empty?
+
+      transaction do
+        found = find_by_canonical_slug(known_slugs, project)
+        meta = found || create(title: wiki_page.title, project_id: project.id)
+
+        meta.update_state(found.nil?, known_slugs, wiki_page)
+
+        # 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 enforce our other invariants
+        # This saves us a query.
+        meta
+      end
+    end
+
+    def self.find_by_canonical_slug(canonical_slug, project)
+      meta, conflict = with_canonical_slug(canonical_slug)
+        .where(project_id: project.id)
+        .limit(2)
+
+      if conflict.present?
+        meta.errors.add(:canonical_slug, 'Duplicate value found')
+        raise CanonicalSlugConflictError.new(meta)
+      end
+
+      meta
+    end
+
+    def canonical_slug
+      strong_memoize(:canonical_slug) { slugs.canonical.first&.slug }
+    end
+
+    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
+
+    def update_state(created, known_slugs, wiki_page)
+      update_wiki_page_attributes(wiki_page)
+      insert_slugs(known_slugs, created, wiki_page.slug)
+      self.canonical_slug = wiki_page.slug
+    end
+
+    def update_columns(attrs = {})
+      super(attrs.reverse_merge(updated_at: Time.now.utc))
+    end
+
+    def self.update_all(attrs = {})
+      super(attrs.reverse_merge(updated_at: Time.now.utc))
+    end
+
+    private
+
+    def update_wiki_page_attributes(page)
+      update_columns(title: page.title) unless page.title == title
+    end
+
+    def insert_slugs(strings, is_new, canonical_slug)
+      creation = Time.now.utc
+
+      slug_attrs = strings.map do |slug|
+        {
+          wiki_page_meta_id: id,
+          slug: slug,
+          canonical: (is_new && slug == canonical_slug),
+          created_at: creation,
+          updated_at: creation
+        }
+      end
+      slugs.insert_all(slug_attrs) unless !is_new && slug_attrs.size == 1
+
+      @canonical_slug = canonical_slug if is_new || strings.size == 1
+    end
+
+    def no_two_metarecords_in_same_project_can_have_same_canonical_slug
+      return unless project_id.present? && canonical_slug.present?
+
+      offending = self.class.with_canonical_slug(canonical_slug).where(project_id: project_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
+end