Add service for migrating pages to zip storage

* we use exclusive lease to guard agains situations when
  new deployment happens at the same time as we try to
  zip pages content
* If project directory is absent(or `public` directory)
  then we mark pages as not deployed for this project

app/models/project.rb

@@ -1829,6 +1829,15 @@ class Project < ApplicationRecord
     ensure_pages_metadatum.update!(pages_deployment: deployment)
   end
 
+  def set_first_pages_deployment!(deployment)
+    ensure_pages_metadatum
+
+    # where().update_all to perform update in the single transaction with check for null
+    ProjectPagesMetadatum
+      .where(project_id: id, pages_deployment_id: nil)
+      .update_all(pages_deployment_id: deployment.id)
+  end
+
   def write_repository_config(gl_full_path: full_path)
     # We'd need to keep track of project full path otherwise directory tree
     # created with hashed storage enabled cannot be usefully imported using

app/services/pages/migrate_legacy_storage_to_deployment_service.rb

+# frozen_string_literal: true
+
+module Pages
+  class MigrateLegacyStorageToDeploymentService
+    ExclusiveLeaseTaken = Class.new(StandardError)
+
+    include ::Pages::LegacyStorageLease
+
+    attr_reader :project
+
+    def initialize(project)
+      @project = project
+    end
+
+    def execute
+      migrated = try_obtain_lease do
+        execute_unsafe
+
+        true
+      end
+
+      raise ExclusiveLeaseTaken, "Can't migrate pages for project #{project.id}: exclusive lease taken" unless migrated
+    end
+
+    private
+
+    def execute_unsafe
+      archive_path, entries_count = ::Pages::ZipDirectoryService.new(project.pages_path).execute
+
+      deployment = nil
+      File.open(archive_path) do |file|
+        deployment = project.pages_deployments.create!(
+          file: file,
+          file_count: entries_count,
+          file_sha256: Digest::SHA256.file(archive_path).hexdigest
+        )
+      end
+
+      project.set_first_pages_deployment!(deployment)
+    rescue ::Pages::ZipDirectoryService::InvalidArchiveError => e
+      Gitlab::ErrorTracking.track_exception(e, project_id: project.id)
+
+      project.mark_pages_as_not_deployed if Feature.enabled?(:pages_migration_mark_as_not_deployed, project)
+    end
+  end
+end

config/feature_flags/development/pages_migration_mark_as_not_deployed.yml

+---
+name: pages_migration_mark_as_not_deployed
+introduced_by_url: https://gitlab.com/gitlab-org/gitlab/-/merge_requests/49473
+rollout_issue_url: 
+milestone: '13.7'
+type: development
+group: group::release
+default_enabled: false

spec/models/project_spec.rb

@@ -6002,6 +6002,43 @@ RSpec.describe Project, factory_default: :keep do
     end
   end
 
+  describe '#set_first_pages_deployment!' do
+    let(:project) { create(:project) }
+    let(:deployment) { create(:pages_deployment, project: project) }
+
+    it "creates new metadata record if none exists yet and sets deployment" do
+      project.pages_metadatum.destroy!
+      project.reload
+
+      project.set_first_pages_deployment!(deployment)
+
+      expect(project.pages_metadatum.reload.pages_deployment).to eq(deployment)
+    end
+
+    it "updates the existing metadara record with deployment" do
+      expect do
+        project.set_first_pages_deployment!(deployment)
+      end.to change { project.pages_metadatum.reload.pages_deployment }.from(nil).to(deployment)
+    end
+
+    it 'only updates metadata for this project' do
+      other_project = create(:project)
+
+      expect do
+        project.set_first_pages_deployment!(deployment)
+      end.not_to change { other_project.pages_metadatum.reload.pages_deployment }.from(nil)
+    end
+
+    it 'does nothing if metadata already references some deployment' do
+      existing_deployment = create(:pages_deployment, project: project)
+      project.set_first_pages_deployment!(existing_deployment)
+
+      expect do
+        project.set_first_pages_deployment!(deployment)
+      end.not_to change { project.pages_metadatum.reload.pages_deployment }.from(existing_deployment)
+    end
+  end
+
   describe '#has_pool_repsitory?' do
     it 'returns false when it does not have a pool repository' do
       subject = create(:project, :repository)

spec/services/pages/migrate_legacy_storage_to_deployment_service_spec.rb

+# frozen_string_literal: true
+
+require 'spec_helper'
+
+RSpec.describe Pages::MigrateLegacyStorageToDeploymentService do
+  let(:project) { create(:project, :repository) }
+
+  let(:service) { described_class.new(project) }
+
+  it 'marks pages as not deployed if public directory is absent' do
+    project.mark_pages_as_deployed
+
+    expect do
+      service.execute
+    end.to change { project.pages_metadatum.reload.deployed }.from(true).to(false)
+  end
+
+  it 'does not mark pages as not deployed if public directory is absent but feature is disabled' do
+    stub_feature_flags(pages_migration_mark_as_not_deployed: false)
+
+    project.mark_pages_as_deployed
+
+    expect do
+      service.execute
+    end.not_to change { project.pages_metadatum.reload.deployed }.from(true)
+  end
+
+  context 'when pages site is deployed to legacy storage' do
+    before do
+      FileUtils.mkdir_p File.join(project.pages_path, "public")
+      File.open(File.join(project.pages_path, "public/index.html"), "w") do |f|
+        f.write("Hello!")
+      end
+    end
+
+    it 'creates pages deployment' do
+      expect do
+        described_class.new(project).execute
+      end.to change { project.reload.pages_deployments.count }.by(1)
+
+      deployment = project.pages_metadatum.pages_deployment
+
+      Zip::File.open(deployment.file.path) do |zip_file|
+        expect(zip_file.glob("public").first.ftype).to eq(:directory)
+        expect(zip_file.glob("public/index.html").first.get_input_stream.read).to eq("Hello!")
+      end
+
+      expect(deployment.file_count).to eq(2)
+      expect(deployment.file_sha256).to eq(Digest::SHA256.file(deployment.file.path).hexdigest)
+    end
+
+    it 'does not change pages deployment if it is set' do
+      old_deployment = create(:pages_deployment, project: project)
+      project.update_pages_deployment!(old_deployment)
+
+      expect do
+        described_class.new(project).execute
+      end.not_to change { project.pages_metadatum.reload.pages_deployment_id }.from(old_deployment.id)
+    end
+
+    it 'raises exception if exclusive lease is taken' do
+      described_class.new(project).try_obtain_lease do
+        expect do
+          described_class.new(project).execute
+        end.to raise_error(described_class::ExclusiveLeaseTaken)
+      end
+    end
+  end
+end