repair_master_template.rb

# this function repairs a blueprint course and its associations when they are broken by a shard split.
# since migration ids depend on the shard number, they will all change after a split. fortunately,
# MasterContentTag remembers the original migration_id so we can use it to build a mapping from old
# to new migration_id, and then go through and replace ids in the blueprint and its associations.
# symptoms of a blueprint that is broken by a shard split include:
#  1. content that is updated in the blueprint gets duplicated instead of updated in
#     the associated courses
#  2. content that was locked in the blueprint remains locked in associated courses
#     but does not appear locked in the blueprint (and toggling the lock doesn't appear to work)
def repair_master_template!(template_id, dry_run: true)
  template = MasterCourses::MasterTemplate.find(template_id)
  template.shard.activate do
    # find master content tags with a mismatched shard number
    tags_to_repair = template.master_content_tags.where.not("migration_id LIKE 'mastercourse_#{template.shard.id}_%'").preload(:content).to_a
    tags_to_repair.reject! { |tag| tag.content.nil? }
    return unless tags_to_repair.any?

    # build a mapping from broken migration id to new migration id
    migration_id_map = {}
    tags_to_repair.each do |tag|
      migration_id_map[tag.migration_id] = template.migration_id_for(tag.content)
    end

    # repair sync history
    # (do this first for the sake of idempotence, because once master content tags are repaired, we
    #  lose the information we need to create the mapping)
    template.master_migrations.each do |mm|
      next unless bad_export_results?(mm)

      mm.transaction do
        # repair sync exceptions
        mm.migration_results.where.not(results: {}).find_each do |result|
          if result.results[:skipped].present?
            result.results[:skipped].map! { |mig_id| migration_id_map[mig_id] || mig_id }
            result.results_will_change!
            result.save!
          end
        end

        # repair sync history
        process_result_hash!(mm.export_results[:selective][:deleted], migration_id_map)
        process_result_hash!(mm.export_results[:selective][:created], migration_id_map)
        process_result_hash!(mm.export_results[:selective][:updated], migration_id_map)
        mm.export_results_will_change!
        mm.save!

        raise ActiveRecord::Rollback, "dry run" if dry_run
      end
    end

    # repair master tags and child course information
    child_subscription_ids = template.child_subscriptions.pluck(:id)
    child_course_ids = template.child_subscriptions.pluck(:child_course_id)
    tags_to_repair.each do |tag|
      old_migration_id = tag.migration_id
      new_migration_id = migration_id_map[old_migration_id]

      tag.transaction do
        # repair child objects
        child_objects = tag.content_type.constantize.where(context_type: 'Course', context_id: child_course_ids, migration_id: old_migration_id)
        child_objects.update_all(migration_id: new_migration_id)

        # repair child tags
        child_tags = MasterCourses::ChildContentTag.where(child_subscription_id: child_subscription_ids, migration_id: old_migration_id)
        child_tags.update_all(migration_id: new_migration_id)

        # repair the master tag
        tag.migration_id = new_migration_id
        begin
          tag.save!
        rescue
          tag.destroy
        end

        raise ActiveRecord::Rollback, "dry run" if dry_run
      end
    end
  end
end

def bad_export_results?(master_migration)
  return false unless master_migration.export_results[:selective].present?
  mig_ids  = master_migration.export_results[:selective][:created].values.flatten
  mig_ids += master_migration.export_results[:selective][:updated].values.flatten
  mig_ids += master_migration.export_results[:selective][:deleted].values.flatten
  mig_ids.any? do |mig_id|
    mig_id =~ /\Amastercourse_(\d+)_/ && $1.to_i != Shard.current.id
  end
end

def process_result_hash!(result_hash, migration_id_map)
  result_hash.transform_values! do |mig_id_array|
    if mig_id_array.is_a?(Array) # it might be { "syllabus": true }
      mig_id_array.map! { |mig_id| migration_id_map[mig_id] || mig_id }
    end
  end
end

def repair_all_master_templates!
  MasterCourses::MasterTemplate.active.where(
    id: MasterCourses::MasterContentTag.where("migration_id NOT LIKE 'mastercourse_#{Shard.current.id}_%'").distinct.select(:master_template_id)
  ).pluck(:id).each do |template_id|
    repair_master_template!(template_id, dry_run: false)
  end
end