class RenameReservedProjectNames < ActiveRecord::Migration[4.2]
  include Gitlab::Database::MigrationHelpers

  DOWNTIME = false

  THREAD_COUNT = 8

  KNOWN_PATHS = %w(.well-known
                   all
                   blame
                   blob
                   commits
                   create
                   create_dir
                   edit
                   files
                   find_file
                   groups
                   hooks
                   issues
                   logs_tree
                   merge_requests
                   new
                   preview
                   projects
                   raw
                   repository
                   robots.txt
                   s
                   snippets
                   teams
                   tree
                   u
                   unsubscribes
                   update
                   users
                   wikis).freeze

  def up
    queues = Array.new(THREAD_COUNT) { Queue.new }
    start = false

    threads = Array.new(THREAD_COUNT) do |index|
      Thread.new do
        queue = queues[index]

        # Wait until we have input to process.
        until start; end

        rename_projects(queue.pop) until queue.empty?
      end
    end

    enum = queues.each

    reserved_projects.each_slice(100) do |slice|
      begin
        queue = enum.next
      rescue StopIteration
        enum.rewind
        retry
      end

      queue << slice
    end

    start = true

    threads.each(&:join)
  end

  def down
    # nothing to do here
  end

  private

  def reserved_projects
    Project.unscoped
      .includes(:namespace)
      .where('EXISTS (SELECT 1 FROM namespaces WHERE projects.namespace_id = namespaces.id)')
      .where('projects.path' => KNOWN_PATHS)
  end

  def route_exists?(full_path)
    quoted_path = ActiveRecord::Base.connection.quote_string(full_path)

    ActiveRecord::Base.connection
      .select_all("SELECT id, path FROM routes WHERE path = '#{quoted_path}'").present?
  end

  # Adds number to the end of the path that is not taken by other route
  def rename_path(namespace_path, path_was)
    counter = 0
    path = "#{path_was}#{counter}"

    while route_exists?("#{namespace_path}/#{path}")
      counter += 1
      path = "#{path_was}#{counter}"
    end

    path
  end

  def rename_projects(projects)
    projects.each do |project|
      id = project.id
      path_was = project.path
      namespace_path = project.namespace.path
      path = rename_path(namespace_path, path_was)

      begin
        # Because project path update is quite complex operation we can't safely
        # copy-paste all code from GitLab. As exception we use Rails code here
        if rename_project_row(project, path)
          after_rename_service(project, path_was, namespace_path).execute
        end
      rescue Exception => e # rubocop: disable Lint/RescueException
        Rails.logger.error "Exception when renaming project #{id}: #{e.message}"
      end
    end
  end

  def rename_project_row(project, path)
    project.respond_to?(:update_attributes) &&
      project.update(path: path) &&
      defined?(Projects::AfterRenameService)
  end

  def after_rename_service(project, path_was, namespace_path)
    AfterRenameService.new(
      project,
      path_before: path_was,
      full_path_before: "#{namespace_path}/#{path_was}"
    ).execute
  end
end