require "active_support/core_ext/module/delegation"

module ActiveStorage
  # Wraps a set of mirror services and provides a single `ActiveStorage::Service` object that will all
  # have the files uploaded to them. A `primary` service is designated to answer calls to `download`, `exists?`,
  # and `url`.
  class Service::MirrorService < Service
    attr_reader :primary, :mirrors

    delegate :download, :exist?, :url, to: :primary

    # Stitch together from named services.
    def self.build(primary:, mirrors:, configurator:, **options) #:nodoc:
      new \
        primary: configurator.build(primary),
        mirrors: mirrors.collect { |name| configurator.build name }
    end

    def initialize(primary:, mirrors:)
      @primary, @mirrors = primary, mirrors
    end

    # Upload the `io` to the `key` specified to all services. If a `checksum` is provided, all services will
    # ensure a match when the upload has completed or raise an `ActiveStorage::IntegrityError`.
    def upload(key, io, checksum: nil)
      each_service.collect do |service|
        service.upload key, io.tap(&:rewind), checksum: checksum
      end
    end

    # Delete the file at the `key` on all services.
    def delete(key)
      perform_across_services :delete, key
    end

    private
      def each_service(&block)
        [ primary, *mirrors ].each(&block)
      end

      def perform_across_services(method, *args)
        # FIXME: Convert to be threaded
        each_service.collect do |service|
          service.public_send method, *args
        end
      end
  end
end