module Skylight
  module Util
    class Component
      attr_accessor :environment, :name

      NAME_FORMAT = /\A[a-zA-Z0-9_-]+\z/
      DEFAULT_NAME = "web".freeze
      WORKER_NAME = "worker".freeze
      DEFAULT_ENVIRONMENT = "production".freeze

      WORKER_PROGRAM_MATCHER = Regexp.union [
        /sidekiq$/i,
        /backburner$/i,
        /delayed_job$/i,
        /que$/i,
        /sneakers$/i,
        /shoryuken$/i
      ]

      WORKER_RAKE_MATCHER = Regexp.union [
        /\Aresque:/,
        /\Abackburner:/,
        /\Ajobs:/, # DelayedJob. can also be `rake jobs:workoff`
        /\Aqu:/,
        /\Aque:/,
        /\Aqc:/,
        /\Asneakers:/
      ]

      def initialize(environment, name)
        @environment = environment || DEFAULT_ENVIRONMENT
        @name        = resolve_name(name)

        raise ArgumentError, "environment can't be blank" if @environment.empty?
        validate_string!(@environment, "environment")
        validate_string!(@name, "name")
      end

      def to_s
        "#{name}:#{environment}"
      end

      def web?
        name == DEFAULT_NAME
      end

      def worker?
        !web?
      end

      # keys here should match those from the main config
      def as_json(*)
        {
          component: name,
          env: environment
        }
      end

      private

        def program_name
          $PROGRAM_NAME
        end

        def argv
          ARGV
        end

        def resolve_name(given_name)
          return DEFAULT_NAME if known_web_context?
          return given_name if given_name
          return WORKER_NAME if known_worker_context?
          DEFAULT_NAME
        end

        def validate_string!(string, kind)
          return true if string =~ NAME_FORMAT
          raise ArgumentError, "#{kind} can only contain lowercase letters, numbers, and dashes"
        end

        def known_web_context?
          rails_server? || rackup? || passenger?
        end

        def known_worker_context?
          return true if program_name =~ WORKER_PROGRAM_MATCHER
          program_name[/rake$/] && argv.any? { |arg| arg =~ WORKER_RAKE_MATCHER }
        end

        def rails_server?
          defined?(Rails::Server)
        end

        def rackup?
          program_name[/rackup$/]
        end

        def passenger?
          program_name[/\APassenger AppPreloader/]
        end
    end
  end
end