# encoding: utf-8
# This file is distributed under New Relic's license terms.
# See https://github.com/newrelic/rpm/blob/master/LICENSE for complete details.

module NewRelic
  module Agent
    # A singleton responsible for determining if the agent should start
    # monitoring.
    #
    # If the agent is in a monitored environment (e.g. production) it will
    # attempt to avoid starting at "inapproriate" times, for example in an IRB
    # session.  On Heroku, logs typically go to STDOUT so agent logs can spam
    # the console during interactive sessions.
    #
    # It should be possible to override Autostart logic with an explicit
    # configuration, for example the NEWRELIC_ENABLE environment variable or
    # agent_enabled key in newrelic.yml
    module Autostart
      extend self


      # The constants and execuatables (i.e. $0) used can be configured with
      # via the config keys 'autostart.blacklisted_constants' and
      # 'autostart.blacklisted_executables'
      def agent_should_start?
          !::NewRelic::Agent.config['autostart.blacklisted_constants'] \
            .split(/\s*,\s*/).any?{ |name| constant_is_defined?(name) } &&
          !::NewRelic::Agent.config['autostart.blacklisted_executables'] \
            .split(/\s*,\s*/).any?{ |bin| File.basename($0) == bin } &&
          !in_blacklisted_rake_task?
      end

      # Lookup whether namespaced constants (e.g. ::Foo::Bar::Baz) are in the
      # environment.
      def constant_is_defined?(const_name)
        const_name.to_s.sub(/\A::/,'').split('::').inject(Object) do |namespace, name|
          begin
            namespace.const_get(name)
          rescue NameError
            false
          end
        end
      end

      def in_blacklisted_rake_task?
        tasks = begin
            ::Rake.application.top_level_tasks
          rescue => e
            ::NewRelic::Agent.logger.debug("Not in Rake environment so skipping blacklisted_rake_tasks check: #{e}")
            []
          end
        !(tasks & ::NewRelic::Agent.config['autostart.blacklisted_rake_tasks'].split(/\s*,\s*/)).empty?
      end
    end
  end
end