# Loads Service definitions from Rails.root/config/umlaut_services.yml
# instantiates services from definitions, by id.
#
# It's terrible we need to do this globally like this, but
# too hard to back out of legacy design now.
class ServiceStore
  @@global_service_store = ServiceStore.new
  def self.global_service_store
    @@global_service_store
  end

  # certain class methods all default to global default ServiceStore,
  # for global ServiceStore. 
  [:config, :service_definitions, :service_definition_for, :'instantiate_service!'].each do |method|
    self.define_singleton_method(method) do |*args|      
      global_service_store.send(method, *args)
    end
  end


  # Returns complete hash loaded from services.yml
  def config
    # cache hash loaded from YAML, ensure it has the keys we expect.
    unless defined? @services_config_list
      yaml_path = File.expand_path("config/umlaut_services.yml", Rails.root)
      @services_config_list = (File.exists? yaml_path) ? YAML::load(File.open(yaml_path)) : {}
      @services_config_list["default"] ||= {}
      @services_config_list["default"]["services"] ||= {}
    end
    return @services_config_list
  end

  # Returns hash keyed by unique service name, value service definition
  # hash.
  def service_definitions
    unless defined? @service_definitions
      @service_definitions = {}
      config.each_pair do |group_name, group|
        if group["services"]
          # Add the group name to each service
          # in the group
          group["services"].each_pair do |service_id, service|
            service["group"] = group_name
          end
          # Merge the group's services into the service definitions.
          @service_definitions.merge!(  group["services"]  )
        end
      end
      # set service_id key in each based on hash key
      @service_definitions.each_pair do |key, hash|
        hash["service_id"] =  key
      end
    end
    return @service_definitions
  end

  def service_definition_for(service_id)
    return service_definitions[service_id]
  end

  # pass in string unique key OR a service definition hash,
  # and a current UmlautRequest.
  # get back instantiated Service object.
  def instantiate_service!(service, request)
    definition = service.kind_of?(Hash) ? service : service_definition_for(service.to_s)
    raise "Service '#{service}'' does not exist in umlaut-services.yml" if definition.nil?
    className = definition["type"] || definition["service_id"]
    classConst = Kernel.const_get(className)
    service = classConst.new(definition)
    service.request = request
    return service
  end
end