text: #
  # Licensed to the Apache Software Foundation (ASF) under one or more
  # contributor license agreements.  See the NOTICE file distributed with
  # this work for additional information regarding copyright ownership.
  # The ASF licenses this file to You under the Apache License, Version 2.0
  # (the "License"); you may not use this file except in compliance with
  # the License.  You may obtain a copy of the License at
  #
  #    http://www.apache.org/licenses/LICENSE-2.0
  #
  # Unless required by applicable law or agreed to in writing, software
  # distributed under the License is distributed on an "AS IS" BASIS,
  # WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
  # See the License for the specific language governing permissions and
  # limitations under the License.
  #
  
  """
  The classes in this file are interfaces for metrics. They are not intended
  to be subclassed or created directly by users. To work with and access metrics,
  users should use the classes and methods exposed in metric.py.
  
  Available classes:
  
  - Metric - Base interface of a metrics object.
  - Counter - Counter metric interface. Allows a count to be incremented or
      decremented during pipeline execution.
  - Distribution - Distribution Metric interface. Allows statistics about the
      distribution of a variable to be collected during pipeline execution.
  - Gauge - Gauge Metric interface. Allows to track the latest value of a
      variable during pipeline execution.
  - MetricName - Namespace and name used to refer to a Metric.
  """
  
  from apache_beam.portability.api import beam_fn_api_pb2
  
  __all__ = ['Metric', 'Counter', 'Distribution', 'Gauge', 'MetricName']
  
  
  class MetricName(object):
    """The name of a metric.
  
    The name of a metric consists of a namespace and a name. The namespace
    allows grouping related metrics together and also prevents collisions
    between multiple metrics of the same name.
    """
    def __init__(self, namespace, name):
      """Initializes ``MetricName``.
  
      Args:
        namespace: A string with the namespace of a metric.
        name: A string with the name of a metric.
      """
      if not namespace:
        raise ValueError('Metric namespace must be non-empty')
      if not name:
        raise ValueError('Metric name must be non-empty')
      self.namespace = namespace
      self.name = name
  
    def __eq__(self, other):
      return (self.namespace == other.namespace and
              self.name == other.name)
  
    def __str__(self):
      return 'MetricName(namespace={}, name={})'.format(
          self.namespace, self.name)
  
    def __hash__(self):
      return hash((self.namespace, self.name))
  
    def to_runner_api(self):
      return beam_fn_api_pb2.Metrics.User.MetricName(
          namespace=self.namespace, name=self.name)
  
    @staticmethod
    def from_runner_api(proto):
      return MetricName(proto.namespace, proto.name)
  
  
  class Metric(object):
    """Base interface of a metric object."""
    pass
  
  
  class Counter(Metric):
    """Counter metric interface. Allows a count to be incremented/decremented
    during pipeline execution."""
    def inc(self, n=1):
      raise NotImplementedError
  
    def dec(self, n=1):
      self.inc(-n)
  
  
  class Distribution(Metric):
    """Distribution Metric interface.
  
    Allows statistics about the distribution of a variable to be collected during
    pipeline execution."""
  
    def update(self, value):
      raise NotImplementedError
  
  
  class Gauge(Metric):
    """Gauge Metric interface.
  
    Allows tracking of the latest value of a variable during pipeline
    execution."""
  
    def set(self, value):
      raise NotImplementedError
  