content: from __future__ import annotations
  
  from collections.abc import Sequence
  
  from ..frames import Frame
  from ..typing import ExtensionName, ExtensionParameter
  
  
  __all__ = ["Extension", "ClientExtensionFactory", "ServerExtensionFactory"]
  
  
  class Extension:
      """
      Base class for extensions.
  
      """
  
      name: ExtensionName
      """Extension identifier."""
  
      def decode(self, frame: Frame, *, max_size: int | None = None) -> Frame:
          """
          Decode an incoming frame.
  
          Args:
              frame: Incoming frame.
              max_size: Maximum payload size in bytes.
  
          Returns:
              Decoded frame.
  
          Raises:
              PayloadTooBig: If decoding the payload exceeds ``max_size``.
  
          """
          raise NotImplementedError
  
      def encode(self, frame: Frame) -> Frame:
          """
          Encode an outgoing frame.
  
          Args:
              frame: Outgoing frame.
  
          Returns:
              Encoded frame.
  
          """
          raise NotImplementedError
  
  
  class ClientExtensionFactory:
      """
      Base class for client-side extension factories.
  
      """
  
      name: ExtensionName
      """Extension identifier."""
  
      def get_request_params(self) -> Sequence[ExtensionParameter]:
          """
          Build parameters to send to the server for this extension.
  
          Returns:
              Parameters to send to the server.
  
          """
          raise NotImplementedError
  
      def process_response_params(
          self,
          params: Sequence[ExtensionParameter],
          accepted_extensions: Sequence[Extension],
      ) -> Extension:
          """
          Process parameters received from the server.
  
          Args:
              params: Parameters received from the server for this extension.
              accepted_extensions: List of previously accepted extensions.
  
          Returns:
              An extension instance.
  
          Raises:
              NegotiationError: If parameters aren't acceptable.
  
          """
          raise NotImplementedError
  
  
  class ServerExtensionFactory:
      """
      Base class for server-side extension factories.
  
      """
  
      name: ExtensionName
      """Extension identifier."""
  
      def process_request_params(
          self,
          params: Sequence[ExtensionParameter],
          accepted_extensions: Sequence[Extension],
      ) -> tuple[list[ExtensionParameter], Extension]:
          """
          Process parameters received from the client.
  
          Args:
              params: Parameters received from the client for this extension.
              accepted_extensions: List of previously accepted extensions.
  
          Returns:
              To accept the offer, parameters to send to the client for this
              extension and an extension instance.
  
          Raises:
              NegotiationError: To reject the offer, if parameters received from
                  the client aren't acceptable.
  
          """
          raise NotImplementedError
  