cli/command.py

# Copyright (c) 2012 The Chromium OS Authors. All rights reserved.
# Use of this source code is governed by a BSD-style license that can be
# found in the LICENSE file.

"""Module that contains meta-logic related to CLI commands.

CLI commands are the subcommands available to the user, such as "deploy" in
`cros deploy` or "shell" in `brillo shell`.

This module contains two important definitions used by all commands:
  CliCommand: The parent class of all CLI commands.
  CommandDecorator: Decorator that must be used to ensure that the command shows
    up in |_commands| and is discoverable.

Commands can be either imported directly or looked up using this module's
ListCommands() function.
"""

from __future__ import print_function

import glob
import os
import sys

from chromite.lib import brick_lib
from chromite.lib import cros_import


_commands = dict()


def _GetToolset():
  """Return the CLI toolset invoked by the user.

  For example, if the user is executing `cros flash`, this will return 'cros'.

  This won't work for unittests so if a certain toolset must be loaded for
  a unittest this should be mocked out to return the desired string.
  """
  return os.path.basename(sys.argv[0])


def _FindModules(subdir_path, toolset):
  """Returns a list of all the relevant python modules in |subdir_path|.

  The modules returned are based on |toolset|, so if |toolset| is 'cros'
  then cros_xxx.py modules will be found.

  Args:
    subdir_path: directory (string) to search for modules in.
    toolset: toolset (string) to find.

  Returns:
    List of filenames (strings).
  """
  modules = []
  for file_path in glob.glob(os.path.join(subdir_path, toolset + '_*.py')):
    if not file_path.endswith('_unittest.py'):
      modules.append(file_path)
  return modules


def _ImportCommands(toolset):
  """Directly imports all |toolset| python modules.

  This method imports the |toolset|_[!unittest] modules which may contain
  commands. When these modules are loaded, declared commands (those that use
  CommandDecorator) will automatically get added to |_commands|.

  Args:
    toolset: toolset (string) to import.
  """
  subdir_path = os.path.join(os.path.dirname(__file__), toolset)
  for file_path in _FindModules(subdir_path, toolset):
    file_name = os.path.basename(file_path)
    mod_name = os.path.splitext(file_name)[0]
    cros_import.ImportModule(('chromite', 'cli', toolset, mod_name))


def ListCommands(toolset=None):
  """Return a dictionary mapping command names to classes.

  Args:
    toolset: toolset (string) to list, None to determine from the commandline.

  Returns:
    A dictionary mapping names (strings) to commands (classes).
  """
  _ImportCommands(toolset or _GetToolset())
  return _commands.copy()


class InvalidCommandError(Exception):
  """Error that occurs when command class fails sanity checks."""
  pass


def CommandDecorator(command_name):
  """Decorator that sanity checks and adds class to list of usable commands."""

  def InnerCommandDecorator(original_class):
    """"Inner Decorator that actually wraps the class."""
    if not hasattr(original_class, '__doc__'):
      raise InvalidCommandError('All handlers must have docstrings: %s' %
                                original_class)

    if not issubclass(original_class, CliCommand):
      raise InvalidCommandError('All Commands must derive from CliCommand: %s' %
                                original_class)

    _commands[command_name] = original_class
    original_class.command_name = command_name

    return original_class

  return InnerCommandDecorator


class CliCommand(object):
  """All CLI commands must derive from this class.

  This class provides the abstract interface for all CLI commands. When
  designing a new command, you must sub-class from this class and use the
  CommandDecorator decorator. You must specify a class docstring as that will be
  used as the usage for the sub-command.

  In addition your command should implement AddParser which is passed in a
  parser that you can add your own custom arguments. See argparse for more
  information.
  """
  # Indicates whether command stats should be uploaded for this command.
  # Override to enable command stats uploading.
  upload_stats = False
  # We set the default timeout to 1 second, to prevent overly long waits for
  # commands to complete.  From manual tests, stat uploads usually take
  # between 0.35s-0.45s in MTV.
  upload_stats_timeout = 1

  # Indicates whether command uses cache related commandline options.
  use_caching_options = False

  def __init__(self, options):
    self.options = options
    brick = brick_lib.FindBrickInPath()
    self.curr_brick_locator = brick.brick_locator if brick else None

  @classmethod
  def AddParser(cls, parser):
    """Add arguments for this command to the parser."""
    parser.set_defaults(command_class=cls)

  def Run(self):
    """The command to run."""
    raise NotImplementedError()