freeipa/ipalib/base.py

# Authors:
#   Jason Gerard DeRose <jderose@redhat.com>
#
# Copyright (C) 2008  Red Hat
# see file 'COPYING' for use and warranty information
#
# This program is free software; you can redistribute it and/or
# modify it under the terms of the GNU General Public License as
# published by the Free Software Foundation; version 2 only
#
# This program is distributed in the hope that it will be useful,
# but WITHOUT ANY WARRANTY; without even the implied warranty of
# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
# GNU General Public License for more details.
#
# You should have received a copy of the GNU General Public License
# along with this program; if not, write to the Free Software
# Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA 02111-1307 USA

"""
Base classes for plug-in architecture and generative API.
"""

import inspect
import exceptions


class NameSpace(object):
	"""
	A read-only namespace of (key, value) pairs that can be accessed
	both as instance attributes and as dictionary items.  For example:

	>>> ns = NameSpace(dict(my_message='Hello world!'))
	>>> ns.my_message
	'Hello world!'
	>>> ns['my_message']
	'Hello world!'

	Keep in mind that Python doesn't offer true ready-only attributes. A
	NameSpace is read-only in that it prevents programmers from
	*accidentally* setting its attributes, but a motivated programmer can
	still set them.

	For example, setting an attribute the normal way will raise an exception:

	>>> ns.my_message = 'some new value'
	(raises exceptions.SetError)

	But a programmer could still set the attribute like this:

	>>> ns.__dict__['my_message'] = 'some new value'

	You should especially not implement a security feature that relies upon
	NameSpace being strictly read-only.
	"""

	__locked = False # Whether __setattr__ has been locked

	def __init__(self, kw, order=None):
		"""
		The `kw` argument is a dict of the (key, value) pairs to be in this
		NameSpace instance.  The optional `order` keyword argument specifies
		the order of the keys in this namespace; if omitted, the default is
		to sort the keys in ascending order.
		"""
		assert isinstance(kw, dict)
		self.__kw = dict(kw)
		for (key, value) in self.__kw.items():
			assert not key.startswith('_')
			setattr(self, key, value)
		if order is None:
			self.__keys = sorted(self.__kw)
		else:
			self.__keys = list(order)
			assert set(self.__keys) == set(self.__kw)
		self.__locked = True

	def __setattr__(self, name, value):
		"""
		Raises an exception if trying to set an attribute after the
		NameSpace has been locked; otherwise calls object.__setattr__().
		"""
		if self.__locked:
			raise exceptions.SetError(name)
		super(NameSpace, self).__setattr__(name, value)

	def __getitem__(self, key):
		"""
		Returns item from namespace named `key`.
		"""
		return self.__kw[key]

	def __hasitem__(self, key):
		"""
		Returns True if namespace has an item named `key`.
		"""
		return key.replace('-', '_') in self.__kw

	def __iter__(self):
		"""
		Yields the names in this NameSpace in ascending order, or in the
		the order specified in `order` kw arg.

		For example:

		>>> ns = NameSpace(dict(attr_b='world', attr_a='hello'))
		>>> list(ns)
		['attr_a', 'attr_b']
		>>> [ns[k] for k in ns]
		['hello', 'world']
		"""
		for key in self.__keys:
			yield key

	def __call__(self):
		"""
		Iterates through the values in this NameSpace in the same order as
		the keys.
		"""
		for key in self.__keys:
			yield self.__kw[key]

	def __len__(self):
		"""
		Returns number of items in this NameSpace.
		"""
		return len(self.__keys)



class Named(object):
	def __get_name(self):
		return self.__class__.__name__
	name = property(__get_name)


class WithObj(Named):
	_obj = None
	__obj = None
	__obj_locked = False

	def __get_obj(self):
		return self.__obj
	def __set_obj(self, obj):
		if self.__obj_locked:
			raise exceptions.TwiceSetError(self.__class__.__name__, 'obj')
		self.__obj_locked = True
		if obj is None:
			assert self.__obj is None
			assert self.obj is None
		else:
			assert isinstance(obj, Named)
			assert isinstance(self._obj, str)
			assert obj.name == self._obj
			self.__obj = obj
			assert self.obj is obj
	obj = property(__get_obj, __set_obj)


class Command(WithObj):
	def __call__(self):
		print 'You called %s()' % self.name

class Property(WithObj):
	pass

class Object(Named):
	__commands = None

	def __get_commands(self):
		return self.__commands
	def __set_commands(self, commands):
		if self.__commands is not None:
			raise exceptions.TwiceSetError(
				self.__class__.__name__, 'commands'
			)
		assert type(commands) is NameSpace
		self.__commands = commands
		assert self.commands is commands
	commands = property(__get_commands, __set_commands)


class Collector(object):
	def __init__(self):
		self.__d = {}
		self.globals = []

	def __getitem__(self, key):
		assert isinstance(key, str)
		if key not in self.__d:
			self.__d[key] = []
		return self.__d[key]

	def __iter__(self):
		for key in self.__d:
			yield key

	def add(self, i):
		assert isinstance(i, WithObj)
		if i._obj is None:
			self.globals.append(i)
		else:
			self[i._obj].append(i)

	def namespaces(self):
		for key in self:
			d = dict((i.name, i) for i in self[key])
			yield (key, NameSpace(d))



class Registrar(object):
	__object = None
	__commands = None
	__properties = None

	def __init__(self):
		self.__tmp_objects = {}
		self.__tmp_commands = {}
		self.__tmp_properties = {}

	def __get_objects(self):
		return self.__objects
	objects = property(__get_objects)

	def __get_commands(self):
		return self.__commands
	commands = property(__get_commands)

	def __get_target(self, i):
		if isinstance(i, Object):
			return (self.__tmp_objects, i.name)
		if isinstance(i, Command):
			return (self.__tmp_commands, i.name)
		assert isinstance(i, Property)


	def register(self, cls):
		assert inspect.isclass(cls)
		assert issubclass(cls, Named)
		i = cls()
		(target, key) = self.__get_target(i)
		target[key] = i

	def finalize(self):
		obj_cmd = Collector()
		for cmd in self.__tmp_commands.values():
			if cmd._obj is None:
				cmd.obj = None
			else:
				obj = self.__tmp_objects[cmd._obj]
				cmd.obj = obj
			obj_cmd.add(cmd)
		self.__objects = NameSpace(self.__tmp_objects)
		self.__commands = NameSpace(self.__tmp_commands)
		for (key, ns) in obj_cmd.namespaces():
			self.objects[key].commands = ns


class API(Registrar):
	__max_cmd_len = None

	def __get_max_cmd_len(self):
		if self.__max_cmd_len is None:
			if self.commands is None:
				return 0
			self.__max_cmd_len = max(len(n) for n in self.commands)
		return self.__max_cmd_len
	max_cmd_len = property(__get_max_cmd_len)