"""Hooks management

This module defined the `Hook` class and registry and a set of abstract classes

for operations.

Hooks are called before / after any individual update of entities / relations

in the repository and on special events such as server startup or shutdown.

Operations may be registered by hooks during a transaction, which will  be

fired when the pool is commited or rollbacked.

Entity hooks (eg before_add_entity, after_add_entity, before_update_entity,

after_update_entity, before_delete_entity, after_delete_entity) all have an

`entity` attribute

Relation (eg before_add_relation, after_add_relation, before_delete_relation,

after_delete_relation) all have `eidfrom`, `rtype`, `eidto` attributes.

Server start/stop hooks (eg server_startup, server_shutdown) have a `repo`

attribute, but *their `_cw` attribute is None*.

Backup/restore hooks (eg server_backup, server_restore) have a `repo` and a

`timestamp` attributes, but *their `_cw` attribute is None*.

Session hooks (eg session_open, session_close) have no special attribute.

:organization: Logilab

:copyright: 2001-2010 LOGILAB S.A. (Paris, FRANCE), license is LGPL v2.

:contact: http://www.logilab.fr/ -- mailto:contact@logilab.fr

:license: GNU Lesser General Public License, v2.1 - http://www.gnu.org/licenses

"""

__docformat__ = "restructuredtext en"

from warnings import warn

from logging import getLogger

from itertools import chain

from logilab.common.decorators import classproperty

from logilab.common.deprecation import deprecated

from logilab.common.logging_ext import set_log_methods

from cubicweb.cwvreg import CWRegistry, VRegistry

from cubicweb.selectors import (objectify_selector, lltrace, ExpectedValueSelector,

                                implements)

from cubicweb.appobject import AppObject

ENTITIES_HOOKS = set(('before_add_entity',    'after_add_entity',

                      'before_update_entity', 'after_update_entity',

                      'before_delete_entity', 'after_delete_entity'))

RELATIONS_HOOKS = set(('before_add_relation',   'after_add_relation' ,

                       'before_delete_relation','after_delete_relation'))

SYSTEM_HOOKS = set(('server_backup', 'server_restore',

                    'server_startup', 'server_shutdown',

                    'session_open', 'session_close'))

ALL_HOOKS = ENTITIES_HOOKS | RELATIONS_HOOKS | SYSTEM_HOOKS

class HooksRegistry(CWRegistry):

    def register(self, obj, **kwargs):

        try:

            iter(obj.events)

        except AttributeError:

            raise

        except:

            raise Exception('bad .events attribute %s on %s.%s' % (

                obj.events, obj.__module__, obj.__name__))

        for event in obj.events:

            if event not in ALL_HOOKS:

                raise Exception('bad event %s on %s.%s' % (

                    event, obj.__module__, obj.__name__))

        super(HooksRegistry, self).register(obj, **kwargs)

    def call_hooks(self, event, req=None, **kwargs):

        kwargs['event'] = event

        for hook in sorted(self.possible_objects(req, **kwargs), key=lambda x: x.order):

            if hook.enabled:

                hook()

            else:

                warn('[3.6] %s: enabled is deprecated' % hook.__class__)

VRegistry.REGISTRY_FACTORY['hooks'] = HooksRegistry

_MARKER = object()

def entity_oldnewvalue(entity, attr):

    """returns the couple (old attr value, new attr value)

    NOTE: will only work in a before_update_entity hook

    """

    # get new value and remove from local dict to force a db query to

    # fetch old value

    newvalue = entity.pop(attr, _MARKER)

    oldvalue = getattr(entity, attr)

    if newvalue is not _MARKER:

        entity[attr] = newvalue

    return oldvalue, newvalue

# some hook specific selectors #################################################

@objectify_selector

@lltrace

def match_event(cls, req, **kwargs):

    if kwargs.get('event') in cls.events:

        return 1

    return 0

@objectify_selector

@lltrace

def enabled_category(cls, req, **kwargs):

    if req is None:

        # server startup / shutdown event

        config = kwargs['repo'].config

    else:

        config = req.vreg.config

    return config.is_hook_activated(cls)

@objectify_selector

@lltrace

def regular_session(cls, req, **kwargs):

    if req is None or req.is_super_session:

        return 0

    return 1

class rechain(object):

    def __init__(self, *iterators):

        self.iterators = iterators

    def __iter__(self):

        return iter(chain(*self.iterators))

class match_rtype(ExpectedValueSelector):

    """accept if parameters specified as initializer arguments are specified

    in named arguments given to the selector

    :param *expected: parameters (eg `basestring`) which are expected to be

                      found in named arguments (kwargs)

    """

    def __init__(self, *expected, **more):

        self.expected = expected

        self.frometypes = more.pop('frometypes', None)

        self.toetypes = more.pop('toetypes', None)

    @lltrace

    def __call__(self, cls, req, *args, **kwargs):

        if kwargs.get('rtype') not in self.expected:

            return 0

        if self.frometypes is not None and \

               req.describe(kwargs['eidfrom'])[0] not in self.frometypes:

            return 0

        if self.toetypes is not None and \

               req.describe(kwargs['eidto'])[0] not in self.toetypes:

            return 0

        return 1

class match_rtype_sets(ExpectedValueSelector):

    """accept if parameters specified as initializer arguments are specified

    in named arguments given to the selector

    """

    def __init__(self, *expected):

        self.expected = expected

    @lltrace

    def __call__(self, cls, req, *args, **kwargs):

        for rel_set in self.expected:

            if kwargs.get('rtype') in rel_set:

                return 1

        return 0

# base class for hook ##########################################################

class Hook(AppObject):

    __registry__ = 'hooks'

    __select__ = match_event() & enabled_category()

    # set this in derivated classes

    events = None

    category = None

    order = 0

    # XXX deprecated

    enabled = True

    @classproperty

    def __regid__(cls):

        warn('[3.6] %s.%s: please specify an id for your hook'

             % (cls.__module__, cls.__name__), DeprecationWarning)

        return str(id(cls))

    @classmethod

    def __registered__(cls, reg):

        super(Hook, cls).__registered__(reg)

        if getattr(cls, 'accepts', None):

            warn('[3.6] %s.%s: accepts is deprecated, define proper __select__'

                 % (cls.__module__, cls.__name__), DeprecationWarning)

            rtypes = []

            for ertype in cls.accepts:

                if ertype.islower():

                    rtypes.append(ertype)

                else:

                    cls.__select__ = cls.__select__ & implements(ertype)

            if rtypes:

                cls.__select__ = cls.__select__ & match_rtype(*rtypes)

        return cls

    known_args = set(('entity', 'rtype', 'eidfrom', 'eidto', 'repo', 'timestamp'))

    def __init__(self, req, event, **kwargs):

        for arg in self.known_args:

            if arg in kwargs:

                setattr(self, arg, kwargs.pop(arg))

        super(Hook, self).__init__(req, **kwargs)

        self.event = event

    def __call__(self):

        if hasattr(self, 'call'):

            cls = self.__class__

            warn('[3.6] %s.%s: call is deprecated, implements __call__'

                 % (cls.__module__, cls.__name__), DeprecationWarning)

            if self.event.endswith('_relation'):

                self.call(self._cw, self.eidfrom, self.rtype, self.eidto)

            elif 'delete' in self.event:

                self.call(self._cw, self.entity.eid)

            elif self.event.startswith('server_'):

                self.call(self.repo)

            elif self.event.startswith('session_'):

                self.call(self._cw)

            else:

                self.call(self._cw, self.entity)

set_log_methods(Hook, getLogger('cubicweb.hook'))

# base classes for relation propagation ########################################

class PropagateSubjectRelationHook(Hook):

    """propagate some `main_rtype` relation on entities linked as object of

    `subject_relations` or as subject of `object_relations` (the watched

    relations).

    This hook ensure that when one of the watched relation is added, the

    `main_rtype` relation is added to the target entity of the relation.

    """

    events = ('after_add_relation',)

    # to set in concrete class

    main_rtype = None

    subject_relations = None

    object_relations = None

    def __call__(self):

        assert self.main_rtype

        for eid in (self.eidfrom, self.eidto):

            etype = self._cw.describe(eid)[0]

            if self.main_rtype not in self._cw.vreg.schema.eschema(etype).subjrels:

                return

        if self.rtype in self.subject_relations:

            meid, seid = self.eidfrom, self.eidto

        else:

            assert self.rtype in self.object_relations

            meid, seid = self.eidto, self.eidfrom

        self._cw.unsafe_execute(

            'SET E %s P WHERE X %s P, X eid %%(x)s, E eid %%(e)s, NOT E %s P'\

            % (self.main_rtype, self.main_rtype, self.main_rtype),

            {'x': meid, 'e': seid}, ('x', 'e'))

class PropagateSubjectRelationAddHook(Hook):

    """propagate to entities at the end of watched relations when a `main_rtype`

    relation is added

    """

    events = ('after_add_relation',)

    # to set in concrete class

    subject_relations = None

    object_relations = None

    def __call__(self):

        eschema = self._cw.vreg.schema.eschema(self._cw.describe(self.eidfrom)[0])

        execute = self._cw.unsafe_execute

        for rel in self.subject_relations:

            if rel in eschema.subjrels:

                execute('SET R %s P WHERE X eid %%(x)s, P eid %%(p)s, '

                        'X %s R, NOT R %s P' % (self.rtype, rel, self.rtype),

                        {'x': self.eidfrom, 'p': self.eidto}, 'x')

        for rel in self.object_relations:

            if rel in eschema.objrels:

                execute('SET R %s P WHERE X eid %%(x)s, P eid %%(p)s, '

                        'R %s X, NOT R %s P' % (self.rtype, rel, self.rtype),

                        {'x': self.eidfrom, 'p': self.eidto}, 'x')

class PropagateSubjectRelationDelHook(Hook):

    """propagate to entities at the end of watched relations when a `main_rtype`

    relation is deleted

    """

    events = ('after_delete_relation',)

    # to set in concrete class

    subject_relations = None

    object_relations = None

    def __call__(self):

        eschema = self._cw.vreg.schema.eschema(self._cw.describe(self.eidfrom)[0])

        execute = self._cw.unsafe_execute

        for rel in self.subject_relations:

            if rel in eschema.subjrels:

                execute('DELETE R %s P WHERE X eid %%(x)s, P eid %%(p)s, '

                        'X %s R' % (self.rtype, rel),

                        {'x': self.eidfrom, 'p': self.eidto}, 'x')

        for rel in self.object_relations:

            if rel in eschema.objrels:

                execute('DELETE R %s P WHERE X eid %%(x)s, P eid %%(p)s, '

                        'R %s X' % (self.rtype, rel),

                        {'x': self.eidfrom, 'p': self.eidto}, 'x')

# abstract classes for operation ###############################################

class Operation(object):

    """an operation is triggered on connections pool events related to

    commit / rollback transations. Possible events are:

    precommit:

      the pool is preparing to commit. You shouldn't do anything things which

      has to be reverted if the commit fail at this point, but you can freely

      do any heavy computation or raise an exception if the commit can't go.

      You can add some new operation during this phase but their precommit

      event won't be triggered

    commit:

      the pool is preparing to commit. You should avoid to do to expensive

      stuff or something that may cause an exception in this event

    revertcommit:

      if an operation failed while commited, this event is triggered for

      all operations which had their commit event already to let them

      revert things (including the operation which made fail the commit)

    rollback:

      the transaction has been either rollbacked either

      * intentionaly

      * a precommit event failed, all operations are rollbacked

      * a commit event failed, all operations which are not been triggered for

        commit are rollbacked

    order of operations may be important, and is controlled according to:

    * operation's class

    """

    def __init__(self, session, **kwargs):

        self.session = session

        self.__dict__.update(kwargs)

        self.register(session)

        # execution information

        self.processed = None # 'precommit', 'commit'

        self.failed = False

    def register(self, session):

        session.add_operation(self, self.insert_index())

    def insert_index(self):

        """return the index of  the lastest instance which is not a

        LateOperation instance

        """

        # faster by inspecting operation in reverse order for heavy transactions

        i = None

        for i, op in enumerate(reversed(self.session.pending_operations)):

            if isinstance(op, (LateOperation, SingleLastOperation)):

                continue

            return -i or None

        if i is None:

            return None

        return -(i + 1)

    def handle_event(self, event):

        """delegate event handling to the opertaion"""

        getattr(self, event)()

    def precommit_event(self):

        """the observed connections pool is preparing a commit"""

    def revertprecommit_event(self):

        """an error went when pre-commiting this operation or a later one

        should revert pre-commit's changes but take care, they may have not

        been all considered if it's this operation which failed

        """

    def commit_event(self):