# copyright 2014 LOGILAB S.A. (Paris, FRANCE), all rights reserved.

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

#

# This file is part of CubicWeb.

#

# CubicWeb is free software: you can redistribute it and/or modify it under the

# terms of the GNU Lesser General Public License as published by the Free

# Software Foundation, either version 2.1 of the License, or (at your option)

# any later version.

#

# CubicWeb 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 Lesser General Public License for more

# details.

#

# You should have received a copy of the GNU Lesser General Public License along

# with CubicWeb.  If not, see <http://www.gnu.org/licenses/>.

"""Hooks for synchronizing computed attributes"""

__docformat__ = "restructuredtext en"

_ = unicode

from collections import defaultdict

from rql import nodes

from cubicweb.server import hook

class RecomputeAttributeOperation(hook.DataOperationMixIn, hook.Operation):

    """Operation to recompute caches of computed attribute at commit time,

    depending on what's have been modified in the transaction and avoiding to

    recompute twice the same attribute

    """

    containercls = dict

    def add_data(self, computed_attribute, eid=None):

        try:

            self._container[computed_attribute].add(eid)

        except KeyError:

            self._container[computed_attribute] = set((eid,))

    def precommit_event(self):

        for computed_attribute_rdef, eids in self.get_data().iteritems():

            attr = computed_attribute_rdef.rtype

            formula  = computed_attribute_rdef.formula

            rql = formula.replace('Any ', 'Any X, ', 1)

            kwargs = None

            # add constraint on X to the formula

            if None in eids : # recompute for all etype if None is found

                rql += ', X is %s' % computed_attribute_rdef.subject

            elif len(eids) == 1:

                rql += ', X eid %(x)s'

                kwargs = {'x': eids.pop()}

            else:

                rql += ', X eid IN (%s)' % ', '.join((str(eid) for eid in eids))

            update_rql = 'SET X %s %%(value)s WHERE X eid %%(x)s' % attr

            for eid, value in self.cnx.execute(rql, kwargs):

                self.cnx.execute(update_rql, {'value': value, 'x': eid})

class EntityWithCACreatedHook(hook.Hook):

    """When creating an entity that has some computed attribute, those

    attributes have to be computed.

    Concret class of this hook are generated at registration time by

    introspecting the schema.

    """

    __abstract__ = True

    events = ('after_add_entity',)

    # list of computed attribute rdefs that have to be recomputed

    computed_attributes = None

    def __call__(self):

        for rdef in self.computed_attributes:

            RecomputeAttributeOperation.get_instance(self._cw).add_data(

                rdef, self.entity.eid)

class RelationInvolvedInCAModifiedHook(hook.Hook):

    """When some relation used in a computed attribute is updated, those

    attributes have to be recomputed.

    Concret class of this hook are generated at registration time by

    introspecting the schema.

    """

    __abstract__ = True

    events = ('after_add_relation', 'before_delete_relation')

    # list of (computed attribute rdef, optimize_on) that have to be recomputed

    optimized_computed_attributes = None

    def __call__(self):

        for rdef, optimize_on in self.optimized_computed_attributes:

            if optimize_on is None:

                eid = None

            else:

                eid = getattr(self, optimize_on)

            RecomputeAttributeOperation.get_instance(self._cw).add_data(rdef, eid)

class AttributeInvolvedInCAModifiedHook(hook.Hook):

    """When some attribute used in a computed attribute is updated, those

    attributes have to be recomputed.

    Concret class of this hook are generated at registration time by

    introspecting the schema.

    """

    __abstract__ = True

    events = ('after_update_entity',)

    # list of (computed attribute rdef, attributes of this entity type involved)

    # that may have to be recomputed

    attributes_computed_attributes = None

    def __call__(self):

        edited_attributes = frozenset(self.entity.cw_edited)

        for rdef, used_attributes in self.attributes_computed_attributes.iteritems():

            if edited_attributes.intersection(used_attributes):

                # XXX optimize if the modified attributes belong to the same

                # entity as the computed attribute

                RecomputeAttributeOperation.get_instance(self._cw).add_data(rdef)

# code generation at registration time #########################################

def _optimize_on(formula_select, rtype):

    """Given a formula and some rtype, tells whether on update of the given

    relation, formula may be recomputed only for rhe relation's subject

    ('eidfrom' returned), object ('eidto' returned) or None.

    Optimizing is only possible when X is used as direct subject/object of this

    relation, else we may miss some necessary update.

    """

    for rel in formula_select.get_nodes(nodes.Relation):

        if rel.r_type == rtype:

            sub = rel.get_variable_parts()[0]

            obj = rel.get_variable_parts()[1]

            if sub.name == 'X':

                return 'eidfrom'

            elif obj.name == 'X':

                return 'eidto'

            else:

                return None

class _FormulaDependenciesMatrix(object):

    """This class computes and represents the dependencies of computed attributes

    towards relations and attributes

    """

    def __init__(self, schema):

        """Analyzes the schema to compute the dependencies"""

        # entity types holding some computed attribute {etype: [computed rdefs]}

        self.computed_attribute_by_etype = defaultdict(list)

        # depending entity types {dep. etype: {computed rdef: dep. etype attributes}}

        self.computed_attribute_by_etype_attrs = defaultdict(lambda: defaultdict(set))

        # depending relations def {dep. rdef: [computed rdefs]

        self.computed_attribute_by_relation = defaultdict(list) # by rdef

        # Walk through all attributes definitions

        for rdef in schema.iter_computed_attributes():

            self.computed_attribute_by_etype[rdef.subject.type].append(rdef)

            # extract the relations it depends upon - `rdef.formula_select` is

            # expected to have been set by finalize_computed_attributes

            select = rdef.formula_select

            for rel_node in select.get_nodes(nodes.Relation):

                rschema = schema.rschema(rel_node.r_type)

                lhs, rhs = rel_node.get_variable_parts()

                for sol in select.solutions:

                    subject_etype = sol[lhs.name]

                    if isinstance(rhs, nodes.VariableRef):

                        object_etypes = set(sol[rhs.name] for sol in select.solutions)

                    else:

                        object_etypes = rschema.objects(subject_etype)

                    for object_etype in object_etypes:

                        if rschema.final:

                            attr_for_computations = self.computed_attribute_by_etype_attrs[subject_etype]

                            attr_for_computations[rdef].add(rschema.type)

                        else:

                            depend_on_rdef = rschema.rdefs[subject_etype, object_etype]

                            self.computed_attribute_by_relation[depend_on_rdef].append(rdef)

    def generate_entity_creation_hooks(self):

        for etype, computed_attributes in self.computed_attribute_by_etype.iteritems():

            regid = 'computed_attribute.%s_created' % etype

            selector = hook.is_instance(etype)

            yield type('%sCreatedHook' % etype,

                       (EntityWithCACreatedHook,),

                       {'__regid__': regid,

                        '__select__':  hook.Hook.__select__ & selector,

                        'computed_attributes': computed_attributes})

    def generate_relation_change_hooks(self):

        for rdef, computed_attributes in self.computed_attribute_by_relation.iteritems():

            regid = 'computed_attribute.%s_modified' % rdef.rtype

            selector = hook.match_rtype(rdef.rtype.type,

                                        frometypes=(rdef.subject.type,),

                                        toetypes=(rdef.object.type,))

            optimized_computed_attributes = []

            for computed_rdef in computed_attributes:

                optimized_computed_attributes.append(

                    (computed_rdef,

                     _optimize_on(computed_rdef.formula_select, rdef.rtype))

                     )

            yield type('%sModifiedHook' % rdef.rtype,

                       (RelationInvolvedInCAModifiedHook,),

                       {'__regid__': regid,

                        '__select__':  hook.Hook.__select__ & selector,

                        'optimized_computed_attributes': optimized_computed_attributes})

    def generate_entity_update_hooks(self):

        for etype, attributes_computed_attributes in self.computed_attribute_by_etype_attrs.iteritems():

            regid = 'computed_attribute.%s_updated' % etype

            selector = hook.is_instance(etype)

            yield type('%sModifiedHook' % etype,

                       (AttributeInvolvedInCAModifiedHook,),

                       {'__regid__': regid,

                        '__select__':  hook.Hook.__select__ & selector,

                        'attributes_computed_attributes': attributes_computed_attributes})

def registration_callback(vreg):

    vreg.register_all(globals().values(), __name__)

    dependencies = _FormulaDependenciesMatrix(vreg.schema)

    for hook_class in dependencies.generate_entity_creation_hooks():

        vreg.register(hook_class)

    for hook_class in dependencies.generate_relation_change_hooks():

        vreg.register(hook_class)

    for hook_class in dependencies.generate_entity_update_hooks():

        vreg.register(hook_class)