#!/usr/bin/python2.5

#

# Copyright 2008 the Melange authors.

#

# Licensed under the Apache License, Version 2.0 (the "License");

# you may not use this file except in compliance with the License.

# You may obtain a copy of the License at

#

#   http://www.apache.org/licenses/LICENSE-2.0

#

# Unless required by applicable law or agreed to in writing, software

# distributed under the License is distributed on an "AS IS" BASIS,

# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.

# See the License for the specific language governing permissions and

# limitations under the License.

"""Helpers functions for updating different kinds of models in datastore.

"""

__authors__ = [

  '"Todd Larsen" <tlarsen@google.com>',

  '"Sverre Rabbelier" <sverer@rabbelier.nl>',

  '"Pawel Solyga" <pawel.solyga@gmail.com>',

  ]

from google.appengine.ext import db

from soc.logic import out_of_band

class Logic:

  """Base logic for entity classes.

  The BaseLogic class functions specific to Entity classes by relying

  on the the child-classes to implement _model, _name and _key_name

  """

  def _updateField(self, model, name, value):

    """Hook called when a field is updated.

    Base classes should override if any special actions need to be

    taken when a field is updated. The field is not updated if the

    method does not return a True value.

    """

    return True

  def getFromKeyName(self, key_name):

    """"Returns User entity for key_name or None if not found.

-

-    Args:

-      key_name: key name of entity

    """

    return self._model.get_by_key_name(key_name)

  def getFromFields(self, **kwargs):

    """Returns the entity for a given link name, or None if not found.

    Args:

      **kwargs: the fields of the entity that uniquely identifies it

    """

    key_name = self.getKeyNameForFields(**kwargs)

    if key_name:

      entity = self._model.get_by_key_name(key_name)

    else:

      entity = None

    return entity

  def getIfFields(self, **kwargs):

    """Returns entity for supplied link name if one exists.

    Args:

      **kwargs: the fields of the entity that uniquely identifies it

    Returns:

      * None if a field is false.

      * Entity for supplied fields

    Raises:

      out_of_band.ErrorResponse if link name is not false, but no entity

      with the supplied link name exists in the Datastore

    """

    if not all(kwargs.values()):

      # exit without error, to let view know that link_name was not supplied

      return None

    entity = self.getFromFields(**kwargs)

    if entity:

      # an entity exist for this link_name, so return that entity

      return entity

    fields = []

    for key, value in kwargs.iteritems():

      fields.extend('"%s" is "%s" ' % (key, value))

    # else: fields were supplied, but there is no Entity that has it

    raise out_of_band.ErrorResponse(

        'There is no %s with %s.' % (self._name, ''.join(fields)), status=404)

  def getKeyNameForFields(self, **kwargs):

    """Return a Datastore key_name for a Entity from the specified fields.

    Args:

      **kwargs: the fields of the entity that uniquely identifies it

    """

    if not all(kwargs.values()):

      return None

    return self._keyName(**kwargs)

  def extractKeyFields(self, fields):

    """Extracts all the fields from that are in the mode's key_fields property

    Args:

      fields: A dict from which the fields should be extracted

    """

    key_fields = {}

    for key, value in fields.iteritems():

      if key in self._model.key_fields:

        key_fields[key] = value

    return key_fields

  def getForLimitAndOffset(self, limit, offset=0):

    """Returns entities for given offset and limit or None if not found.

    Args:

      limit: max amount of entities to return

      offset: optional offset in entities list which defines first entity to

        return; default is zero (first entity)

    """

    query = self._model.all()

    return query.fetch(limit, offset)

  def updateModelProperties(self, model, **model_properties):

    """Update existing model entity using supplied model properties.

    Args:

      model: a model entity

      **model_properties: keyword arguments that correspond to model entity

        properties and their values

    Returns:

      the original model entity with any supplied properties changed

    """

    def update():

      return self._unsafeUpdateModelProperties(model, **model_properties)

    return db.run_in_transaction(update)

  def _unsafeUpdateModelProperties(self, model, **model_properties):

    """(see updateModelProperties)

    Like updateModelProperties(), but not run within a transaction.

    """

    properties = model.properties()

    for prop in properties.values():

      name = prop.name

      if not name in self._skip_properties and name in model_properties:

        value = model_properties[prop.name]

        if self._updateField(model, name, value):

          prop.__set__(model, value)

    model.put()

    return model

  def updateOrCreateFromKeyName(self, properties, key_name):

    """Update existing entity, or create new one with supplied properties.

    Args:

      properties: dict with entity properties and their values

      key_name: the key_name of the entity that uniquely identifies it

    Returns:

      the entity corresponding to the key_name, with any supplied

      properties changed, or a new entity now associated with the

      supplied key_name and properties.

    """

    entity = self.getFromKeyName(key_name)

    if not entity:

      # entity did not exist, so create one in a transaction

      entity = self._model.get_or_insert(key_name, **properties)

    # there is no way to be sure if get_or_insert() returned a new entity or

    # got an existing one due to a race, so update with properties anyway,

    # in a transaction

    return self.updateModelProperties(entity, **properties)

  def updateOrCreateFromFields(self, properties, **kwargs):

    """Like updateOrCreateFromKeyName, but resolves **kwargs to a key_name first.

    """

    # attempt to retrieve the existing entity

    key_name  = self.getKeyNameForFields(**kwargs)

    return self.updateOrCreateFromKeyName(properties, key_name)

  def isDeletable(self, entity):

    """Returns whether the specified entity can be deleted.

    Args:

      entity: an existing entity in datastore

    """

    return True

  def delete(self, entity):

    """Delete existing entity from datastore.

    Args:

      entity: an existing entity in datastore

    """

    entity.delete()