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Filename : util.py
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# -*- test-case-name: txdav.caldav.datastore.test.test_file -*-
##
# Copyright (c) 2010-2017 Apple Inc. All rights reserved.
#
# 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.
##

"""
Common utility functions for a datastores.
"""

from uuid import UUID

from twext.python.log import Logger

from twistedcaldav.memcacher import Memcacher

log = Logger()

_unset = object()


class cached(object):
    """
    This object is a decorator for a 0-argument method which should be called
    only once, and its result cached so that future invocations just return the
    same result without calling the underlying method again.

    @ivar thunk: the function to call to generate a cached value.
    """

    def __init__(self, thunk):
        self.thunk = thunk

    def __get__(self, oself, owner):
        def inner():
            cacheKey = "_" + self.thunk.__name__ + "_cached"
            cached = getattr(oself, cacheKey, _unset)
            if cached is _unset:
                value = self.thunk(oself)
                setattr(oself, cacheKey, value)
                return value
            else:
                return cached
        return inner


class QueryCacher(Memcacher):
    """
    A Memcacher for the object-with-name query (more to come)
    """

    def __init__(self, cachePool="Default", cacheExpireSeconds=3600):
        super(QueryCacher, self).__init__(cachePool, pickle=True)
        self.cacheExpireSeconds = cacheExpireSeconds

    def set(self, key, value):
        return super(QueryCacher, self).set(key, value, expireTime=self.cacheExpireSeconds)

    def delete(self, key):
        return super(QueryCacher, self).delete(key)

    def setAfterCommit(self, transaction, key, value):
        transaction.postCommit(lambda: self.set(key, value))

    def invalidateAfterCommit(self, transaction, key):
        # Invalidate now (so that operations within this transaction see it)
        # and *also* post-commit (because there could be a scheduled setAfterCommit
        # for this key)
        transaction.postCommit(lambda: self.delete(key))
        return self.delete(key)

    # Home objects by UID

    def keyForHomeWithUID(self, homeType, ownerUID, status):
        return "homeWithUID:%s:%s:%s" % (homeType, status, ownerUID)

    # Home objects by id

    def keyForHomeWithID(self, homeType, homeResourceID, status):
        return "homeWithID:%s:%s:%s" % (homeType, status, homeResourceID)

    # Home child objects by name

    def keyForObjectWithName(self, homeResourceID, name):
        return "objectWithName:%s:%s" % (homeResourceID, name)

    # Home child objects by id

    def keyForObjectWithResourceID(self, homeResourceID, resourceID):
        return "objectWithResourceID:%s:%s" % (homeResourceID, resourceID)

    # Home child objects by external id

    def keyForObjectWithBindUID(self, homeResourceID, bindUID):
        return "objectWithBindUID:%s:%s" % (homeResourceID, bindUID)

    # Home metadata (Created/Modified)

    def keyForHomeMetaData(self, homeResourceID):
        return "homeMetaData:%s" % (homeResourceID)

    # HomeChild metadata (Created/Modified (and SUPPORTED_COMPONENTS))

    def keyForHomeChildMetaData(self, resourceID):
        return "homeChildMetaData:%s" % (resourceID)


def normalizeUUIDOrNot(somestr):
    """
    Take a string which may be:

        - the hex format of a UUID

        - a urn:uuid: URI containing a UUID

        - some other random thing

    and return, respectively:

        - the hex format of a UUID converted to upper case

        - a urn:uuid: URI with an upper-cased UUID (but not an upper-cased
          scheme and namespace)

        - some other random thing, unmodified

    @type somestr: L{str}

    @return: L{str}
    """
    uuu = "urn:uuid:"
    isURI = somestr.startswith(uuu)
    if isURI:
        normstr = somestr[len(uuu):]
    else:
        normstr = somestr
    try:
        uu = UUID(normstr)
    except ValueError:
        if isURI:
            log.info("normalizing urn:uuid: without UUID: {uid!r}", uid=somestr)
        # not a UUID, whatever
        return somestr
    else:
        normalForm = str(uu).upper()
        if isURI:
            return uuu + normalForm
        else:
            return normalForm