path: root/libbe/storage/util/properties.py

# Bugs Everywhere - a distributed bugtracker
# Copyright (C) 2008-2012 Chris Ball <cjb@laptop.org>
#                         Gianluca Montecchi <gian@grys.it>
#                         W. Trevor King <wking@tremily.us>
#
# This file is part of Bugs Everywhere.
#
# Bugs Everywhere 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, either version 2 of the License, or (at your option) any
# later version.
#
# Bugs Everywhere 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
# Bugs Everywhere.  If not, see <http://www.gnu.org/licenses/>.

"""Provides a series of useful decorators for defining various types
of properties.

For example usage, consider the unittests at the end of the module.

Notes
-----

See `PEP 318` and Michele Simionato's `decorator documentation` for
more information on decorators.

.. _PEP 318: http://www.python.org/dev/peps/pep-0318/
.. _decorator documentation: http://www.phyast.pitt.edu/~micheles/python/documentation.html

See Also
--------
:py:mod:`libbe.storage.util.settings_object` : bundle properties into a convenient package

"""

import copy
import types

import libbe
if libbe.TESTING == True:
    import unittest


class ValueCheckError (ValueError):
    def __init__(self, name, value, allowed):
        action = "in" # some list of allowed values
        if type(allowed) == types.FunctionType:
            action = "allowed by" # some allowed-value check function
        msg = "%s not %s %s for %s" % (value, action, allowed, name)
        ValueError.__init__(self, msg)
        self.name = name
        self.value = value
        self.allowed = allowed

def Property(funcs):
    """
    End a chain of property decorators, returning a property.
    """
    args = {}
    args["fget"] = funcs.get("fget", None)
    args["fset"] = funcs.get("fset", None)
    args["fdel"] = funcs.get("fdel", None)
    args["doc"] = funcs.get("doc", None)

    #print "Creating a property with"
    #for key, val in args.items(): print key, value
    return property(**args)

def doc_property(doc=None):
    """
    Add a docstring to a chain of property decorators.
    """
    def decorator(funcs=None):
        """
        Takes either a dict of funcs {"fget":fnX, "fset":fnY, ...}
        or a function fn() returning such a dict.
        """
        if hasattr(funcs, "__call__"):
            funcs = funcs() # convert from function-arg to dict
        funcs["doc"] = doc
        return funcs
    return decorator

def local_property(name, null=None, mutable_null=False):
    """
    Define get/set access to per-parent-instance local storage.  Uses
    ._<name>_value to store the value for a particular owner instance.
    If the ._<name>_value attribute does not exist, returns null.

    If mutable_null == True, we only release deepcopies of the null to
    the outside world.
    """
    def decorator(funcs):
        if hasattr(funcs, "__call__"):
            funcs = funcs()
        fget = funcs.get("fget", None)
        fset = funcs.get("fset", None)
        def _fget(self):
            if fget is not None:
                fget(self)
            if mutable_null == True:
                ret_null = copy.deepcopy(null)
            else:
                ret_null = null
            value = getattr(self, "_%s_value" % name, ret_null)
            return value
        def _fset(self, value):
            setattr(self, "_%s_value" % name, value)
            if fset is not None:
                fset(self, value)
        funcs["fget"] = _fget
        funcs["fset"] = _fset
        funcs["name"] = name
        return funcs
    return decorator

def settings_property(name, null=None):
    """
    Similar to local_property, except where local_property stores the
    value in instance._<name>_value, settings_property stores the
    value in instance.settings[name].
    """
    def decorator(funcs):
        if hasattr(funcs, "__call__"):
            funcs = funcs()
        fget = funcs.get("fget", None)
        fset = funcs.get("fset", None)
        def _fget(self):
            if fget is not None:
                fget(self)
            value = self.settings.get(name, null)
            return value
        def _fset(self, value):
            self.settings[name] = value
            if fset is not None:
                fset(self, value)
        funcs["fget"] = _fget
        funcs["fset"] = _fset
        funcs["name"] = name
        return funcs
    return decorator


# Allow comparison and caching with _original_ values for mutables,
# since
#
# >>> a = []
# >>> b = a
# >>> b.append(1)
# >>> a
# [1]
# >>> a==b
# True
def _hash_mutable_value(value):
    return repr(value)
def _init_mutable_property_cache(self):
    if not hasattr(self, "_mutable_property_cache_hash"):
        # first call to _fget for any mutable property
        self._mutable_property_cache_hash = {}
        self._mutable_property_cache_copy = {}
def _set_cached_mutable_property(self, cacher_name, property_name, value):
    _init_mutable_property_cache(self)
    self._mutable_property_cache_hash[(cacher_name, property_name)] = \
        _hash_mutable_value(value)
    self._mutable_property_cache_copy[(cacher_name, property_name)] = \
        copy.deepcopy(value)
def _get_cached_mutable_property(self, cacher_name, property_name, default=None):
    _init_mutable_property_cache(self)
    if (cacher_name, property_name) not in self._mutable_property_cache_copy:
        return default
    return self._mutable_property_cache_copy[(cacher_name, property_name)]
def _cmp_cached_mutable_property(self, cacher_name, property_name, value, default=None):
    _init_mutable_property_cache(self)
    if (cacher_name, property_name) not in self._mutable_property_cache_hash:
        _set_cached_mutable_property(self, cacher_name, property_name, default)
    old_hash = self._mutable_property_cache_hash[(cacher_name, property_name)]
    return cmp(_hash_mutable_value(value), old_hash)


def defaulting_property(default=None, null=None,
                        mutable_default=False):
    """
    Define a default value for get access to a property.
    If the stored value is null, then default is returned.

    If mutable_default == True, we only release deepcopies of the
    default to the outside world.

    null should never escape to the outside world, so don't worry
    about it being a mutable.
    """
    def decorator(funcs):
        if hasattr(funcs, "__call__"):
            funcs = funcs()
        fget = funcs.get("fget")
        fset = funcs.get("fset")
        name = funcs.get("name", "<unknown>")
        def _fget(self):
            value = fget(self)
            if value == null:
                if mutable_default == True:
                    return copy.deepcopy(default)
                else:
                    return default
            return value
        def _fset(self, value):
            if value == default:
                value = null
            fset(self, value)
        funcs["fget"] = _fget
        funcs["fset"] = _fset
        return funcs
    return decorator

def fn_checked_property(value_allowed_fn):
    """
    Define allowed values for get/set access to a property.
    """
    def decorator(funcs):
        if hasattr(funcs, "__call__"):
            funcs = funcs()
        fget = funcs.get("fget")
        fset = funcs.get("fset")
        name = funcs.get("name", "<unknown>")
        def _fget(self):
            value = fget(self)
            if value_allowed_fn(value) != True:
                raise ValueCheckError(name, value, value_allowed_fn)
            return value
        def _fset(self, value):
            if value_allowed_fn(value) != True:
                raise ValueCheckError(name, value, value_allowed_fn)
            fset(self, value)
        funcs["fget"] = _fget
        funcs["fset"] = _fset
        return funcs
    return decorator

def checked_property(allowed=[]):
    """
    Define allowed values for get/set access to a property.
    """
    def decorator(funcs):
        if hasattr(funcs, "__call__"):
            funcs = funcs()
        fget = funcs.get("fget")
        fset = funcs.get("fset")
        name = funcs.get("name", "<unknown>")
        def _fget(self):
            value = fget(self)
            if value not in allowed:
                raise ValueCheckError(name, value, allowed)
            return value
        def _fset(self, value):
            if value not in allowed:
                raise ValueCheckError(name, value, allowed)
            fset(self, value)
        funcs["fget"] = _fget
        funcs["fset"] = _fset
        return funcs
    return decorator

def cached_property(generator, initVal=None, mutable=False):
    """
    Allow caching of values generated by generator(instance), where
    instance is the instance to which this property belongs.  Uses
    ._<name>_cache to store a cache flag for a particular owner
    instance.

    When the cache flag is True or missing and the stored value is
    initVal, the first fget call triggers the generator function,
    whose output is stored in _<name>_cached_value.  That and
    subsequent calls to fget will return this cached value.

    If the input value is no longer initVal (e.g. a value has been
    loaded from disk or set with fset), that value overrides any
    cached value, and this property has no effect.

    When the cache flag is False and the stored value is initVal, the
    generator is not cached, but is called on every fget.

    The cache flag is missing on initialization.  Particular instances
    may override by setting their own flag.

    In the case that mutable == True, all caching is disabled and the
    generator is called whenever the cached value would otherwise be
    used.
    """
    def decorator(funcs):
        if hasattr(funcs, "__call__"):
            funcs = funcs()
        fget = funcs.get("fget")
        name = funcs.get("name", "<unknown>")
        def _fget(self):
            cache = getattr(self, "_%s_cache" % name, True)
            value = fget(self)
            if value == initVal:
                if cache == True and mutable == False:
                    if hasattr(self, "_%s_cached_value" % name):
                        value = getattr(self, "_%s_cached_value" % name)
                    else:
                        value = generator(self)
                        setattr(self, "_%s_cached_value" % name, value)
                else:
                    value = generator(self)
            return value
        funcs["fget"] = _fget
        return funcs
    return decorator

def primed_property(primer, initVal=None, unprimeableVal=None):
    """
    Just like a cached_property, except that instead of returning a
    new value and running fset to cache it, the primer attempts some
    background manipulation (e.g. loads data into instance.settings)
    such that a _second_ pass through fget succeeds.  If the second
    pass doesn't succeed (e.g. no readable storage), we give up and
    return unprimeableVal.

    The 'cache' flag becomes a 'prime' flag, with priming taking place
    whenever ._<name>_prime is True, or is False or missing and
    value == initVal.
    """
    def decorator(funcs):
        if hasattr(funcs, "__call__"):
            funcs = funcs()
        fget = funcs.get("fget")
        name = funcs.get("name", "<unknown>")
        def _fget(self):
            prime = getattr(self, "_%s_prime" % name, False)
            if prime == False:
                value = fget(self)
            if prime == True or (prime == False and value == initVal):
                primer(self)
                value = fget(self)
                if prime == False and value == initVal:
                    return unprimeableVal
            return value
        funcs["fget"] = _fget
        return funcs
    return decorator

def change_hook_property(hook, mutable=False, default=None):
    """Call the function `hook` whenever a value different from the
    current value is set.

    This is useful for saving changes to disk, etc.  This function is
    called *after* the new value has been stored, allowing you to
    change the stored value if you want.

    In the case of mutables, things are slightly trickier.  Because
    the property-owning class has no way of knowing when the value
    changes.  We work around this by caching a private deepcopy of the
    mutable value, and checking for changes whenever the property is
    set (obviously) or retrieved (to check for external changes).  So
    long as you're conscientious about accessing the property after
    making external modifications, mutability won't be a problem::

      t.x.append(5) # external modification
      t.x           # dummy access notices change and triggers hook

    See :py:class:`testChangeHookMutableProperty` for an example of the
    expected behavior.

    Parameters
    ----------
    hook : fn
      `hook(instance, old_value, new_value)`, where `instance` is a
      reference to the class instance to which this property belongs.
    """
    def decorator(funcs):
        if hasattr(funcs, "__call__"):
            funcs = funcs()
        fget = funcs.get("fget")
        fset = funcs.get("fset")
        name = funcs.get("name", "<unknown>")
        def _fget(self, new_value=None, from_fset=False): # only used if mutable == True
            if from_fset == True:
                value = new_value # compare new value with cached
            else:
                value = fget(self) # compare current value with cached
            if _cmp_cached_mutable_property(self, "change hook property", name, value, default) != 0:
                # there has been a change, cache new value
                old_value = _get_cached_mutable_property(self, "change hook property", name, default)
                _set_cached_mutable_property(self, "change hook property", name, value)
                if from_fset == True: # return previously cached value
                    value = old_value
                else: # the value changed while we weren't looking
                    hook(self, old_value, value)
            return value
        def _fset(self, value):
            if mutable == True: # get cached previous value
                old_value = _fget(self, new_value=value, from_fset=True)
            else:
                old_value = fget(self)
            fset(self, value)
            if value != old_value:
                hook(self, old_value, value)
        if mutable == True:
            funcs["fget"] = _fget
        funcs["fset"] = _fset
        return funcs
    return decorator

if libbe.TESTING == True:
    class DecoratorTests(unittest.TestCase):
        def testLocalDoc(self):
            class Test(object):
                @Property
                @doc_property("A fancy property")
                def x():
                    return {}
            self.failUnless(Test.x.__doc__ == "A fancy property",
                            Test.x.__doc__)
        def testLocalProperty(self):
            class Test(object):
                @Property
                @local_property(name="LOCAL")
                def x():
                    return {}
            t = Test()
            self.failUnless(t.x == None, str(t.x))
            t.x = 'z' # the first set initializes ._LOCAL_value
            self.failUnless(t.x == 'z', str(t.x))
            self.failUnless("_LOCAL_value" in dir(t), dir(t))
            self.failUnless(t._LOCAL_value == 'z', t._LOCAL_value)
        def testSettingsProperty(self):
            class Test(object):
                @Property
                @settings_property(name="attr")
                def x():
                    return {}
                def __init__(self):
                    self.settings = {}
            t = Test()
            self.failUnless(t.x == None, str(t.x))
            t.x = 'z' # the first set initializes ._LOCAL_value
            self.failUnless(t.x == 'z', str(t.x))
            self.failUnless("attr" in t.settings, t.settings)
            self.failUnless(t.settings["attr"] == 'z', t.settings["attr"])
        def testDefaultingLocalProperty(self):
            class Test(object):
                @Property
                @defaulting_property(default='y', null='x')
                @local_property(name="DEFAULT", null=5)
                def x(): return {}
            t = Test()
            self.failUnless(t.x == 5, str(t.x))
            t.x = 'x'
            self.failUnless(t.x == 'y', str(t.x))
            t.x = 'y'
            self.failUnless(t.x == 'y', str(t.x))
            t.x = 'z'
            self.failUnless(t.x == 'z', str(t.x))
            t.x = 5
            self.failUnless(t.x == 5, str(t.x))
        def testCheckedLocalProperty(self):
            class Test(object):
                @Property
                @checked_property(allowed=['x', 'y', 'z'])
                @local_property(name="CHECKED")
                def x(): return {}
                def __init__(self):
                    self._CHECKED_value = 'x'
            t = Test()
            self.failUnless(t.x == 'x', str(t.x))
            try:
                t.x = None
                e = None
            except ValueCheckError, e:
                pass
            self.failUnless(type(e) == ValueCheckError, type(e))
        def testTwoCheckedLocalProperties(self):
            class Test(object):
                @Property
                @checked_property(allowed=['x', 'y', 'z'])
                @local_property(name="X")
                def x(): return {}

                @Property
                @checked_property(allowed=['a', 'b', 'c'])
                @local_property(name="A")
                def a(): return {}
                def __init__(self):
                    self._A_value = 'a'
                    self._X_value = 'x'
            t = Test()
            try:
                t.x = 'a'
                e = None
            except ValueCheckError, e:
                pass
            self.failUnless(type(e) == ValueCheckError, type(e))
            t.x = 'x'
            t.x = 'y'
            t.x = 'z'
            try:
                t.a = 'x'
                e = None
            except ValueCheckError, e:
                pass
            self.failUnless(type(e) == ValueCheckError, type(e))
            t.a = 'a'
            t.a = 'b'
            t.a = 'c'
        def testFnCheckedLocalProperty(self):
            class Test(object):
                @Property
                @fn_checked_property(lambda v : v in ['x', 'y', 'z'])
                @local_property(name="CHECKED")
                def x(): return {}
                def __init__(self):
                    self._CHECKED_value = 'x'
            t = Test()
            self.failUnless(t.x == 'x', str(t.x))
            try:
                t.x = None
                e = None
            except ValueCheckError, e:
                pass
            self.failUnless(type(e) == ValueCheckError, type(e))
        def testCachedLocalProperty(self):
            class Gen(object):
                def __init__(self):
                    self.i = 0
                def __call__(self, owner):
                    self.i += 1
                    return self.i
            class Test(object):
                @Property
                @cached_property(generator=Gen(), initVal=None)
                @local_property(name="CACHED")
                def x(): return {}
            t = Test()
            self.failIf("_CACHED_cache" in dir(t),
                        getattr(t, "_CACHED_cache", None))
            self.failUnless(t.x == 1, t.x)
            self.failUnless(t.x == 1, t.x)
            self.failUnless(t.x == 1, t.x)
            t.x = 8
            self.failUnless(t.x == 8, t.x)
            self.failUnless(t.x == 8, t.x)
            t._CACHED_cache = False        # Caching is off, but the stored value
            val = t.x                      # is 8, not the initVal (None), so we
            self.failUnless(val == 8, val) # get 8.
            t._CACHED_value = None         # Now we've set the stored value to None
            val = t.x                      # so future calls to fget (like this)
            self.failUnless(val == 2, val) # will call the generator every time...
            val = t.x
            self.failUnless(val == 3, val)
            val = t.x
            self.failUnless(val == 4, val)
            t._CACHED_cache = True              # We turn caching back on, and get
            self.failUnless(t.x == 1, str(t.x)) # the original cached value.
            del t._CACHED_cached_value          # Removing that value forces a
            self.failUnless(t.x == 5, str(t.x)) # single cache-regenerating call
            self.failUnless(t.x == 5, str(t.x)) # to the genenerator, after which
            self.failUnless(t.x == 5, str(t.x)) # we get the new cached value.
        def testPrimedLocalProperty(self):
            class Test(object):
                def prime(self):
                    self.settings["PRIMED"] = self.primeVal
                @Property
                @primed_property(primer=prime, initVal=None, unprimeableVal=2)
                @settings_property(name="PRIMED")
                def x(): return {}
                def __init__(self):
                    self.settings={}
                    self.primeVal = "initialized"
            t = Test()
            self.failIf("_PRIMED_prime" in dir(t),
                        getattr(t, "_PRIMED_prime", None))
            self.failUnless(t.x == "initialized", t.x)
            t.x = 1
            self.failUnless(t.x == 1, t.x)
            t.x = None
            self.failUnless(t.x == "initialized", t.x)
            t._PRIMED_prime = True
            t.x = 3
            self.failUnless(t.x == "initialized", t.x)
            t._PRIMED_prime = False
            t.x = 3
            self.failUnless(t.x == 3, t.x)
            # test unprimableVal
            t.x = None
            t.primeVal = None
            self.failUnless(t.x == 2, t.x)
        def testChangeHookLocalProperty(self):
            class Test(object):
                def _hook(self, old, new):
                    self.old = old
                    self.new = new

                @Property
                @change_hook_property(_hook)
                @local_property(name="HOOKED")
                def x(): return {}
            t = Test()
            t.x = 1
            self.failUnless(t.old == None, t.old)
            self.failUnless(t.new == 1, t.new)
            t.x = 1
            self.failUnless(t.old == None, t.old)
            self.failUnless(t.new == 1, t.new)
            t.x = 2
            self.failUnless(t.old == 1, t.old)
            self.failUnless(t.new == 2, t.new)
        def testChangeHookMutableProperty(self):
            class Test(object):
                def _hook(self, old, new):
                    self.old = old
                    self.new = new
                    self.hook_calls += 1

                @Property
                @change_hook_property(_hook, mutable=True)
                @local_property(name="HOOKED")
                def x(): return {}
            t = Test()
            t.hook_calls = 0
            t.x = []
            self.failUnless(t.old == None, t.old)
            self.failUnless(t.new == [], t.new)
            self.failUnless(t.hook_calls == 1, t.hook_calls)
            a = t.x
            a.append(5)
            t.x = a
            self.failUnless(t.old == [], t.old)
            self.failUnless(t.new == [5], t.new)
            self.failUnless(t.hook_calls == 2, t.hook_calls)
            t.x = []
            self.failUnless(t.old == [5], t.old)
            self.failUnless(t.new == [], t.new)
            self.failUnless(t.hook_calls == 3, t.hook_calls)
            # now append without reassigning.  this doesn't trigger the
            # change, since we don't ever set t.x, only get it and mess
            # with it.  It does, however, update our t.new, since t.new =
            # t.x and is not a static copy.
            t.x.append(5)
            self.failUnless(t.old == [5], t.old)
            self.failUnless(t.new == [5], t.new)
            self.failUnless(t.hook_calls == 3, t.hook_calls)
            # however, the next t.x get _will_ notice the change...
            a = t.x
            self.failUnless(t.old == [], t.old)
            self.failUnless(t.new == [5], t.new)
            self.failUnless(t.hook_calls == 4, t.hook_calls)
            t.x.append(6) # this append(6) is not noticed yet
            self.failUnless(t.old == [], t.old)
            self.failUnless(t.new == [5,6], t.new)
            self.failUnless(t.hook_calls == 4, t.hook_calls)
            # this append(7) is not noticed, but the t.x get causes the
            # append(6) to be noticed
            t.x.append(7)
            self.failUnless(t.old == [5], t.old)
            self.failUnless(t.new == [5,6,7], t.new)
            self.failUnless(t.hook_calls == 5, t.hook_calls)
            a = t.x # now the append(7) is noticed
            self.failUnless(t.old == [5,6], t.old)
            self.failUnless(t.new == [5,6,7], t.new)
            self.failUnless(t.hook_calls == 6, t.hook_calls)

    suite = unittest.TestLoader().loadTestsFromTestCase(DecoratorTests)