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#
# 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.
import abc
import collections
import itertools
import six
@six.add_metaclass(abc.ABCMeta)
class Function(object):
"""
Abstract base class for template functions.
"""
def __init__(self, stack, fn_name, args):
"""
Initialise with a Stack, the function name and the arguments.
All functions take the form of a single-item map in JSON::
{ <fn_name> : <args> }
"""
super(Function, self).__init__()
self.stack = stack
self.fn_name = fn_name
self.args = args
def validate(self):
"""
Validate arguments without resolving the function.
Function subclasses must override this method to validate their
args.
"""
validate(self.args)
@abc.abstractmethod
def result(self):
"""
Return the result of resolving the function.
Function subclasses must override this method to calculate their
results.
"""
return {self.fn_name: self.args}
def dependencies(self, path):
return dependencies(self.args, '.'.join([path, self.fn_name]))
def dep_attrs(self, resource_name):
return dep_attrs(self.args, resource_name)
def __reduce__(self):
"""
Return a representation of the function suitable for pickling.
This allows the copy module (which works by pickling and then
unpickling objects) to copy a template. Functions in the copy will
return to their original (JSON) form (i.e. a single-element map).
"""
return dict, ([(self.fn_name, self.args)],)
def __repr__(self):
"""
Return a string representation of the function.
The representation includes the function name, arguments and result
(if available), as well as the name of the function class.
"""
try:
result = repr(self.result())
except (TypeError, ValueError):
result = '???'
fntype = type(self)
classname = '.'.join(filter(None,
(getattr(fntype,
attr,
'') for attr in ('__module__',
'__name__'))))
return '<%s {%s: %r} -> %s>' % (classname,
self.fn_name, self.args,
result)
def __eq__(self, other):
"""Compare the result of this function for equality."""
try:
result = self.result()
if isinstance(other, Function):
return result == other.result()
else:
return result == other
except (TypeError, ValueError):
return NotImplemented
def __ne__(self, other):
"""Compare the result of this function for inequality."""
eq = self.__eq__(other)
if eq is NotImplemented:
return NotImplemented
return not eq
def resolve(snippet):
while isinstance(snippet, Function):
snippet = snippet.result()
if isinstance(snippet, collections.Mapping):
return dict((k, resolve(v)) for k, v in snippet.items())
elif (not isinstance(snippet, six.string_types) and
isinstance(snippet, collections.Iterable)):
return [resolve(v) for v in snippet]
return snippet
def validate(snippet):
if isinstance(snippet, Function):
snippet.validate()
elif isinstance(snippet, collections.Mapping):
for v in six.itervalues(snippet):
validate(v)
elif (not isinstance(snippet, six.string_types) and
isinstance(snippet, collections.Iterable)):
for v in snippet:
validate(v)
def dependencies(snippet, path=''):
"""
Return an iterator over Resource dependencies in a template snippet.
The snippet should be already parsed to insert Function objects where
appropriate.
"""
if isinstance(snippet, Function):
return snippet.dependencies(path)
elif isinstance(snippet, collections.Mapping):
def mkpath(key):
return '.'.join([path, unicode(key)])
deps = (dependencies(value,
mkpath(key)) for key, value in snippet.items())
return itertools.chain.from_iterable(deps)
elif (not isinstance(snippet, six.string_types) and
isinstance(snippet, collections.Iterable)):
def mkpath(idx):
return ''.join([path, '[%d]' % idx])
deps = (dependencies(value,
mkpath(i)) for i, value in enumerate(snippet))
return itertools.chain.from_iterable(deps)
else:
return []
def dep_attrs(snippet, resource_name):
"""
Return an iterator over dependent attributes for specified resource_name
in a template snippet.
The snippet should be already parsed to insert Function objects where
appropriate.
"""
if isinstance(snippet, Function):
return snippet.dep_attrs(resource_name)
elif isinstance(snippet, collections.Mapping):
attrs = (dep_attrs(value, resource_name) for value in snippet.items())
return itertools.chain.from_iterable(attrs)
elif (not isinstance(snippet, six.string_types) and
isinstance(snippet, collections.Iterable)):
attrs = (dep_attrs(value, resource_name) for value in snippet)
return itertools.chain.from_iterable(attrs)
return []
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