Allow functions to calculate dependencies

Change-Id: Ic58f54612d3707abc8727a65a28b9c4502eae31a

heat/engine/cfn/functions.py

@@ -12,6 +12,7 @@
 #    under the License.
 
 import collections
+import itertools
 import json
 
 import six
@@ -108,6 +109,10 @@ class ResourceRef(function.Function):
             raise exception.InvalidTemplateReference(resource=resource_name,
                                                      key=path)
 
+    def dependencies(self, path):
+        return itertools.chain(super(ResourceRef, self).dependencies(path),
+                               [self._resource(path)])
+
     def result(self):
         return self._resource().FnGetRefId()
 
@@ -164,6 +169,10 @@ class GetAtt(function.Function):
             raise exception.InvalidTemplateReference(resource=resource_name,
                                                      key=path)
 
+    def dependencies(self, path):
+        return itertools.chain(super(GetAtt, self).dependencies(path),
+                               [self._resource(path)])
+
     def result(self):
         attribute = function.resolve(self._attribute)
 

heat/engine/function.py

@@ -13,6 +13,7 @@
 
 import abc
 import collections
+import itertools
 
 
 class Function(object):
@@ -54,6 +55,9 @@ class Function(object):
         """
         return {self.fn_name: self.args}
 
+    def dependencies(self, path):
+        return dependencies(self.args, '.'.join([path, self.fn_name]))
+
     def __reduce__(self):
         """
         Return a representation of the function suitable for pickling.
@@ -130,3 +134,35 @@ def validate(snippet):
           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, basestring) 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 []

heat/tests/test_function.py

@@ -22,6 +22,9 @@ class TestFunction(function.Function):
         if len(self.args) < 2:
             raise Exception(_('Need more arguments'))
 
+    def dependencies(self, path):
+        return ['foo', 'bar']
+
     def result(self):
         return 'wibble'
 
@@ -122,3 +125,20 @@ class ValidateTest(HeatTestCase):
         snippet = {'foo': 'bar', 'blarg': self.func}
         ex = self.assertRaises(Exception, function.validate, snippet)
         self.assertEqual('Need more arguments', str(ex))
+
+
+class DependenciesTest(HeatTestCase):
+    func = TestFunction(None, 'test', None)
+
+    scenarios = [
+        ('function', dict(snippet=func)),
+        ('nested_map', dict(snippet={'wibble': func})),
+        ('nested_list', dict(snippet=['wibble', func])),
+        ('deep_nested', dict(snippet=[{'wibble': ['wibble', func]}])),
+    ]
+
+    def test_dependencies(self):
+        deps = list(function.dependencies(self.snippet))
+        self.assertIn('foo', deps)
+        self.assertIn('bar', deps)
+        self.assertEqual(2, len(deps))