Base class for deciders

To align decider classes interface
new base class introduced in this patch

Change-Id: I42c69d3daa89153f1f3f9da32bccaf8d840ab1be

taskflow/engines/action_engine/analyzer.py

@@ -14,6 +14,7 @@
 #    License for the specific language governing permissions and limitations
 #    under the License.
 
+import abc
 import functools
 import itertools
 
@@ -23,7 +24,33 @@ import six
 from taskflow import states as st
 
 
-class IgnoreDecider(object):
+@six.add_metaclass(abc.ABCMeta)
+class Decider(object):
+    """Base class for deciders.
+
+    Provides interface to be implemented by sub-classes
+    Decider checks whether next atom in flow should be executed or not
+    """
+
+    @abc.abstractmethod
+    def check(self, runtime):
+        """Returns bool of whether this decider should allow running."""
+
+    @abc.abstractmethod
+    def affect(self, runtime):
+        """If the :py:func:`~.check` returns false, affects associated atoms.
+
+        """
+
+    def check_and_affect(self, runtime):
+        """Handles :py:func:`~.check` + :py:func:`~.affect` in right order."""
+        proceed = self.check(runtime)
+        if not proceed:
+            self.affect(runtime)
+        return proceed
+
+
+class IgnoreDecider(Decider):
     """Checks any provided edge-deciders and determines if ok to run."""
 
     def __init__(self, atom, edge_deciders):
@@ -51,15 +78,8 @@ class IgnoreDecider(object):
         runtime.reset_nodes(itertools.chain([self._atom], successors_iter),
                             state=st.IGNORE, intention=st.IGNORE)
 
-    def check_and_affect(self, runtime):
-        """Handles :py:func:`~.check` + :py:func:`~.affect` in right order."""
-        proceed = self.check(runtime)
-        if not proceed:
-            self.affect(runtime)
-        return proceed
 
-
-class NoOpDecider(object):
+class NoOpDecider(Decider):
     """No-op decider that says it is always ok to run & has no effect(s)."""
 
     def check(self, runtime):
@@ -69,13 +89,6 @@ class NoOpDecider(object):
     def affect(self, runtime):
         """Does nothing."""
 
-    def check_and_affect(self, runtime):
-        """Handles :py:func:`~.check` + :py:func:`~.affect` in right order.
-
-        Does nothing.
-        """
-        return self.check(runtime)
-
 
 class Analyzer(object):
     """Analyzes a compilation and aids in execution processes.