Change the Natlink engine to use window-specific rule activation

Natlink allows activating rules globally or for specific windows.
Dragonfly now uses the latter instead of the former, since there is
no real reason why Dragonfly should use the global context; it is
enough to, at speech start, activate rules for the foreground window
only.

dragonfly/engines/backend_natlink/engine.py

@@ -40,7 +40,6 @@
 
 from six        import text_type, binary_type, string_types, PY2
 
-
 from dragonfly.engines.base  import (EngineBase, EngineError, MimicFailure,
                                     GrammarWrapperBase)
 from dragonfly.engines.backend_natlink.speaker    import NatlinkSpeaker
@@ -148,6 +147,10 @@ def __init__(self, retain_dir=None):
             self._retain_dir = None
             self._log.error(err)
 
+        # Note: The default value of this variable will be overwritten when
+        #  speech is first detected.
+        self._last_window_handle = 0
+
     def apply_threading_fix(self):
         """
         Start a thread and engine timer internally to allow Python threads
@@ -282,8 +285,15 @@ def activate_rule(self, rule, grammar):
         wrapper = self._get_grammar_wrapper(grammar)
         if not wrapper:
             return
+
+        # Activate the rule.
+        # Note: The rule is only activated for the current window, but this
+        #  should not be a problem.
         grammar_object = wrapper.grammar_object
-        grammar_object.activate(rule.name, 0)
+        try:
+            grammar_object.activate(rule.name, self._last_window_handle)
+        except self.natlink.BadWindow:
+            pass
 
     def deactivate_rule(self, rule, grammar):
         self._log.debug("Deactivating rule %s in grammar %s." % (rule.name, grammar.name))
@@ -428,6 +438,7 @@ def __init__(self, grammar, grammar_object, engine, recobs_manager):
     def begin_callback(self, module_info):
         executable, title, handle = tuple(map_word(word)
                                           for word in module_info)
+        self.engine._last_window_handle = handle
         self.grammar.process_begin(executable, title, handle)
 
     def _decode_grammar_rules(self, state, words, results, *args):

dragonfly/grammar/rule_base.py

@@ -221,8 +221,9 @@ def process_begin(self, executable, title, handle):
                 if self._active:
                     self.deactivate()
         else:
-            if not self._active:
-                self.activate()
+            # Always instruct the engine to activate non-contextual rules.
+            #  This is necessary for the DNS back-end only.
+            self.activate()
             self._process_begin()
 
     def activate(self, force=False):