[pitivi] undo: Allow PropertyChangedActions to merge

[Thibault Saunier <tsaunier src gnome org>]

commit 00e79c4fa52afeddcd33d900d0cf25fda0594088
Author: Alexandru Băluț <alexandru balut gmail com>
Date:   Sat Feb 11 23:20:36 2017 +0100

    undo: Allow PropertyChangedActions to merge
    
    This is useful for example when dragging a clip, instead of recording
    multiple actions representing each change of the clip's 'start', only
    one is recorded (assuming no other actions interfere).
    
    Reviewed-by: Thibault Saunier <tsaunier gnome org>
    Differential Revision: https://phabricator.freedesktop.org/D1658

 pitivi/undo/undo.py |    8 ++++++++
 tests/test_undo.py  |   24 ++++++++++++++++++++++--
 2 files changed, 30 insertions(+), 2 deletions(-)
---
diff --git a/pitivi/undo/undo.py b/pitivi/undo/undo.py
index 845cbbd..1108804 100644
--- a/pitivi/undo/undo.py
+++ b/pitivi/undo/undo.py
@@ -403,6 +403,14 @@ class PropertyChangedAction(UndoableAutomaticObjectAction):
     def undo(self):
         self.auto_object.set_property(self.field_name, self.old_value)
 
+    def expand(self, action):
+        if not isinstance(action, PropertyChangedAction) or \
+                self.auto_object != action.auto_object or \
+                self.field_name != action.field_name:
+            return False
+        self.new_value = action.new_value
+        return True
+
 
 class GObjectObserver(GObject.Object):
     """Monitor for GObject.Object's props, reporting UndoableActions.
diff --git a/tests/test_undo.py b/tests/test_undo.py
index 03b9b29..214bf7a 100644
--- a/tests/test_undo.py
+++ b/tests/test_undo.py
@@ -22,6 +22,7 @@ from unittest import TestCase
 from gi.repository import GES
 
 from pitivi.undo.undo import GObjectObserver
+from pitivi.undo.undo import PropertyChangedAction
 from pitivi.undo.undo import UndoableAction
 from pitivi.undo.undo import UndoableActionLog
 from pitivi.undo.undo import UndoableActionStack
@@ -381,6 +382,7 @@ class TestGObjectObserver(TestCase):
         stack, = action_log.stacks
 
         clip = GES.TitleClip()
+        clip.props.start = 1
         unused_observer = GObjectObserver(clip, ["start"], action_log)
 
         self.assertEqual(len(stack.done_actions), 0)
@@ -391,7 +393,25 @@ class TestGObjectObserver(TestCase):
         self.assertEqual(len(stack.done_actions), 1)
 
         clip.props.start = 4
-        self.assertEqual(len(stack.done_actions), 2)
+        self.assertEqual(len(stack.done_actions), 1)
         action = stack.done_actions[-1]
-        self.assertEqual(action.old_value, 2)
+        self.assertEqual(action.old_value, 1)
         self.assertEqual(action.new_value, 4)
+
+
+class TestPropertyChangedAction(TestCase):
+
+    def test_expand(self):
+        stack = UndoableActionStack("good one!")
+        gobject = mock.Mock()
+        stack.push(PropertyChangedAction(gobject, "field", 5, 7))
+        stack.push(PropertyChangedAction(gobject, "field", 11, 13))
+        self.assertEqual(len(stack.done_actions), 1, stack.done_actions)
+        self.assertEqual(stack.done_actions[0].old_value, 5)
+        self.assertEqual(stack.done_actions[0].new_value, 13)
+
+        stack.push(PropertyChangedAction(gobject, "field2", 0, 1))
+        self.assertEqual(len(stack.done_actions), 2, stack.done_actions)
+
+        stack.push(PropertyChangedAction(mock.Mock(), "field", 0, 1))
+        self.assertEqual(len(stack.done_actions), 3, stack.done_actions)