From 0d42146e79a53d331366ab8ed5119910d5744f10 Mon Sep 17 00:00:00 2001
From: Kovid Goyal <kovid@kovidgoyal.net>
Date: Sun, 21 Sep 2014 16:26:52 +0530
Subject: [PATCH] Some debugging for the History stack

---
 src/calibre/gui2/viewer/ui.py | 23 ++++++++++++++++++++---
 1 file changed, 20 insertions(+), 3 deletions(-)

diff --git a/src/calibre/gui2/viewer/ui.py b/src/calibre/gui2/viewer/ui.py
index 85369f0518..5c3784ebdb 100644
--- a/src/calibre/gui2/viewer/ui.py
+++ b/src/calibre/gui2/viewer/ui.py
@@ -102,7 +102,7 @@ class Metadata(QWebView):  # {{{
 
 class History(list):  # {{{
 
-    def __init__(self, action_back, action_forward):
+    def __init__(self, action_back=None, action_forward=None):
         self.action_back = action_back
         self.action_forward = action_forward
         super(History, self).__init__(self)
@@ -112,8 +112,10 @@ class History(list):  # {{{
         self.set_actions()
 
     def set_actions(self):
-        self.action_back.setDisabled(self.back_pos is None)
-        self.action_forward.setDisabled(self.forward_pos is None)
+        if self.action_back is not None:
+            self.action_back.setDisabled(self.back_pos is None)
+        if self.action_forward is not None:
+            self.action_forward.setDisabled(self.forward_pos is None)
 
     def back(self, from_pos):
         # Back clicked
@@ -153,6 +155,21 @@ class History(list):  # {{{
         # There can be no forward
         self.forward_pos = None
         self.set_actions()
+
+    def __str__(self):
+        return 'History: Items=%s back_pos=%s insert_pos=%s forward_pos=%s' % (tuple(self), self.back_pos, self.insert_pos, self.forward_pos)
+
+def test_history():
+    h = History()
+    for i in xrange(4):
+        h.add(i)
+    for i in reversed(xrange(4)):
+        h.back(i)
+    print (h)
+    h.forward(0)
+    print (h)
+    h.add(1)
+    print (h)
 # }}}
 
 class Main(MainWindow):