Add commands to go to the prev/next change in the list

When viewing a change, 'n' and 'p' will jump to the next and
previous changes (respectively) from the most recent list of changes
without pushing the current change on to the navigation history.

This streamlines the process when reviewing many changes in
sequence.

Change-Id: I31d4b30cd8d7bd6f5c5c4376033e43421fbe6c5b

gertty/app.py

@@ -146,10 +146,11 @@ class App(object):
 
         self.popup(dialog)
 
-    def changeScreen(self, widget):
+    def changeScreen(self, widget, push=True):
         self.log.debug("Changing screen to %s" % (widget,))
         self.status.update(title=widget.title)
-        self.screens.append(self.loop.widget)
+        if push:
+            self.screens.append(self.loop.widget)
         self.loop.widget = widget
 
     def backScreen(self, target_widget=None):

gertty/view/change.py

@@ -274,6 +274,8 @@ class ChangeView(urwid.WidgetWrap):
 <c>      Checkout the most recent revision into the local repo.
 <d>      Show the diff of the mont recent revision.
 <k>      Toggle the hidden flag for the current change.
+<n>      Go to the next change in the list.
+<p>      Go to the previous change in the list.
 <r>      Leave a review for the most recent revision.
 <u>      Back to the list of changes.
 <v>      Toggle the reviewed flag for the current change.
@@ -571,6 +573,19 @@ class ChangeView(urwid.WidgetWrap):
             widget = self.app.findChangeList()
             self.app.backScreen(widget)
             return None
+        if r in ['n', 'p']:
+            widget = self.app.findChangeList()
+            if r == 'n':
+                new_change_key = widget.getNextChangeKey(self.change_key)
+            else:
+                new_change_key = widget.getPrevChangeKey(self.change_key)
+            if new_change_key:
+                try:
+                    view = ChangeView(self.app, new_change_key)
+                    self.app.changeScreen(view, push=False)
+                except gertty.view.DisplayError as e:
+                    self.app.error(e.message)
+            return None
         if r == 'ctrl r':
             self.app.sync.submitTask(
                 sync.SyncChangeTask(self.change_rest_id, priority=sync.HIGH_PRIORITY))

gertty/view/change_list.py

@@ -121,6 +121,22 @@ class ChangeListView(urwid.WidgetWrap):
             self.listbox.body.remove(row)
             del self.change_rows[key]
 
+    def getNextChangeKey(self, change_key):
+        row = self.change_rows.get(change_key)
+        i = self.listbox.body.index(row)
+        if i+1 >= len(self.listbox.body):
+            return None
+        row = self.listbox.body[i+1]
+        return row.change_key
+
+    def getPrevChangeKey(self, change_key):
+        row = self.change_rows.get(change_key)
+        i = self.listbox.body.index(row)
+        if i <= 0:
+            return None
+        row = self.listbox.body[i-1]
+        return row.change_key
+
     def toggleReviewed(self, change_key):
         with self.app.db.getSession() as session:
             change = session.getChange(change_key)