Display file header in top line of diff

To remind the user of the path of the file shown at the top of the
diff, always display the filename there, even after the file header
has scrolled past the top of the screen.

Change-Id: Icf3419647c2ccec45f878fbdc882e3d624eadebb

gertty/view/diff.py

@@ -110,6 +110,9 @@ class BaseFileHeader(urwid.Button):
     def selectable(self):
         return True
 
+class BaseFileReminder(urwid.WidgetWrap):
+    pass
+
 class DiffContextButton(urwid.WidgetWrap):
     def selectable(self):
         return True
@@ -232,7 +235,8 @@ class BaseDiffView(urwid.WidgetWrap):
                 comment_filenames.add(comment.file)
         repo = self.app.getRepo(self.project_name)
         self._w.contents.append((self.app.header, ('pack', 1)))
-        self._w.contents.append((urwid.Divider(), ('pack', 1)))
+        self.file_reminder = self.makeFileReminder()
+        self._w.contents.append((self.file_reminder, ('pack', 1)))
         lines = []  # The initial set of lines to display
         self.file_diffs = [{}, {}]  # Mapping of fn -> DiffFile object (old, new)
         # this is a list of files:
@@ -343,6 +347,9 @@ class BaseDiffView(urwid.WidgetWrap):
     def makeFileHeader(self, diff, comment_lists):
         raise NotImplementedError
 
+    def makeFileReminder(self):
+        raise NotImplementedError
+
     def interested(self, event):
         if not ((isinstance(event, sync.ChangeAddedEvent) and
                  self.change_key in event.related_change_keys)
@@ -358,10 +365,37 @@ class BaseDiffView(urwid.WidgetWrap):
         #TODO
         pass
 
+    def getContextAtTop(self, size):
+        middle, top, bottom = self.listbox.calculate_visible(size, True)
+        if top and top[1]:
+            (widget, pos, rows) = top[1][-1]
+        elif middle:
+            pos = middle[2]
+        # Make sure the first header shows up as soon as it scrolls up
+        if pos > 1:
+            pos -= 1
+        context = None
+        while True:
+            item = self.listbox.body[pos]
+            if hasattr(item, 'context'):
+                break
+            pos -= 1
+        if pos > 0:
+            context = item.context
+        return context
+
     def keypress(self, size, key):
         old_focus = self.listbox.focus
         r = super(BaseDiffView, self).keypress(size, key)
         new_focus = self.listbox.focus
+
+        context = self.getContextAtTop(size)
+        if context:
+            self.file_reminder.set(context.old_fn,
+                                   context.new_fn)
+        else:
+            self.file_reminder.set('', '')
+
         commands = self.app.config.keymap.getCommands(r)
         if (isinstance(old_focus, BaseDiffCommentEdit) and
             (old_focus != new_focus or (keymap.PREV_SCREEN in commands))):

gertty/view/side_diff.py

@@ -105,6 +105,16 @@ class SideFileHeader(BaseFileHeader):
                'filename': 'focused-filename'}
         self._w = urwid.AttrMap(col, None, focus_map=map)
 
+class SideFileReminder(BaseFileReminder):
+    def __init__(self):
+        self.old_text = urwid.Text(('filename', ''))
+        self.new_text = urwid.Text(('filename', ''))
+        col = urwid.Columns([self.old_text, self.new_text])
+        super(SideFileReminder, self).__init__(col)
+
+    def set(self, old, new):
+        self.old_text.set_text(('filename', old))
+        self.new_text.set_text(('filename', new))
 
 class SideDiffView(BaseDiffView):
     def makeLines(self, diff, lines_to_add, comment_lists):
@@ -148,6 +158,9 @@ class SideDiffView(BaseDiffView):
                                                  old_comment, new_comment))
         return lines
 
+    def makeFileReminder(self):
+        return SideFileReminder()
+
     def makeFileHeader(self, diff, comment_lists):
         context = LineContext(
             self.old_revision_key, self.new_revision_key,

gertty/view/unified_diff.py

@@ -105,6 +105,20 @@ class UnifiedFileHeader(BaseFileHeader):
                'filename': 'focused-filename'}
         self._w = urwid.AttrMap(col, None, focus_map=map)
 
+class UnifiedFileReminder(BaseFileReminder):
+    def __init__(self):
+        self.old_text = urwid.Text(('filename', ''))
+        self.new_text = urwid.Text(('filename', ''))
+        self.col = urwid.Columns([('pack', self.old_text),
+                                  ('pack', self.new_text),
+                                  urwid.Text(u'')], dividechars=2)
+        super(UnifiedFileReminder, self).__init__(self.col)
+
+    def set(self, old, new):
+        self.old_text.set_text(('filename', old))
+        self.new_text.set_text(('filename', new))
+        self.col._invalidate()
+
 class UnifiedDiffView(BaseDiffView):
     def makeLines(self, diff, lines_to_add, comment_lists):
         lines = []
@@ -153,6 +167,9 @@ class UnifiedDiffView(BaseDiffView):
                                                     new_comment))
         return lines
 
+    def makeFileReminder(self):
+        return UnifiedFileReminder()
+
     def makeFileHeader(self, diff, comment_lists):
         context = LineContext(
             self.old_revision_key, self.new_revision_key,