widgets/search: cleanup ThreadlineWidget

Remove unnecessary instance variables that are only really needed within
one function. Prepare the class for async rebuild.

1 files changed, 33 insertions, 25 deletions

diff --git a/alot/widgets/search.py b/alot/widgets/search.py
index d511f2f7..dda171ac 100644
--- a/alot/widgets/search.py
+++ b/alot/widgets/search.py
@@ -12,31 +12,36 @@ from .utils import AttrFlipWidget
 from .globals import TagWidget
 
 
-class ThreadlineWidget(urwid.AttrMap):
+class ThreadlineWidget(urwid.WidgetPlaceholder):
     """
     selectable line widget that represents a :class:`~alot.db.Thread`
     in the :class:`~alot.buffers.SearchBuffer`.
     """
+
+    tid = None
+
+    _dbman   = None
+    _thread  = None
+
+    _widgets = None
+
     def __init__(self, tid, dbman):
-        self.dbman = dbman
-        self.tid = tid
-        self.thread = None  # will be set by refresh()
-        self.structure = None
+        self.tid    = tid
+        self._dbman = dbman
+
+        super().__init__(urwid.Text(''))
+
         self.rebuild()
-        normal = self.structure['normal']
-        focussed = self.structure['focus']
-        urwid.AttrMap.__init__(self, self.columns, normal, focussed)
 
     def rebuild(self):
-        self.thread = self.dbman.get_thread(self.tid)
-        self.widgets = []
-        self.structure = settings.get_threadline_theming(self.thread)
+        thread    = self._dbman.get_thread(self.tid)
+        structure = settings.get_threadline_theming(thread)
 
         columns = []
 
         # combine width info and widget into an urwid.Column entry
         def add_column(width, part):
-            width_tuple = self.structure[partname]['width']
+            width_tuple = structure[partname]['width']
             if width_tuple[0] == 'weight':
                 columnentry = width_tuple + (part,)
             else:
@@ -44,30 +49,33 @@ class ThreadlineWidget(urwid.AttrMap):
             columns.append(columnentry)
 
         # create a column for every part of the threadline
-        for partname in self.structure['parts']:
+        widgets = []
+        for partname in structure['parts']:
             # build widget(s) around this part's content and remember them so
             # that self.render() may change local attributes.
             if partname == 'tags':
-                width, part = build_tags_part(self.thread.get_tags(),
-                                              self.structure['tags']['normal'],
-                                              self.structure['tags']['focus'])
+                width, part = build_tags_part(thread.get_tags(),
+                                              structure['tags']['normal'],
+                                              structure['tags']['focus'])
                 if part:
                     add_column(width, part)
                     for w in part.widget_list:
-                        self.widgets.append(w)
+                        widgets.append(w)
             else:
-                width, part = build_text_part(partname, self.thread,
-                                              self.structure[partname])
+                width, part = build_text_part(partname, thread,
+                                              structure[partname])
                 add_column(width, part)
-                self.widgets.append(part)
+                widgets.append(part)
 
-        self.columns = urwid.Columns(columns, dividechars=1)
-        self.original_widget = self.columns
+        columns              = urwid.Columns(columns, dividechars = 1)
+        self.original_widget = urwid.AttrMap(columns, structure['normal'], structure['focus'])
+        self._thread         = thread
+        self._widgets        = widgets
 
     def render(self, size, focus=False):
-        for w in self.widgets:
+        for w in self._widgets:
             w.set_map('focus' if focus else 'normal')
-        return urwid.AttrMap.render(self, size, focus)
+        return super().render(size, focus)
 
     def selectable(self):
         return True
@@ -76,7 +84,7 @@ class ThreadlineWidget(urwid.AttrMap):
         return key
 
     def get_thread(self):
-        return self.thread
+        return self._thread
 
 
 def build_tags_part(tags, attr_normal, attr_focus):