buffers/thread: do not construct the message widgets until they are needed

1 files changed, 24 insertions, 16 deletions

diff --git a/alot/buffers/thread.py b/alot/buffers/thread.py
index d47faa31..33405be4 100644
--- a/alot/buffers/thread.py
+++ b/alot/buffers/thread.py
@@ -5,6 +5,7 @@
 
 import asyncio
 import enum
+from   functools import cached_property
 import logging
 
 import urwid
@@ -18,6 +19,16 @@ class _ThreadBufFocus(enum.Enum):
     TREE    = enum.auto()
     MESSAGE = enum.auto()
 
+class _LazyMessageWidget:
+    msg = None
+
+    def __init__(self, msg):
+        self.msg = msg
+
+    @cached_property
+    def wgt(self):
+        return MessageWidget(self.msg)
+
 class ThreadBuffer(Buffer):
     """displays a thread as a tree of messages."""
 
@@ -28,7 +39,7 @@ class ThreadBuffer(Buffer):
 
     # list of the widgets containing the message body
     # indexed by its depth-first position in the thread tree
-    _msg_widgets    = None
+    _messages       = None
     # widget showing the thread tree
     _msgtree_widget = None
     # decorations around the msgtree widget
@@ -87,9 +98,9 @@ class ThreadBuffer(Buffer):
 
     def _update_cur_msg(self):
         pos = self._msgtree_widget.body.focus
-        if pos is not None and pos < len(self._msg_widgets):
+        if pos is not None and pos < len(self._messages):
             logging.debug('displaying message %s ', pos)
-            self._cur_msg_holder.original_widget = self._msg_widgets[pos]
+            self._cur_msg_holder.original_widget = self._messages[pos].wgt
 
     def translated_tags_str(self, intersection=False):
         tags = self.thread.get_tags(intersection=intersection)
@@ -108,7 +119,7 @@ class ThreadBuffer(Buffer):
         return info
 
     def rebuild(self):
-        self._msg_widgets = []
+        self._messages = []
         self._msgtree_widget.body.clear()
         self._cur_msg_holder.original_widget = urwid.SolidFill()
 
@@ -119,11 +130,8 @@ class ThreadBuffer(Buffer):
 
         list_walker = self._msgtree_widget.body
         for pos, msg in enumerate(self.thread.message_list):
-            msg_wgt = MessageWidget(msg)
-            wgt     = ThreadNode(msg, self.thread, pos, self._indent_width)
-
-            self._msg_widgets.append(msg_wgt)
-            list_walker.append(wgt)
+            self._messages.append(_LazyMessageWidget(msg))
+            list_walker.append(ThreadNode(msg, self.thread, pos, self._indent_width))
 
         # approximate weight for one terminal line
         # substract 3 for decoration and panels
@@ -133,11 +141,11 @@ class ThreadBuffer(Buffer):
         # the number of messages in it plus 2 (for surrounding decoration) -
         # scaled to approximately one line per message - up to maximum weight of
         # half the screen
-        tree_weight = min(line_weight * (len(self._msg_widgets) + 2), 0.5)
+        tree_weight = min(line_weight * (len(self._messages) + 2), 0.5)
         self.msgtree_weight = tree_weight
 
-        if len(self._msg_widgets) > 0:
-            self._cur_msg_holder.original_widget = self._msg_widgets[0]
+        if len(self._messages) > 0:
+            self._cur_msg_holder.original_widget = self._messages[0].wgt
 
     @property
     def msgtree_weight(self):
@@ -155,7 +163,7 @@ class ThreadBuffer(Buffer):
     def get_selected_message_widget(self):
         """Return currently focused :class:`MessageWidget`."""
         pos = self.get_selected_message_position()
-        return self._msg_widgets[pos]
+        return self._messages[pos].wgt
 
     def get_selected_message(self):
         """Return focussed :class:`~alot.db.message.Message`."""
@@ -176,8 +184,8 @@ class ThreadBuffer(Buffer):
         """
         Iterate over all the message widgets in this buffer
         """
-        for w in self._msg_widgets:
-            yield w
+        for m in self._messages:
+            yield m.wgt
 
     def set_focus(self, pos):
         "Set the focus in the underlying body widget."
@@ -267,7 +275,7 @@ class ThreadBuffer(Buffer):
             raise ValueError('Invalid focus_propery direction: ' + str(direction))
 
         for pos in walk:
-            if prop(self._msg_widgets[pos]):
+            if prop(self._messages[pos].wgt):
                 self.set_focus(pos)
                 break