add prevctype command

Author: Felix Van der Jeugt

alot/commands/thread.py

@@ -1208,3 +1208,16 @@ def apply(self, ui):
         message_tree.next_contenttype()
         message_tree.reassemble()
         tbuffer.refresh()
+
+@registerCommand(MODE, 'prevctype', help='display the previous contenttype')
+class PrevCTypeCommand(Command):
+
+    """display the next contenttype"""
+    repeatable = True
+
+    def apply(self, ui):
+        tbuffer = ui.current_buffer
+        message_tree = tbuffer.get_selected_messagetree()
+        message_tree.prev_contenttype()
+        message_tree.reassemble()
+        tbuffer.refresh()

alot/widgets/thread.py

@@ -290,6 +290,10 @@ def next_contenttype(self):
         self._current_contenttype += 1
         self._current_contenttype %= len(self._get_content_parts())
 
+    def prev_contenttype(self):
+        self._current_contenttype -= 1
+        self._current_contenttype %= len(self._get_content_parts())
+
     def _get_headers(self):
         if self.display_all_headers is True:
             if self._all_headers_tree is None: