Create shortcut to undo back to main branch

CONTRIBUTIONS.md

@@ -51,6 +51,7 @@ Many thanks to these additional authors:
 * Carton He for contributions to sgf parsing and handling.
 * "blamarche" for adding the board coordinates toggle.
 * "pdeblanc" for adding the ancient chinese scoring option.
+* "LiamHz" for adding the undo to main branch keyboard shortcut.
 
 ## Translators
 

README.md

@@ -184,6 +184,7 @@ In addition to shortcuts mentioned above and those shown in the main menu:
 * **[Ctrl-delete]** Delete current node.
 * **[c]** Collapse/Uncollapse the branch from the current node to the previous branching point.
 * **[b]** Go back to the previous branching point.
+* **[Shift-b]** Go back the the main branch.
 * **[n]** As in clicking the forward red arrow, go to one move before the next mistake (orange or worse) by a human player.
 * **[Shift-n]** As in clicking the backward red arrow, go to one move before the previous mistake.
 * **[scroll up]**: Undo move. Only works when hovering the cursor over the board.

katrain/__main__.py

@@ -610,6 +610,8 @@ class KaTrainGui(Screen, KaTrainBase):
             self.controls.set_status(i18n._("Copied SGF to clipboard."), STATUS_INFO)
         elif keycode[1] == "v" and ctrl_pressed:
             self.load_sgf_from_clipboard()
+        elif keycode[1] == "b" and shift_pressed:
+            self("undo", "main-branch")
         elif keycode[1] in shortcuts.keys() and not ctrl_pressed:
             shortcut = shortcuts[keycode[1]]
             if isinstance(shortcut, Widget):

katrain/core/game.py

@@ -279,9 +279,14 @@ class Game:
                 self._calculate_groups()
             return
         break_on_branch = False
+        break_on_main_branch = False
+        last_branching_node = cn
         if n_times == "branch":
             n_times = 9999
             break_on_branch = True
+        elif n_times == "main-branch":
+            n_times = 9999
+            break_on_main_branch = True
         for move in range(n_times):
             if (
                 stop_on_mistake is not None
@@ -297,6 +302,10 @@ class Game:
                 cn = cn.parent
             if break_on_branch and len(cn.children) > 1:
                 break
+            elif break_on_main_branch and len(cn.children) > 1:
+                last_branching_node = cn
+        if break_on_main_branch:
+            cn = last_branching_node
         self.set_current_node(cn)
 
     def redo(self, n_times=1, stop_on_mistake=None):