click -> clone

pigeon_magnet_solver/board.py

@@ -89,7 +89,7 @@ class Board:
         old_row = self.rows[row]
         self.rows[row] = old_row[:col] + value + old_row[col+1:]
 
-    def click(self, index: int) -> None:
+    def click(self, index: int) -> Self:
         # check is clickable
         row, col = index // self.width, index % self.width
         assert self.rows[row][col] == "1", f"{index} is not clickable!"
@@ -105,6 +105,12 @@ class Board:
         # rotate neighbors
         nb_rot = rotate_r([self[rc] for rc in nb_rc])
 
-        # set new neighbors
+        # create new state
+        result = self.__class__(
+            rows=self.rows.copy(),
+            buttons=self.buttons,
+        )
         for rc, val in zip(nb_rc, nb_rot):
-            self[rc] = val
+            result[rc] = val
+
+        return result

tests/test_board.py

@@ -13,6 +13,9 @@ def test_default():
     assert board.binary_repr == (4, 11, 3), "Wrong binary repr"
     assert board.solution_class == (1, 3, 2), "Wrong solution class"
 
+    assert board.click(4).binary_repr == (4, 14, 3)
+    assert board.click(5).binary_repr == (4, 11, 6)
+
     for idx in (3, 7):
         with pytest.raises(AssertionError):
             board.click(idx)