Add a SetObjectExtruderOperation class

It handles setting an extruder for an object.

Contributes to CURA-3609

cura/Settings/SetObjectExtruderOperation.py

@@ -0,0 +1,27 @@
+# Copyright (c) 2017 Ultimaker B.V.
+# Cura is released under the terms of the AGPLv3 or higher.
+
+from UM.Scene.SceneNode import SceneNode
+from UM.Operations.Operation import Operation
+
+from cura.Settings.SettingOverrideDecorator import SettingOverrideDecorator
+
+##  Simple operation to set the extruder a certain object should be printed with.
+class SetObjectExtruderOperation(Operation):
+    def __init__(self, node: SceneNode, extruder_id: str) -> None:
+        self._node = node
+        self._extruder_id = extruder_id
+        self._previous_extruder_id = None
+        self._decorator_added = False
+
+    def undo(self):
+        if self._previous_extruder_id:
+            self._node.callDecoration("setActiveExtruder", self._previous_extruder_id)
+
+    def redo(self):
+        stack = self._node.callDecoration("getStack") #Don't try to get the active extruder since it may be None anyway.
+        if not stack:
+            self._node.addDecorator(SettingOverrideDecorator())
+
+        self._previous_extruder_id = self._node.callDecoration("getActiveExtruder")
+        self._node.callDecoration("setActiveExtruder", self._extruder_id)