feat: Control widget for enum fields (dropdown box)

Change-Id: Id762960d4a9ef6b18a5b35c5528928f32d79d248
diff --git a/dcs/config/ui/enum_widget.py b/dcs/config/ui/enum_widget.py
new file mode 100644
index 0000000..138af3a
--- /dev/null
+++ b/dcs/config/ui/enum_widget.py
@@ -0,0 +1,49 @@
+#  SPDX-License-Identifier: MPL-2.0
+#    Copyright (c) 2022 Philipp Le <philipp@philipple.de>.
+#  This Source Code Form is subject to the terms of the Mozilla Public
+#  License, v. 2.0. If a copy of the MPL was not distributed with this
+#  file, You can obtain one at https://mozilla.org/MPL/2.0/.
+
+
+from typing import Type
+from tkinter import ttk, StringVar
+from pydantic import BaseModel
+from enum import Enum
+
+from .base import make_config_widget_base
+
+
+class EnumDropdownWidget(make_config_widget_base(ttk.OptionMenu)):
+    MODEL_TYPE = Enum
+    FLAVOUR = 'dropdown'
+
+    def __init__(self, model: BaseModel, model_key: str, tp: Type, parent, *args, **kwargs):
+        self._var = StringVar(parent)
+        super().__init__(model, model_key, tp, parent, self._var, *args, **kwargs)
+
+    def _get_choices(self):
+        return [val for val in self.type_.__members__.values()]
+
+    def _get_choices_str(self):
+        return [str(val.value) for val in self._get_choices()]
+
+    def sync_out(self) -> None:
+        try:
+            index = self._get_choices_str().index(self._var.get())
+            val = self._get_choices()[index]
+            setattr(self.model, self.model_key, val)
+            self.notify_change()
+        except ValueError:
+            # Tolerate temporarily invalid values
+            raise
+            pass
+
+    def sync_in(self) -> None:
+        val = getattr(self.model, self.model_key)
+        index = self._get_choices().index(val)
+        choices = self._get_choices_str()
+        self.set_menu(choices[index], *choices)
+
+    def _config_widget(self):
+        self._var.trace('w', lambda x, y, z: self.sync_out())
+        self.sync_in()
diff --git a/dcs/config/ui/ui_create.py b/dcs/config/ui/ui_create.py
index 1499b61..da3f935 100644
--- a/dcs/config/ui/ui_create.py
+++ b/dcs/config/ui/ui_create.py
@@ -12,11 +12,13 @@
 from .base import ConfigWidget
 from .num_widget import NumWidget
 from .str_widget import StrWidget
+from .enum_widget import EnumDropdownWidget
 
 
 _CLASS_REGISTRY: List[Type[ConfigWidget]] = [
     NumWidget,
     StrWidget,
+    EnumDropdownWidget,
 ]