Add on-exit callback management and check for active USB printing

CURA-5384

cura/TaskManagement/OnExitCallbackManager.py

@@ -0,0 +1,69 @@
+# Copyright (c) 2018 Ultimaker B.V.
+# Cura is released under the terms of the LGPLv3 or higher.
+
+from typing import TYPE_CHECKING, List
+
+from UM.Logger import Logger
+
+if TYPE_CHECKING:
+    from cura.CuraApplication import CuraApplication
+
+
+#
+# This class manages a all registered upon-exit checks that need to be perform when the application tries to exit.
+# For example, to show a confirmation dialog when there is USB printing in progress, etc. All callbacks will be called
+# in the order of when they got registered. If all callbacks "passes", that is, for example, if the user clicks "yes"
+# on the exit confirmation dialog or nothing that's blocking the exit, then the application will quit after that.
+#
+class OnExitCallbackManager:
+
+    def __init__(self, application: "CuraApplication") -> None:
+        self._application = application
+        self._on_exit_callback_list = list()  # type: List[callable]
+        self._current_callback_idx = 0
+        self._is_all_checks_passed = False
+
+    def addCallback(self, callback: callable) -> None:
+        self._on_exit_callback_list.append(callback)
+        Logger.log("d", "on-app-exit callback [%s] added.", callback)
+
+    # Reset the current state so the next time it will call all the callbacks again.
+    def resetCurrentState(self) -> None:
+        self._current_callback_idx = 0
+        self._is_all_checks_passed = False
+
+    def getIsAllChecksPassed(self) -> bool:
+        return self._is_all_checks_passed
+
+    # Trigger the next callback if available. If not, it means that all callbacks have "passed", which means we should
+    # not block the application to quit, and it will call the application to actually quit.
+    def triggerNextCallback(self) -> None:
+        # Get the next callback and schedule that if
+        this_callback = None
+        if self._current_callback_idx < len(self._on_exit_callback_list):
+            this_callback = self._on_exit_callback_list[self._current_callback_idx]
+            self._current_callback_idx += 1
+
+        if this_callback is not None:
+            Logger.log("d", "Scheduled the next on-app-exit callback [%s]", this_callback)
+            self._application.callLater(this_callback)
+        else:
+            Logger.log("d", "No more on-app-exit callbacks to process. Tell the app to exit.")
+
+            self._is_all_checks_passed = True
+
+            # Tell the application to exit
+            self._application.callLater(self._application.closeApplication)
+
+    # This is the callback function which an on-exit callback should call when it finishes, it should provide the
+    # "should_proceed" flag indicating whether this check has "passed", or in other words, whether quiting the
+    # application should be blocked. If the last on-exit callback doesn't block the quiting, it will call the next
+    # registered on-exit callback if available.
+    def onCurrentCallbackFinished(self, should_proceed: bool = True) -> None:
+        if not should_proceed:
+            Logger.log("d", "on-app-exit callback finished and we should not proceed.")
+            # Reset the state
+            self.resetCurrentState()
+            return
+
+        self.triggerNextCallback()