fix: Ensure mutual exclusivity and improve first backup logic

Centralize Mutual Exclusivity Logic:** Refactored the "Full Backup" and
     "Incremental" mutual exclusivity logic into a shared utility function (
     `enforce_backup_type_exclusivity`) in `pyimage_ui/shared_logic.py`. This ensures
     consistent behavior across both the main application view and the advanced settings.
Corrected Main View Exclusivity:** Resolved the issue where users could select
     both "Full Backup" and "Incremental" simultaneously in the main view. The checkboxes
     now correctly enforce mutual exclusivity.
Enhanced "First Backup" Handling:** Improved the logic for the initial backup.
     If no existing backup is detected in the destination, the system automatically
     enforces a "Full Backup" and disables the relevant checkboxes in the main view. This
     prevents incorrect backup types for new destinations.

main_app.py

@@ -18,6 +18,7 @@ from core.data_processing import DataProcessing
 from pyimage_ui.drawing import Drawing
 from pyimage_ui.navigation import Navigation
 from pyimage_ui.actions import Actions
+from pyimage_ui.shared_logic import enforce_backup_type_exclusivity
 
 
 class MainApplication(tk.Tk):
@@ -348,10 +349,10 @@ class MainApplication(tk.Tk):
         self.bypass_security_var = tk.BooleanVar()
 
         self.full_backup_cb = ttk.Checkbutton(checkbox_frame, text=Msg.STR["full_backup"],
-                                              variable=self.vollbackup_var, command=lambda: self._enforce_main_backup_type_exclusivity("full"))
+                                              variable=self.vollbackup_var, command=lambda: enforce_backup_type_exclusivity(self.vollbackup_var, self.inkrementell_var, self.vollbackup_var.get()))
         self.full_backup_cb.pack(side=tk.LEFT, padx=5)
         self.incremental_cb = ttk.Checkbutton(checkbox_frame, text=Msg.STR["incremental"],
-                                              variable=self.inkrementell_var, command=lambda: self._enforce_main_backup_type_exclusivity("incremental"))
+                                              variable=self.inkrementell_var, command=lambda: enforce_backup_type_exclusivity(self.inkrementell_var, self.vollbackup_var, self.inkrementell_var.get()))
         self.incremental_cb.pack(side=tk.LEFT, padx=5)
         self.test_run_cb = ttk.Checkbutton(checkbox_frame, text=Msg.STR["test_run"],
                                            variable=self.testlauf_var)
@@ -461,13 +462,7 @@ class MainApplication(tk.Tk):
         else:
             self.encrypted_cb.config(state="normal")
 
-    def _enforce_main_backup_type_exclusivity(self, changed_var):
-        # This is only active if no 'force' setting is applied
-        if self.full_backup_cb.cget('state') == 'normal':
-            if changed_var == "full" and self.vollbackup_var.get():
-                self.inkrementell_var.set(False)
-            elif changed_var == "incremental" and self.inkrementell_var.get():
-                self.vollbackup_var.set(False)
+    
 
 
 if __name__ == "__main__":

pyimage_ui/actions.py

@@ -18,15 +18,32 @@ class Actions:
         self.app = app
 
     def _check_for_first_backup(self):
-        if (self.app.left_canvas_data.get('folder') == "Computer" and
-                self.app.destination_path and
-                not os.listdir(self.app.destination_path)):
-            self.app.is_first_backup = True
-            # Enforce full backup, and uncheck incremental
+        # This logic only applies if no override from advanced settings is active
+        if self.app.full_backup_cb.cget('state') != 'normal':
+            self.app.is_first_backup = False # Ensure this is reset if controls are disabled
+            return
+
+        # A "first backup" situation exists if the destination is selected but empty.
+        # This applies to both Computer and User folder backups.
+        is_first_backup_situation = (self.app.destination_path and
+                                     os.path.isdir(self.app.destination_path) and
+                                     not os.listdir(self.app.destination_path))
+
+        self.app.is_first_backup = is_first_backup_situation
+
+        if is_first_backup_situation:
+            # It's the first backup, so it MUST be a full backup.
             self.app.vollbackup_var.set(True)
             self.app.inkrementell_var.set(False)
+            # Disable controls so user cannot change this.
+            self.app.full_backup_cb.config(state="disabled")
+            self.app.incremental_cb.config(state="disabled")
         else:
-            self.app.is_first_backup = False
+            # A backup already exists, so the user can choose.
+            # Re-enable controls.
+            self.app.full_backup_cb.config(state="normal")
+            self.app.incremental_cb.config(state="normal")
+            # We don't set the value here, preserving the user's last choice.
 
     def on_sidebar_button_click(self, button_text):
         if not self.app.canvas_frame.winfo_viewable():

pyimage_ui/advanced_settings_frame.py

@@ -6,6 +6,7 @@ import fnmatch
 
 from app_config import AppConfig, Msg
 from shared_libs.animated_icon import AnimatedIcon
+from pyimage_ui.shared_logic import enforce_backup_type_exclusivity
 
 class AdvancedSettingsFrame(tk.Toplevel):
     def __init__(self, master, config_manager, app_instance, **kwargs):
@@ -63,8 +64,8 @@ class AdvancedSettingsFrame(tk.Toplevel):
         self.force_compression_var = tk.BooleanVar()
         self.force_encryption_var = tk.BooleanVar()
 
-        ttk.Checkbutton(defaults_frame, text=Msg.STR["force_full_backup"], variable=self.force_full_var, command=lambda: self._enforce_backup_type_exclusivity("full")).pack(anchor=tk.W)
-        ttk.Checkbutton(defaults_frame, text=Msg.STR["force_incremental_backup"], variable=self.force_incremental_var, command=lambda: self._enforce_backup_type_exclusivity("incremental")).pack(anchor=tk.W)
+        ttk.Checkbutton(defaults_frame, text=Msg.STR["force_full_backup"], variable=self.force_full_var, command=lambda: enforce_backup_type_exclusivity(self.force_full_var, self.force_incremental_var, self.force_full_var.get())).pack(anchor=tk.W)
+        ttk.Checkbutton(defaults_frame, text=Msg.STR["force_incremental_backup"], variable=self.force_incremental_var, command=lambda: enforce_backup_type_exclusivity(self.force_incremental_var, self.force_full_var, self.force_incremental_var.get())).pack(anchor=tk.W)
         ttk.Checkbutton(defaults_frame, text=Msg.STR["force_compression"], variable=self.force_compression_var).pack(anchor=tk.W)
         ttk.Checkbutton(defaults_frame, text=Msg.STR["force_encryption"], variable=self.force_encryption_var).pack(anchor=tk.W)
         
@@ -98,12 +99,6 @@ class AdvancedSettingsFrame(tk.Toplevel):
         if self.app_instance:
             self.app_instance.update_backup_options_from_config()
 
-    def _enforce_backup_type_exclusivity(self, changed_var):
-        if changed_var == "full" and self.force_full_var.get():
-            self.force_incremental_var.set(False)
-        elif changed_var == "incremental" and self.force_incremental_var.get():
-            self.force_full_var.set(False)
-
     def _load_backup_defaults(self):
         self.force_full_var.set(self.config_manager.get_setting("force_full_backup", False))
         self.force_incremental_var.set(self.config_manager.get_setting("force_incremental_backup", False))

pyimage_ui/shared_logic.py

@@ -0,0 +1,12 @@
+# pyimage_ui/shared_logic.py
+
+def enforce_backup_type_exclusivity(var_to_set, other_var, is_checked):
+    """
+    Enforces mutual exclusivity between two tkinter BooleanVars.
+
+    :param var_to_set: The BooleanVar of the checkbox that was clicked.
+    :param other_var: The other BooleanVar in the exclusive pair.
+    :param is_checked: The new state of the clicked checkbox.
+    """
+    if is_checked:
+        other_var.set(False)