Enable sell button according to available aircraft

also added a tooltip which gives the user the hint that maybe the aircraft is assigned to mission and therefore the button is disabled

changelog.md

@@ -18,6 +18,7 @@ Saves from 4.x are not compatible with 5.0.
 * **[Kneeboard]** Minimum required fuel estimates have been added to the kneeboard for aircraft with supporting data (currently only the Hornet).
 * **[Kneeboard]** QNH (pressure MSL) and temperature have been added to the kneeboard.
 * **[New Game Wizard]** Can now customize the player's air wing before campaign start to disable or rename squadrons.
+* **[UI]** Sell Button for aircraft will be disabled if there are no units available to be sold or all are already assigned to a mission
 
 ## Fixes
 

qt_ui/windows/basemenu/QRecruitBehaviour.py

@@ -80,7 +80,13 @@ class PurchaseGroup(QGroupBox):
 
     def update_state(self) -> None:
         self.buy_button.setEnabled(self.recruiter.enable_purchase(self.unit_type))
+        self.buy_button.setToolTip(
+            self.recruiter.purchase_tooltip(self.buy_button.isEnabled())
+        )
         self.sell_button.setEnabled(self.recruiter.enable_sale(self.unit_type))
+        self.sell_button.setToolTip(
+            self.recruiter.sell_tooltip(self.sell_button.isEnabled())
+        )
         self.amount_bought.setText(f"<b>{self.pending_units}</b>")
 
 
@@ -223,6 +229,18 @@ class QRecruitBehaviour:
     def enable_sale(self, unit_type: UnitType) -> bool:
         return True
 
+    def purchase_tooltip(self, is_enabled: bool) -> str:
+        if is_enabled:
+            return "Buy unit. Use Shift or Ctrl key to buy multiple units at once."
+        else:
+            return "Unit can not be bought."
+
+    def sell_tooltip(self, is_enabled: bool) -> str:
+        if is_enabled:
+            return "Sell unit. Use Shift or Ctrl key to buy multiple units at once."
+        else:
+            return "Unit can not be sold."
+
     def info(self, unit_type: UnitType) -> None:
         self.info_window = QUnitInfoWindow(self.game_model.game, unit_type)
         self.info_window.show()

qt_ui/windows/basemenu/airfield/QAircraftRecruitmentMenu.py

@@ -85,9 +85,13 @@ class QAircraftRecruitmentMenu(QFrame, QRecruitBehaviour):
         return True
 
     def enable_sale(self, unit_type: AircraftType) -> bool:
-        if not self.cp.can_operate(unit_type):
-            return False
-        return True
+        return self.can_be_sold(unit_type)
+
+    def sell_tooltip(self, is_enabled: bool) -> str:
+        if is_enabled:
+            return "Sell unit. Use Shift or Ctrl key to sell multiple units at once."
+        else:
+            return "Can not be sold because either no aircraft are available or are already assigned to a mission."
 
     def buy(self, unit_type: AircraftType) -> bool:
         if self.maximum_units > 0:
@@ -112,15 +116,17 @@ class QAircraftRecruitmentMenu(QFrame, QRecruitBehaviour):
         self.hangar_status.update_label()
         return True
 
+    def can_be_sold(self, unit_type: AircraftType) -> bool:
+        inventory = self.game_model.game.aircraft_inventory.for_control_point(self.cp)
+        pending_deliveries = self.pending_deliveries.units.get(unit_type, 0)
+        return self.cp.can_operate(unit_type) and (
+            pending_deliveries > 0 or inventory.available(unit_type) > 0
+        )
+
     def sell(self, unit_type: AircraftType) -> bool:
         # Don't need to remove aircraft from the inventory if we're canceling
         # orders.
-        if self.pending_deliveries.units.get(unit_type, 0) <= 0:
-            global_inventory = self.game_model.game.aircraft_inventory
-            inventory = global_inventory.for_control_point(self.cp)
-            try:
-                inventory.remove_aircraft(unit_type, 1)
-            except ValueError:
+        if not self.can_be_sold(unit_type):
             QMessageBox.critical(
                 self,
                 "Could not sell aircraft",
@@ -130,6 +136,12 @@ class QAircraftRecruitmentMenu(QFrame, QRecruitBehaviour):
                 QMessageBox.Ok,
             )
             return False
+
+        inventory = self.game_model.game.aircraft_inventory.for_control_point(self.cp)
+        pending_deliveries = self.pending_deliveries.units.get(unit_type, 0)
+        if pending_deliveries <= 0 < inventory.available(unit_type):
+            inventory.remove_aircraft(unit_type, 1)
+
         super().sell(unit_type)
         self.hangar_status.update_label()