tweak the airlift procurement

- only buy airlift capable aircraft if there is one friendly cp without a factory which can only be reached via airlift
- prevent that an airlift procurement gets fulfilled at a different cp than the requesting one. this ensures that the cp also has a factory to produce ground units which can then be transported
- fixes an infinite buy loop if the fulfilling cp has no factory and the requesting cp has no space for airlift
- have always 2 reserve transport planes at the biggest CP

changelog.md

@@ -10,6 +10,7 @@ Saves from 4.x are not compatible with 5.0.
 * **[Campaign AI]** Player front line stances can now be automated. Improved stance selection for AI.
 * **[Campaign AI]** Reworked layout of hold, join, split, and ingress points. Should result in much shorter flight plans in general while still maintaining safe join/split/hold points.
 * **[Campaign AI]** Auto-planning mission range limits are now specified per-aircraft. On average this means that longer range missions will now be plannable. The limit only accounts for the direct distance to the target, not the path taken.
+* **[Campaign AI]** Transport aircraft will now be bought only if necessary at control points which can produce ground units and are capable to operate transport aircraft.
 * **[Campaign AI]** Aircraft will now only be automatically purchased or assigned at appropriate bases. Naval aircraft will default to only operating from carriers, Harriers will default to LHAs and shore bases, helicopters will operate from anywhere. This can be customized per-squadron.
 * **[Kneeboard]** Minimum required fuel estimates have been added to the kneeboard for aircraft with supporting data (currently only the Hornet).
 * **[New Game Wizard]** Can now customize the player's air wing before campaign start to disable or rename squadrons.

game/transfers.py

@@ -722,9 +722,39 @@ class PendingTransfers:
             ):
                 self.order_airlift_assets_at(control_point)
 
-    @staticmethod
-    def desired_airlift_capacity(control_point: ControlPoint) -> int:
-        return 4 if control_point.has_factory else 0
+    def desired_airlift_capacity(self, control_point: ControlPoint) -> int:
+
+        if control_point.has_factory:
+            is_major_hub = control_point.total_aircraft_parking > 0
+            # Check if there is a CP which is only reachable via Airlift
+            transit_network = self.network_for(control_point)
+            for cp in self.game.theater.control_points_for(self.player):
+                # check if the CP has no factory, is reachable from the current
+                # position and can only be reached with airlift connections
+                if (
+                    cp.can_deploy_ground_units
+                    and not cp.has_factory
+                    and transit_network.has_link(control_point, cp)
+                    and not any(
+                        link_type
+                        for link, link_type in transit_network.nodes[cp].items()
+                        if not link_type == TransitConnection.Airlift
+                    )
+                ):
+                    return 4
+
+                if (
+                    is_major_hub
+                    and cp.has_factory
+                    and cp.total_aircraft_parking > control_point.total_aircraft_parking
+                ):
+                    is_major_hub = False
+
+            if is_major_hub:
+                # If the current CP is a major hub keep always 2 planes on reserve
+                return 2
+
+        return 0
 
     def current_airlift_capacity(self, control_point: ControlPoint) -> int:
         inventory = self.game.aircraft_inventory.for_control_point(control_point)
@@ -739,9 +769,16 @@ class PendingTransfers:
         )
 
     def order_airlift_assets_at(self, control_point: ControlPoint) -> None:
-        gap = self.desired_airlift_capacity(
-            control_point
-        ) - self.current_airlift_capacity(control_point)
+        unclaimed_parking = control_point.unclaimed_parking(self.game)
+        # Buy a maximum of unclaimed_parking only to prevent that aircraft procurement
+        # take place at another base
+        gap = min(
+            [
+                self.desired_airlift_capacity(control_point)
+                - self.current_airlift_capacity(control_point),
+                unclaimed_parking,
+            ]
+        )
 
         if gap <= 0:
             return
@@ -751,6 +788,10 @@ class PendingTransfers:
             # aesthetic.
             gap += 1
 
+        if gap > unclaimed_parking:
+            # Prevent to buy more aircraft than possible
+            return
+
         self.game.coalition_for(self.player).add_procurement_request(
             AircraftProcurementRequest(control_point, FlightType.TRANSPORT, gap)
         )