Rework trains to encourage alliances (#1697)

## Description:

This update encourages alliances by modifying how train-based trading
works. Trading is now restricted to allied networks, and allied trades
offer better rewards than self-trades, incentivizing cooperation.

Changes:
- Train destinations are now limited to stations owned by the player or
their allies.
    - Delivering a train to one’s own station grants 4,000 gold.
- Delivering a train to an ally’s station grants 5,000 gold to both the
sender and the receiver.

This system encourages players to form alliances, especially with
factory-focused players.


## Please complete the following:

- [x] I have added screenshots for all UI updates
- [x] I process any text displayed to the user through translateText()
and I've added it to the en.json file
- [x] I have added relevant tests to the test directory
- [x] I confirm I have thoroughly tested these changes and take full
responsibility for any bugs introduced
- [x] I have read and accepted the CLA agreement (only required once).

## Please put your Discord username so you can be contacted if a bug or
regression is found:

IngloriousTom

src/core/configuration/DefaultConfig.ts

@@ -329,7 +329,7 @@ export class DefaultConfig implements Config {
     return Math.min(1400, Math.round(20 * Math.pow(numberOfStations, 0.5)));
   }
   trainGold(): Gold {
-    return BigInt(10_000);
+    return BigInt(4_000);
   }
   trainStationMinRange(): number {
     return 15;

src/core/execution/TrainExecution.ts

@@ -32,6 +32,10 @@ export class TrainExecution implements Execution {
     private numCars: number,
   ) {}
 
+  public owner(): Player {
+    return this.player;
+  }
+
   init(mg: Game, ticks: number): void {
     this.mg = mg;
     const stations = this.railNetwork.findStationsPath(

src/core/game/GameUpdates.ts

@@ -69,9 +69,9 @@ export type GameUpdate =
 
 export interface BonusEventUpdate {
   type: GameUpdateType.BonusEvent;
+  player: PlayerID;
   tile: TileRef;
   gold: number;
-  workers: number;
   troops: number;
 }
 

src/core/game/PlayerImpl.ts

@@ -704,9 +704,9 @@ export class PlayerImpl implements Player {
     if (tile) {
       this.mg.addUpdate({
         type: GameUpdateType.BonusEvent,
+        player: this.id(),
         tile,
         gold: Number(toAdd),
-        workers: 0,
         troops: 0,
       });
     }

src/core/game/TrainStation.ts

@@ -25,8 +25,15 @@ class CityStopHandler implements TrainStopHandler {
     trainExecution: TrainExecution,
   ): void {
     const level = BigInt(station.unit.level() + 1);
-    const goldBonus = (mg.config().trainGold() * level) / this.factor;
-    station.unit.owner().addGold(goldBonus, station.tile());
+    let goldBonus = (mg.config().trainGold() * level) / this.factor;
+    const stationOwner = station.unit.owner();
+    const trainOwner = trainExecution.owner();
+    // Share revenue with the station owner if it's not the current player
+    if (stationOwner.isFriendly(trainOwner)) {
+      goldBonus += BigInt(1_000); // Bonus for everybody when trading with an ally!
+      stationOwner.addGold(goldBonus, station.tile());
+    }
+    trainOwner.addGold(goldBonus, station.tile());
   }
 }
 
@@ -39,8 +46,15 @@ class PortStopHandler implements TrainStopHandler {
     trainExecution: TrainExecution,
   ): void {
     const level = BigInt(station.unit.level() + 1);
-    const goldBonus = (mg.config().trainGold() * level) / this.factor;
-    station.unit.owner().addGold(goldBonus, station.tile());
+    let goldBonus = (mg.config().trainGold() * level) / this.factor;
+    const stationOwner = station.unit.owner();
+    const trainOwner = trainExecution.owner();
+    // Share revenue with the station owner if it's not the current player
+    if (stationOwner.isFriendly(trainOwner)) {
+      goldBonus += BigInt(1_000); // Bonus for everybody when trading with an ally!
+      stationOwner.addGold(goldBonus, station.tile());
+    }
+    trainOwner.addGold(goldBonus, station.tile());
   }
 }
 
@@ -51,7 +65,15 @@ class FactoryStopHandler implements TrainStopHandler {
     station: TrainStation,
     trainExecution: TrainExecution,
   ): void {
-    station.unit.owner().addGold(mg.config().trainGold(), station.tile());
+    let goldBonus = mg.config().trainGold();
+    const stationOwner = station.unit.owner();
+    const trainOwner = trainExecution.owner();
+    // Share revenue with the station owner if it's not the current player
+    if (stationOwner.isFriendly(trainOwner)) {
+      goldBonus += BigInt(1_000); // Bonus for everybody when trading with an ally!
+      stationOwner.addGold(goldBonus, station.tile());
+    }
+    trainOwner.addGold(goldBonus, station.tile());
   }
 }
 
@@ -207,7 +229,10 @@ export class Cluster {
   availableForTrade(player: Player): Set<TrainStation> {
     const tradingStations = new Set<TrainStation>();
     for (const station of this.stations) {
-      if (station.tradeAvailable(player)) {
+      if (
+        station.unit.owner() === player ||
+        station.unit.owner().isFriendly(player)
+      ) {
         tradingStations.add(station);
       }
     }