Record train trading stats (#2891)

## Description:

The current gold stats don’t include gold generated by trains, even
though this is a significant part of the economy for many players.

This PR tracks those stats with two values:
- other players trains visits the player station
- the player trains visits any station

Linked to this infra PR: https://github.com/openfrontio/infra/pull/242

## 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

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

IngloriousTom

src/core/StatsSchemas.ts

@@ -78,6 +78,8 @@ export const GOLD_INDEX_WORK = 0; // Gold earned by workers
 export const GOLD_INDEX_WAR = 1; // Gold earned by conquering players
 export const GOLD_INDEX_TRADE = 2; // Gold earned by trade ships
 export const GOLD_INDEX_STEAL = 3; // Gold earned by capturing trade ships
+export const GOLD_INDEX_TRAIN_SELF = 4; // Gold earned by own trains
+export const GOLD_INDEX_TRAIN_OTHER = 5; // Gold earned by other players trains
 
 // Other Units
 export const OTHER_INDEX_BUILT = 0; // Structures and warships built

src/core/game/Stats.ts

@@ -101,4 +101,10 @@ export interface Stats {
 
   // player was killed (0 tiles)
   playerKilled(player: Player, tick: number): void;
+
+  // Player's train arrives at any station, generating gold
+  trainSelfTrade(player: Player, gold: number | bigint): void;
+
+  // Another player's train arrives at own station
+  trainExternalTrade(player: Player, goldPlayer: number | bigint);
 }

src/core/game/StatsImpl.ts

@@ -13,6 +13,8 @@ import {
   BOMB_INDEX_LAUNCH,
   GOLD_INDEX_STEAL,
   GOLD_INDEX_TRADE,
+  GOLD_INDEX_TRAIN_OTHER,
+  GOLD_INDEX_TRAIN_SELF,
   GOLD_INDEX_WAR,
   GOLD_INDEX_WORK,
   NukeType,
@@ -274,5 +276,13 @@ export class StatsImpl implements Stats {
     this._addPlayerKilled(player, tick);
   }
 
+  trainSelfTrade(player: Player, gold: BigIntLike): void {
+    this._addGold(player, GOLD_INDEX_TRAIN_SELF, gold);
+  }
+
+  trainExternalTrade(player: Player, gold: BigIntLike): void {
+    this._addGold(player, GOLD_INDEX_TRAIN_OTHER, gold);
+  }
+
   lobbyFillTime(fillTimeMs: number): void {}
 }

src/core/game/TrainStation.ts

@@ -12,11 +12,7 @@ interface TrainStopHandler {
   onStop(mg: Game, station: TrainStation, trainExecution: TrainExecution): void;
 }
 
-/**
- * All stop handlers share the same logic for the time being
- * Behavior to be defined
- */
-class CityStopHandler implements TrainStopHandler {
+class TradeStationStopHandler implements TrainStopHandler {
   onStop(
     mg: Game,
     station: TrainStation,
@@ -24,31 +20,14 @@ class CityStopHandler implements TrainStopHandler {
   ): void {
     const stationOwner = station.unit.owner();
     const trainOwner = trainExecution.owner();
-    const goldBonus = mg.config().trainGold(rel(trainOwner, stationOwner));
+    const gold = mg.config().trainGold(rel(trainOwner, stationOwner));
     // Share revenue with the station owner if it's not the current player
     if (trainOwner !== stationOwner) {
-      stationOwner.addGold(goldBonus, station.tile());
-    }
-    trainOwner.addGold(goldBonus, station.tile());
-  }
-}
-
-class PortStopHandler implements TrainStopHandler {
-  constructor(private random: PseudoRandom) {}
-  onStop(
-    mg: Game,
-    station: TrainStation,
-    trainExecution: TrainExecution,
-  ): void {
-    const stationOwner = station.unit.owner();
-    const trainOwner = trainExecution.owner();
-    const goldBonus = mg.config().trainGold(rel(trainOwner, stationOwner));
-
-    trainOwner.addGold(goldBonus, station.tile());
-    // Share revenue with the station owner if it's not the current player
-    if (trainOwner !== stationOwner) {
-      stationOwner.addGold(goldBonus, station.tile());
+      stationOwner.addGold(gold, station.tile());
+      mg.stats().trainExternalTrade(trainOwner, gold);
     }
+    trainOwner.addGold(gold, station.tile());
+    mg.stats().trainSelfTrade(trainOwner, gold);
   }
 }
 
@@ -64,8 +43,8 @@ export function createTrainStopHandlers(
   random: PseudoRandom,
 ): Partial<Record<UnitType, TrainStopHandler>> {
   return {
-    [UnitType.City]: new CityStopHandler(),
-    [UnitType.Port]: new PortStopHandler(random),
+    [UnitType.City]: new TradeStationStopHandler(),
+    [UnitType.Port]: new TradeStationStopHandler(),
     [UnitType.Factory]: new FactoryStopHandler(),
   };
 }

tests/core/game/TrainStation.test.ts

@@ -22,6 +22,10 @@ describe("TrainStation", () => {
       }),
       addUpdate: vi.fn(),
       addExecution: vi.fn(),
+      stats: vi.fn().mockReturnValue({
+        trainExternalTrade: vi.fn(),
+        trainSelfTrade: vi.fn(),
+      }),
     } as any;
 
     player = {