increase mirv price with total number of merged launched (#2621)

## Description:

To prevent MAD stalemates, have the price of MIRVs increase after each
launch. This will encourage players to launch a MIRV once they have
enough money for it. Also reduce the price of the first MIRV to 25
million to reduce snowballing, each subsequent MIRV cost an extra 15
million:

1. 25 million
2. 40 million
3. 60 million
4. etc



## 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:

evan

src/core/game/Game.ts

@@ -175,7 +175,7 @@ export enum GameMapSize {
 }
 
 export interface UnitInfo {
-  cost: (player: Player) => Gold;
+  cost: (game: Game, player: Player) => Gold;
   // Determines if its owner changes when its tile is conquered.
   territoryBound: boolean;
   maxHealth?: number;
@@ -753,7 +753,6 @@ export interface Game extends GameMap {
   nations(): Nation[];
 
   numTilesWithFallout(): number;
-  // Optional as it's not initialized before the end of spawn phase
   stats(): Stats;
 
   addUpdate(update: GameUpdate): void;

src/core/game/PlayerImpl.ts

@@ -864,7 +864,7 @@ export class PlayerImpl implements Player {
       );
     }
 
-    const cost = this.mg.unitInfo(type).cost(this);
+    const cost = this.mg.unitInfo(type).cost(this.mg, this);
     const b = new UnitImpl(
       type,
       this.mg,
@@ -911,7 +911,9 @@ export class PlayerImpl implements Player {
     if (this.mg.config().isUnitDisabled(unit.type())) {
       return false;
     }
-    if (this._gold < this.mg.config().unitInfo(unit.type()).cost(this)) {
+    if (
+      this._gold < this.mg.config().unitInfo(unit.type()).cost(this.mg, this)
+    ) {
       return false;
     }
     if (unit.owner() !== this) {
@@ -921,7 +923,7 @@ export class PlayerImpl implements Player {
   }
 
   upgradeUnit(unit: Unit) {
-    const cost = this.mg.unitInfo(unit.type()).cost(this);
+    const cost = this.mg.unitInfo(unit.type()).cost(this.mg, this);
     this.removeGold(cost);
     unit.increaseLevel();
     this.recordUnitConstructed(unit.type());
@@ -944,7 +946,7 @@ export class PlayerImpl implements Player {
             ? false
             : this.canBuild(u, tile, validTiles),
         canUpgrade: canUpgrade,
-        cost: this.mg.config().unitInfo(u).cost(this),
+        cost: this.mg.config().unitInfo(u).cost(this.mg, this),
       } as BuildableUnit;
     });
   }
@@ -958,7 +960,7 @@ export class PlayerImpl implements Player {
       return false;
     }
 
-    const cost = this.mg.unitInfo(unitType).cost(this);
+    const cost = this.mg.unitInfo(unitType).cost(this.mg, this);
     if (!this.isAlive() || this.gold() < cost) {
       return false;
     }

src/core/game/Stats.ts

@@ -6,6 +6,8 @@ export interface Stats {
   getPlayerStats(player: Player): PlayerStats | null;
   stats(): AllPlayersStats;
 
+  numMirvsLaunched(): bigint;
+
   // Player attacks target
   attack(
     player: Player,

src/core/game/StatsImpl.ts

@@ -26,7 +26,7 @@ import {
   unitTypeToBombUnit,
   unitTypeToOtherUnit,
 } from "../StatsSchemas";
-import { Player, TerraNullius } from "./Game";
+import { Player, TerraNullius, UnitType } from "./Game";
 import { Stats } from "./Stats";
 
 type BigIntLike = bigint | number;
@@ -42,6 +42,12 @@ function _bigint(value: BigIntLike): bigint {
 export class StatsImpl implements Stats {
   private readonly data: AllPlayersStats = {};
 
+  private _numMirvLaunched: bigint = 0n;
+
+  numMirvsLaunched(): bigint {
+    return this._numMirvLaunched;
+  }
+
   getPlayerStats(player: Player): PlayerStats {
     const clientID = player.clientID();
     if (clientID === null) return undefined;
@@ -217,6 +223,9 @@ export class StatsImpl implements Stats {
     target: Player | TerraNullius,
     type: NukeType,
   ): void {
+    if (type === UnitType.MIRV) {
+      this._numMirvLaunched++;
+    }
     this._addBomb(player, type, BOMB_INDEX_LAUNCH, 1);
   }