[Bug] Fix Beat Up dealing NaN damage with Multi-Lens (#3165)

* Fix Beat Up dealing NaN damage with Multi-Lens

* Simplify allyCount logic

src/data/move.ts

@@ -2867,7 +2867,12 @@ export class BeatUpAttr extends VariablePowerAttr {
    */
   apply(user: Pokemon, target: Pokemon, move: Move, args: any[]): boolean {
     const power = args[0] as Utils.NumberHolder;
-    const allyIndex = user.turnData.hitCount - user.turnData.hitsLeft;
+
+    const party = user.isPlayer() ? user.scene.getParty() : user.scene.getEnemyParty();
+    const allyCount = party.filter(pokemon => {
+      return pokemon.id === user.id || !pokemon.status?.effect;
+    }).length;
+    const allyIndex = (user.turnData.hitCount - user.turnData.hitsLeft) % allyCount;
     power.value = beatUpFunc(user, allyIndex);
     return true;
   }

src/test/moves/beat_up.test.ts

@@ -0,0 +1,106 @@
+import { afterEach, beforeAll, beforeEach, describe, expect, it, vi } from "vitest";
+import Phaser from "phaser";
+import GameManager from "#app/test/utils/gameManager";
+import Overrides from "#app/overrides";
+import { Species } from "#app/enums/species.js";
+import { Moves } from "#app/enums/moves.js";
+import { Abilities } from "#app/enums/abilities.js";
+import { getMovePosition } from "../utils/gameManagerUtils";
+import { MoveEffectPhase } from "#app/phases.js";
+import { StatusEffect } from "#app/enums/status-effect.js";
+
+const TIMEOUT = 20 * 1000; // 20 sec timeout
+
+describe("Moves - Beat Up", () => {
+  let phaserGame: Phaser.Game;
+  let game: GameManager;
+
+  beforeAll(() => {
+    phaserGame = new Phaser.Game({
+      type: Phaser.HEADLESS,
+    });
+  });
+
+  afterEach(() => {
+    game.phaseInterceptor.restoreOg();
+  });
+
+  beforeEach(() => {
+    game = new GameManager(phaserGame);
+    vi.spyOn(Overrides, "BATTLE_TYPE_OVERRIDE", "get").mockReturnValue("single");
+
+    vi.spyOn(Overrides, "OPP_SPECIES_OVERRIDE", "get").mockReturnValue(Species.SNORLAX);
+    vi.spyOn(Overrides, "OPP_LEVEL_OVERRIDE", "get").mockReturnValue(100);
+    vi.spyOn(Overrides, "OPP_MOVESET_OVERRIDE", "get").mockReturnValue(Array(4).fill(Moves.SPLASH));
+    vi.spyOn(Overrides, "OPP_ABILITY_OVERRIDE", "get").mockReturnValue(Abilities.INSOMNIA);
+
+    vi.spyOn(Overrides, "STARTING_LEVEL_OVERRIDE", "get").mockReturnValue(100);
+    vi.spyOn(Overrides, "MOVESET_OVERRIDE", "get").mockReturnValue([Moves.BEAT_UP]);
+  });
+
+  it(
+    "should hit once for each healthy player Pokemon",
+    async () => {
+      await game.startBattle([Species.MAGIKARP, Species.BULBASAUR, Species.CHARMANDER, Species.SQUIRTLE, Species.PIKACHU, Species.EEVEE]);
+
+      const playerPokemon = game.scene.getPlayerPokemon();
+      const enemyPokemon = game.scene.getEnemyPokemon();
+      let enemyStartingHp = enemyPokemon.hp;
+
+      game.doAttack(getMovePosition(game.scene, 0, Moves.BEAT_UP));
+
+      await game.phaseInterceptor.to(MoveEffectPhase);
+
+      expect(playerPokemon.turnData.hitCount).toBe(6);
+      expect(enemyPokemon.hp).toBeLessThan(enemyStartingHp);
+
+      while (playerPokemon.turnData.hitsLeft > 0) {
+        enemyStartingHp = enemyPokemon.hp;
+        await game.phaseInterceptor.to(MoveEffectPhase);
+        expect(enemyPokemon.hp).toBeLessThan(enemyStartingHp);
+      }
+    }, TIMEOUT
+  );
+
+  it(
+    "should not count player Pokemon with status effects towards hit count",
+    async () => {
+      await game.startBattle([Species.MAGIKARP, Species.BULBASAUR, Species.CHARMANDER, Species.SQUIRTLE, Species.PIKACHU, Species.EEVEE]);
+
+      const playerPokemon = game.scene.getPlayerPokemon();
+
+      game.scene.getParty()[1].trySetStatus(StatusEffect.BURN);
+
+      game.doAttack(getMovePosition(game.scene, 0, Moves.BEAT_UP));
+
+      await game.phaseInterceptor.to(MoveEffectPhase);
+
+      expect(playerPokemon.turnData.hitCount).toBe(5);
+    }, TIMEOUT
+  );
+
+  it(
+    "should hit twice for each player Pokemon if the user has Multi-Lens",
+    async () => {
+      vi.spyOn(Overrides, "STARTING_HELD_ITEMS_OVERRIDE", "get").mockReturnValue([{name: "MULTI_LENS", count: 1}]);
+      await game.startBattle([Species.MAGIKARP, Species.BULBASAUR, Species.CHARMANDER, Species.SQUIRTLE, Species.PIKACHU, Species.EEVEE]);
+
+      const playerPokemon = game.scene.getPlayerPokemon();
+      const enemyPokemon = game.scene.getEnemyPokemon();
+      let enemyStartingHp = enemyPokemon.hp;
+
+      game.doAttack(getMovePosition(game.scene, 0, Moves.BEAT_UP));
+
+      await game.phaseInterceptor.to(MoveEffectPhase);
+
+      expect(playerPokemon.turnData.hitCount).toBe(12);
+      expect(enemyPokemon.hp).toBeLessThan(enemyStartingHp);
+
+      while (playerPokemon.turnData.hitsLeft > 0) {
+        enemyStartingHp = enemyPokemon.hp;
+        await game.phaseInterceptor.to(MoveEffectPhase);
+        expect(enemyPokemon.hp).toBeLessThan(enemyStartingHp);
+      }
+    }, TIMEOUT
+  );
+});