[Dev] Add overrides for alternating between single and double battles

src/battle-scene.ts

@@ -1233,12 +1233,19 @@ export default class BattleScene extends SceneBase {
       newDouble = !!double;
     }
 
-    if (Overrides.BATTLE_TYPE_OVERRIDE === "double") {
-      newDouble = true;
-    }
-    /* Override battles into single only if not fighting with trainers */
-    if (newBattleType !== BattleType.TRAINER && Overrides.BATTLE_TYPE_OVERRIDE === "single") {
-      newDouble = false;
+    if (!isNullOrUndefined(Overrides.BATTLE_TYPE_OVERRIDE)) {
+      if (Overrides.BATTLE_TYPE_OVERRIDE === "double"
+        || (Overrides.BATTLE_TYPE_OVERRIDE === "odd-doubles" && (newWaveIndex % 2))
+        || (Overrides.BATTLE_TYPE_OVERRIDE === "even-doubles" && !(newWaveIndex % 2))
+      ) {
+        newDouble = true;
+      } else if (newBattleType !== BattleType.TRAINER) {
+        /**
+         * Override battles into single only if not fighting with trainers.
+         * @see {@link https://github.com/pagefaultgames/pokerogue/issues/1948 | GitHub Issue #1948}
+         */
+        newDouble = false;
+      }
     }
 
     const lastBattle = this.currentBattle;

src/overrides.ts

@@ -47,7 +47,18 @@ class DefaultOverrides {
   /** a specific seed (default: a random string of 24 characters) */
   readonly SEED_OVERRIDE: string = "";
   readonly WEATHER_OVERRIDE: WeatherType = WeatherType.NONE;
-  readonly BATTLE_TYPE_OVERRIDE: "double" | "single" | null = null;
+  /**
+   * If `null`, ignore this override.
+   *
+   * If `"single"`, set every non-trainer battle to be a single battle.
+   *
+   * If `"double"`, set every battle (including trainer battles) to be a double battle.
+   *
+   * If `"even-doubles"`, follow the `"double"` rule on even wave numbers, and follow the `"single"` rule on odd wave numbers.
+   *
+   * If `"odd-doubles"`, follow the `"double"` rule on odd wave numbers, and follow the `"single"` rule on even wave numbers.
+   */
+  readonly BATTLE_TYPE_OVERRIDE: "double" | "single" | "even-doubles" | "odd-doubles" | null = null;
   readonly STARTING_WAVE_OVERRIDE: number = 0;
   readonly STARTING_BIOME_OVERRIDE: Biome = Biome.TOWN;
   readonly ARENA_TINT_OVERRIDE: TimeOfDay | null = null;

src/test/battle/double_battle.test.ts

@@ -1,4 +1,6 @@
 import { Status } from "#app/data/status-effect";
+import { Abilities } from "#enums/abilities";
+import { GameModes, getGameMode } from "#app/game-mode";
 import { BattleEndPhase } from "#app/phases/battle-end-phase";
 import { TurnInitPhase } from "#app/phases/turn-init-phase";
 import { Moves } from "#enums/moves";
@@ -6,9 +8,11 @@ import { Species } from "#enums/species";
 import { StatusEffect } from "#enums/status-effect";
 import GameManager from "#test/utils/gameManager";
 import Phaser from "phaser";
-import { afterEach, beforeAll, beforeEach, describe, expect, it } from "vitest";
+import { afterEach, beforeAll, beforeEach, describe, expect, it, vi } from "vitest";
 
 describe("Double Battles", () => {
+  const DOUBLE_CHANCE = 8; // Normal chance of double battle is 1/8
+
   let phaserGame: Phaser.Game;
   let game: GameManager;
 
@@ -56,4 +60,40 @@ describe("Double Battles", () => {
     await game.phaseInterceptor.to(TurnInitPhase);
     expect(game.scene.getPlayerField().filter(p => !p.isFainted())).toHaveLength(2);
   }, 20000);
+
+  it("randomly chooses between single and double battles if there is no battle type override", async () => {
+    let rngSweepProgress = 0; // Will simulate RNG rolls by slowly increasing from 0 to 1
+    let doubleCount = 0;
+    let singleCount = 0;
+
+    vi.spyOn(Phaser.Math.RND, "realInRange").mockImplementation((min: number, max: number) => {
+      return rngSweepProgress * (max - min) + min;
+    });
+
+    game.override.enemyMoveset(Moves.SPLASH)
+      .moveset(Moves.SPLASH)
+      .enemyAbility(Abilities.BALL_FETCH)
+      .ability(Abilities.BALL_FETCH);
+
+    // Play through endless, waves 1 to 9, counting number of double battles from waves 2 to 9
+    await game.classicMode.startBattle([ Species.BULBASAUR ]);
+    game.scene.gameMode = getGameMode(GameModes.ENDLESS);
+
+    for (let i = 0; i < DOUBLE_CHANCE; i++) {
+      rngSweepProgress = (i + 0.5) / DOUBLE_CHANCE;
+
+      game.move.select(Moves.SPLASH);
+      await game.doKillOpponents();
+      await game.toNextWave();
+
+      if (game.scene.getEnemyParty().length === 1) {
+        singleCount++;
+      } else if (game.scene.getEnemyParty().length === 2) {
+        doubleCount++;
+      }
+    }
+
+    expect(doubleCount).toBe(1);
+    expect(singleCount).toBe(DOUBLE_CHANCE - 1);
+  });
 });

src/test/utils/helpers/overridesHelper.ts

@@ -242,7 +242,7 @@ export class OverridesHelper extends GameManagerHelper {
    * @param battleType battle type to set
    * @returns `this`
    */
-  public battleType(battleType: "single" | "double" | null): this {
+  public battleType(battleType: "single" | "double" | "even-doubles" | "odd-doubles" | null): this {
     vi.spyOn(Overrides, "BATTLE_TYPE_OVERRIDE", "get").mockReturnValue(battleType);
     this.log(`Battle type set to ${battleType} only!`);
     return this;