implementing friend guard ability

src/data/ability.ts

@@ -330,6 +330,20 @@ export class ReceivedMoveDamageMultiplierAbAttr extends PreDefendAbAttr {
   }
 }
 
+export class FriendGuardAbAttr extends PreDefendAbAttr {
+  private damageMultiplier: number;
+
+  constructor(damageMultiplier: number) {
+    super();
+    this.damageMultiplier = damageMultiplier;
+  }
+
+  applyPreDefend(pokemon: Pokemon, passive: boolean, simulated: boolean, attacker: Pokemon, move: Move, cancelled: Utils.BooleanHolder, args: any[]): boolean {
+    (args[0] as Utils.NumberHolder).value = Utils.toDmgValue((args[0] as Utils.NumberHolder).value * this.damageMultiplier);
+    return true;
+  }
+}
+
 export class ReceivedTypeDamageMultiplierAbAttr extends ReceivedMoveDamageMultiplierAbAttr {
   constructor(moveType: Type, damageMultiplier: number) {
     super((target, user, move) => user.getMoveType(move) === moveType, damageMultiplier);
@@ -5260,8 +5274,8 @@ export function initAbilities() {
     new Ability(Abilities.HEALER, 5)
       .conditionalAttr(pokemon => pokemon.getAlly() && Utils.randSeedInt(10) < 3, PostTurnResetStatusAbAttr, true),
     new Ability(Abilities.FRIEND_GUARD, 5)
-      .ignorable()
+      .attr(FriendGuardAbAttr, .25)
-      .unimplemented(),
+      .ignorable(),
     new Ability(Abilities.WEAK_ARMOR, 5)
       .attr(PostDefendStatStageChangeAbAttr, (target, user, move) => move.category === MoveCategory.PHYSICAL, Stat.DEF, -1)
       .attr(PostDefendStatStageChangeAbAttr, (target, user, move) => move.category === MoveCategory.PHYSICAL, Stat.SPD, 2),

src/field/pokemon.ts

@@ -22,7 +22,7 @@ import { reverseCompatibleTms, tmSpecies, tmPoolTiers } from "#app/data/balance/
 import { BattlerTag, BattlerTagLapseType, EncoreTag, GroundedTag, HighestStatBoostTag, SubstituteTag, TypeImmuneTag, getBattlerTag, SemiInvulnerableTag, TypeBoostTag, MoveRestrictionBattlerTag, ExposedTag, DragonCheerTag, CritBoostTag, TrappedTag, TarShotTag, AutotomizedTag, PowerTrickTag } from "../data/battler-tags";
 import { WeatherType } from "#app/data/weather";
 import { ArenaTagSide, NoCritTag, WeakenMoveScreenTag } from "#app/data/arena-tag";
-import { Ability, AbAttr, StatMultiplierAbAttr, BlockCritAbAttr, BonusCritAbAttr, BypassBurnDamageReductionAbAttr, FieldPriorityMoveImmunityAbAttr, IgnoreOpponentStatStagesAbAttr, MoveImmunityAbAttr, PreDefendFullHpEndureAbAttr, ReceivedMoveDamageMultiplierAbAttr, ReduceStatusEffectDurationAbAttr, StabBoostAbAttr, StatusEffectImmunityAbAttr, TypeImmunityAbAttr, WeightMultiplierAbAttr, allAbilities, applyAbAttrs, applyStatMultiplierAbAttrs, applyPreApplyBattlerTagAbAttrs, applyPreAttackAbAttrs, applyPreDefendAbAttrs, applyPreSetStatusAbAttrs, UnsuppressableAbilityAbAttr, SuppressFieldAbilitiesAbAttr, NoFusionAbilityAbAttr, MultCritAbAttr, IgnoreTypeImmunityAbAttr, DamageBoostAbAttr, IgnoreTypeStatusEffectImmunityAbAttr, ConditionalCritAbAttr, applyFieldStatMultiplierAbAttrs, FieldMultiplyStatAbAttr, AddSecondStrikeAbAttr, UserFieldStatusEffectImmunityAbAttr, UserFieldBattlerTagImmunityAbAttr, BattlerTagImmunityAbAttr, MoveTypeChangeAbAttr, FullHpResistTypeAbAttr, applyCheckTrappedAbAttrs, CheckTrappedAbAttr, PostSetStatusAbAttr, applyPostSetStatusAbAttrs } from "#app/data/ability";
+import { Ability, AbAttr, StatMultiplierAbAttr, BlockCritAbAttr, BonusCritAbAttr, BypassBurnDamageReductionAbAttr, FieldPriorityMoveImmunityAbAttr, IgnoreOpponentStatStagesAbAttr, MoveImmunityAbAttr, PreDefendFullHpEndureAbAttr, ReceivedMoveDamageMultiplierAbAttr, ReduceStatusEffectDurationAbAttr, StabBoostAbAttr, StatusEffectImmunityAbAttr, TypeImmunityAbAttr, WeightMultiplierAbAttr, allAbilities, applyAbAttrs, applyStatMultiplierAbAttrs, applyPreApplyBattlerTagAbAttrs, applyPreAttackAbAttrs, applyPreDefendAbAttrs, applyPreSetStatusAbAttrs, UnsuppressableAbilityAbAttr, SuppressFieldAbilitiesAbAttr, NoFusionAbilityAbAttr, MultCritAbAttr, IgnoreTypeImmunityAbAttr, DamageBoostAbAttr, IgnoreTypeStatusEffectImmunityAbAttr, ConditionalCritAbAttr, applyFieldStatMultiplierAbAttrs, FieldMultiplyStatAbAttr, AddSecondStrikeAbAttr, UserFieldStatusEffectImmunityAbAttr, UserFieldBattlerTagImmunityAbAttr, BattlerTagImmunityAbAttr, MoveTypeChangeAbAttr, FullHpResistTypeAbAttr, applyCheckTrappedAbAttrs, CheckTrappedAbAttr, PostSetStatusAbAttr, applyPostSetStatusAbAttrs, FriendGuardAbAttr } from "#app/data/ability";
 import PokemonData from "#app/system/pokemon-data";
 import { BattlerIndex } from "#app/battle";
 import { Mode } from "#app/ui/ui";
@@ -2659,9 +2659,15 @@ export default abstract class Pokemon extends Phaser.GameObjects.Container {
       this.scene.applyModifiers(EnemyDamageReducerModifier, false, damage);
     }
 
+
     /** Apply this Pokemon's post-calc defensive modifiers (e.g. Fur Coat) */
     if (!ignoreAbility) {
       applyPreDefendAbAttrs(ReceivedMoveDamageMultiplierAbAttr, this, source, move, cancelled, simulated, damage);
+
+      /** Additionally apply friend guard damage reduction if ally has it. */
+      if (this.scene.currentBattle.double && this.getAlly().isActive()) {
+        applyPreDefendAbAttrs(FriendGuardAbAttr, this.getAlly(), source, move, cancelled, simulated, damage);
+      }
     }
 
     // This attribute may modify damage arbitrarily, so be careful about changing its order of application.

src/test/abilities/friend_guard.test.ts

@@ -0,0 +1,58 @@
+import { Moves } from "#enums/moves";
+import { Species } from "#enums/species";
+import { Abilities } from "#enums/abilities";
+import GameManager from "#test/utils/gameManager";
+import Phaser from "phaser";
+import { afterEach, beforeAll, beforeEach, describe, expect, it } from "vitest";
+import { BattlerIndex } from "#app/battle";
+import { PlayerPokemon } from "#app/field/pokemon";
+
+describe("Moves - Friend Guard", () => {
+  let phaserGame: Phaser.Game;
+  let game: GameManager;
+  let hp1: number;
+  let hp2: number;
+  beforeAll(() => {
+    phaserGame = new Phaser.Game({
+      type: Phaser.HEADLESS,
+    });
+  });
+
+  afterEach(() => {
+    game.phaseInterceptor.restoreOg();
+  });
+
+  beforeEach(() => {
+    game = new GameManager(phaserGame);
+    game.override
+      .battleType("double")
+      .enemyAbility(Abilities.BALL_FETCH)
+      .enemyMoveset([ Moves.TACKLE, Moves.SPLASH ])
+      .enemySpecies(Species.SHUCKLE)
+      .moveset([ Moves.SPLASH ]);
+  });
+
+  it("first part of test, getting hp without friend guard", async () => {
+    await game.classicMode.startBattle([ Species.BULBASAUR, Species.BULBASAUR ]);
+    const party = game.scene.getParty()! as PlayerPokemon[];
+    game.move.select(Moves.SPLASH);
+    game.move.select(Moves.SPLASH, 1);
+    await game.forceEnemyMove(Moves.TACKLE, BattlerIndex.PLAYER);
+    await game.forceEnemyMove(Moves.SPLASH);
+    await game.toNextTurn();
+    hp1 = party[0].hp;
+  });
+
+  it("second part of test, getting hp with friend guard and comparing", async () => {
+    game.override.ability(Abilities.FRIEND_GUARD);
+    await game.classicMode.startBattle([ Species.BULBASAUR, Species.BULBASAUR ]);
+    const party = game.scene.getParty()! as PlayerPokemon[];
+    game.move.select(Moves.SPLASH);
+    game.move.select(Moves.SPLASH, 1);
+    await game.forceEnemyMove(Moves.TACKLE, BattlerIndex.PLAYER);
+    await game.forceEnemyMove(Moves.SPLASH);
+    await game.toNextTurn();
+    hp2 = party[0].hp;
+    expect(hp2).toBeGreaterThan(hp1);
+  });
+});