[Ability] Implement Tera Shell (#3856)

* Implement Tera Shell

* Apply suggestions from code review

Co-authored-by: NightKev <34855794+DayKev@users.noreply.github.com>

* Update src/data/ability.ts

Co-authored-by: Adrian T. <68144167+torranx@users.noreply.github.com>

* Add comments and fixed damage condition to `applyPreDefend`

* Fix speed tie breaking things in tera shell test

* Change deprecated `startBattle` calls

---------

Co-authored-by: NightKev <34855794+DayKev@users.noreply.github.com>
Co-authored-by: Adrian T. <68144167+torranx@users.noreply.github.com>

src/data/ability.ts

@@ -8,7 +8,7 @@ import { Weather, WeatherType } from "./weather";
 import { BattlerTag, GroundedTag, GulpMissileTag, SemiInvulnerableTag } from "./battler-tags";
 import { StatusEffect, getNonVolatileStatusEffects, getStatusEffectDescriptor, getStatusEffectHealText } from "./status-effect";
 import { Gender } from "./gender";
-import Move, { AttackMove, MoveCategory, MoveFlags, MoveTarget, FlinchAttr, OneHitKOAttr, HitHealAttr, allMoves, StatusMove, SelfStatusMove, VariablePowerAttr, applyMoveAttrs, IncrementMovePriorityAttr, VariableMoveTypeAttr, RandomMovesetMoveAttr, RandomMoveAttr, NaturePowerAttr, CopyMoveAttr, MoveAttr, MultiHitAttr, ChargeAttr, SacrificialAttr, SacrificialAttrOnHit, NeutralDamageAgainstFlyingTypeMultiplierAttr } from "./move";
+import Move, { AttackMove, MoveCategory, MoveFlags, MoveTarget, FlinchAttr, OneHitKOAttr, HitHealAttr, allMoves, StatusMove, SelfStatusMove, VariablePowerAttr, applyMoveAttrs, IncrementMovePriorityAttr, VariableMoveTypeAttr, RandomMovesetMoveAttr, RandomMoveAttr, NaturePowerAttr, CopyMoveAttr, MoveAttr, MultiHitAttr, ChargeAttr, SacrificialAttr, SacrificialAttrOnHit, NeutralDamageAgainstFlyingTypeMultiplierAttr, FixedDamageAttr } from "./move";
 import { ArenaTagSide, ArenaTrapTag } from "./arena-tag";
 import { Stat, getStatName } from "./pokemon-stat";
 import { BerryModifier, PokemonHeldItemModifier } from "../modifier/modifier";
@@ -475,6 +475,47 @@ export class NonSuperEffectiveImmunityAbAttr extends TypeImmunityAbAttr {
   }
 }
 
+/**
+ * Attribute implementing the effects of {@link https://bulbapedia.bulbagarden.net/wiki/Tera_Shell_(Ability) | Tera Shell}
+ * When the source is at full HP, incoming attacks will have a maximum 0.5x type effectiveness multiplier.
+ * @extends PreDefendAbAttr
+ */
+export class FullHpResistTypeAbAttr extends PreDefendAbAttr {
+  /**
+   * Reduces a type multiplier to 0.5 if the source is at full HP.
+   * @param pokemon {@linkcode Pokemon} the Pokemon with this ability
+   * @param passive n/a
+   * @param simulated n/a (this doesn't change game state)
+   * @param attacker n/a
+   * @param move {@linkcode Move} the move being used on the source
+   * @param cancelled n/a
+   * @param args `[0]` a container for the move's current type effectiveness multiplier
+   * @returns `true` if the move's effectiveness is reduced; `false` otherwise
+   */
+  applyPreDefend(pokemon: Pokemon, passive: boolean, simulated: boolean, attacker: Pokemon, move: Move | null, cancelled: Utils.BooleanHolder | null, args: any[]): boolean | Promise<boolean> {
+    const typeMultiplier = args[0];
+    if (!(typeMultiplier && typeMultiplier instanceof Utils.NumberHolder)) {
+      return false;
+    }
+
+    if (move && move.hasAttr(FixedDamageAttr)) {
+      return false;
+    }
+
+    if (pokemon.isFullHp() && typeMultiplier.value > 0.5) {
+      typeMultiplier.value = 0.5;
+      return true;
+    }
+    return false;
+  }
+
+  getTriggerMessage(pokemon: Pokemon, abilityName: string, ...args: any[]): string {
+    return i18next.t("abilityTriggers:fullHpResistType", {
+      pokemonNameWithAffix: getPokemonNameWithAffix(pokemon)
+    });
+  }
+}
+
 export class PostDefendAbAttr extends AbAttr {
   applyPostDefend(pokemon: Pokemon, passive: boolean, simulated: boolean, attacker: Pokemon, move: Move, hitResult: HitResult | null, args: any[]): boolean | Promise<boolean> {
     return false;
@@ -5761,10 +5802,10 @@ export function initAbilities() {
       .attr(NoTransformAbilityAbAttr)
       .attr(NoFusionAbilityAbAttr),
     new Ability(Abilities.TERA_SHELL, 9)
+      .attr(FullHpResistTypeAbAttr)
       .attr(UncopiableAbilityAbAttr)
       .attr(UnswappableAbilityAbAttr)
-      .ignorable()
-      .unimplemented(),
+      .ignorable(),
     new Ability(Abilities.TERAFORM_ZERO, 9)
       .attr(UncopiableAbilityAbAttr)
       .attr(UnswappableAbilityAbAttr)

src/field/pokemon.ts

@@ -22,7 +22,7 @@ import { BattlerTag, BattlerTagLapseType, EncoreTag, GroundedTag, HighestStatBoo
 import { WeatherType } from "../data/weather";
 import { TempBattleStat } from "../data/temp-battle-stat";
 import { ArenaTagSide, NoCritTag, WeakenMoveScreenTag } from "../data/arena-tag";
-import { Ability, AbAttr, BattleStatMultiplierAbAttr, BlockCritAbAttr, BonusCritAbAttr, BypassBurnDamageReductionAbAttr, FieldPriorityMoveImmunityAbAttr, IgnoreOpponentStatChangesAbAttr, MoveImmunityAbAttr, PreDefendFullHpEndureAbAttr, ReceivedMoveDamageMultiplierAbAttr, ReduceStatusEffectDurationAbAttr, StabBoostAbAttr, StatusEffectImmunityAbAttr, TypeImmunityAbAttr, WeightMultiplierAbAttr, allAbilities, applyAbAttrs, applyBattleStatMultiplierAbAttrs, applyPreApplyBattlerTagAbAttrs, applyPreAttackAbAttrs, applyPreDefendAbAttrs, applyPreSetStatusAbAttrs, UnsuppressableAbilityAbAttr, SuppressFieldAbilitiesAbAttr, NoFusionAbilityAbAttr, MultCritAbAttr, IgnoreTypeImmunityAbAttr, DamageBoostAbAttr, IgnoreTypeStatusEffectImmunityAbAttr, ConditionalCritAbAttr, applyFieldBattleStatMultiplierAbAttrs, FieldMultiplyBattleStatAbAttr, AddSecondStrikeAbAttr, IgnoreOpponentEvasionAbAttr, UserFieldStatusEffectImmunityAbAttr, UserFieldBattlerTagImmunityAbAttr, BattlerTagImmunityAbAttr, MoveTypeChangeAbAttr } from "../data/ability";
+import { Ability, AbAttr, BattleStatMultiplierAbAttr, BlockCritAbAttr, BonusCritAbAttr, BypassBurnDamageReductionAbAttr, FieldPriorityMoveImmunityAbAttr, IgnoreOpponentStatChangesAbAttr, MoveImmunityAbAttr, PreDefendFullHpEndureAbAttr, ReceivedMoveDamageMultiplierAbAttr, ReduceStatusEffectDurationAbAttr, StabBoostAbAttr, StatusEffectImmunityAbAttr, TypeImmunityAbAttr, WeightMultiplierAbAttr, allAbilities, applyAbAttrs, applyBattleStatMultiplierAbAttrs, applyPreApplyBattlerTagAbAttrs, applyPreAttackAbAttrs, applyPreDefendAbAttrs, applyPreSetStatusAbAttrs, UnsuppressableAbilityAbAttr, SuppressFieldAbilitiesAbAttr, NoFusionAbilityAbAttr, MultCritAbAttr, IgnoreTypeImmunityAbAttr, DamageBoostAbAttr, IgnoreTypeStatusEffectImmunityAbAttr, ConditionalCritAbAttr, applyFieldBattleStatMultiplierAbAttrs, FieldMultiplyBattleStatAbAttr, AddSecondStrikeAbAttr, IgnoreOpponentEvasionAbAttr, UserFieldStatusEffectImmunityAbAttr, UserFieldBattlerTagImmunityAbAttr, BattlerTagImmunityAbAttr, MoveTypeChangeAbAttr, FullHpResistTypeAbAttr } from "../data/ability";
 import PokemonData from "../system/pokemon-data";
 import { BattlerIndex } from "../battle";
 import { Mode } from "../ui/ui";
@@ -1276,6 +1276,11 @@ export default abstract class Pokemon extends Phaser.GameObjects.Container {
       }
     }
 
+    // Apply Tera Shell's effect to attacks after all immunities are accounted for
+    if (!ignoreAbility && move.category !== MoveCategory.STATUS) {
+      applyPreDefendAbAttrs(FullHpResistTypeAbAttr, this, source, move, cancelledHolder, simulated, typeMultiplier);
+    }
+
     return (!cancelledHolder.value ? typeMultiplier.value : 0) as TypeDamageMultiplier;
   }
 

src/locales/en/ability-trigger.json

@@ -12,6 +12,7 @@
   "blockItemTheft": "{{pokemonNameWithAffix}}'s {{abilityName}}\nprevents item theft!",
   "typeImmunityHeal": "{{pokemonNameWithAffix}}'s {{abilityName}}\nrestored its HP a little!",
   "nonSuperEffectiveImmunity": "{{pokemonNameWithAffix}} avoided damage\nwith {{abilityName}}!",
+  "fullHpResistType": "{{pokemonNameWithAffix}} made its shell gleam!\nIt's distorting type matchups!",
   "moveImmunity": "It doesn't affect {{pokemonNameWithAffix}}!",
   "reverseDrain": "{{pokemonNameWithAffix}} sucked up the liquid ooze!",
   "postDefendTypeChange": "{{pokemonNameWithAffix}}'s {{abilityName}}\nmade it the {{typeName}} type!",

src/test/abilities/tera_shell.test.ts

@@ -0,0 +1,111 @@
+import { Abilities } from "#app/enums/abilities";
+import { Moves } from "#app/enums/moves";
+import { Species } from "#app/enums/species";
+import { HitResult } from "#app/field/pokemon.js";
+import GameManager from "#test/utils/gameManager";
+import Phaser from "phaser";
+import { afterEach, beforeAll, beforeEach, describe, expect, it, vi } from "vitest";
+
+const TIMEOUT = 10 * 1000; // 10 second timeout
+
+describe("Abilities - Tera Shell", () => {
+  let phaserGame: Phaser.Game;
+  let game: GameManager;
+
+  beforeAll(() => {
+    phaserGame = new Phaser.Game({
+      type: Phaser.HEADLESS,
+    });
+  });
+
+  afterEach(() => {
+    game.phaseInterceptor.restoreOg();
+  });
+
+  beforeEach(() => {
+    game = new GameManager(phaserGame);
+    game.override
+      .battleType("single")
+      .ability(Abilities.TERA_SHELL)
+      .moveset([Moves.SPLASH])
+      .enemySpecies(Species.SNORLAX)
+      .enemyAbility(Abilities.INSOMNIA)
+      .enemyMoveset(Array(4).fill(Moves.MACH_PUNCH))
+      .startingLevel(100)
+      .enemyLevel(100);
+  });
+
+  it(
+    "should change the effectiveness of non-resisted attacks when the source is at full HP",
+    async () => {
+      await game.classicMode.startBattle([Species.SNORLAX]);
+
+      const playerPokemon = game.scene.getPlayerPokemon()!;
+      vi.spyOn(playerPokemon, "getMoveEffectiveness");
+
+      game.move.select(Moves.SPLASH);
+
+      await game.phaseInterceptor.to("MoveEndPhase");
+      expect(playerPokemon.getMoveEffectiveness).toHaveLastReturnedWith(0.5);
+
+      await game.toNextTurn();
+
+      game.move.select(Moves.SPLASH);
+
+      await game.phaseInterceptor.to("MoveEndPhase");
+      expect(playerPokemon.getMoveEffectiveness).toHaveLastReturnedWith(2);
+    }, TIMEOUT
+  );
+
+  it(
+    "should not override type immunities",
+    async () => {
+      game.override.enemyMoveset(Array(4).fill(Moves.SHADOW_SNEAK));
+
+      await game.classicMode.startBattle([Species.SNORLAX]);
+
+      const playerPokemon = game.scene.getPlayerPokemon()!;
+      vi.spyOn(playerPokemon, "getMoveEffectiveness");
+
+      game.move.select(Moves.SPLASH);
+
+      await game.phaseInterceptor.to("MoveEndPhase");
+      expect(playerPokemon.getMoveEffectiveness).toHaveLastReturnedWith(0);
+    }, TIMEOUT
+  );
+
+  it(
+    "should not override type multipliers less than 0.5x",
+    async () => {
+      game.override.enemyMoveset(Array(4).fill(Moves.QUICK_ATTACK));
+
+      await game.classicMode.startBattle([Species.AGGRON]);
+
+      const playerPokemon = game.scene.getPlayerPokemon()!;
+      vi.spyOn(playerPokemon, "getMoveEffectiveness");
+
+      game.move.select(Moves.SPLASH);
+
+      await game.phaseInterceptor.to("MoveEndPhase");
+      expect(playerPokemon.getMoveEffectiveness).toHaveLastReturnedWith(0.25);
+    }, TIMEOUT
+  );
+
+  it(
+    "should not affect the effectiveness of fixed-damage moves",
+    async () => {
+      game.override.enemyMoveset(Array(4).fill(Moves.DRAGON_RAGE));
+
+      await game.classicMode.startBattle([Species.CHARIZARD]);
+
+      const playerPokemon = game.scene.getPlayerPokemon()!;
+      vi.spyOn(playerPokemon, "apply");
+
+      game.move.select(Moves.SPLASH);
+
+      await game.phaseInterceptor.to("BerryPhase", false);
+      expect(playerPokemon.apply).toHaveLastReturnedWith(HitResult.EFFECTIVE);
+      expect(playerPokemon.hp).toBe(playerPokemon.getMaxHp() - 40);
+    }, TIMEOUT
+  );
+});