Implement Destiny Bond move (#1104)

* Use getBattleStat instead of getStat in BattleStatRatioPowerAttr

* Change unnecessary let into const

* Refactor BattleStatRatioPowerAttr into two distinct classes

* Add TSDoc for the new classes

* Implementation of Destiny Bond

* Add TSDocs

* Make the move fail in boss battles

* Fix boss immunity and ally fainting

* Update docs

* Add doc of return value of tag lapse

* Fix ESLint

src/data/battler-tags.ts

@@ -254,6 +254,51 @@ export class ConfusedTag extends BattlerTag {
   }
 }
 
+/**
+ * Tag applied to the {@linkcode Move.DESTINY_BOND} user.
+ * @extends BattlerTag
+ * @see {@linkcode apply}
+ */
+export class DestinyBondTag extends BattlerTag {
+  constructor(sourceMove: Moves, sourceId: integer) {
+    super(BattlerTagType.DESTINY_BOND, BattlerTagLapseType.PRE_MOVE, 1, sourceMove, sourceId);
+  }
+
+  /**
+   * Lapses either before the user's move and does nothing
+   * or after receiving fatal damage. When the damage is fatal,
+   * the attacking Pokemon is taken down as well, unless it's a boss.
+   *
+   * @param {Pokemon} pokemon Pokemon that is attacking the Destiny Bond user.
+   * @param {BattlerTagLapseType} lapseType CUSTOM or PRE_MOVE
+   * @returns false if the tag source fainted or one turn has passed since the application
+   */
+  lapse(pokemon: Pokemon, lapseType: BattlerTagLapseType): boolean {
+    if (lapseType !== BattlerTagLapseType.CUSTOM) {
+      return super.lapse(pokemon, lapseType);
+    }
+    const source = pokemon.scene.getPokemonById(this.sourceId);
+    if (!source.isFainted()) {
+      return true;
+    }
+
+    if (source.getAlly() === pokemon) {
+      return false;
+    }
+
+    const targetMessage = getPokemonMessage(pokemon, "");
+
+    if (pokemon.isBossImmune()) {
+      pokemon.scene.queueMessage(`${targetMessage} is unaffected\nby the effects of Destiny Bond.`);
+      return false;
+    }
+
+    pokemon.scene.queueMessage(`${getPokemonMessage(source, ` took\n${targetMessage} down with it!`)}`);
+    pokemon.damageAndUpdate(pokemon.hp, HitResult.ONE_HIT_KO, false, false, true);
+    return false;
+  }
+}
+
 export class InfatuatedTag extends BattlerTag {
   constructor(sourceMove: integer, sourceId: integer) {
     super(BattlerTagType.INFATUATED, BattlerTagLapseType.MOVE, 1, sourceMove, sourceId);
@@ -1416,6 +1461,8 @@ export function getBattlerTag(tagType: BattlerTagType, turnCount: integer, sourc
     return new MagnetRisenTag(tagType, sourceMove);
   case BattlerTagType.MINIMIZED:
     return new MinimizeTag();
+  case BattlerTagType.DESTINY_BOND:
+    return new DestinyBondTag(sourceMove, sourceId);
   case BattlerTagType.NONE:
   default:
     return new BattlerTag(tagType, BattlerTagLapseType.CUSTOM, turnCount, sourceMove, sourceId);

src/data/enums/battler-tag-type.ts

@@ -56,5 +56,6 @@ export enum BattlerTagType {
   CHARGED = "CHARGED",
   GROUNDED = "GROUNDED",
   MAGNET_RISEN = "MAGNET_RISEN",
-  MINIMIZED = "MINIMIZED"
+  MINIMIZED = "MINIMIZED",
+  DESTINY_BOND = "DESTINY_BOND"
 }

src/data/move.ts

@@ -4704,6 +4704,31 @@ export class MoneyAttr extends MoveEffectAttr {
   }
 }
 
+/**
+ * Applies {@linkcode BattlerTagType.DESTINY_BOND} to the user.
+ *
+ * @extends MoveEffectAttr
+ */
+export class DestinyBondAttr extends MoveEffectAttr {
+  constructor() {
+    super(true, MoveEffectTrigger.PRE_APPLY);
+  }
+
+  /**
+   * Applies {@linkcode BattlerTagType.DESTINY_BOND} to the user.
+   * @param user {@linkcode Pokemon} that is having the tag applied to.
+   * @param target {@linkcode Pokemon} N/A
+   * @param move {@linkcode Move} {@linkcode Move.DESTINY_BOND}
+   * @param {any[]} args N/A
+   * @returns true
+   */
+  apply(user: Pokemon, target: Pokemon, move: Move, args: any[]): boolean {
+    user.scene.queueMessage(`${getPokemonMessage(user, " is trying\nto take its foe down with it!")}`);
+    user.addTag(BattlerTagType.DESTINY_BOND, undefined, move.id, user.id);
+    return true;
+  }
+}
+
 export class LastResortAttr extends MoveAttr {
   getCondition(): MoveConditionFunc {
     return (user: Pokemon, target: Pokemon, move: Move) => {
@@ -5405,8 +5430,7 @@ export function initMoves() {
       .unimplemented(),
     new SelfStatusMove(Moves.DESTINY_BOND, Type.GHOST, -1, 5, -1, 0, 2)
       .ignoresProtect()
-      .condition(failOnBossCondition)
-      .unimplemented(),
+      .attr(DestinyBondAttr),
     new StatusMove(Moves.PERISH_SONG, Type.NORMAL, -1, 5, -1, 0, 2)
       .attr(FaintCountdownAttr)
       .ignoresProtect()

src/field/pokemon.ts

@@ -1790,6 +1790,9 @@ export default abstract class Pokemon extends Phaser.GameObjects.Container {
 
         console.log("damage", damage.value, move.name, power.value, sourceAtk, targetDef);
 
+        // In case of fatal damage, this tag would have gotten cleared before we could lapse it.
+        const destinyTag = this.getTag(BattlerTagType.DESTINY_BOND);
+
         const oneHitKo = result === HitResult.ONE_HIT_KO;
         if (damage.value) {
           if (this.getHpRatio() === 1) {
@@ -1850,6 +1853,9 @@ export default abstract class Pokemon extends Phaser.GameObjects.Container {
 
         if (damage) {
           this.scene.clearPhaseQueueSplice();
+
+          const attacker = this.scene.getPokemonById(source.id);
+          destinyTag?.lapse(attacker, BattlerTagLapseType.CUSTOM);
         }
       }
       break;