Heart Swap implementation. (#712)

* Heart Swap implementation.

 Simply switches the values in 3 arrays.

* Fixed missing space

* Removed some lines.

Removed a for loop.

* Removed an unneccesary line

* TSDoc commentation added

* Changed message method to be more descriptive

* Adjusted message line to be consistent with Pokemon Showdown

* Adjusted priorBoostArray to priorBoost integer

Only one values is relevant at a time, so the array was pointless, woops.

src/data/move.ts

@@ -1775,6 +1775,37 @@ export class ResetStatsAttr extends MoveEffectAttr {
   }
 }
 
+/**
+ * Attribute used for moves which swap the user and the target's stat changes.
+ */
+export class SwapStatsAttr extends MoveEffectAttr
+{
+    /**
+   * Swaps the user and the target's stat changes.
+   * @param user Pokemon that used the move
+   * @param target The target of the move
+   * @param move Move with this attribute
+   * @param args N/A
+   * @returns true if the function succeeds
+   */
+    apply(user: Pokemon, target: Pokemon, move: Move, args: any []): boolean
+    {
+        if (!super.apply(user, target, move, args))
+            return false; //Exits if the move can't apply
+        let priorBoost : integer; //For storing a stat boost
+        for (let s = 0; s < target.summonData.battleStats.length; s++)
+          {
+            priorBoost = user.summonData.battleStats[s]; //Store user stat boost
+            user.summonData.battleStats[s] = target.summonData.battleStats[s]; //Applies target boost to self
+            target.summonData.battleStats[s] = priorBoost; //Applies stored boost to target
+          }
+        target.updateInfo();
+        user.updateInfo();
+        target.scene.queueMessage(getPokemonMessage(user, ' switched stat changes with the target!'));
+        return true;
+    }
+}
+
 export class HpSplitAttr extends MoveEffectAttr {
   apply(user: Pokemon, target: Pokemon, move: Move, args: any[]): Promise<boolean> {
     return new Promise(resolve => {
@@ -5181,7 +5212,7 @@ export function initMoves() {
       .attr(AddArenaTrapTagAttr, ArenaTagType.TOXIC_SPIKES)
       .target(MoveTarget.ENEMY_SIDE),
     new StatusMove(Moves.HEART_SWAP, Type.PSYCHIC, -1, 10, -1, 0, 4)
-      .unimplemented(),
+      .attr(SwapStatsAttr),
     new SelfStatusMove(Moves.AQUA_RING, Type.WATER, -1, 20, -1, 0, 4)
       .attr(AddBattlerTagAttr, BattlerTagType.AQUA_RING, true, true),
     new SelfStatusMove(Moves.MAGNET_RISE, Type.ELECTRIC, -1, 10, -1, 0, 4)