From f1458dea457369b7c3b4423c61a66d510e990c2f Mon Sep 17 00:00:00 2001
From: PhallenTree <168426989+PhallenTree@users.noreply.github.com>
Date: Sun, 22 Dec 2024 22:39:07 +0000
Subject: [PATCH] Fixes Regenerator healing past maxHP (#5861)

---
 src/battle_script_commands.c      |  6 ++--
 test/battle/ability/regenerator.c | 50 +++++++++++++++++++++++++++++++
 2 files changed, 53 insertions(+), 3 deletions(-)
 create mode 100644 test/battle/ability/regenerator.c

diff --git a/src/battle_script_commands.c b/src/battle_script_commands.c
index 25d1f78996..21ed966dd1 100644
--- a/src/battle_script_commands.c
+++ b/src/battle_script_commands.c
@@ -15121,10 +15121,10 @@ static void Cmd_switchoutabilities(void)
             break;
         case ABILITY_REGENERATOR:
         {
-            u32 regenerate = GetNonDynamaxMaxHP(gBattlerAttacker) / 3;
+            u32 regenerate = GetNonDynamaxMaxHP(battler) / 3;
             regenerate += gBattleMons[battler].hp;
-            if (gBattleStruct->moveDamage[gBattlerAttacker] > gBattleMons[battler].maxHP)
-                gBattleStruct->moveDamage[gBattlerAttacker] = gBattleMons[battler].maxHP;
+            if (regenerate > gBattleMons[battler].maxHP)
+                regenerate = gBattleMons[battler].maxHP;
             BtlController_EmitSetMonData(battler, BUFFER_A, REQUEST_HP_BATTLE,
                                          1u << *(gBattleStruct->battlerPartyIndexes + battler),
                                          sizeof(regenerate),
diff --git a/test/battle/ability/regenerator.c b/test/battle/ability/regenerator.c
new file mode 100644
index 0000000000..0f1b432772
--- /dev/null
+++ b/test/battle/ability/regenerator.c
@@ -0,0 +1,50 @@
+#include "global.h"
+#include "test/battle.h"
+
+SINGLE_BATTLE_TEST("Regenerator heals 1/3 of max HP upon switching out")
+{
+    u32 currHP;
+    PARAMETRIZE { currHP = 1; }
+    PARAMETRIZE { currHP = 2; }
+    PARAMETRIZE { currHP = 3; }
+    GIVEN {
+        PLAYER(SPECIES_SLOWBRO) { Ability(ABILITY_REGENERATOR); HP(currHP); }
+        PLAYER(SPECIES_WOBBUFFET);
+        OPPONENT(SPECIES_WOBBUFFET);
+    } WHEN {
+        TURN { SWITCH(player, 1); }
+        TURN { SWITCH(player, 0); }
+    } SCENE {
+        SWITCH_OUT_MESSAGE("Slowbro");
+        SEND_IN_MESSAGE("Wobbuffet");
+        SWITCH_OUT_MESSAGE("Wobbuffet");
+        SEND_IN_MESSAGE("Slowbro");
+    } THEN {
+        EXPECT_EQ(player->hp, player->maxHP / 3 + currHP);
+    }
+}
+
+SINGLE_BATTLE_TEST("Regenerator heals 1/3 of max HP upon switching out but doesn't surpass max HP")
+{
+    u32 currHP;
+    PARAMETRIZE { currHP = 5; }
+    PARAMETRIZE { currHP = 4; }
+    PARAMETRIZE { currHP = 3; }
+    PARAMETRIZE { currHP = 2; }
+    PARAMETRIZE { currHP = 1; }
+    GIVEN {
+        PLAYER(SPECIES_SLOWBRO) { Ability(ABILITY_REGENERATOR); HP(currHP); MaxHP(5); }
+        PLAYER(SPECIES_WOBBUFFET);
+        OPPONENT(SPECIES_WOBBUFFET);
+    } WHEN {
+        TURN { SWITCH(player, 1); }
+        TURN { SWITCH(player, 0); }
+    } SCENE {
+        SWITCH_OUT_MESSAGE("Slowbro");
+        SEND_IN_MESSAGE("Wobbuffet");
+        SWITCH_OUT_MESSAGE("Wobbuffet");
+        SEND_IN_MESSAGE("Slowbro");
+    } THEN {
+        EXPECT_LE(player->hp, player->maxHP);
+    }
+}