Ability Patch

include/item_use.h

@@ -12,6 +12,7 @@ void ItemUseOutOfBattle_SSTicket(u8);
 void ItemUseOutOfBattle_WailmerPail(u8);
 void ItemUseOutOfBattle_Medicine(u8);
 void ItemUseOutOfBattle_AbilityCapsule(u8);
+void ItemUseOutOfBattle_AbilityPatch(u8);
 void ItemUseOutOfBattle_ReduceEV(u8);
 void ItemUseOutOfBattle_SacredAsh(u8);
 void ItemUseOutOfBattle_PPRecovery(u8);

include/party_menu.h

@@ -50,6 +50,7 @@ void DrawHeldItemIconsForTrade(u8 *partyCounts, u8 *partySpriteIds, u8 whichPart
 void CB2_ShowPartyMenuForItemUse(void);
 void ItemUseCB_Medicine(u8 taskId, TaskFunc task);
 void ItemUseCB_AbilityCapsule(u8 taskId, TaskFunc task);
+void ItemUseCB_AbilityPatch(u8 taskId, TaskFunc task);
 void ItemUseCB_ReduceEV(u8 taskId, TaskFunc task);
 void ItemUseCB_PPRecovery(u8 taskId, TaskFunc task);
 void ItemUseCB_PPUp(u8 taskId, TaskFunc task);

src/data/items.h

@@ -1095,7 +1095,7 @@ const struct Item gItems[] =
         .description = sAbilityPatchDesc,
         .pocket = POCKET_ITEMS,
         .type = ITEM_USE_PARTY_MENU,
-        .fieldUseFunc = ItemUseOutOfBattle_CannotUse, // Todo
+        .fieldUseFunc = ItemUseOutOfBattle_AbilityPatch,
     },
 
 // Mints

src/item_use.c

@@ -755,6 +755,12 @@ void ItemUseOutOfBattle_AbilityCapsule(u8 taskId)
     SetUpItemUseCallback(taskId);
 }
 
+void ItemUseOutOfBattle_AbilityPatch(u8 taskId)
+{
+    gItemUseCB = ItemUseCB_AbilityPatch;
+    SetUpItemUseCallback(taskId);
+}
+
 void ItemUseOutOfBattle_ReduceEV(u8 taskId)
 {
     gItemUseCB = ItemUseCB_ReduceEV;

src/party_menu.c

@@ -4475,6 +4475,100 @@ void ItemUseCB_AbilityCapsule(u8 taskId, TaskFunc task)
     gTasks[taskId].func = Task_AbilityCapsule;
 }
 
+void Task_AbilityPatch(u8 taskId)
+{
+    static const u8 askText[] = _("Would you like to change {STR_VAR_1}'s\nability to {STR_VAR_2}?");
+    static const u8 doneText[] = _("{STR_VAR_1}'s ability became\n{STR_VAR_2}!{PAUSE_UNTIL_PRESS}");
+    s16 *data = gTasks[taskId].data;
+
+    switch (tState)
+    {
+    case 0:
+
+    // If Hidden Abilities have been implemented without the use of Pokémon Expansion and added to the `abilities` field
+    // as ability no. 3 (eg. {ABILITY_OVERGROW, ABILITY_NONE, ABILITY_CHLOROPHYLL} )
+    // you can remove this #ifdef.
+    #ifdef POKEMON_EXPANSION
+        // Can't use.
+        if (gBaseStats[tSpecies].abilities[tAbilityNum] == 0
+            || !tSpecies
+            || GetMonData(&gPlayerParty[tMonId], MON_DATA_ABILITY_NUM, NULL) > 1
+            )
+    #endif
+        {
+            gPartyMenuUseExitCallback = FALSE;
+            PlaySE(SE_SELECT);
+            DisplayPartyMenuMessage(gText_WontHaveEffect, 1);
+            ScheduleBgCopyTilemapToVram(2);
+            gTasks[taskId].func = Task_ClosePartyMenuAfterText;
+            return;
+        }
+        gPartyMenuUseExitCallback = TRUE;
+        GetMonNickname(&gPlayerParty[tMonId], gStringVar1);
+        StringCopy(gStringVar2, gAbilityNames[GetAbilityBySpecies(tSpecies, tAbilityNum)]);
+        StringExpandPlaceholders(gStringVar4, askText);
+        PlaySE(SE_SELECT);
+        DisplayPartyMenuMessage(gStringVar4, 1);
+        ScheduleBgCopyTilemapToVram(2);
+        tState++;
+        break;
+    case 1:
+        if (!IsPartyMenuTextPrinterActive())
+        {
+            PartyMenuDisplayYesNoMenu();
+            tState++;
+        }
+        break;
+    case 2:
+        switch (Menu_ProcessInputNoWrapClearOnChoose())
+        {
+        case 0:
+            tState++;
+            break;
+        case 1:
+        case MENU_B_PRESSED:
+            gPartyMenuUseExitCallback = FALSE;
+            PlaySE(SE_SELECT);
+            ScheduleBgCopyTilemapToVram(2);
+            // Don't exit party selections screen, return to choosing a mon.
+            ClearStdWindowAndFrameToTransparent(6, 0);
+            ClearWindowTilemap(6);
+            DisplayPartyMenuStdMessage(5);
+            gTasks[taskId].func = (void *)GetWordTaskArg(taskId, tOldFunc);
+            return;
+        }
+        break;
+    case 3:
+        PlaySE(SE_USE_ITEM);
+        StringExpandPlaceholders(gStringVar4, doneText);
+        DisplayPartyMenuMessage(gStringVar4, 1);
+        ScheduleBgCopyTilemapToVram(2);
+        tState++;
+        break;
+    case 4:
+        if (!IsPartyMenuTextPrinterActive())
+            tState++;
+        break;
+    case 5:
+        SetMonData(&gPlayerParty[tMonId], MON_DATA_ABILITY_NUM, &tAbilityNum);
+        RemoveBagItem(gSpecialVar_ItemId, 1);
+        gTasks[taskId].func = Task_ClosePartyMenu;
+        break;
+    }
+}
+
+void ItemUseCB_AbilityPatch(u8 taskId, TaskFunc task)
+{
+    s16 *data = gTasks[taskId].data;
+
+    tState = 0;
+    tMonId = gPartyMenu.slotId;
+    tSpecies = GetMonData(&gPlayerParty[tMonId], MON_DATA_SPECIES, NULL);
+    tAbilityNum = 2;
+    SetWordTaskArg(taskId, tOldFunc, (uintptr_t)(gTasks[taskId].func));
+    gTasks[taskId].func = Task_AbilityPatch;
+}
+
 #undef tState
 #undef tSpecies
 #undef tAbilityNum