From 8f044f29bf1806a6b301b4195ea2f761b63060b6 Mon Sep 17 00:00:00 2001
From: tom-overton <tom.overton@outlook.com>
Date: Thu, 20 Oct 2022 22:05:04 -0700
Subject: Gen 4: Add support for Guaranteed Pokemon Catching

---
 .../sneed/pkrandom/constants/Gen4Constants.java    |  2 ++
 .../sneed/pkrandom/romhandlers/Gen4RomHandler.java | 26 ++++++++++++++++++++++
 2 files changed, 28 insertions(+)

diff --git a/src/com/sneed/pkrandom/constants/Gen4Constants.java b/src/com/sneed/pkrandom/constants/Gen4Constants.java
index 7a0acfa..1309073 100644
--- a/src/com/sneed/pkrandom/constants/Gen4Constants.java
+++ b/src/com/sneed/pkrandom/constants/Gen4Constants.java
@@ -770,6 +770,8 @@ public class Gen4Constants {
 
     public static final String friendshipValueForEvoLocator = "DC286AD3";
 
+    public static final String catchFailBranchLocator = "FF2901D30425";
+
     public static final int[] dpptOverworldDexMaps = new int[] {
             1,  2,  3,  4,  5, -1, -1,  6, -1,  7, // 0-9 (cities, pkmn league, wind/ironworks)
             -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, // 10-19 (all mt coronet)
diff --git a/src/com/sneed/pkrandom/romhandlers/Gen4RomHandler.java b/src/com/sneed/pkrandom/romhandlers/Gen4RomHandler.java
index 7d12c47..cc98c3b 100755
--- a/src/com/sneed/pkrandom/romhandlers/Gen4RomHandler.java
+++ b/src/com/sneed/pkrandom/romhandlers/Gen4RomHandler.java
@@ -5265,6 +5265,7 @@ public class Gen4RomHandler extends AbstractDSRomHandler {
         if (romEntry.romType == Gen4Constants.Type_Plat || romEntry.romType == Gen4Constants.Type_HGSS) {
             available |= MiscTweak.UPDATE_ROTOM_FORME_TYPING.getValue();
         }
+        available |= MiscTweak.GUARANTEED_POKEMON_CATCHING.getValue();
         return available;
     }
 
@@ -5291,6 +5292,8 @@ public class Gen4RomHandler extends AbstractDSRomHandler {
             applyFastDistortionWorld();
         } else if (tweak == MiscTweak.UPDATE_ROTOM_FORME_TYPING) {
             updateRotomFormeTyping();
+        } else if (tweak == MiscTweak.GUARANTEED_POKEMON_CATCHING) {
+            enableGuaranteedPokemonCatching();
         }
     }
 
@@ -5530,6 +5533,29 @@ public class Gen4RomHandler extends AbstractDSRomHandler {
         pokes[Species.Gen4Formes.rotomM].secondaryType = Type.GRASS;
     }
 
+    private void enableGuaranteedPokemonCatching() {
+        try {
+            byte[] battleOverlay = readOverlay(romEntry.getInt("BattleOvlNumber"));
+            int offset = find(battleOverlay, Gen4Constants.catchFailBranchLocator);
+            if (offset > 0) {
+                // In Cmd_handleballthrow (name taken from pokeemerald decomp), the middle of the function checks
+                // if the odds of catching a Pokemon is greater than 254; if it is, then the Pokemon is automatically
+                // caught. In ASM, this is represented by:
+                // cmp r1, #0xFF
+                // bcc oddsLessThanOrEqualTo254
+                // The below code just nops these two instructions so that we *always* act like our odds are 255,
+                // and Pokemon are automatically caught no matter what.
+                battleOverlay[offset] = 0x00;
+                battleOverlay[offset + 1] = 0x00;
+                battleOverlay[offset + 2] = 0x00;
+                battleOverlay[offset + 3] = 0x00;
+                writeOverlay(romEntry.getInt("BattleOvlNumber"), battleOverlay);
+            }
+        } catch (IOException e) {
+            throw new RandomizerIOException(e);
+        }
+    }
+
     @Override
     public void applyCorrectStaticMusic(Map<Integer,Integer> specialMusicStaticChanges) {
         List<Integer> replaced = new ArrayList<>();
-- 
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