From 4197ffa859e1d5396584895db21567def66f1106 Mon Sep 17 00:00:00 2001
From: tom-overton <tom.overton@outlook.com>
Date: Fri, 21 Oct 2022 08:12:30 -0700
Subject: Gen 5: Add support for Guaranteed Catching Pokemon

---
 .../sneed/pkrandom/constants/Gen5Constants.java    |  2 ++
 .../sneed/pkrandom/romhandlers/Gen5RomHandler.java | 26 ++++++++++++++++++++++
 2 files changed, 28 insertions(+)

diff --git a/src/com/sneed/pkrandom/constants/Gen5Constants.java b/src/com/sneed/pkrandom/constants/Gen5Constants.java
index 110e1b4..56e49e9 100644
--- a/src/com/sneed/pkrandom/constants/Gen5Constants.java
+++ b/src/com/sneed/pkrandom/constants/Gen5Constants.java
@@ -375,6 +375,8 @@ public class Gen5Constants {
 
     public static final String friendshipValueForEvoLocator = "DC282FD3";
 
+    public static final String perfectOddsBranchLocator = "08DB002801D0012000E0";
+
     public static final List<Integer> consumableHeldItems = setupAllConsumableItems();
 
     private static List<Integer> setupAllConsumableItems() {
diff --git a/src/com/sneed/pkrandom/romhandlers/Gen5RomHandler.java b/src/com/sneed/pkrandom/romhandlers/Gen5RomHandler.java
index 538c8da..05081b5 100755
--- a/src/com/sneed/pkrandom/romhandlers/Gen5RomHandler.java
+++ b/src/com/sneed/pkrandom/romhandlers/Gen5RomHandler.java
@@ -2426,6 +2426,7 @@ public class Gen5RomHandler extends AbstractDSRomHandler {
         if (romEntry.romType == Gen5Constants.Type_BW2) {
             available |= MiscTweak.FORCE_CHALLENGE_MODE.getValue();
         }
+        available |= MiscTweak.GUARANTEED_POKEMON_CATCHING.getValue();
         return available;
     }
 
@@ -2461,6 +2462,8 @@ public class Gen5RomHandler extends AbstractDSRomHandler {
             updateTypeEffectiveness();
         } else if (tweak == MiscTweak.FORCE_CHALLENGE_MODE) {
             forceChallengeMode();
+        } else if (tweak == MiscTweak.GUARANTEED_POKEMON_CATCHING) {
+            enableGuaranteedPokemonCatching();
         }
     }
 
@@ -2639,6 +2642,29 @@ public class Gen5RomHandler extends AbstractDSRomHandler {
         }
     }
 
+    private void enableGuaranteedPokemonCatching() {
+        try {
+            byte[] battleOverlay = readOverlay(romEntry.getInt("BattleOvlNumber"));
+            int offset = find(battleOverlay, Gen5Constants.perfectOddsBranchLocator);
+            if (offset > 0) {
+                // The game checks to see if your odds are greater then or equal to 255 using the following
+                // code. Note that they compare to 0xFF000 instead of 0xFF; it looks like all catching code
+                // probabilities are shifted like this?
+                // mov r0, #0xFF
+                // lsl r0, r0, #0xC
+                // cmp r7, r0
+                // blt oddsLessThanOrEqualTo254
+                // The below code just nops the branch out so it always acts like our odds are 255, and
+                // Pokemon are automatically caught no matter what.
+                battleOverlay[offset] = 0x00;
+                battleOverlay[offset + 1] = 0x00;
+                writeOverlay(romEntry.getInt("BattleOvlNumber"), battleOverlay);
+            }
+        } catch (IOException e) {
+            throw new RandomizerIOException(e);
+        }
+    }
+
     private boolean genericIPSPatch(byte[] data, String ctName) {
         String patchName = romEntry.tweakFiles.get(ctName);
         if (patchName == null) {
-- 
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