From f5218faea73983172a593f2caae9058769c0b7db Mon Sep 17 00:00:00 2001
From: Bryce Wilson <gyroscope15@gmail.com>
Date: Fri, 16 Aug 2024 13:23:47 -0700
Subject: [PATCH] Pokemon Emerald: Ensure dig tutor is always usable (#3660)

* Pokemon Emerald: Ensure dig tutor is always usable

* Pokemon Emerald: Clarify comment

Co-authored-by: Exempt-Medic <60412657+Exempt-Medic@users.noreply.github.com>

---------

Co-authored-by: Exempt-Medic <60412657+Exempt-Medic@users.noreply.github.com>
---
 worlds/pokemon_emerald/rom.py | 20 +++++++++++++++-----
 1 file changed, 15 insertions(+), 5 deletions(-)

diff --git a/worlds/pokemon_emerald/rom.py b/worlds/pokemon_emerald/rom.py
index 968a103ccd25..75d7d575846d 100644
--- a/worlds/pokemon_emerald/rom.py
+++ b/worlds/pokemon_emerald/rom.py
@@ -817,6 +817,8 @@ def _randomize_opponent_battle_type(world: "PokemonEmeraldWorld", patch: Pokemon
 
 
 def _randomize_move_tutor_moves(world: "PokemonEmeraldWorld", patch: PokemonEmeraldProcedurePatch, easter_egg: Tuple[int, int]) -> None:
+    FORTREE_MOVE_TUTOR_INDEX = 24
+
     if easter_egg[0] == 2:
         for i in range(30):
             patch.write_token(
@@ -840,18 +842,26 @@ def _randomize_move_tutor_moves(world: "PokemonEmeraldWorld", patch: PokemonEmer
     # Always set Fortree move tutor to Dig
     patch.write_token(
         APTokenTypes.WRITE,
-        data.rom_addresses["gTutorMoves"] + (24 * 2),
+        data.rom_addresses["gTutorMoves"] + (FORTREE_MOVE_TUTOR_INDEX * 2),
         struct.pack("<H", data.constants["MOVE_DIG"])
     )
 
     # Modify compatibility
     if world.options.tm_tutor_compatibility.value != -1:
         for species in data.species.values():
+            compatibility = bool_array_to_int([
+                world.random.randrange(0, 100) < world.options.tm_tutor_compatibility.value
+                for _ in range(32)
+            ])
+
+            # Make sure Dig tutor has reasonable (>=50%) compatibility
+            if world.options.tm_tutor_compatibility.value < 50:
+                compatibility &= ~(1 << FORTREE_MOVE_TUTOR_INDEX)
+                if world.random.random() < 0.5:
+                    compatibility |= 1 << FORTREE_MOVE_TUTOR_INDEX
+
             patch.write_token(
                 APTokenTypes.WRITE,
                 data.rom_addresses["sTutorLearnsets"] + (species.species_id * 4),
-                struct.pack("<I", bool_array_to_int([
-                    world.random.randrange(0, 100) < world.options.tm_tutor_compatibility.value
-                    for _ in range(32)
-                ]))
+                struct.pack("<I", compatibility)
             )