Add a limited bag api

pokemonred_puffer/data/bag.py

@@ -0,0 +1,61 @@
+from ctypes import LittleEndianStructure, Union, c_uint8
+
+from pyboy import PyBoy
+
+from pokemonred_puffer.data.items import Items
+
+
+BAG_CAPACITY = 20
+BAG_LENGTH_BYTES = 2 * BAG_CAPACITY
+
+
+class BagItem(LittleEndianStructure):
+    _pack_ = 1
+    _fields = [("Item", c_uint8), ("Quantity", c_uint8)]
+
+
+class Bag(Union):
+    _pack_ = 1
+    _fields = [("bag", BAG_CAPACITY * BagItem), ("asbytes", c_uint8 * BAG_LENGTH_BYTES)]
+
+    def __init__(self, emu: PyBoy):
+        _, self.wBagItems = self.pyboy.symbol_lookup("wBagItems")
+        _, self.wNumBagItems = self.pyboy.symbol_lookup("wNumBagItems")
+        self.numBagItems = emu.memory[self.wNumBagItems]
+        self.as_bytes = (c_uint8 * BAG_LENGTH_BYTES)(
+            *emu.memory[self.wBagItems : self.wBagItems + BAG_LENGTH_BYTES]
+        )
+        self.emu = emu
+
+    def add(self, item: Items, quantity: int) -> bool:
+        if self.numBagItems >= BAG_CAPACITY:
+            return False
+        try:
+            idx = self.as_bytes[::2].index(item.value)
+            self.as_bytes[idx + 1] += min(99, quantity + self.as_bytes[idx + 1])
+        except ValueError:
+            self.as_bytes[self.numBagItems] = item.value
+            self.as_bytes[self.numBagItems + 1] = quantity
+            self.numBagItems += 1
+        self.emu.memory[self.wNumBagItems] = self.numBagItems
+        self.emu.memory[self.wBagItems : self.wBagItems + BAG_LENGTH_BYTES] = self.as_bytes
+        return True
+
+    def remove(self, item: Items, quantity: int) -> bool:
+        if self.numBagItems >= BAG_CAPACITY:
+            return False
+        try:
+            idx = self.as_bytes[::2].index(item.value)
+        except ValueError:
+            return False
+        new_quantity = max(0, self.as_bytes[idx + 1] - quantity)
+        if new_quantity > 0:
+            self.as_bytes[idx + 1] = new_quantity
+        else:
+            # Remove from bag
+            self.as_bytes[idx:-2] = self.as_bytes[idx + 2 :]
+            self.numBagItems -= 1
+            self.as_bytes[2 * self.numBagItems :] = 0xFF
+        self.emu.memory[self.wNumBagItems] = self.numBagItems
+        self.emu.memory[self.wBagItems : self.wBagItems + BAG_LENGTH_BYTES] = self.as_bytes
+        return True