Init

src/main/java/systems/brn/regexinghoppers/mixin/RegexingHopperMixin.java

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+package systems.brn.regexinghoppers.mixin;
+
+import net.minecraft.block.entity.HopperBlockEntity;
+import net.minecraft.inventory.Inventory;
+import net.minecraft.item.ItemStack;
+import net.minecraft.registry.Registries;
+import net.minecraft.util.math.Direction;
+import org.spongepowered.asm.mixin.Debug;
+import org.spongepowered.asm.mixin.Mixin;
+import org.spongepowered.asm.mixin.injection.At;
+import org.spongepowered.asm.mixin.injection.Inject;
+import org.spongepowered.asm.mixin.injection.callback.CallbackInfoReturnable;
+import systems.brn.regexinghoppers.RegexingHoppers;
+
+@Debug(export = true) // Enables exporting for the targets of this mixin
+@Mixin(HopperBlockEntity.class)
+public class RegexingHopperMixin {
+
+    @Inject(method = "transfer(Lnet/minecraft/inventory/Inventory;Lnet/minecraft/inventory/Inventory;Lnet/minecraft/item/ItemStack;ILnet/minecraft/util/math/Direction;)Lnet/minecraft/item/ItemStack;",
+    at = @At(value = "HEAD"),
+            cancellable = true
+    )
+    private static void processContainer(Inventory from, Inventory _to, ItemStack stack, int slot, Direction side, CallbackInfoReturnable<ItemStack> cir) {
+        final String itemName = Registries.ITEM.getId(stack.getItem()).toString();
+        if(from != null) {
+            if (RegexingHoppers.shouldNotMove(from, itemName)) {
+                cir.setReturnValue(stack);
+                return;
+            }
+        }
+        if(_to != null) {
+            if (RegexingHoppers.shouldNotMove(_to, itemName)) {
+                cir.setReturnValue(stack);
+                return;
+            }
+        }
+    }
+}