Init

src/main/java/systems/brn/regexinghoppers/RegexingHoppers.java

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+package systems.brn.regexinghoppers;
+
+import net.fabricmc.api.ModInitializer;
+import net.minecraft.inventory.Inventory;
+import net.minecraft.screen.NamedScreenHandlerFactory;
+import org.slf4j.Logger;
+import org.slf4j.LoggerFactory;
+
+import java.util.regex.Matcher;
+import java.util.regex.Pattern;
+import java.util.regex.PatternSyntaxException;
+
+public class RegexingHoppers implements ModInitializer {
+    // This logger is used to write text to the console and the log file.
+    // It is considered best practice to use your mod id as the logger's name.
+    // That way, it's clear which mod wrote info, warnings, and errors.
+    public static final Logger LOGGER = LoggerFactory.getLogger("RegexingHoppers");
+
+    @Override
+    public void onInitialize() {
+        // This code runs as soon as Minecraft is in a mod-load-ready state.
+        // However, some things (like resources) may still be uninitialized.
+        // Proceed with mild caution.
+
+        LOGGER.info("RegexingHoppers initialized!");
+    }
+
+    public static boolean shouldNotMove(Inventory hopper, String itemName) {
+        NamedScreenHandlerFactory factory = (NamedScreenHandlerFactory) hopper;
+        String customName = factory.getDisplayName().getLiteralString();
+        if (customName != null) {
+            try {
+                Pattern pattern = Pattern.compile(customName);
+                // Check if the text matches the regex
+                Matcher matcher = pattern.matcher(itemName);
+                return !matcher.matches();
+            } catch (PatternSyntaxException ignored) {
+            }
+        }
+        return false;
+    }
+}

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;
+            }
+        }
+    }
+}

src/main/resources/fabric.mod.json

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+{
+  "schemaVersion": 1,
+  "id": "regexinghoppers",
+  "version": "${version}",
+  "name": "RegexingHoppers",
+  "description": "Adds advanced item filtering capabilities to hoppers using regular expressions.",
+  "authors": [
+    "BRNSystems"
+  ],
+  "contact": {
+    "repo": "https://git.brn.systems/BRNSystems/RegexingHoppers"
+  },
+  "license": "MIT",
+  "icon": "icon.png",
+  "environment": "*",
+  "entrypoints": {
+    "main": [
+      "systems.brn.regexinghoppers.RegexingHoppers"
+    ]
+  },
+  "mixins": [
+    "regexinghoppers.mixins.json"
+  ],
+  "depends": {
+    "fabricloader": ">=${loader_version}",
+    "fabric": "*",
+    "minecraft": "${minecraft_version}"
+  }
+}

src/main/resources/regexinghoppers.mixins.json

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+{
+  "required": true,
+  "minVersion": "0.8",
+  "package": "systems.brn.regexinghoppers.mixin",
+  "compatibilityLevel": "JAVA_21",
+  "mixins": [
+    "RegexingHopperMixin"
+  ],
+  "client": [
+  ],
+  "injectors": {
+    "defaultRequire": 1
+  }
+}