1 files changed, 65 insertions, 0 deletions
diff --git a/src/main/java/com/notnite/gloppers/mixin/HopperBlockEntityMixin.java b/src/main/java/com/notnite/gloppers/mixin/HopperBlockEntityMixin.java
new file mode 100644
index 0000000..78468ac
--- /dev/null
+++ b/src/main/java/com/notnite/gloppers/mixin/HopperBlockEntityMixin.java
@@ -0,0 +1,65 @@
+package com.notnite.gloppers.mixin;
+
+import com.notnite.gloppers.Gloppers;
+import net.fabricmc.api.EnvType;
+import net.fabricmc.api.Environment;
+import net.minecraft.block.entity.Hopper;
+import net.minecraft.block.entity.HopperBlockEntity;
+import net.minecraft.inventory.Inventory;
+import net.minecraft.item.ItemStack;
+import net.minecraft.util.math.Direction;
+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.Redirect;
+import org.spongepowered.asm.mixin.injection.callback.CallbackInfoReturnable;
+
+@Environment(EnvType.SERVER)
+@Mixin(HopperBlockEntity.class)
+public class HopperBlockEntityMixin {
+    private static int dirtySlotState = 0;
+
+    // We can't decrement the item stack before it gets passed to transfer, because we may not be allowed to transfer,
+    // eating an item. We know removeStack will get called immediately before transfer, so while it's messy, we can use
+    // a static variable to keep track of what slot we're removing from.
+    @Redirect(
+        method = "insert",
+        at = @At(value = "INVOKE", target = "Lnet/minecraft/inventory/Inventory;removeStack(II)Lnet/minecraft/item/ItemStack;")
+    )
+    private static ItemStack insert$gloppersRemoveStack(Inventory instance, int slot, int amount) {
+        dirtySlotState = slot;
+        return instance.getStack(slot);
+    }
+
+    // This works by mixing into the call of HopperBlockEntity::transfer and returning a stubbed item stack if it's not
+    // allowed to transfer. I wanted to instead insert a continue statement into the for loop, but I couldn't figure out
+    // a good way to do that.
+    @Redirect(
+        method = "insert",
+        at = @At(value = "INVOKE", target = "Lnet/minecraft/block/entity/HopperBlockEntity;transfer(Lnet/minecraft/inventory/Inventory;Lnet/minecraft/inventory/Inventory;Lnet/minecraft/item/ItemStack;Lnet/minecraft/util/math/Direction;)Lnet/minecraft/item/ItemStack;")
+    )
+    private static ItemStack insert$gloppersTransfer(
+        Inventory from, Inventory to, ItemStack stack, Direction side
+    ) {
+        if (!Gloppers.INSTANCE.canTransfer(to, stack)) {
+            // The return value of this is only used to check if it's empty, and if so, returns that it succeeded.
+            // We can just return the item stack we were given, as we didn't remove from it.
+            return stack;
+        }
+
+        // Make sure to remove the item here, because we didn't in the actual call.
+        return HopperBlockEntity.transfer(from, to, from.removeStack(dirtySlotState, 1), side);
+    }
+
+    // This handles the case where a hopper extracts from a hopper above it (such as two anvils facing forward, stacked
+    // on top of one another).
+    @Inject(
+        method = "extract(Lnet/minecraft/block/entity/Hopper;Lnet/minecraft/inventory/Inventory;ILnet/minecraft/util/math/Direction;)Z",
+        at = @At("HEAD"),
+        cancellable = true
+    )
+    private static void extract(Hopper hopper, Inventory inventory, int slot, Direction side, CallbackInfoReturnable<Boolean> cir) {
+        var item = inventory.getStack(slot);
+        if (!Gloppers.INSTANCE.canTransfer(hopper, item)) cir.setReturnValue(false);
+    }
+}