more work + tests

Author: ghzdude

src/main/java/gregtech/api/capability/impl/ItemHandlerList.java

@@ -100,15 +100,15 @@ public boolean add(IItemHandler handler) {
 
     @Override
     public void add(int index, IItemHandler element) {
-        if (invalidIndex(index)) return;
-        int currentSlotIndex = handlerBySlotIndex.size();
-        if (baseIndexOffset.containsKey(element)) {
+//        Objects.checkIndex(index, size());
+        if (handlerList.contains(element)) {
             throw new IllegalArgumentException("Attempted to add item handler " + element + " twice");
         }
-        handlerList.add(element);
-        baseIndexOffset.put(element, currentSlotIndex);
+        handlerList.add(index, element);
+        int offset = handlerBySlotIndex.size();
+        baseIndexOffset.put(element, offset);
         for (int slotIndex = 0; slotIndex < element.getSlots(); slotIndex++) {
-            handlerBySlotIndex.put(currentSlotIndex + slotIndex, element);
+            handlerBySlotIndex.put(offset + slotIndex, element);
         }
     }
 
@@ -119,19 +119,28 @@ public IItemHandler get(int index) {
 
     @Override
     public IItemHandler remove(int index) {
-        if (invalidIndex(index)) return null;
-        var handler = get(index);
+//        Objects.checkIndex(index, size());
+        var handler2 = get(index);
+        int offset2 = baseIndexOffset.getInt(handler2);
+
         for (int i = index; i < size(); i++) {
-            int offset = baseIndexOffset.getInt(get(i));
-            for (int j = 0; j < get(index).getSlots(); j++) {
+            int offset = baseIndexOffset.removeInt(get(i));
+            for (int j = 0; j < get(i).getSlots(); j++) {
                 handlerBySlotIndex.remove(offset + j);
             }
-            baseIndexOffset.removeInt(handler);
         }
-        return handler;
-    }
 
-    private boolean invalidIndex(int index) {
-        return index < 0 || index >= handlerList.size();
+        var removed = handlerList.remove(index);
+        for (var handler : handlerList) {
+            if (baseIndexOffset.containsKey(handler))
+                continue;
+
+            int offset = handlerBySlotIndex.size();
+            baseIndexOffset.put(handler, offset);
+            for (int i = 0; i < handler.getSlots(); i++) {
+                handlerBySlotIndex.put(offset + i, handler);
+            }
+        }
+        return removed;
     }
 }

src/test/java/gregtech/api/capability/impl/ItemHandlerListTest.java

@@ -0,0 +1,36 @@
+package gregtech.api.capability.impl;
+
+import gregtech.Bootstrap;
+
+import net.minecraftforge.items.ItemStackHandler;
+
+import org.hamcrest.MatcherAssert;
+import org.junit.jupiter.api.BeforeAll;
+import org.junit.jupiter.api.Test;
+
+import java.util.Collections;
+
+public class ItemHandlerListTest {
+
+    @BeforeAll
+    public static void bootstrap() {
+        Bootstrap.perform();
+    }
+
+    @Test
+    public void testListOperations() {
+        var list = new ItemHandlerList(Collections.emptyList());
+
+        // test add
+        list.add(new ItemStackHandler(16));
+//        MatcherAssert.assertThat("size is wrong", list.getSlots() == 16);
+        list.add(new ItemStackHandler(16));
+//        MatcherAssert.assertThat("size is wrong", list.getSlots() == 32);
+//        MatcherAssert.assertThat("size is wrong", list.size() == 2);
+
+        // test removal
+        list.remove(0);
+//        MatcherAssert.assertThat("size is wrong", list.getSlots() == 16);
+//        MatcherAssert.assertThat("size is wrong", list.size() == 1);
+    }
+}