and little more

divinemc-server/src/main/java/space/bxteam/divinemc/util/lithium/HashedReferenceList.java

@@ -0,0 +1,281 @@
+package space.bxteam.divinemc.util.lithium;
+
+import it.unimi.dsi.fastutil.objects.Reference2IntOpenHashMap;
+import it.unimi.dsi.fastutil.objects.ReferenceArrayList;
+import it.unimi.dsi.fastutil.objects.ReferenceOpenHashSet;
+import org.jetbrains.annotations.NotNull;
+
+import java.util.Collection;
+import java.util.Iterator;
+import java.util.List;
+import java.util.ListIterator;
+import java.util.NoSuchElementException;
+
+/**
+ * Wraps a {@link List} with a hash table which provides O(1) lookups for {@link Collection#contains(Object)}. The type
+ * contained by this list must use reference-equality semantics.
+ */
+@SuppressWarnings("SuspiciousMethodCalls")
+public class HashedReferenceList<T> implements List<T> {
+    private final ReferenceArrayList<T> list;
+    private final Reference2IntOpenHashMap<T> counter;
+
+    public HashedReferenceList(List<T> list) {
+        this.list = new ReferenceArrayList<>();
+        this.list.addAll(list);
+
+        this.counter = new Reference2IntOpenHashMap<>();
+        this.counter.defaultReturnValue(0);
+
+        for (T obj : this.list) {
+            this.counter.addTo(obj, 1);
+        }
+    }
+
+    @Override
+    public int size() {
+        return this.list.size();
+    }
+
+    @Override
+    public boolean isEmpty() {
+        return this.list.isEmpty();
+    }
+
+    @Override
+    public boolean contains(Object o) {
+        return this.counter.containsKey(o);
+    }
+
+    @Override
+    public Iterator<T> iterator() {
+        return this.listIterator();
+    }
+
+    @Override
+    public Object[] toArray() {
+        return this.list.toArray();
+    }
+
+    @Override
+    public <T1> T1[] toArray(T1 @NotNull [] a) {
+        return this.list.toArray(a);
+    }
+
+    @Override
+    public boolean add(T t) {
+        this.trackReferenceAdded(t);
+
+        return this.list.add(t);
+    }
+
+    @Override
+    public boolean remove(Object o) {
+        this.trackReferenceRemoved(o);
+
+        return this.list.remove(o);
+    }
+
+    @Override
+    public boolean containsAll(Collection<?> c) {
+        for (Object obj : c) {
+            if (!this.counter.containsKey(obj)) {
+                return false;
+            }
+        }
+
+        return true;
+    }
+
+    @Override
+    public boolean addAll(Collection<? extends T> c) {
+        for (T obj : c) {
+            this.trackReferenceAdded(obj);
+        }
+
+        return this.list.addAll(c);
+    }
+
+    @Override
+    public boolean addAll(int index, Collection<? extends T> c) {
+        for (T obj : c) {
+            this.trackReferenceAdded(obj);
+        }
+
+        return this.list.addAll(index, c);
+    }
+
+    @Override
+    public boolean removeAll(@NotNull Collection<?> c) {
+        if (this.size() >= 2 && c.size() > 4 && c instanceof List) {
+            //HashReferenceList uses reference equality, so using ReferenceOpenHashSet is fine
+            c = new ReferenceOpenHashSet<>(c);
+        }
+        this.counter.keySet().removeAll(c);
+        return this.list.removeAll(c);
+    }
+
+    @Override
+    public boolean retainAll(@NotNull Collection<?> c) {
+        this.counter.keySet().retainAll(c);
+        return this.list.retainAll(c);
+    }
+
+    @Override
+    public void clear() {
+        this.counter.clear();
+        this.list.clear();
+    }
+
+    @Override
+    public T get(int index) {
+        return this.list.get(index);
+    }
+
+    @Override
+    public T set(int index, T element) {
+        T prev = this.list.set(index, element);
+
+        if (prev != element) {
+            if (prev != null) {
+                this.trackReferenceRemoved(prev);
+            }
+
+            this.trackReferenceAdded(element);
+        }
+
+        return prev;
+    }
+
+    @Override
+    public void add(int index, T element) {
+        this.trackReferenceAdded(element);
+
+        this.list.add(index, element);
+    }
+
+    @Override
+    public T remove(int index) {
+        T prev = this.list.remove(index);
+
+        if (prev != null) {
+            this.trackReferenceRemoved(prev);
+        }
+
+        return prev;
+    }
+
+    @Override
+    public int indexOf(Object o) {
+        return this.list.indexOf(o);
+    }
+
+    @Override
+    public int lastIndexOf(Object o) {
+        return this.list.lastIndexOf(o);
+    }
+
+    @Override
+    public ListIterator<T> listIterator() {
+        return this.listIterator(0);
+    }
+
+    @Override
+    public ListIterator<T> listIterator(int index) {
+        return new ListIterator<>() {
+            private final ListIterator<T> inner = HashedReferenceList.this.list.listIterator(index);
+
+            @Override
+            public boolean hasNext() {
+                return this.inner.hasNext();
+            }
+
+            @Override
+            public T next() {
+                return this.inner.next();
+            }
+
+            @Override
+            public boolean hasPrevious() {
+                return this.inner.hasPrevious();
+            }
+
+            @Override
+            public T previous() {
+                return this.inner.previous();
+            }
+
+            @Override
+            public int nextIndex() {
+                return this.inner.nextIndex();
+            }
+
+            @Override
+            public int previousIndex() {
+                return this.inner.previousIndex();
+            }
+
+            @Override
+            public void remove() {
+                int last = this.previousIndex();
+
+                if (last == -1) {
+                    throw new NoSuchElementException();
+                }
+
+                T prev = HashedReferenceList.this.get(last);
+
+                if (prev != null) {
+                    HashedReferenceList.this.trackReferenceRemoved(prev);
+                }
+
+                this.inner.remove();
+            }
+
+            @Override
+            public void set(T t) {
+                int last = this.previousIndex();
+
+                if (last == -1) {
+                    throw new NoSuchElementException();
+                }
+
+                T prev = HashedReferenceList.this.get(last);
+
+                if (prev != t) {
+                    if (prev != null) {
+                        HashedReferenceList.this.trackReferenceRemoved(prev);
+                    }
+
+                    HashedReferenceList.this.trackReferenceAdded(t);
+                }
+
+                this.inner.remove();
+            }
+
+            @Override
+            public void add(T t) {
+                HashedReferenceList.this.trackReferenceAdded(t);
+
+                this.inner.add(t);
+            }
+        };
+    }
+
+    @Override
+    public List<T> subList(int fromIndex, int toIndex) {
+        return this.list.subList(fromIndex, toIndex);
+    }
+
+    private void trackReferenceAdded(T t) {
+        this.counter.addTo(t, 1);
+    }
+
+    @SuppressWarnings("unchecked")
+    private void trackReferenceRemoved(Object o) {
+        if (this.counter.addTo((T) o, -1) <= 1) {
+            this.counter.removeInt(o);
+        }
+    }
+
+}