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JHotDraw8 Immutable Collections
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/*
 * @(#)ImmutableSetFacade.java
 * Copyright © 2023 The authors and contributors of JHotDraw. MIT License.
 */

package org.jhotdraw8.icollection.facade;

import org.jhotdraw8.icollection.immutable.ImmutableSet;
import org.jhotdraw8.icollection.impl.iteration.IteratorSpliterator;
import org.jhotdraw8.icollection.impl.iteration.Iterators;
import org.jhotdraw8.icollection.readonly.AbstractReadOnlySet;
import org.jhotdraw8.icollection.readonly.ReadOnlyCollection;

import java.util.Collection;
import java.util.HashSet;
import java.util.Iterator;
import java.util.LinkedHashSet;
import java.util.Set;
import java.util.Spliterator;
import java.util.function.Function;

/**
 * Provides a {@link ImmutableSet} facade to a set of {@code ImmutableSet} functions.
 *
 * @param  the element type
 */
public class ImmutableSetFacade extends AbstractReadOnlySet implements ImmutableSet {
    private final Set target;
    private final Function, Set> cloneFunction;

    public ImmutableSetFacade(Set target, Function, Set> cloneFunction) {
        this.target = target;
        this.cloneFunction = cloneFunction;
    }

    @SuppressWarnings("unchecked")
    @Override
    public  ImmutableSet empty() {
        return new ImmutableSetFacade<>(new LinkedHashSet<>(), k -> (Set) ((LinkedHashSet) k).clone());
    }

    @Override
    public ImmutableSet add(E element) {
        Set clone = cloneFunction.apply(target);
        return clone.add(element) ? new ImmutableSetFacade<>(clone, cloneFunction) : this;
    }

    @Override
    public ImmutableSet addAll(Iterable c) {
        Set clone = cloneFunction.apply(target);
        boolean changed = false;
        for (E e : c) {
            changed |= clone.add(e);
        }
        return changed ? new ImmutableSetFacade<>(clone, cloneFunction) : this;
    }

    @Override
    public ImmutableSet remove(E element) {
        Set clone = cloneFunction.apply(target);
        return clone.remove(element) ? new ImmutableSetFacade<>(clone, cloneFunction) : this;
    }

    @Override
    public ImmutableSet removeAll(Iterable c) {
        Set clone = cloneFunction.apply(target);
        boolean changed = false;
        for (Object e : c) {
            changed |= clone.remove(e);
        }
        return changed ? new ImmutableSetFacade<>(clone, cloneFunction) : this;
    }

    @SuppressWarnings("unchecked")
    @Override
    public ImmutableSet retainAll(Iterable c) {
        if (isEmpty()) {
            return this;
        }
        Set clone = cloneFunction.apply(target);
        Collection collection;
        if (c instanceof ReadOnlyCollection rc) {
            collection = (Collection) rc.asCollection();
        } else if (c instanceof Collection cc) {
            collection = (Collection) cc;
        } else {
            collection = new HashSet<>();
            c.forEach(e -> collection.add((E) e));
        }
        return clone.retainAll(collection) ? new ImmutableSetFacade<>(clone, cloneFunction) : this;
    }

    @Override
    public int size() {
        return target.size();
    }

    @Override
    public boolean contains(Object o) {
        return target.contains(o);
    }

    @Override
    public int maxSize() {
        return Integer.MAX_VALUE;
    }

    @Override
    public Iterator iterator() {
        return Iterators.unmodifiableIterator(target.iterator());
    }

    @Override
    public Spliterator spliterator() {
        return new IteratorSpliterator<>(iterator(), size(), characteristics(), null);
    }

    @Override
    public Set toMutable() {
        return cloneFunction.apply(target);
    }


    @Override
    public int characteristics() {
        return Spliterator.IMMUTABLE | super.characteristics();
    }
}