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JHotDraw8 Utility classes for Collections
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/*
 * @(#)MappedList.java
 * Copyright © 2023 The authors and contributors of JHotDraw. MIT License.
 */
package org.jhotdraw8.collection.mapped;

import org.jspecify.annotations.Nullable;

import java.util.AbstractList;
import java.util.Iterator;
import java.util.List;
import java.util.Spliterator;
import java.util.function.Consumer;
import java.util.function.Function;

/**
 * Maps a {@link List} to a different element type.
 * 
 * The underlying list is referenced - not copied.
 *
 * @param  the mapped element type
 * @param  the original element type
 * @author Werner Randelshofer
 */
public final class MappedList extends AbstractList {

    private final List backingList;
    private final Function mapf;

    public MappedList(List backingList, Function mapf) {
        this.backingList = backingList;
        this.mapf = mapf;
    }

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

    @Override
    public E get(int index) {
        return mapf.apply(backingList.get(index));
    }

    @Override
    public Iterator iterator() {
        return new Iterator<>() {
            private final Iterator i = backingList.iterator();

            @Override
            public boolean hasNext() {
                return i.hasNext();
            }

            @Override
            public E next() {
                return mapf.apply(i.next());
            }

            @Override
            public void remove() {
                throw new UnsupportedOperationException();
            }
        };
    }

    @Override
    public Spliterator spliterator() {
        class MappingSpliterator implements Spliterator {
            private final Spliterator i;

            public MappingSpliterator(Spliterator i) {
                this.i = i;
            }

            @Override
            public boolean tryAdvance(Consumer action) {
                return i.tryAdvance(f -> action.accept(mapf.apply(f)));
            }

            @Override
            public @Nullable Spliterator trySplit() {
                Spliterator fSpliterator = i.trySplit();
                return fSpliterator == null ? null : new MappingSpliterator(fSpliterator);
            }

            @Override
            public long estimateSize() {
                return i.estimateSize();
            }

            @Override
            public int characteristics() {
                return i.characteristics();
            }
        }
        return new MappingSpliterator(backingList.spliterator());
    }

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

    @Override
    public List subList(int fromIndex, int toIndex) {
        return new MappedList<>(backingList.subList(fromIndex, toIndex), mapf);
    }
}