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package org.aksw.commons.collection.observable;


import java.util.function.Predicate;

import com.google.common.collect.Multiset;

/**
 * A predicate backed by a multiset of items that are considered as discarded.
 * predicate.test(x) will return false as long as the multiset contains x (true otherwise).
 * Whenever the multiset contained x then x's cardinality is reduced by 1
 * (by removing one occurrence of x from the multiset)
 *
 * This is useful to create collection views that hide a specific number of items.
 *
 *
 * @author raven
 *
 * @param 
 */
public class PredicateFromMultisetOfDiscardedItems
    implements Predicate
{
    protected Multiset discards;

    public PredicateFromMultisetOfDiscardedItems(Multiset discards) {
        super();
        this.discards = discards;
    }

    public static  Predicate create(Multiset discards) {
        return new PredicateFromMultisetOfDiscardedItems<>(discards);
    }

    @Override
    public boolean test(T t) {
        boolean isDiscarded = discards.contains(t);

        if (isDiscarded) {
            discards.remove(t);
        }

        return !isDiscarded;
    }
}