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Common utility classes

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package com.nls.util;

import java.util.Collection;
import java.util.List;
import java.util.Set;
import java.util.function.Function;
import java.util.stream.Collectors;

public class CollectionDifference {
    private final Collection oldCollection;
    private final Collection newCollection;
    private final Function comparisonMapper;

    public CollectionDifference(Collection oldCollection, Collection newCollection) {
        this(oldCollection, newCollection, Function.identity());
    }

    public CollectionDifference(Collection oldCollection, Collection newCollection, Function comparisonMapper) {
        this.oldCollection = oldCollection;
        this.newCollection = newCollection;
        this.comparisonMapper = comparisonMapper;
    }

    public List added() {
        Set newValues = newCollection.stream().map(comparisonMapper).collect(Collectors.toSet());
        Set oldValues = oldCollection.stream().map(comparisonMapper).collect(Collectors.toSet());
        newValues.removeAll(oldValues);
        return newCollection.stream().filter(o -> newValues.contains(comparisonMapper.apply(o))).collect(Collectors.toList());
    }

    public List removed() {
        Set newValues = newCollection.stream().map(comparisonMapper).collect(Collectors.toSet());
        Set oldValues = oldCollection.stream().map(comparisonMapper).collect(Collectors.toSet());
        oldValues.removeAll(newValues);
        return oldCollection.stream().filter(o -> oldValues.contains(comparisonMapper.apply(o))).collect(Collectors.toList());
    }

    public > C addToCollection(C collection) {
        collection.addAll(added());
        return collection;
    }

    public > C removeFromCollection(C collection) {
        collection.removeAll(removed());
        return collection;
    }

    public > C updateCollection(C collection) {
        addToCollection(collection);
        removeFromCollection(collection);
        return collection;
    }
}