server/protocols/jmap-rfc-8621/src/main/java/org/apache/james/jmap/utils/KeywordsCombiner.java

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package org.apache.james.jmap.utils;

import java.util.List;
import java.util.Set;
import java.util.function.BinaryOperator;

import org.apache.james.jmap.model.Keyword;
import org.apache.james.jmap.model.Keywords;

import com.google.common.collect.ImmutableList;
import com.google.common.collect.ImmutableSet;
import com.google.common.collect.Sets;

public class KeywordsCombiner implements BinaryOperator<Keywords> {
    private static final ImmutableList<Keyword> KEYWORD_TO_INTERSECT = ImmutableList.of(Keyword.DRAFT);
    private static final ImmutableList<Keyword> KEYWORD_NOT_TO_UNION = KEYWORD_TO_INTERSECT;

    private Keywords.KeywordsFactory keywordsFactory;

    public KeywordsCombiner() {
        this.keywordsFactory = Keywords.lenientFactory();
    }

    @Override
    public Keywords apply(Keywords keywords, Keywords keywords2) {
        return keywordsFactory
            .fromSet(Sets.union(
                        union(keywords.getKeywords(), keywords2.getKeywords(), KEYWORD_NOT_TO_UNION),
                        intersect(keywords.getKeywords(), keywords2.getKeywords(), KEYWORD_TO_INTERSECT)));
    }

    public Set<Keyword> union(Set<Keyword> set1, Set<Keyword> set2, List<Keyword> exceptKeywords) {
        return Sets.union(set1, set2)
            .stream()
            .filter(keyword -> !exceptKeywords.contains(keyword))
            .collect(ImmutableSet.toImmutableSet());
    }

    public Set<Keyword> intersect(Set<Keyword> set1, Set<Keyword> set2, List<Keyword> forKeywords) {
        return Sets.intersection(set1, set2)
            .stream()
            .filter(forKeywords::contains)
            .collect(ImmutableSet.toImmutableSet());
    }
}