org.apache.james.jmap.utils.SortingHierarchicalCollections.java Source code

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package org.apache.james.jmap.utils;

import java.util.Collection;
import java.util.List;
import java.util.Map;
import java.util.Optional;
import java.util.function.Function;
import java.util.stream.Collectors;

import org.apache.james.jmap.utils.DependencyGraph.CycleDetectedException;

import com.google.common.collect.Lists;

public class SortingHierarchicalCollections<T, Id> {

    private final Function<T, Id> index;
    private final Function<T, Optional<Id>> parentId;

    public SortingHierarchicalCollections(Function<T, Id> index, Function<T, Optional<Id>> parentId) {
        this.index = index;
        this.parentId = parentId;
    }

    public List<T> sortFromRootToLeaf(Collection<T> elements) throws CycleDetectedException {

        Map<Id, T> mapOfElementsById = indexElementsById(elements);

        DependencyGraph<T> graph = new DependencyGraph<>(m -> parentId.apply(m).map(mapOfElementsById::get));

        elements.stream().forEach(graph::registerItem);

        return graph.getBuildChain().collect(Collectors.toList());
    }

    private Map<Id, T> indexElementsById(Collection<T> elements) {
        return elements.stream().collect(Collectors.toMap(index, Function.identity()));
    }

    public List<T> sortFromLeafToRoot(Collection<T> elements) throws CycleDetectedException {
        return Lists.reverse(sortFromRootToLeaf(elements));
    }
}