package jnpf.flowable.util;

import jnpf.exception.WorkFlowException;

import java.util.ArrayList;
import java.util.Collection;
import java.util.Collections;
import java.util.HashSet;
import java.util.List;
import java.util.Set;

/**
 * 按逆向拓扑顺序获取退回路径，目标节点不参与退回事件。
 */
final class BackEventPathResolver {

    private BackEventPathResolver() {
    }

    @FunctionalInterface
    interface PreviousNodes {
        List<String> get(String nodeCode) throws WorkFlowException;
    }

    static List<String> resolve(String current, Collection<String> targets, Collection<String> afterTargets,
                                PreviousNodes previousNodes) throws WorkFlowException {
        Set<String> allowed = new HashSet<>(afterTargets);
        allowed.removeAll(targets);
        allowed.add(current);
        List<String> postOrder = new ArrayList<>();
        visit(current, allowed, new HashSet<>(), previousNodes, postOrder);
        Collections.reverse(postOrder);
        return postOrder;
    }

    private static void visit(String current, Set<String> allowed, Set<String> visited,
                              PreviousNodes previousNodes, List<String> postOrder) throws WorkFlowException {
        if (!allowed.contains(current) || !visited.add(current)) {
            return;
        }
        for (String previous : previousNodes.get(current)) {
            visit(previous, allowed, visited, previousNodes, postOrder);
        }
        postOrder.add(current);
    }
}