package com.pig4cloud.pigx.common.core.util.tree;

import java.util.*;
import java.util.function.Function;
import java.util.stream.Collectors;

/**
 * 通用樹結(jié)構(gòu)構(gòu)建工具類
 *
 * <p>重要說明：
 * <ol>
 *   <li>所有節(jié)點必須具有唯一ID</li>
 *   <li>父節(jié)點不存在時自動成為根節(jié)點</li>
 *   <li>節(jié)點排序依賴comparator實現(xiàn)</li>
 *   <li>支持循環(huán)依賴檢測和錯誤路徑提示</li>
 * </ol>
 *
 * @param <T> 原始數(shù)據(jù)類型
 * @param <K> 節(jié)點ID類型（建議使用包裝類型）
 */
public class TreeBuilder<T, K> {
    private final Function<T, K> idGetter;
    private final Function<T, K> parentIdGetter;
    private final ChildSetter<T> childSetter;
    private final Comparator<T> comparator;

    /**
     * 構(gòu)造方法
     */
    public TreeBuilder(Function<T, K> idGetter,
                       Function<T, K> parentIdGetter,
                       ChildSetter<T> childSetter,
                       Comparator<T> comparator) {

        this.idGetter = Objects.requireNonNull(idGetter, "ID獲取器不能為null");
        this.parentIdGetter = Objects.requireNonNull(parentIdGetter, "父ID獲取器不能為null");
        this.childSetter = Objects.requireNonNull(childSetter, "子節(jié)點設(shè)置器不能為null");
        this.comparator = Objects.requireNonNull(comparator, "排序比較器不能為null");
    }

    /**
     * 構(gòu)建完整樹結(jié)構(gòu)
     */
    public List<T> buildTree(List<T> items) {
        Objects.requireNonNull(items, "節(jié)點列表不能為null");
        if (items.isEmpty()) return Collections.emptyList();

        // 1. 構(gòu)建數(shù)據(jù)索引
        Map<K, T> nodeMap = createNodeMap(items);
        Map<K, List<T>> parentChildrenMap = items.stream()
                .collect(Collectors.groupingBy(
                        parentIdGetter,
                        LinkedHashMap::new,  // 保持插入順序
                        Collectors.toList()
                ));

        // 2. 循環(huán)依賴檢測
        detectCyclicDependencies(items, nodeMap);

        // 3. 構(gòu)建樹結(jié)構(gòu)
        nodeMap.forEach((nodeId, node) -> {
            List<T> children = parentChildrenMap.getOrDefault(nodeId, Collections.emptyList())
                    .stream()
                    .sorted(comparator)
                    .collect(Collectors.toList());

            childSetter.setChildren(node, Collections.unmodifiableList(children));
        });

        // 4. 獲取根節(jié)點（parentId為null或不存在于nodeMap）
        return items.stream()
                .filter(item -> isRootNode(item, nodeMap))
                .sorted(comparator)
                .collect(Collectors.toList());

    }

    /**
     * 判斷是否為根節(jié)點（抽離方法提升可讀性）
     */
    private boolean isRootNode(T item, Map<K, T> nodeMap) {
        K parentId = parentIdGetter.apply(item);
        return parentId == null || !nodeMap.containsKey(parentId);
    }

    /**
     * 構(gòu)建搜索結(jié)果樹
     */
    public List<T> buildSearchTree(List<T> allItems, Set<K> matchIds) {
        Objects.requireNonNull(allItems, "節(jié)點列表不能為null");
        Objects.requireNonNull(matchIds, "匹配ID集合不能為null");

        Set<K> relatedIds = findRelatedIds(allItems, matchIds);
        List<T> relatedItems = allItems.stream()
                .filter(item -> relatedIds.contains(idGetter.apply(item)))
                .collect(Collectors.toList());

        return buildTree(relatedItems);
    }

    /**
     * 創(chuàng)建節(jié)點ID映射表（含重復(fù)檢測）
     */
    private Map<K, T> createNodeMap(List<T> items) {
        Map<K, T> map = new LinkedHashMap<>(items.size());
        for (T item : items) {
            K id = idGetter.apply(item);
            if (map.containsKey(id)) {
                throw new IllegalArgumentException(String.format(
                        "發(fā)現(xiàn)重復(fù)節(jié)點ID: %s (沖突對象1: %s, 沖突對象2: %s)",
                        id, map.get(id), item));
            }
            map.put(id, item);
        }
        return map;
    }

    /**
     * 循環(huán)依賴檢測核心邏輯
     */
    private void detectCyclicDependencies(List<T> items, Map<K, T> nodeMap) {
        Set<K> verifiedNodes = new HashSet<>();
        Map<K, K> idToParentMap = items.stream()
                .collect(Collectors.toMap(idGetter, parentIdGetter));

        for (T item : items) {
            K currentId = idGetter.apply(item);
            if (verifiedNodes.contains(currentId)) continue;

            Set<K> path = new LinkedHashSet<>();
            K tracingId = currentId;

            while (tracingId != null) {
                if (!path.add(tracingId)) {
                    throw new CyclicDependencyException(buildCyclePath(path, tracingId));
                }

                // 短路已驗證節(jié)點
                if (verifiedNodes.contains(tracingId)) break;

                K parentId = idToParentMap.get(tracingId);
                if (parentId == null) break;

                // 直接循環(huán)檢測
                if (parentId.equals(tracingId)) {
                    throw new CyclicDependencyException("直接循環(huán)依賴: " + tracingId);
                }

                tracingId = parentId;
            }
            verifiedNodes.addAll(path);
        }
    }

    /**
     * 構(gòu)造循環(huán)路徑描述
     */
    private String buildCyclePath(Set<K> path, K duplicateId) {
        List<K> pathList = new ArrayList<>(path);
        int index = pathList.indexOf(duplicateId);
        List<K> cycle = pathList.subList(index, pathList.size());
        return "檢測到循環(huán)依賴鏈: " + cycle.stream()
                .map(Object::toString)
                .collect(Collectors.joining(" → "));
    }

    /**
     * 查找相關(guān)ID集合（匹配節(jié)點+路徑節(jié)點）
     */
    private Set<K> findRelatedIds(List<T> allItems, Set<K> matchIds) {
        Map<K, K> idToParentMap = allItems.stream()
                .collect(Collectors.toMap(idGetter, parentIdGetter));

        return matchIds.stream()
                .flatMap(id -> traceAncestors(id, idToParentMap).stream())
                .collect(Collectors.toSet());
    }

    /**
     * 追溯父節(jié)點鏈
     */
    private Set<K> traceAncestors(K startId, Map<K, K> idToParentMap) {
        Set<K> ancestors = new LinkedHashSet<>();
        K currentId = startId;

        while (currentId != null && ancestors.add(currentId)) {
            currentId = idToParentMap.get(currentId);
        }
        return ancestors;
    }

    /**
     * 自定義循環(huán)依賴異常
     */
    public static class CyclicDependencyException extends RuntimeException {
        public CyclicDependencyException(String message) {
            super(message);
        }
    }

    /**
     * 子節(jié)點設(shè)置接口
     */
    @FunctionalInterface
    public interface ChildSetter<T> {
        void setChildren(T parent, List<T> children);
    }

    /* 快捷構(gòu)造方法 */

    public static <T, K> TreeBuilder<T, K> create(
            Function<T, K> idGetter,
            Function<T, K> parentIdGetter,
            ChildSetter<T> childSetter,
            Comparator<T> comparator) {
        return new TreeBuilder<>(idGetter, parentIdGetter, childSetter, comparator);
    }

    public static <T, K extends Comparable<? super K>> TreeBuilder<T, K> createWithNaturalOrder(
            Function<T, K> idGetter,
            Function<T, K> parentIdGetter,
            ChildSetter<T> childSetter) {
        return new TreeBuilder<>(
                idGetter,
                parentIdGetter,
                childSetter,
                Comparator.comparing(idGetter, Comparator.nullsLast(Comparator.naturalOrder()))
        );
    }
}

Map<K, T> nodeMap = createNodeMap(items);
Map<K, List<T>> parentChildrenMap = items.stream()
        .collect(Collectors.groupingBy(...));

Set<K> path = new LinkedHashSet<>();
while (tracingId != null) {
    if (!path.add(tracingId)) {
        throw new CyclicDependencyException(...);
    }
    // 追溯父節(jié)點鏈
}

Set<K> traceAncestors(K startId) {
    // 向上追溯所有祖先節(jié)點
}

childSetter.setChildren(node, 
    children.stream()
        .sorted(comparator)
        .collect(Collectors.toList())
);

public class CyclicDependencyException extends RuntimeException {
    // 攜帶具體循環(huán)路徑信息
}

@FunctionalInterface
public interface ChildSetter<T> {
    void setChildren(T parent, List<T> children);
}

TreeBuilder<Department, Long> builder = 
    new TreeBuilder<>(..., (parent, children) -> parent.setChildDepts(children));

List<Menu> menus = getFromDB();

TreeBuilder<Menu, Integer> builder = TreeBuilder.create(
    Menu::getId,
    Menu::getParentId,
    (parent, children) -> parent.setChildren(children),
    Comparator.comparing(Menu::getSortOrder)
);

List<Menu> tree = builder.buildTree(menus);

Set<Integer> matchIds = searchService.findIds("關(guān)鍵");
List<Menu> resultTree = builder.buildSearchTree(allMenus, matchIds);