export class TreeUtil<T extends TreeNode<T>> {
  map: {[k: string]: number} = {};
  roots: T[] = [];

  /**
   * @field status
   * @type
   * 0 - 未成功执行 `config` 方法;
   * 1 - 已成功执行 `config` 方法;
   */
  status: 0 | 1 = 0;

  pIdField!: keyof T;
  childIdField!: keyof T;
  levelIdField!: keyof T;

  constructor() {}

  /**
   * @function config - 配置字段名称
   * @param pIdField - parent id 对应的字段
   * @param childIdField - 节点 id 对应的字段
   * @param levelIdField - 节点 level 对应的字段
   * @example
   * ``` ts
   * T = {
   *  pId: 0,
   *  id: 1
   * }
   * ```
   * 则 `pIdField` 值为 ‘pId’, `childIdField` 的值为 1
   */
  config(pIdField: any, childIdField: any, levelIdField?: any): this {
    this.pIdField = pIdField;
    this.childIdField = childIdField;
    this.levelIdField = levelIdField;
    this.status = 1;
    return this;
  }

  /**
   * @function toTree
   * @param list - 源数据
   * @param isSorted 是否是已根据 level 排序（祖先节点在前）的数据
   * @description
   * 如果是已排序数据，则合并两次循环
   * @link https://stackoverflow.com/questions/18017869/build-tree-array-from-flat-array-in-javascript/22072374
   */
  toTree(list: T[], isSorted = false): T[] {
    if (this.status === 0) {
      throw new Error('Please execute config method first!');
    }
    // list.sort((a, b) => (a[this.levelIdField] as any) - b[this.levelIdField]);
    if (isSorted) {
      list.forEach((node, index) => {
        this.initMap(node, index);
        this.addChildNode(this.roots, list, node);
      });
    } else {
      list.forEach(this.initMap.bind(this));
      list.forEach((node, index) => {
        this.addChildNode(this.roots, list, node);
      });
    }
    return JSON.parse(JSON.stringify(this.roots));
  }

  initMap(node: T, index: number): void {
    this.map[node.id] = index;
    node.children = [];
  }
  addChildNode(target: T[], sources: T[],childNode: T): void {
    if (childNode[this.pIdField] !== 0) {
      sources[this.map[childNode.pId]].children.push(childNode);
    } else {
      target.push(childNode);
    }
  }
}

interface TreeNode<U> {
  [k: string]: any;
  children: U[];
}