import * as Page from "../types/page";

// type Queue = [() => void, () => void];

export default class Loader {
  private $pages: Record<string, Page.Options>;
  private $status: Record<string, 1 | 2>; // 页面的加载状态：1正在加载  2加载完成
  private $queue: Record<string, any[]> = {};

  constructor() {
    this.$pages = {};
    this.$status = {};
    // this.$queue = {};
  }

  /**
   * 通过fetch发送请求
   * @param url
   */
  private fetch(url: string) {
    fetch(url)
      .then((response) => {
        let data = response.json();
        this.$pages[url] = data as any;
        this.$queue[url].forEach(([resolve, reject]) => {
          resolve(this.$pages[url]);
        });
        this.$status[url] = 2;
      })
      .catch((e) => {
        this.$queue[url].forEach(([resolve, reject]) => {
          reject(this.$pages[url]);
        });
        delete this.$status[url];
      })
      .finally(() => {
        this.$queue[url] = [];
      });
  }

  /**
   * 加载页面
   * @param url
   * @param force
   */
  public load(url: string, force = false): Promise<Page.Options> {
    // this.$queue[url] = this.$queue[url] || []
    // 正在加载
    if (this.$status[url] === 1) {
      return new Promise<Page.Options>((resolve, reject) => {
        this.$queue[url].push([resolve, reject]);
      });
    }
    // 不强制加载，且已经加载过
    if (!force && this.$status[url] === 2) {
      return Promise.resolve(this.$pages[url]);
    }
    // 没加载过
    return new Promise<Page.Options>((resolve, reject) => {
      this.$queue[url] = [[resolve, reject]];
      this.fetch(url);
    });
  }
}