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export function versioned(url: string): Versioned | undefined {  for (const Impl of IMPLS) {    const v = new Impl(url) as Versioned;    if (v.regexp.test(url)) {      return v;    }  }}
export interface Versioned {  url: string;  // all versions of the url  all: () => Promise<string[]>;  // url at a given version  at(version: string): Versioned;  // current version of url  current: () => string;  // is url valid for this Versioned  regexp: RegExp;}
function defaultAt(that: Versioned, version: string): string {  return that.url.replace(/\@([^\/]*?)\//, `@${version}/`);}
function defaultCurrent(that: Versioned): string {  const v = that.url.match(/\@([^\/]*?)\//);  if (v === null) {    throw Error(`Unable to find version in ${that.url}`);  }  return v[1];}
function defaultName(that: Versioned): string {  const n = that.url.match(/([^\/\"\']*?)\@[^\'\"]*/);  if (n === null) {    throw new Error(`Package name not found in ${that.url}`);  }  return n[1];}
// There must be a better way...const GR_CACHE: Map<string, string[]> = new Map<string, string[]>();async function githubReleases(owner: string, repo: string): Promise<string[]> {  const cacheKey = `${owner}/${repo}`;  if (GR_CACHE.has(cacheKey)) {    return GR_CACHE.get(cacheKey)!;  }  const page = await fetch(`http://github.com/${owner}/${repo}/releases.atom`);  const text = await page.text();  // naively, we grab all the titles, except the first which is the page titleL  const m = text.matchAll(/<title>(.*?)\<\/title\>/g);  const versions = [...m].map(x => x[1]).slice(1);  GR_CACHE.set(cacheKey, versions);  return versions;}
let denoLandDB: any;
class DenoLand implements Versioned {  url: string;
  constructor(url: string) {    this.url = url;  }
  name(): string {    return defaultName(this);  }
  async all(): Promise<string[]> {    if (!denoLandDB) {      const dbUrl =        "https://raw.githubusercontent.com/denoland/deno_website2/master/src/database.json";      denoLandDB = await (await fetch(dbUrl)).json();    }    let res: any;    try {      res = denoLandDB[this.name()];    } catch {      throw new Error(`${this.name()} not found in deno land json`);    }
    const { type, owner, repo } = res;    if (type !== "github") {      throw new Error(`${this.name()} has unsupported type ${type}`);    }
    return await githubReleases(owner, repo);  }
  at(version: string): Versioned {    const url = defaultAt(this, version);    return new DenoLand(url);  }
  current(): string {    return defaultCurrent(this);  }
  regexp: RegExp = /https?:\/\/deno.land\/x\/[^\/\"\']*?\@[^\'\"]*/;}
class DenoStd implements Versioned {  url: string;
  constructor(url: string) {    this.url = url;  }
  async all(): Promise<string[]> {    return await githubReleases("denoland", "deno");  }
  at(version: string): Versioned {    const url = defaultAt(this, version);    return new DenoStd(url);  }
  current(): string {    return defaultCurrent(this);  }
  regexp: RegExp = /https?:\/\/deno.land\/std\@[^\'\"]*/;}
class Unpkg implements Versioned {  url: string;
  name(): string {    return defaultName(this);  }
  constructor(url: string) {    this.url = url;  }
  async all(): Promise<string[]> {    const page = await fetch(`https://unpkg.com/browse/${this.name()}/`);    const text = await page.text();    // naively, we grab all the titles, except the first which is the page titleL    const m = [...text.matchAll(/\<option value\=\"(.*?)\"\>/g)];    m.reverse();    return m.map(x => x[1]);  }
  at(version: string): Versioned {    const url = defaultAt(this, version);    return new Unpkg(url);  }
  current(): string {    return defaultCurrent(this);  }
  regexp: RegExp = /https?:\/\/unpkg.com\/[^\/\"\']*?\@[^\'\"]*/;}
class Denopkg implements Versioned {  url: string;
  owner(): string {    return this.url.split("/")[3];  }
  repo(): string {    return defaultName(this);  }
  constructor(url: string) {    this.url = url;  }
  async all(): Promise<string[]> {    return await githubReleases(this.owner(), this.repo());  }
  at(version: string): Versioned {    const url = defaultAt(this, version);    return new Denopkg(url);  }
  current(): string {    return defaultCurrent(this);  }
  regexp: RegExp =    /https?:\/\/denopkg.com\/[^\/\"\']*?\/[^\/\"\']*?\@[^\'\"]*/;}
// TODO Pika
export const IMPLS = [DenoStd, DenoLand, Unpkg, Denopkg];