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import {  createHash,  dirname,  ensureDir,  exists,  extname,  join,  resolve,} from "./deps.ts";import { fetchFile } from "./file_fetcher.ts";import { directory } from "./cache.ts";
export interface Policy {  maxAge: number;  strict?: boolean;}
export const RELOAD_POLICY: Policy = {  maxAge: -1,};
function checkPolicy(file: File, policy: Policy): boolean {  // birthtime is not available on all platforms.  if (!file.lstat.birthtime && !policy.strict) return true;  if (!file.lstat.birthtime) return false;  if (policy.maxAge < 0) return false;
  const now = new Date();  const then = file.lstat.birthtime;  const delta = (now.getTime() - then.getTime()) / 1000;  const stale = delta > policy.maxAge;  return stale;}
export enum Origin {  CACHE = "cache",  FETCH = "fetch",}
interface IFile {  url: URL;  hash: string;  path: string;  metapath: string;  meta: Metadata;  lstat: Deno.FileInfo;  origin: Origin;
  policy?: Policy;  ns?: string;}
export type File = Readonly<IFile>;
export interface Metadata {  headers?: { [key: string]: string };  url: string;}
export class FileWrapper {  hash: string;  path: string;  metapath: string;
  constructor(public url: URL, public policy?: Policy, public ns?: string) {    this.hash = hash(url);    this.path = path(url, ns);    this.metapath = metapath(url, ns);  }
  async exists(): Promise<boolean> {    return await exists(this.path);  }
  async remove(): Promise<void> {    await Deno.remove(this.path);    await Deno.remove(this.metapath);  }
  async ensure(): Promise<void> {    return await ensureDir(dirname(this.path));  }
  async read(): Promise<File> {    const meta = await metaread(this.url, this.ns);    return {      ...this,      lstat: await Deno.lstat(this.path),      meta,      origin: Origin.CACHE,    };  }
  async fetch(): Promise<File> {    const meta = await fetchFile(this.url, this.path);    await metasave(meta, this.url, this.ns);    return {      ...this,      lstat: await Deno.lstat(this.path),      meta,      origin: Origin.FETCH,    };  }
  async get(): Promise<File> {    await this.ensure();    if (await this.exists()) {      const file = await this.read();      if (!this.policy) return file;      if (checkPolicy(file, this.policy)) return file;    }
    return await this.fetch();  }}
function hash(url: URL) {  const formatted = `${url.pathname}${url.search ? "?" + url.search : ""}`;  return createHash("sha256").update(formatted).toString();}
function path(url: URL, ns?: string) {  let path = [directory()];  if (ns) path.push(ns);  path = path.concat([url.protocol.slice(0, -1), url.hostname, hash(url)]);  return resolve(`${join(...path)}${extname(url.pathname)}`);}
function metapath(url: URL, ns?: string) {  return resolve(`${path(url, ns)}.metadata.json`);}
async function metasave(meta: Metadata, url: URL, ns?: string): Promise<void> {  await Deno.writeTextFile(metapath(url, ns), JSON.stringify(meta));}
async function metaread(url: URL, ns?: string): Promise<Metadata> {  const metadata = await Deno.readTextFile(metapath(url, ns));  return JSON.parse(metadata) as Metadata;}