import { parse } from "https://deno.land/std@0.195.0/yaml/mod.ts";
import { join, fromFileUrl } from "https://deno.land/std@0.193.0/path/mod.ts";

export const PAGES_PATH = join(fromFileUrl(import.meta.url), "../pages.yaml");

export interface PageDescription {
  name: string;
  description: string;
}

async function readPagesDescription() {
  const pagesText = await Deno.readTextFile(PAGES_PATH);
  const pages = parse(pagesText) as PageDescription[];
  return pages;
}

function watchFile(
  path: string,
  callback: () => void | Promise<void>,
) {
  const watcherRef = Deno.watchFs(path);
  (async () => {
    for await (const event of watcherRef) {
      if (event.kind == "modify") {
        await callback();
      }
    }
  })();
  const closeHandler = () => {
    watcherRef.close();
  };
  Deno.addSignalListener("SIGINT", closeHandler);
  return ()=>{
    Deno.removeSignalListener("SIGINT", closeHandler);
    closeHandler();
  }
}

let pages_meta: PageDescription[] = [];
let mtime = 0;
let lastest_disposer = () => {};
export async function get_pages_meta(): Promise<[PageDescription[],number]>{
  if (pages_meta.length == 0) {
    pages_meta = await readPagesDescription();
    mtime = Date.now();
    lastest_disposer();
    lastest_disposer = watchFile(PAGES_PATH, async () => {
      pages_meta = await readPagesDescription();
      mtime = Date.now();
    });
  }
  return [pages_meta, mtime];
}