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import { merge } from "../core/utils.ts";import onDemand from "../middlewares/on_demand.ts";
import type { Page, Site } from "../core.ts";import type { Router } from "../middlewares/on_demand.ts";
export interface Options {  /** A function to return the page file associated with the provided url */  router?: Router;}
// Default optionsexport const defaults: Options = {};
/** A plugin to generate pages on demand in the server side */export default function (userOptions?: Partial<Options>) {  const options = merge(defaults, userOptions);
  return (site: Site) => {    if (!options.router) {      const router = new JsonRouter(site.src("_routes.json"));      router.startCollecting(site);      options.router = router.match.bind(router);    }
    const { router } = options;
    site.options.server.middlewares ||= [];    site.options.server.middlewares.push(onDemand({ site, router }));  };}
/** Class to load and manage static routes in a JSON file *  Used by default if no router is provided */export class JsonRouter {  /** Filename to save the {url: path} of on-demand pages */  #routesFile: string;
  /** Pages that must be generated on demand */  #routes?: Map<string, string>;
  constructor(routesFile: string) {    this.#routesFile = routesFile;  }
  async match(url: URL): Promise<string | undefined> {    if (!this.#routes) {      await this.#loadRoutes();    }
    const { pathname } = url;    const path = this.#routes?.get(pathname);
    // Handle urls like /example as /example/    if (!path && !pathname.endsWith("/")) {      return this.#routes?.get(pathname + "/");    }
    return path;  }
  startCollecting(site: Site): void {    // Events to collect and save the routes automatically    site.addEventListener(      "afterRender",      () => this.#collectRoutes(site.pages),    );    site.addEventListener("afterBuild", () => this.#saveRoutes());
    // Ignore the routes file by the watcher    site.options.watcher.ignore.push(this.#routesFile);  }
  /** Collect the routes of all pages with data.ondemand = true */  #collectRoutes(pages: Page[]): void {    const routes = new Map<string, string>();
    pages.forEach((page) => {      if (page.data.ondemand) {        routes.set(page.data.url as string, page.src.path + page.src.ext);      }    });
    this.#routes = routes;  }
  /** Load the routes from the routesFile */  async #loadRoutes(): Promise<void> {    try {      const pages = JSON.parse(        await Deno.readTextFile(this.#routesFile),      ) as Record<string, string>;      this.#routes = new Map(Object.entries(pages));    } catch {      this.#routes = new Map();    }  }
  /** Save the routes into the routesFile */  async #saveRoutes(): Promise<void> {    if (!this.#routes?.size) {      return;    }
    const data: Record<string, string> = {};    this.#routes.forEach((path, url) => data[url] = path);
    await Deno.writeTextFile(      this.#routesFile,      JSON.stringify(data, null, 2) + "\n",    );  }}