life-config.ts

import { z } from "zod";
import * as fs from "fs/promise";

export class LifeConfig<T extends z.ZodObject<any>> {
  bootstrapProcess: Promise<void>;
  watchingProcess: null | Promise<void> = null;
  store: null | z.infer<T> = null;
  ready = Promise.withResolvers<null>();
  subs = new Set<(state: z.infer<T>) => void>();

  constructor(
    private file: string | { toString(): string },
    private schema: T,
  ) {
    this.bootstrapProcess = this.bootstrap();
  }

  async bootstrap() {
    await this.load();
    this.watchingProcess = this.startWatchFile();
  }

  async startWatchFile() {
    for await (const event of fs.watch(new URL(`${this.file}`).pathname)) {
      await this.load();
    }
  }

  async load() {
    const store = this.schema.parse(
      JSON.parse(await fs.readFile(new URL(`${this.file}`), "utf-8")),
    );
    this.store = store;
    this.subs.forEach((cb) => cb(store));
    this.ready.resolve(null);
  }

  async wait() {
    await this.bootstrapProcess;
    await this.ready.promise;
  }

  async setup(cb: (state: z.infer<T>) => void) {
    if (this.store) cb(this.store);
    this.subs.add(cb);
    return () => this.subs.delete(cb);
  }
}

sample.ts

import { z } from "zod";
import { LifeConfig } from "./life-config.ts"

const lifeConfig = new LifeConfig(
  "config.json",
  z.object({
    prefixLog: z.string(),
  }),
);

await lifeConfig.wait();

let logger = (message: string) => comsole.log(`${lifeConfig.store.prefixLog} ${message}`);

lifeConfig.setup(() => {
  logger = (message: string) => comsole.log(`${lifeConfig.store.prefixLog} ${message}`);
});