import fsPromises from "node:fs/promises";

export interface WatcherEvent {
  eventType: "change" | "rename";
  filename: string | null;
}

export type WatcherEventHandler = (event: WatcherEvent) => Promise<void>;

export class Watcher {
  readonly #abortController: AbortController;
  readonly #eventLoop: Promise<void>;

  constructor(path: string, eventHandler: WatcherEventHandler) {
    this.#abortController = new AbortController();

    const events = fsPromises.watch(path, {
      recursive: true,
      signal: this.#abortController.signal,
    });

    this.#eventLoop = new Promise(async () => {
      for await (const event of events) {
        await eventHandler(event);
      }
    });
  }

  public close(): Promise<void> {
    this.#abortController.abort();
    return this.#eventLoop;
  }
}

import type { WatcherEvent } from "./watcher.js";
import type { BuildInfo } from "../../../types/artifacts.js";

import path from "node:path";

import { exists, readJsonFile } from "@ignored/hardhat-vnext-utils/fs";

import { BUILD_INFO_DIR_NAME } from "../artifacts/artifacts-manager.js";

import { Watcher } from "./watcher.js";

...

  const watcher = new Watcher(
    path.join(hre.config.paths.artifacts, BUILD_INFO_DIR_NAME),
    async ({ eventType, filename }: WatcherEvent) => {
      log(`Detected ${eventType} in ${filename}`);

      if (
        filename === null ||
        filename.endsWith(".output.json") ||
        !(await exists(filename))
      ) {
        return;
      }

      const filenameOutput = filename.replace(".json", ".output.json");
      if (await exists(filenameOutput)) {
        return;
      }

      const buildInfo: BuildInfo = await readJsonFile(filename);
      const buildInfoOutput = await readJsonFile(filenameOutput);

      try {
        await provider.request({
          method: "hardhat_addCompilationResult",
          params: [buildInfo.solcVersion, buildInfo.input, buildInfoOutput],
        });
      } catch (error) {
        log(error);
      }
    },
  );
  
  ...
  
  await watcher.close();
  
...