watcher.ts

/**
 * @license
 * Copyright Google LLC All Rights Reserved.
 *
 * Use of this source code is governed by an MIT-style license that can be
 * found in the LICENSE file at https://angular.io/license
 */

import { FSWatcher } from 'chokidar';

export class ChangedFiles {
  readonly added = new Set<string>();
  readonly modified = new Set<string>();
  readonly removed = new Set<string>();

  toDebugString(): string {
    const content = {
      added: Array.from(this.added),
      modified: Array.from(this.modified),
      removed: Array.from(this.removed),
    };

    return JSON.stringify(content, null, 2);
  }
}

export interface BuildWatcher extends AsyncIterableIterator<ChangedFiles> {
  add(paths: string | readonly string[]): void;
  remove(paths: string | readonly string[]): void;
  close(): Promise<void>;
}

export function createWatcher(options?: {
  polling?: boolean;
  interval?: number;
  ignored?: string[];
}): BuildWatcher {
  const watcher = new FSWatcher({
    ...options,
    disableGlobbing: true,
    ignoreInitial: true,
  });

  const nextQueue: ((value?: ChangedFiles) => void)[] = [];
  let currentChanges: ChangedFiles | undefined;
  let nextWaitTimeout: NodeJS.Timeout | undefined;

  watcher.on('all', (event, path) => {
    switch (event) {
      case 'add':
        currentChanges ??= new ChangedFiles();
        currentChanges.added.add(path);
        break;
      case 'change':
        currentChanges ??= new ChangedFiles();
        currentChanges.modified.add(path);
        break;
      case 'unlink':
        currentChanges ??= new ChangedFiles();
        currentChanges.removed.add(path);
        break;
      default:
        return;
    }

    // Wait 250ms from next change to better capture groups of file save operations.
    if (!nextWaitTimeout) {
      nextWaitTimeout = setTimeout(() => {
        nextWaitTimeout = undefined;
        const next = nextQueue.shift();
        if (next) {
          const value = currentChanges;
          currentChanges = undefined;
          next(value);
        }
      }, 250);
      nextWaitTimeout?.unref();
    }
  });

  return {
    [Symbol.asyncIterator]() {
      return this;
    },

    async next() {
      if (currentChanges && nextQueue.length === 0) {
        const result = { value: currentChanges };
        currentChanges = undefined;

        return result;
      }

      return new Promise((resolve) => {
        nextQueue.push((value) => resolve(value ? { value } : { done: true, value }));
      });
    },

    add(paths) {
      watcher.add(paths);
    },

    remove(paths) {
      watcher.unwatch(paths);
    },

    async close() {
      try {
        await watcher.close();
        if (nextWaitTimeout) {
          clearTimeout(nextWaitTimeout);
        }
      } finally {
        let next;
        while ((next = nextQueue.shift()) !== undefined) {
          next();
        }
      }
    },
  };
}