Recursively prepend a header banner to all files in directory

headers.ts

const fs = require('fs').promises;
const path = require('path');

interface Params {
  dir: string;
  header: string;
  predicate: (filePath: string) => Boolean;
}

interface WalkTree {
  (params: Omit<Params, 'header'>): AsyncGenerator<string, void, void>;
}

interface Headers {
  (params: Params): Promise<void>;
}

export const walkTree: WalkTree = async function*({ dir, predicate }) {
  const files = await fs.readdir(dir);

  for (const file of files) {
    const filePath = path.join(dir, file);
    const stat = await fs.stat(filePath);

    if (stat.isDirectory()) {
      yield* walkTree({ dir: filePath, predicate });
    } else if (predicate(file)) {
      yield filePath;
    }
  }
};

export const headers: Headers = async ({ dir, header, predicate }) => {
  for await (const filePath of walkTree({ dir, predicate })) {
    const start = process.hrtime();

    const data = Buffer.from(await fs.readFile(filePath));

    if (data.indexOf(header) === 0) continue;

    const fd = await fs.open(filePath, 'w+');

    await fd.write(header, 0, header.length, 0);
    await fd.write(data, 0, data.length, header.length);
    await fd.close();

    const [, ns] = process.hrtime(start);
    const ms = ns / 1000000;

    console.info(`${filePath} ${ms}ms`);
  }
};

const header = `\/**
 * Copyright (c) Seamless Payments, Inc.
 *
 * This source code is licensed under the MIT license found in the
 * LICENSE file in the root directory of this source tree.
 */\n\n`;

headers({
  dir: '.',
  header,
  predicate: filePath => /\.java$/.test(filePath),
});