import { ChildProcessWithoutNullStreams, spawn } from 'child_process';

export function stdoutOn(bat: ChildProcessWithoutNullStreams): Promise<string> {
  return new Promise((resolve) => {
    bat.stdout.on('data', (data: Buffer) => {
      resolve(data.toString());
    });
  });
}

export async function getFileRowsNumber(filePath: string): Promise<number> {
  const res = await stdoutOn(spawn('wc', ['-l', filePath]));
  return Promise.resolve(Number(/\d+\s/.exec(res)));
}

export async function getFileHeadData(filePath: string, count: number): Promise<string[]> {
  const rows = await getFileRowsNumber(filePath);
  if (rows <= 0) {
    return Promise.resolve([]);
  }

  const res = await stdoutOn(spawn('head', ['-n', count.toString(), filePath]));
  return Promise.resolve(res.split('\n', count));
}

export async function getFileMiddleData(filePath: string, count: number): Promise<string[]> {
  const rows = await getFileRowsNumber(filePath);
  if (rows <= count) {
    return Promise.resolve([]);
  }

  const halfRows = Math.floor(rows / 2);
  const halfCount = Math.floor(count / 2);
  const start = halfRows - halfCount;
  const end = count % 2 === 0 ? halfRows + halfCount - 1 : halfRows + halfCount;
  const res = await stdoutOn(spawn('sed', ['-n', `${start},${end}p`, filePath]));
  return Promise.resolve(res.split('\n', count));
}

export async function getFileTailData(filePath: string, count: number): Promise<string[]> {
  const rows = await getFileRowsNumber(filePath);
  if (rows <= 0) {
    return Promise.resolve([]);
  }

  const res = await stdoutOn(spawn('tail', ['-n', count.toString(), filePath]));
  return Promise.resolve(res.split('\n', count));
}