export default function changelog(args: string[], _opts: any, logger: Logger): void {
  if (args.length == 0) {
    logger.fatal('publish changelog <start-tag>');
    return;
  }

  cl(config, null, {from: args[0]})
    .on('error', function (err: Error) {
      logger.error('Failed to generate changelog: ' + err);
    })
    .pipe(changelogStream)
    .on('close', prependDelta);
}

export async function prependChangelogFromLatestTag(changelogPath: string, releaseName: string) {
  const outputStream: Readable = conventionalChangelog(
    /* core options */ {preset: 'angular'},
    /* context options */ {title: releaseName},
    /* raw-commits options */ null,
    /* commit parser options */ null,
    /* writer options */ createChangelogWriterOptions(changelogPath));

  // Stream for reading the existing changelog. This is necessary because we want to
  // actually prepend the new changelog to the existing one.
  const previousChangelogStream = createReadStream(changelogPath);

  return new Promise((resolve, reject) => {
    // Sequentially merge the changelog output and the previous changelog stream, so that
    // the new changelog section comes before the existing versions. Afterwards, pipe into the
    // changelog file, so that the changes are reflected on file system.
    const mergedCompleteChangelog = merge2(outputStream, previousChangelogStream);

    // Wait for the previous changelog to be completely read because otherwise we would
    // read and write from the same source which causes the content to be thrown off.
    previousChangelogStream.on('end', () => {
      mergedCompleteChangelog.pipe(createWriteStream(changelogPath))
        .once('error', (error: any) => reject(error))
        .once('finish', () => resolve());
    });
  });
}