import { readFile } from 'node:fs/promises';
import { spawn } from 'node:child_process';

/**
 * gitRevParse spawns a git rev-parse command and reports its stdout
 * in a resolved promise or a rejected error on completion,
 * depending on the exit code.
 */
const gitRevParse = (rev) => new Promise((resolve, reject) => {
  let commit = '', err = '';
  const proc = spawn('git', ['rev-parse', '--short', rev]);
  proc.stdout.on('data', (data) => commit += data.toString().trim());
  proc.stderr.on('data', (data) => err += err.toString());
  proc.on('close', (code) => code === 0 ? resolve(commit) : reject(err));
});

/**
 * replaceOnCopyPlugin is an esbuild plugin. it loads files as utf-8 text
 * and replaces certain placeholders with their values computed on plugin setup.
 * the fileFilter is a regexp matching names or extensions of the files to process,
 * passed to esbuild's onLoad as is.
 *
 * the following placeholders are replaced:
 *
 * #[PKG_VERSION]# -> npm package version
 * #[GIT_COMMIT]#  -> short git commit at current HEAD
 */
export const replaceOnCopyPlugin = (fileFilter) => {
  return {
    name: 'replace-on-copy',
    setup(build) {
      const appVersion = process.env.npm_package_version;
      const gitHeadCommit = gitRevParse('HEAD');

      build.onLoad({filter: fileFilter}, async (args) => {
        const gitCommitHash = await gitHeadCommit;
        let text = await readFile(args.path, 'utf8');
        text = text.replaceAll('#[PKG_VERSION]#', appVersion);
        text = text.replaceAll('#[GIT_COMMIT]#', gitCommitHash);
        return {
          contents: text,
          loader: 'copy',
        }
      });
    }
  }
}