// Write the current commit into src/build-info.js.
//
// Runs before serving and before building, so what is on screen always names
// the commit it came from. The file is tracked rather than generated-and-
// ignored so that a fresh clone works without running anything first; it
// changes at most once per commit, and only when the value actually differs.

import { execFileSync } from 'node:child_process';
import { readFileSync, writeFileSync } from 'node:fs';
import { resolve, dirname } from 'node:path';
import { fileURLToPath } from 'node:url';

const root = resolve(dirname(fileURLToPath(import.meta.url)), '..');
const target = resolve(root, 'src/build-info.js');

function commit() {
  try {
    const sha = execFileSync('git', ['rev-parse', '--short', 'HEAD'], { cwd: root, stdio: 'pipe' })
      .toString().trim();
    const dirty = execFileSync('git', ['status', '--porcelain'], { cwd: root, stdio: 'pipe' })
      .toString().trim().length > 0;
    return dirty ? `${sha}+` : sha;
  } catch {
    return 'dev';
  }
}

const next = `// Stamped by tools/stamp.js, which runs before \`npm run serve\` and
// \`npm run build\`. The commit is whatever HEAD was at stamp time, so a dist
// file says exactly which commit produced it.
export const BUILD = {
  commit: '${commit()}',
  builtAt: '${new Date().toISOString().slice(0, 10)}',
};
`;

const current = readFileSync(target, 'utf8');
// Only the date differs on a same-commit restamp; leave the file alone then,
// so a working tree does not churn every time the server starts.
const strip = (text) => text.replace(/builtAt: '[^']*'/, '');
if (strip(current) !== strip(next)) {
  writeFileSync(target, next, 'utf8');
  console.log(`stamped build ${commit()}`);
}