/**
 * ─────────────────────────────────────────────
 *  SPB Git — Personal Git Platform
 * ─────────────────────────────────────────────
 *  Author  : Simon-Pierre Boucher
 *  Contact : contact@spboucher.ai
 *  File    : src/git/archive.mjs
 *  Purpose : zip / tar.gz snapshot generation with per-sha caching
 *  License : MIT © Simon-Pierre Boucher
 * ─────────────────────────────────────────────
 */

import { spawn } from 'node:child_process';
import { createWriteStream, createReadStream, existsSync, renameSync, statSync, rmSync } from 'node:fs';
import { mkdirSync } from 'node:fs';
import { dirname } from 'node:path';
import { randomBytes } from 'node:crypto';

export const ARCHIVE_FORMATS = Object.freeze({
  zip: { ext: 'zip', mime: 'application/zip', gitFormat: 'zip' },
  'tar.gz': { ext: 'tar.gz', mime: 'application/gzip', gitFormat: 'tar.gz' },
});

/**
 * Produce (or reuse) a snapshot archive for `<repo>@<sha>` and stream it.
 * @param {{repos: object, cache: object}} ctx
 * @param {string} repo
 * @param {string} sha resolved commit sha
 * @param {'zip'|'tar.gz'} format
 * @param {import('fastify').FastifyReply} reply
 * @param {string} downloadName filename presented to the client (no extension)
 */
export async function sendArchive(ctx, repo, sha, format, reply, downloadName) {
  const spec = ARCHIVE_FORMATS[format];
  if (!spec) {
    return reply.code(400).send({ error: { code: 'bad_format', message: 'zip or tar.gz only' } });
  }
  const cachePath = ctx.cache.repoPath(repo, sha, `archive.${spec.ext}`);

  if (!existsSync(cachePath)) {
    mkdirSync(dirname(cachePath), { recursive: true });
    const tmp = `${cachePath}.${randomBytes(4).toString('hex')}.tmp`;
    const ok = await new Promise((resolve) => {
      const child = spawn(
        'git',
        ['archive', `--format=${spec.gitFormat}`, `--prefix=${downloadName}/`, sha],
        { cwd: ctx.repos.dir(repo) },
      );
      const out = createWriteStream(tmp);
      child.stdout.pipe(out);
      child.on('error', () => resolve(false));
      child.on('close', (code) => {
        out.close(() => resolve(code === 0));
      });
    });
    if (!ok) {
      rmSync(tmp, { force: true });
      return reply.code(500).send({ error: { code: 'archive_failed', message: 'could not create archive' } });
    }
    renameSync(tmp, cachePath);
  }

  const size = statSync(cachePath).size;
  reply
    .header('Content-Type', spec.mime)
    .header('Content-Length', size)
    .header('Content-Disposition', `attachment; filename="${downloadName}.${spec.ext}"`)
    .header('Cache-Control', 'public, max-age=31536000, immutable')
    .header('X-Content-Type-Options', 'nosniff');
  return reply.send(createReadStream(cachePath));
}