/**
 * A bed's forge: a checkout's HEAD carried into a fresh bare repository, which a git daemon then serves.
 *
 * **A shallow checkout is carried as it is** (novox/hq issue 689). The lab module checks every repository
 * out shallow, and a fresh bare repository refuses a push whose history ends in a cut ("shallow update not
 * allowed"), so the genesis bed raised its anchor and forge and then skipped. The bare repository accepts
 * the cut (`receive.shallowUpdate`) and serves the history the checkout holds: the bed serves the commit
 * under test, and nothing it raises reads further back than the run's checkout does. Unshallowing first is
 * not an option in a lab run: the forge credential is gone once the run's clones are done, so a private
 * repository could not be fetched again.
 */

import { execFileSync } from "node:child_process";

/**
 * Initialise `bare` and push `checkout`'s HEAD into it under each of `branches`. Returns the commit served.
 */
export function carry(checkout: string, bare: string, branches: string[] = ["main"]): string {
  execFileSync("git", ["init", "-q", "--bare", bare]);
  // No collection after the push: one run in the background rewrites the objects while they are carried.
  execFileSync("git", ["-C", bare, "config", "receive.autogc", "false"]);
  // The lab's checkouts are shallow, and a bare repository refuses a shallow push without this.
  execFileSync("git", ["-C", bare, "config", "receive.shallowUpdate", "true"]);
  const [first, ...rest] = branches;
  execFileSync("git", ["-C", checkout, "push", "-q", "--force", bare, `HEAD:refs/heads/${first}`], { stdio: "pipe" });
  const head = execFileSync("git", ["-C", checkout, "rev-parse", "HEAD"], { encoding: "utf8" }).trim();
  // The other branches are set in the bare repository itself: a shallow push of several refs at once has
  // receive-pack fail every ref after the first ("remote failed to report status").
  for (const branch of rest) execFileSync("git", ["-C", bare, "update-ref", `refs/heads/${branch}`, head]);
  return head;
}