import { existsSync } from 'node:fs';
import { join } from 'node:path';

/**
 * Is there anything to update to?
 *
 * ── The rule, and why it is about TAGS rather than commits ──
 *
 * Until 2026-08-27 "update" meant `git pull` and re-install, unconditionally, for every plugin. Nothing
 * could say whether there was anything to pull, so the button was always offered and usually did nothing
 * — and "Update all" was a row of no-ops with a spinner on it.
 *
 * Tags fix that, and the owner's rule has two halves:
 *
 *   · **A checkout NOT at a tag is always updateable.** It is somewhere between releases — mid-development,
 *     or on a commit somebody pushed without tagging. There is no claim being made about it, so pulling is
 *     always reasonable.
 *   · **A checkout AT a tag is updateable only when a NEWER tag exists.** It is at a release, and a release
 *     is a claim that this is a finished thing. Offering an update that lands on the same release is how
 *     you teach someone to ignore the button.
 *
 * ── Why "newer" is not a version comparison ──
 *
 * The obvious implementation parses `2026.08.27.01` and compares. It is wrong the first time a plugin is
 * tagged `v2` or `1.0.0-rc1`, and wrong SILENTLY — a plugin that never offers an update looks like a
 * plugin nobody has released.
 *
 * So newness is asked of git instead: the newest tag REACHABLE FROM THE REMOTE BRANCH. If the tag at HEAD
 * is that tag, this checkout is at the latest release. If it is a different one, the remote has moved on.
 * That holds for any tag names anyone ever chooses, including ones that do not sort.
 *
 * ── Where "the newest tag" comes from: the catalogue, not this machine's refs ──
 *
 * Every answer here is local, and this is called once per plugin on a request that renders a list —
 * twenty-one network round trips would make the plugins screen feel broken. That left one hard problem:
 * refs on disk go stale. Tags arrived at clone and at the fetch `pullPlugin` does, so you learned an
 * update existed BY UPDATING. A machine that had not touched a plugin since August compared this
 * morning's release against a snapshot from before it existed and said, truthfully and uselessly, that
 * it was at the latest.
 *
 * That was patched with a rate-limited background `git fetch` per checkout, which worked and was the
 * wrong shape: every host in the fleet polling twenty-one repositories to re-derive a fact one place
 * already knows. The marketplace publishes releases now — see `servers/marketplace/sync.ts` — so the
 * newest release is simply asked of the catalogue, which every host already fetches for the store.
 *
 *   published tag (catalogue)  vs  tag at HEAD (this checkout)   →  differ, so there is an update
 *
 * DIFFERENCE, not ordering. `2026.08.27.01` parses fine until somebody tags `v2`, and then it fails
 * silently. Two strings that are not equal is a comparison that cannot rot.
 *
 * ── The git rule stays, for a plugin the store cannot speak for ──
 *
 * A checkout of something unpublished — a plugin being written, one never registered — has no catalogue
 * entry, and the fallback below is the old rule against local remote-tracking refs. Those refs are no
 * longer refreshed here, so for that case this can miss a tag until something else fetches. That is the
 * accepted cost: the alternative was every machine polling every repository forever to cover a case that
 * only arises on a developer's own box, where `git fetch` is a thing they were about to run anyway.
 */

export type ReleaseState = {
  /** The tag this checkout is exactly at, or null when it is between releases. */
  tagAtHead: string | null;
  /** The newest tag reachable from the tracked remote branch, as git orders them. */
  newestTag: string | null;
  updateable: boolean;
  /** Why, in words a UI can show without restating the rule. */
  reason: 'untagged' | 'new-release' | 'at-latest' | 'not-a-checkout';
};

const run = async (dir: string, args: string[]): Promise<string | null> => {
  const proc = Bun.spawn(['git', '-C', dir, ...args], { stdout: 'pipe', stderr: 'ignore' });
  const out = await new Response(proc.stdout).text();
  return (await proc.exited) === 0 ? out.trim() || null : null;
};

/**
 * @param publishedTag The tag the marketplace says is this plugin's newest release, or null when the
 *   catalogue has nothing to say — an unregistered plugin, one never tagged, or a store that could not
 *   be reached. Null falls through to the git rule rather than to a guess.
 */
export async function releaseState(dir: string, publishedTag: string | null = null): Promise<ReleaseState> {
  const none = { tagAtHead: null, newestTag: null };
  if (!existsSync(join(dir, '.git'))) {
    // Copied in by hand or bundled. Nothing to compare, and nothing to pull either — `pullPlugin` says
    // the same thing when asked.
    return { ...none, updateable: false, reason: 'not-a-checkout' };
  }

  // `--exact-match`, so this is "the tag AT this commit", not "the last tag before it". Fails, and
  // therefore returns null, when HEAD is between releases — which is the first half of the rule.
  const tagAtHead = await run(dir, ['describe', '--exact-match', '--tags', 'HEAD']);

  if (publishedTag) {
    // Reported even when HEAD is untagged, so the UI can say what pressing Update lands on. The old
    // code returned a bare null here and the button read "Update" with nothing after it.
    if (!tagAtHead) return { tagAtHead: null, newestTag: publishedTag, updateable: true, reason: 'untagged' };
    return publishedTag === tagAtHead
      ? { tagAtHead, newestTag: publishedTag, updateable: false, reason: 'at-latest' }
      : { tagAtHead, newestTag: publishedTag, updateable: true, reason: 'new-release' };
  }

  if (!tagAtHead) return { ...none, updateable: true, reason: 'untagged' };

  // Asked of the REMOTE branch, not of HEAD: a tag pushed after this checkout was made is not reachable
  // from HEAD and would be invisible if we described HEAD instead.
  const branch = (await run(dir, ['rev-parse', '--abbrev-ref', 'HEAD'])) ?? 'master';
  const newestTag =
    (await run(dir, ['describe', '--tags', '--abbrev=0', `origin/${branch}`])) ??
    (await run(dir, ['describe', '--tags', '--abbrev=0', 'origin/HEAD']));

  // No remote tags known yet — a checkout whose origin has never been fetched for tags. Not updateable
  // rather than "always updateable": claiming an update exists on no evidence is the worse error.
  if (!newestTag) return { tagAtHead, newestTag: null, updateable: false, reason: 'at-latest' };

  return newestTag === tagAtHead
    ? { tagAtHead, newestTag, updateable: false, reason: 'at-latest' }
    : { tagAtHead, newestTag, updateable: true, reason: 'new-release' };
}