/**
 * Static-config subscriber store for the build bus
 * ([[openspec/changes/build-bus-poll-cd/proposal.md]] Phase 2-lite).
 *
 * The first cut of cross-machine event distribution skips the
 * registry-server switchboard described in §6 of the spec — instead
 * the operator maintains a JSON file under their celilo data dir
 * that lists each subscriber URL + secret + match rule. This file
 * is the single source of truth for publishes that originate on
 * this machine.
 *
 * File layout (default `~/Library/Application Support/celilo/build-bus-subscribers.json`
 * on macOS, similar XDG path on Linux — see config/paths.ts):
 *
 *   {
 *     "subscribers": [
 *       {
 *         "name": "lunacycle build box",
 *         "url": "https://lunacycle.lab/build-bus",
 *         "secret": "<hmac-secret>",
 *         "match": { "registry": "npm", "packagePattern": "@celilo/*" }
 *       }
 *     ]
 *   }
 *
 * Override the file path with the CELILO_BUILD_BUS_SUBSCRIBERS_PATH
 * env var (used by integration tests).
 */

import { existsSync, mkdirSync, readFileSync, writeFileSync } from 'node:fs';
import { dirname, join } from 'node:path';
import type { Subscriber } from '@celilo/event-bus/build-bus';
import { getDataDir } from '../../config/paths';

const FILE_NAME = 'build-bus-subscribers.json';

interface StoreFile {
  subscribers: Subscriber[];
}

/**
 * Resolve the subscriber-store path. Respects
 * CELILO_BUILD_BUS_SUBSCRIBERS_PATH for testability; otherwise
 * lives alongside the rest of celilo's per-machine state under
 * getDataDir().
 */
export function subscriberStorePath(): string {
  return process.env.CELILO_BUILD_BUS_SUBSCRIBERS_PATH ?? join(getDataDir(), FILE_NAME);
}

/**
 * Load the subscriber list. Missing file → empty list (treat as
 * "no subscribers configured"; this is the silent-no-op path that
 * keeps the build-bus opt-in). Malformed JSON throws so the operator
 * notices.
 */
export function loadSubscribers(): Subscriber[] {
  const path = subscriberStorePath();
  if (!existsSync(path)) return [];
  const content = readFileSync(path, 'utf-8');
  let parsed: StoreFile;
  try {
    parsed = JSON.parse(content) as StoreFile;
  } catch (err) {
    throw new Error(`Could not parse ${path}: ${err instanceof Error ? err.message : String(err)}`);
  }
  if (!Array.isArray(parsed.subscribers)) {
    throw new Error(`${path} has no "subscribers" array at the top level.`);
  }
  return parsed.subscribers;
}

/**
 * Replace the subscriber list. Creates the parent dir if needed,
 * writes atomically (temp file + rename) so a failed write doesn't
 * leave a corrupt store.
 */
export function saveSubscribers(subscribers: Subscriber[]): void {
  const path = subscriberStorePath();
  mkdirSync(dirname(path), { recursive: true });
  const tmp = `${path}.tmp`;
  writeFileSync(tmp, `${JSON.stringify({ subscribers }, null, 2)}\n`);
  // Bun supports rename via the standard Node fs API; this fails fast
  // on EXDEV but the temp + path live in the same dir so cross-FS
  // isn't a concern.
  const { renameSync } = require('node:fs') as typeof import('node:fs');
  renameSync(tmp, path);
}

/**
 * Add a subscriber. If one with the same URL exists, replace it
 * (idempotent re-adds with updated secret/match are common when an
 * operator rotates credentials). Returns the prior subscriber, if any.
 */
export function addSubscriber(subscriber: Subscriber): { replaced?: Subscriber } {
  const existing = loadSubscribers();
  const prior = existing.find((s) => s.url === subscriber.url);
  const next = existing.filter((s) => s.url !== subscriber.url);
  next.push(subscriber);
  saveSubscribers(next);
  return prior ? { replaced: prior } : {};
}

/**
 * Remove a subscriber by URL. Returns the removed entry, if any.
 */
export function removeSubscriberByUrl(url: string): Subscriber | undefined {
  const existing = loadSubscribers();
  const prior = existing.find((s) => s.url === url);
  if (!prior) return undefined;
  saveSubscribers(existing.filter((s) => s.url !== url));
  return prior;
}