/**
 * Patch: reduce microsub feed polling batch concurrency from 5 to 3.
 *
 * With 50 subscribed feeds and 9 at low tiers (16–32 min refresh), concurrent
 * XML/JSON parsing drives p99 event loop lag to ~187ms and sustained CPU to
 * 20–35%. Reducing BATCH_CONCURRENCY from 5 to 3 smooths the spikes without
 * affecting throughput (scheduler runs every 60s; typical cycle processes 1–4
 * feeds anyway).
 */
import { access, readFile, writeFile } from "node:fs/promises";

const MARKER = "// [patch] microsub-batch-concurrency";

const OLD_SNIPPET = `const BATCH_CONCURRENCY = 5; // Process 5 feeds at a time`;
const NEW_SNIPPET = `const BATCH_CONCURRENCY = 3; // Process 3 feeds at a time ${MARKER}`;

const candidates = [
  "node_modules/@rmdes/indiekit-endpoint-microsub/lib/polling/scheduler.js",
  "node_modules/@indiekit/indiekit/node_modules/@rmdes/indiekit-endpoint-microsub/lib/polling/scheduler.js",
];

async function exists(filePath) {
  try {
    await access(filePath);
    return true;
  } catch {
    return false;
  }
}

let applied = 0;
let skipped = 0;

for (const filePath of candidates) {
  if (!(await exists(filePath))) continue;

  const src = await readFile(filePath, "utf8");

  if (src.includes(MARKER)) {
    skipped++;
    continue;
  }

  if (!src.includes(OLD_SNIPPET)) {
    console.warn(
      `[patch] microsub-batch-concurrency: upstream format changed in ${filePath}`,
    );
    continue;
  }

  await writeFile(filePath, src.replace(OLD_SNIPPET, NEW_SNIPPET), "utf8");
  applied++;
}

if (applied > 0) {
  console.log(
    `[patch] microsub-batch-concurrency: applied to ${applied} file(s)`,
  );
} else if (skipped > 0) {
  console.log(`[patch] microsub-batch-concurrency: already applied`);
}