import { getPool } from "../../db/index.js";

// Lockless: concurrent cold misses may both compute, last writer wins.
export async function getCached(userId, tag, ttlMs, compute) {
  let client = await getPool();
  try {
    const hit = (
      await client.query(
        `SELECT data FROM cache
         WHERE user_id = $1 AND tag = $2
           AND updated_ts > NOW() - ($3 * interval '1 millisecond')`,
        [userId, tag, ttlMs],
      )
    ).rows[0];
    if (hit) return hit.data;
  } finally {
    await client.release();
  }

  const data = await compute();

  client = await getPool();
  try {
    await client.query(
      `INSERT INTO cache (user_id, tag, data) VALUES ($1, $2, $3::jsonb)
       ON CONFLICT (user_id, tag) DO UPDATE SET data = EXCLUDED.data, updated_ts = NOW()`,
      [userId, tag, data],
    );
  } finally {
    await client.release();
  }
  return data;
}