#!/usr/bin/env node

import postgres from 'postgres';

const DATABASE_URL = process.env.DATABASE_URL ?? '<DATABASE_URL>';
const QUERY_PARAM = process.env.QUERY_PARAM ?? '<QUERY_PARAM>';
const BATCH_SIZE = 100;

const META_QUERY = `
  select
    pg_backend_pid() as backend_pid,
    pg_is_in_recovery() as is_in_recovery,
    current_setting('statement_timeout') as statement_timeout
`;

const BASE_QUERY = `
  select
    id,
    row_number() over (order by id) - 1 as row_number
  from your_table_or_function_here
  where your_filter_column = $1
`;

const sql = postgres(DATABASE_URL, {
  max: 1,
  prepare: true,
  connection: {
    application_name: 'cursor-repro',
  },
});

try {
  const [meta] = await sql.unsafe(META_QUERY);
  console.log(JSON.stringify({ type: 'meta', ...meta }));

  const [countRow] = await sql.unsafe(
    `select count(*)::bigint as count from (${BASE_QUERY}) q`,
    [QUERY_PARAM]
  );

  let cursorCount = 0;

  for await (const rows of sql.unsafe(BASE_QUERY, [QUERY_PARAM]).cursor(BATCH_SIZE)) {
    cursorCount += rows.length;

    console.log(
      JSON.stringify({
        type: 'batch',
        batchSize: rows.length,
        cursorCount,
        firstId: rows[0]?.id ?? null,
        lastId: rows.at(-1)?.id ?? null,
        firstRowNumber: rows[0]?.row_number ?? null,
        lastRowNumber: rows.at(-1)?.row_number ?? null,
      })
    );
  }

  const expectedCount = Number(countRow.count);

  console.log(
    JSON.stringify({
      type: 'result',
      expectedCount,
      cursorCount,
      outcome: cursorCount === expectedCount ? 'match' : 'mismatch',
    })
  );
} catch (error) {
  console.error(
    JSON.stringify({
      type: 'error',
      message: error instanceof Error ? error.message : String(error),
      code: error?.code ?? null,
      severity: error?.severity ?? null,
      routine: error?.routine ?? null,
    })
  );

  process.exitCode = 1;
} finally {
  await sql.end({ timeout: 5 });
}