import { writeSync } from "node:fs";

const STDERR_JSONL_WRITE_RETRY_LIMIT = 100;

/**
 * Write one complete JSONL record to fd 2.
 * Retries EAGAIN/EINTR and short writes; never writes stdout.
 */
export function writeStderrJsonlRecord(
  record: unknown,
  write: typeof writeSync = writeSync,
): void {
  const bytes = Buffer.from(`${JSON.stringify(record)}\n`);
  let offset = 0;
  let retries = 0;
  while (offset < bytes.length) {
    try {
      const written = write(2, bytes, offset, bytes.length - offset);
      if (written <= 0) throw new Error("stderr JSONL write made no progress");
      offset += written;
      retries = 0;
    } catch (error) {
      const code = (error as NodeJS.ErrnoException).code;
      if ((code === "EAGAIN" || code === "EINTR") && retries++ < STDERR_JSONL_WRITE_RETRY_LIMIT) continue;
      throw error;
    }
  }
}