import { existsSync, readFileSync } from "node:fs";

export async function waitForFile(path, child, timeoutMs, pollMs = 50) {
  const deadline = Date.now() + timeoutMs;
  while (!existsSync(path)) {
    if (child.exitCode !== null) {
      throw new Error(`endpoint exited before publishing ${path} (${child.exitCode}); ${diagnostics(child)}`);
    }
    if (Date.now() > deadline) {
      throw new Error(`timed out after ${timeoutMs}ms waiting for ${path}; ${diagnostics(child)}`);
    }
    await new Promise((resolve) => setTimeout(resolve, pollMs));
  }
  return readFileSync(path, "utf8").trim();
}

function diagnostics(child) {
  return `stdout=${JSON.stringify(child.diagnostics?.stdout ?? "")} stderr=${JSON.stringify(child.diagnostics?.stderr ?? "")}`;
}