// Core delegation logic: spawn the qwen-code CLI non-interactively and capture its reply.
// Kept separate from the MCP server wiring (qwen-delegate-server.ts) so it's unit-testable
// without a live MCP connection or a live qwen endpoint.

import { spawn, type ChildProcess } from "node:child_process";

export interface DelegateResult {
  ok: boolean;
  output: string; // stdout (ok) or combined error detail (!ok)
}

export interface DelegateOptions {
  /** Milliseconds before giving up. qwen-code has been observed taking 3-6 min for a trivial, 
   * takes time to warm up on the first request,
   * prompt against a local model proxy, so default generous — see research/qwen-mcp-delegation.md. */
  timeoutMs?: number;
  /** Injectable for tests. Defaults to node:child_process's spawn. */
  spawnFn?: typeof spawn;
}

const DEFAULT_TIMEOUT_MS = 10 * 60 * 1000; // 10 min

/**
 * Runs `qwen -p "<prompt>"` non-interactively and returns its trimmed stdout.
 * qwen-code prints startup warnings (e.g. failed MCP sub-servers) to stderr; those are
 * ignored on success and surfaced only when the run itself fails.
 */
export function delegateToQwen (
  prompt: string,
  options: DelegateOptions = {},
): Promise<DelegateResult> {
  const { timeoutMs = DEFAULT_TIMEOUT_MS, spawnFn = spawn } = options;

  return new Promise((resolve) => {
    const child: ChildProcess = spawnFn("qwen", ["-p", prompt], {
      shell: true, // qwen.cmd on Windows needs a shell to resolve
      stdio: ["ignore", "pipe", "pipe"],
    });

    let stdout = "";
    let stderr = "";
    let settled = false;

    const timer = setTimeout(() => {
      if (settled) return;
      settled = true;
      child.kill();
      resolve({ ok: false, output: `qwen timed out after ${timeoutMs}ms` });
    }, timeoutMs);

    child.stdout?.on("data", (chunk) => (stdout += chunk));
    child.stderr?.on("data", (chunk) => (stderr += chunk));

    child.on("error", (err) => {
      if (settled) return;
      settled = true;
      clearTimeout(timer);
      resolve({ ok: false, output: `failed to start qwen: ${err.message}` });
    });

    child.on("close", (code) => {
      if (settled) return;
      settled = true;
      clearTimeout(timer);
      if (code === 0) {
        resolve({ ok: true, output: stdout.trim() });
      } else {
        const detail = stderr.trim() || stdout.trim() || "(no output)";
        resolve({ ok: false, output: `qwen exited with code ${code}: ${detail}` });
      }
    });
  });
}