import { spawn, type ChildProcess } from "node:child_process";
import { mkdtemp, rm } from "node:fs/promises";
import os from "node:os";
import path from "node:path";
import { fileURLToPath } from "node:url";

const APP_ROOT = fileURLToPath(new URL("..", import.meta.url));

const START_TIMEOUT_MS = 60_000;
const KILL_TIMEOUT_MS = 5_000;

/**
 * A real runner child process, as the provisioner (story 06) will spawn
 * it: config via env only, port discovered from the stdout `listening`
 * line. `output()` exposes everything the process ever wrote — the
 * credential-leak assertions grep it.
 */
export interface SpawnedRunner {
  port: number;
  workspaceDir: string;
  /** Combined stdout + stderr captured so far. */
  output: () => string;
  stop: () => Promise<void>;
}

export async function spawnRunner(options: {
  token: string;
}): Promise<SpawnedRunner> {
  const workspaceDir = await mkdtemp(
    path.join(os.tmpdir(), "veect-runner-ws-"),
  );
  const child: ChildProcess = spawn(
    process.execPath,
    ["--import", "tsx", "src/main.ts"],
    {
      cwd: APP_ROOT,
      env: {
        ...process.env,
        RUNNER_TOKEN: options.token,
        RUNNER_WORKSPACE_DIR: workspaceDir,
        RUNNER_PORT: "0",
        RUNNER_HEARTBEAT_MS: "250",
      },
      stdio: ["ignore", "pipe", "pipe"],
    },
  );

  let captured = "";
  child.stdout?.on("data", (chunk: Buffer) => {
    captured += chunk.toString("utf8");
  });
  child.stderr?.on("data", (chunk: Buffer) => {
    captured += chunk.toString("utf8");
  });

  const stop = async (): Promise<void> => {
    if (child.exitCode === null && child.signalCode === null) {
      const exited = new Promise<void>((resolve) =>
        child.once("exit", () => resolve()),
      );
      const killTimer = setTimeout(
        () => child.kill("SIGKILL"),
        KILL_TIMEOUT_MS,
      );
      killTimer.unref();
      child.kill("SIGTERM");
      await exited;
      clearTimeout(killTimer);
    }
    await rm(workspaceDir, { recursive: true, force: true });
  };

  const port = await new Promise<number>((resolve, reject) => {
    const deadline = setTimeout(() => {
      reject(
        new Error(
          `runner did not announce a port within ${START_TIMEOUT_MS}ms:\n${captured}`,
        ),
      );
    }, START_TIMEOUT_MS);
    const poll = setInterval(() => {
      if (child.exitCode !== null) {
        clearTimeout(deadline);
        clearInterval(poll);
        reject(
          new Error(
            `runner exited before listening (code ${child.exitCode}):\n${captured}`,
          ),
        );
        return;
      }
      for (const line of captured.split("\n")) {
        if (!line.includes('"listening"')) continue;
        try {
          const parsed = JSON.parse(line) as { event?: string; port?: number };
          if (parsed.event === "listening" && typeof parsed.port === "number") {
            clearTimeout(deadline);
            clearInterval(poll);
            resolve(parsed.port);
            return;
          }
        } catch {
          // partial line — keep polling
        }
      }
    }, 50);
  }).catch(async (error: unknown) => {
    await stop();
    throw error;
  });

  return { port, workspaceDir, output: () => captured, stop };
}