/**
 * DaemonMode server management.
 *
 * DaemonManager handles the lifecycle of a persistent Julia process that serves
 * code-execution requests via DaemonMode.jl, eliminating TTFX on every call.
 *
 * ensureDaemonInstalled checks whether DaemonMode.jl is available in the global
 * Julia environment and installs it if not.
 */

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

import { projectPort } from "./utils.ts";

// ─── Types ────────────────────────────────────────────────────────────────────

interface DaemonState {
  process: ChildProcess;
  projectPath: string | undefined; // undefined = Julia global environment
  port: number;
}

// ─── DaemonManager ────────────────────────────────────────────────────────────

export class DaemonManager {
  private _state: DaemonState | undefined;

  get isRunning(): boolean              { return !!this._state; }
  get port(): number | undefined        { return this._state?.port; }
  get projectPath(): string | undefined { return this._state?.projectPath; }

  stop(): void {
    if (this._state) {
      try { this._state.process.kill("SIGTERM"); } catch {}
      this._state = undefined;
    }
  }

  launch(projectPath: string | undefined): void {
    this.stop();
    const port = projectPort(projectPath ?? "@global");
    const initCode = [
      "try; using Revise; catch; end",
      "using DaemonMode",
      `serve(${port})`,
    ].join("; ");
    const args = ["--startup-file=no"];
    if (projectPath) args.push(`--project=${projectPath}`);
    args.push("-e", initCode);
    const proc = spawn("julia", args, { detached: false, stdio: "ignore" });
    proc.unref();
    this._state = { process: proc, projectPath, port };
  }

  waitUntilReady(timeoutMs = 120_000): Promise<boolean> {
    if (!this._state) return Promise.resolve(false);
    const port = this._state.port;
    return new Promise((resolve) => {
      const deadline = Date.now() + timeoutMs;
      function attempt() {
        if (Date.now() > deadline) { resolve(false); return; }
        const socket = new net.Socket();
        socket.setTimeout(1_000);
        socket.on("connect", () => { socket.destroy(); resolve(true); });
        socket.on("error",   () => { socket.destroy(); setTimeout(attempt, 2_000); });
        socket.on("timeout", () => { socket.destroy(); setTimeout(attempt, 2_000); });
        socket.connect(port, "127.0.0.1");
      }
      attempt();
    });
  }
}

// ─── Installation ─────────────────────────────────────────────────────────────

type ExecFn = (
  cmd: string,
  args: string[],
  opts: { timeout: number }
) => Promise<{ stdout: string; code: number }>;

export async function ensureDaemonInstalled(execFn: ExecFn): Promise<boolean> {
  const probe = await execFn(
    "julia", ["--startup-file=no", "-e", 'using DaemonMode; println("ok")'],
    { timeout: 30_000 }
  );
  if (probe.stdout.trim() === "ok") return true;
  const install = await execFn(
    "julia", ["--startup-file=no", "-e", 'import Pkg; Pkg.add("DaemonMode")'],
    { timeout: 120_000 }
  );
  return install.code === 0;
}