/**
 * 端口注册文件：单一真相源，供看门狗 / 面板 / 手动脚本定位「实际端口」。
 * 零 pi 依赖的纯业务模块。
 *
 * 背景：Web 面板的端口可能因冲突而从 8123 漂移到 8124/8125。任何一方要
 * 「找面板」，都不该写死端口，而应读注册文件拿到实际端口。
 */

import { existsSync, readFileSync, writeFileSync, mkdirSync } from "node:fs";
import { dirname, join } from "node:path";
import { homedir } from "node:os";

export const DEFAULT_WEB_PORT = 8123;
export const PORT_FILE = join(homedir(), ".pi", "agent", "ocgo-web-port");

export interface PortIo {
  exists(path: string): boolean;
  read(path: string): string | undefined;
  write(path: string, data: string): void;
  mkdir(dir: string): void;
  dirname(path: string): string;
}

const nodePortIo: PortIo = {
  exists: existsSync,
  read: (p) => (existsSync(p) ? readFileSync(p, "utf-8") : undefined),
  write: writeFileSync,
  mkdir: (d) => mkdirSync(d, { recursive: true }),
  dirname,
};

/** 把实际端口写入注册文件。 */
export function writePortFile(port: number, path = PORT_FILE, io: PortIo = nodePortIo): void {
  io.mkdir(io.dirname(path));
  io.write(path, String(port));
}

/** 读取注册文件里的端口；未注册返回 DEFAULT_WEB_PORT。 */
export function readPortFile(path = PORT_FILE, io: PortIo = nodePortIo): number {
  const raw = io.read(path)?.trim();
  const n = Number(raw);
  return Number.isInteger(n) && n > 0 ? n : DEFAULT_WEB_PORT;
}

/** 探测给定端口上的 Web 面板是否在响应（GET /api/status 返回 ok）。 */
export async function probePort(
  port: number,
  host = "127.0.0.1",
  timeoutMs = 1500,
  fetchImpl: (url: string, init?: { headers?: Record<string, string>; signal?: AbortSignal }) => Promise<{ ok: boolean }> = fetch as never,
): Promise<boolean> {
  try {
    const ctrl = new AbortController();
    const t = setTimeout(() => ctrl.abort(), timeoutMs);
    const res = await fetchImpl(`http://${host}:${port}/api/status`, {
      headers: { Accept: "application/json" },
      signal: ctrl.signal,
    });
    clearTimeout(t);
    return res.ok;
  } catch {
    return false;
  }
}