import { execSync, spawn, type ChildProcess } from 'node:child_process';
import fs from 'node:fs';
import http from 'node:http';
import path from 'node:path';

const sleep = (ms: number): Promise<void> => new Promise(resolve => setTimeout(resolve, ms));

interface JsonResponse {
  status: number;
  json: Record<string, unknown>;
}

/** 怎么拉起后端：源码模式是 .venv 的 python + backend/main.py，打包后是 resources/backend 里的冻结 exe。 */
export interface BackendLaunch {
  command: string;
  args: string[];
  cwd: string;
  env: Record<string, string>;
}

export function devBackendLaunch(rootDir: string): BackendLaunch {
  const venv = process.platform === 'win32'
    ? path.join(rootDir, '.venv', 'Scripts', 'python.exe')
    : path.join(rootDir, '.venv', 'bin', 'python');
  const command = fs.existsSync(venv) ? venv : process.platform === 'win32' ? 'python' : 'python3';
  return { command, args: ['backend/main.py'], cwd: rootDir, env: {} };
}

export function packagedBackendLaunch(resourcesPath: string, homeDir: string): BackendLaunch {
  const executable = process.platform === 'win32' ? 'school-assistant-backend.exe' : 'school-assistant-backend';
  return {
    command: path.join(resourcesPath, 'backend', executable),
    args: [],
    cwd: homeDir,
    env: {
      ASSISTANT_HOME: homeDir,
      KNOWLEDGE_DIR: path.join(resourcesPath, 'knowledge'),
    },
  };
}

/** Python FastAPI 后端的生命周期：Electron 是它唯一的所有者。 */
export class BackendManager {
  private child: ChildProcess | null = null;

  constructor(private readonly launch: BackendLaunch, private readonly apiPort: number) {}

  get apiBase(): string {
    return `http://127.0.0.1:${this.apiPort}/api`;
  }

  request(method: string, pathname: string, body?: unknown, timeoutMs = 1500): Promise<JsonResponse> {
    return new Promise((resolve, reject) => {
      const data = body === undefined ? null : JSON.stringify(body);
      const req = http.request({
        host: '127.0.0.1',
        port: this.apiPort,
        path: `/api${pathname}`,
        method,
        headers: {
          'Content-Type': 'application/json',
          ...(data ? { 'Content-Length': Buffer.byteLength(data) } : {}),
        },
        timeout: timeoutMs,
      }, res => {
        let buffer = '';
        res.on('data', chunk => { buffer += chunk; });
        res.on('end', () => {
          let json: Record<string, unknown> = {};
          try { json = buffer ? JSON.parse(buffer) as Record<string, unknown> : {}; } catch { json = {}; }
          resolve({ status: res.statusCode ?? 0, json });
        });
      });
      req.on('timeout', () => req.destroy(new Error('timeout')));
      req.on('error', reject);
      if (data) req.write(data);
      req.end();
    });
  }

  async info(): Promise<Record<string, unknown> | null> {
    try {
      const res = await this.request('GET', '/health');
      return res.status === 200 ? res.json : null;
    } catch {
      return null;
    }
  }

  private pidsOnPort(): number[] {
    if (process.platform !== 'win32') return [];
    try {
      const out = execSync('netstat -ano -p tcp', { encoding: 'utf8' });
      const pids = new Set<number>();
      for (const line of out.split(/\r?\n/)) {
        const match = line.trim().match(/^TCP\s+\S+:(\d+)\s+\S+\s+LISTENING\s+(\d+)$/);
        if (match && parseInt(match[1], 10) === this.apiPort) pids.add(parseInt(match[2], 10));
      }
      return [...pids].filter(pid => pid > 0);
    } catch {
      return [];
    }
  }

  /** 端口上若已有后端（上次没退干净 / 手动起的），先关掉，保证连的是最新代码。 */
  async stopStale(): Promise<void> {
    const info = await this.info();
    if (!info) return;
    console.log(`[electron] 端口 ${this.apiPort} 上已有后端 (pid ${String(info.pid ?? '?')})，先关闭它`);
    try { await this.request('POST', '/shutdown'); } catch { /* 旧版本没有 /shutdown */ }
    for (let i = 0; i < 10; i += 1) {
      await sleep(300);
      if (!(await this.info())) return;
    }
    for (const pid of this.pidsOnPort()) {
      try { process.kill(pid, 'SIGKILL'); console.log(`[electron] 已强制结束 pid ${pid}`); } catch (error) {
        console.warn(`[electron] 结束 pid ${pid} 失败: ${(error as Error).message}`);
      }
    }
    for (let i = 0; i < 10; i += 1) {
      await sleep(300);
      if (!(await this.info())) return;
    }
    console.warn('[electron] 旧后端仍在运行，新后端可能无法绑定端口');
  }

  start(extraEnv: Record<string, string>): void {
    if (!fs.existsSync(this.launch.command) && path.isAbsolute(this.launch.command)) {
      console.error(`[electron] 找不到后端可执行文件: ${this.launch.command}`);
    }
    this.child = spawn(this.launch.command, this.launch.args, {
      cwd: this.launch.cwd,
      env: { ...process.env, PYTHONUTF8: '1', API_PORT: String(this.apiPort), ...this.launch.env, ...extraEnv },
      stdio: 'inherit',
      windowsHide: true,
    });
    this.child.on('exit', code => {
      console.log(`[electron] 后端进程退出 code=${String(code)}`);
      this.child = null;
    });
    this.child.on('error', error => console.error('Failed to start backend:', error));
  }

  async waitReady(maxAttempts = 120): Promise<Record<string, unknown>> {
    for (let i = 0; i < maxAttempts; i += 1) {
      const info = await this.info();
      if (info) return info;
      await sleep(500);
    }
    throw new Error('Backend not reachable');
  }

  stop(): void {
    if (!this.child) return;
    this.request('POST', '/shutdown').catch(() => undefined);
    const child = this.child;
    this.child = null;
    setTimeout(() => { try { child.kill(); } catch { /* already gone */ } }, 500);
  }

  /** 渲染层 IPC 用的代理：把请求转给后端并抛出可读错误。 */
  async apiFetch(pathname: string, init: { method?: string; body?: unknown } = {}): Promise<unknown> {
    const response = await fetch(`${this.apiBase}${pathname}`, {
      method: init.method ?? 'GET',
      headers: { 'Content-Type': 'application/json' },
      body: init.body === undefined ? undefined : JSON.stringify(init.body),
    });
    const data = await response.json().catch(() => ({})) as Record<string, unknown>;
    if (!response.ok) {
      const detail = typeof data.detail === 'string' ? data.detail : response.statusText;
      throw new Error(detail);
    }
    return data;
  }
}