/**
 * Lego 09 — Surveillance Engine (PID Polling & Socket Stream)
 *
 * Discovers the PIDs for n8n (node), ollama_llama_server, and the NestJS
 * process itself. Polls every 500ms via pidusage and exposes the live
 * metrics payload so the Gateway can broadcast monitor:data to all clients.
 *
 * Port-Level Heartbeat: n8n is only included in metrics when both a PID is
 * found AND port 5678 is actively accepting TCP connections.
 *
 * Webhook Probe: every 10 s, NestJS attempts a real HTTP POST to N8N_WEBHOOK_URL
 * with a ping payload. If n8n responds (any non-network-error), the agent is
 * considered ready. This status is broadcast via monitor:status so the UI can
 * show "Agent Ready / Not Ready" independently of process metrics.
 */

import { Injectable, OnModuleInit, OnModuleDestroy, Logger } from '@nestjs/common';
import * as net from 'net';
import * as pidusage from 'pidusage';
import find from 'find-process';

export interface MonitorPayload {
  service: string;
  pid: number;
  cpu: number;
  memory: number;
  timestamp: Date;
}

export interface MonitorStatus {
  n8nWebhookReady: boolean;
  timestamp: Date;
}

@Injectable()
export class SurveillanceService implements OnModuleInit, OnModuleDestroy {
  private readonly logger = new Logger(SurveillanceService.name);

  // Live metrics — the Gateway reads these on every tick
  private _latestMetrics: MonitorPayload[] = [];

  // Callback registered by the Gateway so it receives every poll result
  private onMetricsUpdate: ((metrics: MonitorPayload[]) => void) | null = null;
  // Callback for webhook probe results
  private onStatusUpdate: ((status: MonitorStatus) => void) | null = null;

  private pollInterval: NodeJS.Timeout | null = null;
  private webhookProbeInterval: NodeJS.Timeout | null = null;

  // Cached result of the last webhook probe
  private _n8nWebhookReady = false;
  private readonly n8nWebhookUrl = process.env['N8N_WEBHOOK_URL'] ?? '';

  // Tracked PIDs: resolved once and re-used (re-discovered when null)
  private pidMap: Record<string, number | null> = {
    NestJS: process.pid,  // Always known immediately
    n8n: null,
    Ollama: null,
  };

  // ─── Lifecycle ─────────────────────────────────────────────────────────────

  async onModuleInit() {
    this.logger.log('🟢 SurveillanceService booting — starting 500ms PID poll loop');
    await this.discoverPids();
    this.pollInterval = setInterval(() => this.tick(), 500);
    // Probe the n8n webhook immediately, then every 10 s
    await this.probeWebhook();
    this.webhookProbeInterval = setInterval(() => this.probeWebhook(), 10_000);
  }

  onModuleDestroy() {
    if (this.pollInterval) clearInterval(this.pollInterval);
    if (this.webhookProbeInterval) clearInterval(this.webhookProbeInterval);
    this.logger.log('🔴 SurveillanceService stopped');
  }

  // ─── Public API ────────────────────────────────────────────────────────────

  registerMetricsCallback(cb: (metrics: MonitorPayload[]) => void) {
    this.onMetricsUpdate = cb;
  }

  registerStatusCallback(cb: (status: MonitorStatus) => void) {
    this.onStatusUpdate = cb;
  }

  getLatestMetrics(): MonitorPayload[] {
    return this._latestMetrics;
  }

  getLatestStatus(): MonitorStatus {
    return { n8nWebhookReady: this._n8nWebhookReady, timestamp: new Date() };
  }

  // ─── Port-Level Heartbeat ──────────────────────────────────────────────────

  /**
   * Opens a short-lived TCP connection to host:port.
   * Resolves true if the port accepts the connection within 800 ms.
   * Resolves false on ECONNREFUSED, timeout, or any error.
   */
  private portListening(host: string, port: number): Promise<boolean> {
    return new Promise((resolve) => {
      const socket = new net.Socket();
      const done = (result: boolean) => {
        socket.destroy();
        resolve(result);
      };
      socket.setTimeout(800);
      socket.once('connect', () => done(true));
      socket.once('timeout', () => done(false));
      socket.once('error', () => done(false));
      socket.connect(port, host);
    });
  }

  // ─── Webhook Probe ─────────────────────────────────────────────────────────

  /**
   * POSTs a lightweight ping to the n8n webhook URL.
   * Any HTTP response (even 4xx) means the webhook is registered and n8n is
   * accepting requests — we treat that as "ready".
   * A network error (ECONNREFUSED, timeout, DNS failure) means "not ready".
   */
  private async probeWebhook(): Promise<void> {
    if (!this.n8nWebhookUrl) {
      if (this._n8nWebhookReady) {
        this._n8nWebhookReady = false;
        this.emitStatus();
      }
      return;
    }

    try {
      const controller = new AbortController();
      const timeout = setTimeout(() => controller.abort(), 3_000);
      const res = await fetch(this.n8nWebhookUrl, {
        method: 'POST',
        headers: { 'Content-Type': 'application/json' },
        body: JSON.stringify({ __ping: true }),
        signal: controller.signal,
      });
      clearTimeout(timeout);
      const ready = res.status < 500; // 2xx/3xx/4xx all mean n8n responded
      if (ready !== this._n8nWebhookReady) {
        this._n8nWebhookReady = ready;
        this.logger.log(`🔗 n8n webhook probe: ${ready ? '✅ ready' : '⚠️ 5xx'}`);
        this.emitStatus();
      }
    } catch {
      if (this._n8nWebhookReady) {
        this._n8nWebhookReady = false;
        this.logger.warn('⚠️ n8n webhook unreachable — agent marked NOT READY');
        this.emitStatus();
      }
    }
  }

  private emitStatus(): void {
    if (this.onStatusUpdate) {
      this.onStatusUpdate({ n8nWebhookReady: this._n8nWebhookReady, timestamp: new Date() });
    }
  }

  // ─── PID Discovery ─────────────────────────────────────────────────────────

  /**
   * Uses find-process to locate n8n and Ollama PIDs.
   * Called once at boot and retried on each tick for any service still null.
   * n8n PID is only accepted if port 5678 is also actively listening.
   */
  private async discoverPids() {
    // --- n8n: a Node.js process whose command line contains "n8n" ---
    if (!this.pidMap['n8n']) {
      try {
        const nodeProcs = await find('name', 'node', true);
        const n8nProc = nodeProcs.find(
          (p: any) => p.cmd && p.cmd.toLowerCase().includes('n8n'),
        );
        if (n8nProc) {
          // Port-level guard: only accept the PID if n8n is actually serving
          const portUp = await this.portListening('127.0.0.1', 5678);
          if (portUp) {
            this.pidMap['n8n'] = n8nProc.pid;
            this.logger.log(`🔍 n8n PID discovered: ${n8nProc.pid} (port 5678 ✓)`);
          } else {
            this.logger.warn(`⚠️ n8n PID ${n8nProc.pid} found but port 5678 is not listening — treating as offline`);
          }
        }
      } catch (e) {
        // n8n not running yet — will retry next tick
      }
    }

    // --- Ollama: match the server child process by executable name ---
    if (!this.pidMap['Ollama']) {
      try {
        // On Windows the process is "ollama_llama_server.exe"; on Linux "ollama"
        const ollamaNames = ['ollama_llama_server', 'ollama'];
        for (const name of ollamaNames) {
          const procs = await find('name', name, true);
          if (procs.length > 0) {
            this.pidMap['Ollama'] = procs[0].pid;
            this.logger.log(`🔍 Ollama PID discovered: ${procs[0].pid} (${name})`);
            break;
          }
        }
      } catch (e) {
        // Ollama not running yet — will retry next tick
      }
    }
  }

  // ─── Poll Tick ─────────────────────────────────────────────────────────────

  private async tick() {
    // Port re-verification: if n8n PID is known, confirm port 5678 is still up.
    // A zombie n8n process (PID alive, port dead) is evicted so discovery retries.
    if (this.pidMap['n8n'] !== null) {
      const portUp = await this.portListening('127.0.0.1', 5678);
      if (!portUp) {
        this.logger.warn(`⚠️ n8n port 5678 went silent — evicting PID ${this.pidMap['n8n']}`);
        this.pidMap['n8n'] = null;
      }
    }

    // Retry PID discovery for any services still unknown
    const hasMissingPids = Object.values(this.pidMap).some((v) => v === null);
    if (hasMissingPids) await this.discoverPids();

    const activePids = Object.entries(this.pidMap).filter(
      ([, pid]) => pid !== null,
    ) as [string, number][];

    if (activePids.length === 0) return;

    const pidsToQuery = activePids.map(([, pid]) => pid);

    let stats: Record<number, pidusage.Status>;
    try {
      stats = await pidusage(pidsToQuery);
    } catch (e) {
      // A process may have died — invalidate its PID so it gets re-discovered
      this.invalidateDeadPids(e);
      return;
    }

    const metrics: MonitorPayload[] = activePids.map(([service, pid]) => ({
      service,
      pid,
      cpu: parseFloat((stats[pid]?.cpu ?? 0).toFixed(2)),
      memory: stats[pid]?.memory ?? 0,   // bytes — let the UI format it
      timestamp: new Date(),
    }));

    this._latestMetrics = metrics;

    if (this.onMetricsUpdate) {
      this.onMetricsUpdate(metrics);
    }
  }

  // ─── Helpers ───────────────────────────────────────────────────────────────

  private invalidateDeadPids(error: any) {
    // pidusage throws with the bad PID in the message — reset it so we re-search
    const msg = String(error);
    for (const [service, pid] of Object.entries(this.pidMap)) {
      if (pid !== null && msg.includes(String(pid)) && service !== 'NestJS') {
        this.logger.warn(`⚠️ PID ${pid} (${service}) appears dead — resetting`);
        this.pidMap[service] = null;
      }
    }
  }
}