torrent/src/core/seeder/FakeSeeder.ts

import { EventEmitter } from "node:events";
import type { Config } from "@config/Config";
import type { ClientProfile } from "../client/ClientProfile.js";
import type { TorrentFileInfo } from "../torrent/TorrentFile.js";
import { HttpTracker } from "../tracker/HttpTracker.js";
import type { ITracker } from "../tracker/ITracker.js";
import type { TrackerResponse } from "../tracker/TrackerResponse.js";
import { UdpTracker } from "../tracker/UdpTracker.js";
import { SpeedSimulator } from "./SpeedSimulator.js";

export type SeederStatus = "idle" | "running" | "paused" | "stopping" | "stopped" | "error";

export interface SeederState {
  infoHashHex: string;
  name: string;
  trackerUrl: string;
  uploaded: number;
  downloaded: number;
  left: number;
  status: SeederStatus;
  lastAnnounce: Date | null;
  lastInterval: number;
  seeders: number;
  leechers: number;
  peers: number;
  error: string | null;
}

export interface AnnounceRecord {
  timestamp: Date;
  trackerUrl: string;
  uploaded: number;
  seeders?: number;
  leechers?: number;
  peers: number;
  event: string;
}

export class FakeSeeder extends EventEmitter {
  // Typed on() overloads — avoids unsafe declaration merging
  on(event: "announce", listener: (record: AnnounceRecord) => void): this;
  on(event: "stopped", listener: () => void): this;
  on(event: "stateChange", listener: (state: SeederState) => void): this;
  on(event: string, listener: (...args: unknown[]) => void): this {
    return super.on(event, listener) as this;
  }
  private readonly torrent: TorrentFileInfo;
  private readonly profile: ClientProfile;
  private readonly config: Config;
  private readonly trackers: ITracker[];
  private readonly speedSim: SpeedSimulator;

  private status: SeederStatus = "idle";
  private uploaded = 0;
  private readonly downloaded = 0;
  private left: number;
  private lastAnnounce: Date | null = null;
  private lastInterval = 1800;
  private lastSeeder = 0;
  private lastLeecher = 0;
  private lastPeers = 0;
  private error: string | null = null;
  private announceTimer: ReturnType<typeof setTimeout> | null = null;
  private tickTimer: ReturnType<typeof setInterval> | null = null;
  private lastTickTime = Date.now();

  constructor(torrent: TorrentFileInfo, profile: ClientProfile, config: Config) {
    super();
    this.torrent = torrent;
    this.profile = profile;
    this.config = config;
    this.left = 0; // We're a seeder — we have the full file
    this.speedSim = new SpeedSimulator({
      minUploadRateBytesPerSec: config.minUploadRateBytesPerSec,
      maxUploadRateBytesPerSec: config.maxUploadRateBytesPerSec,
    });
    this.trackers = buildTrackers(torrent.announceList);
  }

  get infoHashHex(): string {
    return this.torrent.infoHashHex;
  }

  getState(): SeederState {
    return {
      infoHashHex: this.torrent.infoHashHex,
      name: this.torrent.name,
      trackerUrl: this.torrent.announce,
      uploaded: this.uploaded,
      downloaded: this.downloaded,
      left: this.left,
      status: this.status,
      lastAnnounce: this.lastAnnounce,
      lastInterval: this.lastInterval,
      seeders: this.lastSeeder,
      leechers: this.lastLeecher,
      peers: this.lastPeers,
      error: this.error,
    };
  }

  async start(): Promise<void> {
    if (this.status === "running") return;
    this.setStatus("running");

    // Start speed tick
    this.startTickTimer();

    // First announce: started
    await this.doAnnounce("started");
    this.scheduleNextAnnounce();
  }

  async pause(): Promise<void> {
    if (this.status !== "running") return;

    if (this.announceTimer) {
      clearTimeout(this.announceTimer);
      this.announceTimer = null;
    }
    if (this.tickTimer) {
      clearInterval(this.tickTimer);
      this.tickTimer = null;
    }

    // Notify trackers we're leaving the swarm (best-effort)
    await Promise.allSettled(
      this.trackers.map((t) =>
        t.stop({
          infoHash: this.torrent.infoHash,
          peerId: this.profile.peerId,
          port: this.config.announcePort,
          uploaded: this.uploaded,
          downloaded: this.downloaded,
          left: this.left,
          userAgent: this.profile.userAgent,
          key: this.profile.key,
        })
      )
    );

    this.setStatus("paused");
  }

  async resume(): Promise<void> {
    if (this.status !== "paused") return;
    this.setStatus("running");

    // Restart speed tick
    this.startTickTimer();

    // Re-announce as started then resume loop
    await this.doAnnounce("started");
    this.scheduleNextAnnounce();
  }

  async stop(): Promise<void> {
    if (this.status === "stopped" || this.status === "stopping") return;
    const wasPaused = this.status === "paused";
    this.setStatus("stopping");

    if (this.announceTimer) {
      clearTimeout(this.announceTimer);
      this.announceTimer = null;
    }
    if (this.tickTimer) {
      clearInterval(this.tickTimer);
      this.tickTimer = null;
    }

    // If already paused, trackers were already notified — skip the stopped announce
    if (!wasPaused) {
      await Promise.allSettled(
        this.trackers.map((t) =>
          t.stop({
            infoHash: this.torrent.infoHash,
            peerId: this.profile.peerId,
            port: this.config.announcePort,
            uploaded: this.uploaded,
            downloaded: this.downloaded,
            left: this.left,
            userAgent: this.profile.userAgent,
            key: this.profile.key,
          })
        )
      );
    }

    this.setStatus("stopped");
    this.emit("stopped");
  }

  /** Starts the 5-second speed simulation tick timer */
  private startTickTimer(): void {
    this.lastTickTime = Date.now();
    this.tickTimer = setInterval(() => {
      try {
        const now = Date.now();
        const delta = now - this.lastTickTime;
        this.lastTickTime = now;
        this.uploaded += this.speedSim.tick(delta);
        this.emit("stateChange", this.getState());
      } catch (err) {
        console.error("[seeder] Tick error:", err);
      }
    }, 5_000);
  }

  private scheduleNextAnnounce(): void {
    const intervalMs = this.lastInterval * 1000;
    this.announceTimer = setTimeout(async () => {
      await this.doAnnounce("");
      if (this.status === "running") {
        this.scheduleNextAnnounce();
      }
    }, intervalMs);
  }

  private async doAnnounce(event: "started" | "stopped" | "completed" | ""): Promise<void> {
    const params = {
      infoHash: this.torrent.infoHash,
      peerId: this.profile.peerId,
      port: this.config.announcePort,
      uploaded: this.uploaded,
      downloaded: this.downloaded,
      left: this.left,
      event,
      userAgent: this.profile.userAgent,
      compact: true,
      numWant: 50,
      key: this.profile.key,
    };

    // Announce to all trackers, collect results
    const results = await Promise.allSettled(this.trackers.map((t) => t.announce(params)));

    let bestInterval = this.lastInterval;

    for (let i = 0; i < results.length; i++) {
      const result = results[i];
      const tracker = this.trackers[i];

      if (result.status === "fulfilled") {
        const res: TrackerResponse = result.value;
        this.lastAnnounce = new Date();
        this.lastSeeder = res.seeders ?? this.lastSeeder;
        this.lastLeecher = res.leechers ?? this.lastLeecher;
        this.lastPeers = res.peers.length;
        bestInterval = Math.min(bestInterval, res.interval);
        this.error = null; // clear any previous error

        const record: AnnounceRecord = {
          timestamp: this.lastAnnounce,
          trackerUrl: tracker.url,
          uploaded: this.uploaded,
          seeders: res.seeders,
          leechers: res.leechers,
          peers: res.peers.length,
          event,
        };
        this.emit("announce", record);
      } else {
        this.error = result.reason instanceof Error ? result.reason.message : String(result.reason);
        // Fallback: scrape to at least get current seeder/leecher counts
        if (tracker.scrape && this.status === "running") {
          tracker
            .scrape(this.torrent.infoHash)
            .then((stats) => {
              if (stats && this.status === "running") {
                this.lastSeeder = stats.seeders;
                this.lastLeecher = stats.leechers;
                this.emit("stateChange", this.getState());
              }
            })
            .catch((err) => {
              console.warn(`[seeder] Scrape fallback failed for ${tracker.url}:`, err);
            });
        }
      }
    }

    this.lastInterval = bestInterval;
    this.emit("stateChange", this.getState());
  }

  private setStatus(s: SeederStatus): void {
    this.status = s;
    this.emit("stateChange", this.getState());
  }
}

/**
 * Reject tracker URLs that point to private/internal networks (SSRF protection).
 * Checks the hostname against RFC 1918, loopback, link-local, and metadata ranges.
 */
function isPrivateHost(hostname: string): boolean {
  // Strip IPv6 brackets
  const host = hostname.replace(/^\[|\]$/g, "");

  // Loopback
  if (host === "localhost" || host === "::1" || host.startsWith("127.")) return true;

  // Cloud metadata endpoints
  if (host === "169.254.169.254" || host === "metadata.google.internal") return true;

  // IPv4 private ranges
  const ipv4 = host.match(/^(\d+)\.(\d+)\.\d+\.\d+$/);
  if (ipv4) {
    const [, a, b] = ipv4.map(Number);
    if (a === 10) return true; // 10.0.0.0/8
    if (a === 172 && b >= 16 && b <= 31) return true; // 172.16.0.0/12
    if (a === 192 && b === 168) return true; // 192.168.0.0/16
    if (a === 169 && b === 254) return true; // 169.254.0.0/16 link-local
    if (a === 0) return true; // 0.0.0.0/8
  }

  return false;
}

function buildTrackers(urls: string[]): ITracker[] {
  return urls
    .map((url): ITracker | null => {
      try {
        const parsed = new URL(url);
        if (isPrivateHost(parsed.hostname)) {
          console.warn(`[tracker] Skipping private/internal URL: ${url}`);
          return null;
        }
        if (url.startsWith("http://") || url.startsWith("https://")) {
          return new HttpTracker(url);
        }
        if (url.startsWith("udp://")) {
          return new UdpTracker(url);
        }
      } catch {
        console.warn(`[tracker] Skipping malformed URL: ${url}`);
      }
      return null;
    })
    .filter((t): t is ITracker => t !== null);
}