import { WebSocketServer, WebSocket } from "ws";
import http from "node:http";
import { ConnectionManager } from "./connections.js";
import { generateChallenge, verifyAuthResponse } from "./auth.js";
import { verify, buildSignablePayload } from "../crypto/signing.js";
import { PairingStore } from "../pairing/pairing.js";
import {
  type Envelope,
  type MessageType,
  MESSAGE_TYPES,
  PING_INTERVAL_MS,
  PONG_TIMEOUT_MS,
} from "../protocol/spec.js";

export interface RelayServerConfig {
  port: number;
  host?: string;
}

interface PendingAuth {
  challenge: Buffer;
  createdAt: number;
}

/**
 * CookieBridge Relay Server.
 *
 * HTTP endpoints:
 *   POST /pair         — initiate a pairing session
 *   POST /pair/accept  — accept a pairing session
 *   GET  /health       — health check
 *
 * WebSocket:
 *   /ws — authenticated device connection for message relay
 */
export class RelayServer {
  private httpServer: http.Server;
  private wss: WebSocketServer;
  private connections: ConnectionManager;
  private pairingStore: PairingStore;
  private pendingAuths = new Map<WebSocket, PendingAuth>();
  private authenticatedDevices = new Map<WebSocket, string>(); // ws -> deviceId
  private pingIntervals = new Map<WebSocket, ReturnType<typeof setInterval>>();

  constructor(private config: RelayServerConfig) {
    this.connections = new ConnectionManager();
    this.pairingStore = new PairingStore();

    this.httpServer = http.createServer(this.handleHttp.bind(this));
    this.wss = new WebSocketServer({ server: this.httpServer });
    this.wss.on("connection", this.handleConnection.bind(this));
  }

  start(): Promise<void> {
    return new Promise((resolve) => {
      this.httpServer.listen(
        this.config.port,
        this.config.host ?? "0.0.0.0",
        () => resolve(),
      );
    });
  }

  stop(): Promise<void> {
    return new Promise((resolve) => {
      for (const interval of this.pingIntervals.values()) {
        clearInterval(interval);
      }
      this.wss.close(() => {
        this.httpServer.close(() => resolve());
      });
    });
  }

  get port(): number {
    const addr = this.httpServer.address();
    if (addr && typeof addr === "object") return addr.port;
    return this.config.port;
  }

  // --- HTTP ---

  private handleHttp(req: http.IncomingMessage, res: http.ServerResponse): void {
    if (req.method === "GET" && req.url === "/health") {
      res.writeHead(200, { "Content-Type": "application/json" });
      res.end(JSON.stringify({ status: "ok", connections: this.connections.connectedCount }));
      return;
    }

    if (req.method === "POST" && req.url === "/pair") {
      this.handlePairCreate(req, res);
      return;
    }

    if (req.method === "POST" && req.url === "/pair/accept") {
      this.handlePairAccept(req, res);
      return;
    }

    res.writeHead(404);
    res.end("Not found");
  }

  private handlePairCreate(req: http.IncomingMessage, res: http.ServerResponse): void {
    this.readBody(req, (body) => {
      try {
        const { deviceId, x25519PubKey } = JSON.parse(body);
        if (!deviceId || !x25519PubKey) {
          res.writeHead(400, { "Content-Type": "application/json" });
          res.end(JSON.stringify({ error: "Missing deviceId or x25519PubKey" }));
          return;
        }
        const session = this.pairingStore.create(deviceId, x25519PubKey);
        res.writeHead(201, { "Content-Type": "application/json" });
        res.end(JSON.stringify({ pairingCode: session.pairingCode, expiresAt: session.expiresAt }));
      } catch {
        res.writeHead(400, { "Content-Type": "application/json" });
        res.end(JSON.stringify({ error: "Invalid JSON" }));
      }
    });
  }

  private handlePairAccept(req: http.IncomingMessage, res: http.ServerResponse): void {
    this.readBody(req, (body) => {
      try {
        const { deviceId, x25519PubKey, pairingCode } = JSON.parse(body);
        if (!deviceId || !x25519PubKey || !pairingCode) {
          res.writeHead(400, { "Content-Type": "application/json" });
          res.end(JSON.stringify({ error: "Missing required fields" }));
          return;
        }
        const session = this.pairingStore.consume(pairingCode);
        if (!session) {
          res.writeHead(404, { "Content-Type": "application/json" });
          res.end(JSON.stringify({ error: "Invalid or expired pairing code" }));
          return;
        }
        // Return both peers' info
        res.writeHead(200, { "Content-Type": "application/json" });
        res.end(
          JSON.stringify({
            initiator: {
              deviceId: session.deviceId,
              x25519PubKey: session.x25519PubKey,
            },
            acceptor: {
              deviceId,
              x25519PubKey,
            },
          }),
        );
      } catch {
        res.writeHead(400, { "Content-Type": "application/json" });
        res.end(JSON.stringify({ error: "Invalid JSON" }));
      }
    });
  }

  private readBody(req: http.IncomingMessage, cb: (body: string) => void): void {
    let data = "";
    req.on("data", (chunk: Buffer) => {
      data += chunk.toString();
      if (data.length > 64 * 1024) {
        req.destroy();
      }
    });
    req.on("end", () => cb(data));
  }

  // --- WebSocket ---

  private handleConnection(ws: WebSocket): void {
    // Send auth challenge
    const challenge = generateChallenge();
    this.pendingAuths.set(ws, { challenge, createdAt: Date.now() });
    ws.send(JSON.stringify({ type: "auth_challenge", challenge: challenge.toString("hex") }));

    ws.on("message", (data: Buffer) => {
      this.handleMessage(ws, data);
    });

    ws.on("close", () => {
      this.handleDisconnect(ws);
    });

    ws.on("error", () => {
      this.handleDisconnect(ws);
    });

    // Auth timeout — disconnect if not authenticated within 10s
    setTimeout(() => {
      if (this.pendingAuths.has(ws)) {
        ws.close(4000, "Auth timeout");
        this.pendingAuths.delete(ws);
      }
    }, 10_000);
  }

  private handleMessage(ws: WebSocket, data: Buffer): void {
    let msg: Record<string, unknown>;
    try {
      msg = JSON.parse(data.toString());
    } catch {
      ws.send(JSON.stringify({ type: "error", error: "Invalid JSON" }));
      return;
    }

    // Handle auth response
    if (msg.type === "auth_response") {
      this.handleAuthResponse(ws, msg);
      return;
    }

    // All other messages require authentication
    const deviceId = this.authenticatedDevices.get(ws);
    if (!deviceId) {
      ws.send(JSON.stringify({ type: "error", error: "Not authenticated" }));
      return;
    }

    // Handle ping/pong
    if (msg.type === MESSAGE_TYPES.PING) {
      ws.send(JSON.stringify({ type: MESSAGE_TYPES.PONG }));
      return;
    }

    // Handle relay messages
    if (
      msg.type === MESSAGE_TYPES.COOKIE_SYNC ||
      msg.type === MESSAGE_TYPES.COOKIE_DELETE ||
      msg.type === MESSAGE_TYPES.ACK
    ) {
      this.handleRelayMessage(ws, deviceId, msg as unknown as Envelope);
      return;
    }

    ws.send(JSON.stringify({ type: "error", error: "Unknown message type" }));
  }

  private handleAuthResponse(ws: WebSocket, msg: Record<string, unknown>): void {
    const pending = this.pendingAuths.get(ws);
    if (!pending) {
      ws.send(JSON.stringify({ type: "error", error: "No pending auth challenge" }));
      return;
    }

    const { deviceId, sig } = msg as { deviceId: string; sig: string };
    if (!deviceId || !sig) {
      ws.close(4002, "Invalid auth response");
      return;
    }

    const sigBuf = Buffer.from(sig, "hex");
    const pubBuf = Buffer.from(deviceId, "hex");

    if (!verifyAuthResponse(pending.challenge, sigBuf, pubBuf)) {
      ws.close(4003, "Auth failed");
      this.pendingAuths.delete(ws);
      return;
    }

    // Authenticated
    this.pendingAuths.delete(ws);
    this.authenticatedDevices.set(ws, deviceId);
    this.connections.register(deviceId, ws);

    ws.send(JSON.stringify({ type: "auth_ok", deviceId }));

    // Start ping interval
    const interval = setInterval(() => {
      if (ws.readyState === 1) {
        ws.send(JSON.stringify({ type: MESSAGE_TYPES.PING }));
      }
    }, PING_INTERVAL_MS);
    this.pingIntervals.set(ws, interval);
  }

  private handleRelayMessage(ws: WebSocket, fromDeviceId: string, envelope: Envelope): void {
    // Verify the 'from' matches the authenticated device
    if (envelope.from !== fromDeviceId) {
      ws.send(JSON.stringify({ type: "error", error: "Sender mismatch" }));
      return;
    }

    // Verify signature
    const signable = buildSignablePayload({
      type: envelope.type,
      from: envelope.from,
      to: envelope.to,
      nonce: envelope.nonce,
      payload: envelope.payload,
      timestamp: envelope.timestamp,
    });
    const sigBuf = Buffer.from(envelope.sig, "hex");
    const pubBuf = Buffer.from(fromDeviceId, "hex");

    if (!verify(signable, sigBuf, pubBuf)) {
      ws.send(JSON.stringify({ type: "error", error: "Invalid signature" }));
      return;
    }

    // Route to recipient
    const delivered = this.connections.send(envelope.to, envelope);

    // Acknowledge to sender
    ws.send(
      JSON.stringify({
        type: MESSAGE_TYPES.ACK,
        ref: envelope.nonce,
        delivered,
      }),
    );
  }

  private handleDisconnect(ws: WebSocket): void {
    const deviceId = this.authenticatedDevices.get(ws);
    if (deviceId) {
      this.connections.remove(deviceId, ws);
      this.authenticatedDevices.delete(ws);
    }
    this.pendingAuths.delete(ws);
    const interval = this.pingIntervals.get(ws);
    if (interval) {
      clearInterval(interval);
      this.pingIntervals.delete(ws);
    }
  }
}