/**
 * WebSocket upgrade handler for terminal sessions.
 * Handles /ws/terminal/:id binary WebSocket connections.
 */
import { WebSocketServer, type WebSocket } from "ws";
import type { IncomingMessage } from "node:http";
import type { Duplex } from "node:stream";
import type { TerminalManager } from "./terminal-manager.js";

const TERMINAL_PATH_PREFIX = "/ws/terminal/";

export interface TerminalGateway {
  wss: WebSocketServer;
  /** Parse terminal ID from URL, returns null if not a terminal URL. */
  parseTerminalId(url: string): string | null;
  /** Handle WebSocket upgrade for a terminal URL. */
  handleUpgrade(request: IncomingMessage, socket: Duplex, head: Buffer): void;
  /** Close the WebSocket server. */
  close(): void;
}

export function createTerminalGateway(manager: TerminalManager): TerminalGateway {
  const wss = new WebSocketServer({ noServer: true });

  function parseTerminalId(url: string): string | null {
    if (!url.startsWith(TERMINAL_PATH_PREFIX)) return null;
    const id = url.slice(TERMINAL_PATH_PREFIX.length);
    return id.length > 0 ? id : null;
  }

  function handleUpgrade(request: IncomingMessage, socket: Duplex, head: Buffer): void {
    const termId = parseTerminalId(request.url ?? "");
    if (!termId || !manager.get(termId)) {
      socket.destroy();
      return;
    }

    wss.handleUpgrade(request, socket, head, (ws: WebSocket) => {
      manager.attach(termId, ws);
    });
  }

  function close(): void {
    for (const client of wss.clients) {
      client.close();
    }
    wss.close();
  }

  return { wss, parseTerminalId, handleUpgrade, close };
}