// The entire contract the server side needs from a socket. Four methods.
//
// This is what replaces the old `ws` dependency. Before, `SessionServer` (then
// `WebSocketServer`) built its own `ws` server from an `http.Server`, which made
// `ws` a hard dependency of the package and pinned it to Node. Now the caller
// brings the socket and this package never touches a WebSocket implementation on
// the server side — so it runs on Node (`ws`), Bun, Deno and Cloudflare Workers
// without knowing which.
//
// Subscriptions return their own unsubscribe function rather than taking an
// `off(type, listener)`: it is the one shape every runtime can implement without
// keeping a listener registry, and it is what makes the adapters below ~10 lines.

export interface SocketTransport {
  send(data: string): void;
  close(): void;
  /** @returns unsubscribe */
  onMessage(listener: (data: string) => void): () => void;
  /** @returns unsubscribe */
  onClose(listener: () => void): () => void;
}

/** The `addEventListener` shape: browsers, Deno, Cloudflare Workers. */
interface EventTargetLike {
  send(data: string): void;
  close(): void;
  addEventListener(type: string, listener: (event: any) => void): void;
  removeEventListener(type: string, listener: (event: any) => void): void;
}

/** The `.on()` shape: `ws` on Node. */
interface EventEmitterLike {
  send(data: string): void;
  close(): void;
  on(type: string, listener: (...args: any[]) => void): void;
  off(type: string, listener: (...args: any[]) => void): void;
}

/**
 * Adapts an `addEventListener`-style socket — a browser `WebSocket`,
 * `Deno.upgradeWebSocket`'s socket, or a Cloudflare Workers `WebSocketPair` end.
 */
export function fromEventTarget(socket: EventTargetLike): SocketTransport {
  return {
    send: data => socket.send(data),
    close: () => socket.close(),

    onMessage(listener) {
      const handler = (event: MessageEvent) => listener(String(event.data));
      socket.addEventListener('message', handler);
      return () => socket.removeEventListener('message', handler);
    },

    onClose(listener) {
      const handler = () => listener();
      socket.addEventListener('close', handler);
      return () => socket.removeEventListener('close', handler);
    },
  };
}

/**
 * Adapts a Node `EventEmitter`-style socket — a `ws` connection.
 *
 * `ws` v8 hands the payload as a `Buffer` even for text frames, so it is
 * stringified here. Binary frames therefore arrive as their UTF-8
 * interpretation; this package only ever speaks JSON.
 */
export function fromEventEmitter(socket: EventEmitterLike): SocketTransport {
  return {
    send: data => socket.send(data),
    close: () => socket.close(),

    onMessage(listener) {
      const handler = (data: unknown) => listener(String(data));
      socket.on('message', handler);
      return () => socket.off('message', handler);
    },

    onClose(listener) {
      const handler = () => listener();
      socket.on('close', handler);
      return () => socket.off('close', handler);
    },
  };
}