import { emitter } from '@amatiasq/emitter';

import { SocketTransport } from '../transport.js';

/**
 * One connection on the server, speaking typed JSON. The mirror image of
 * `JsonSocket`: `TIn` is what the client sends, `TOut` is what you send back.
 *
 * This was `NiceSocket`, and it used to `extend` the `ws` `WebSocket` class —
 * which meant `NiceSocketServer` could not simply construct one (the instances
 * come from `ws`, already built) and grafted the two methods onto each incoming
 * socket with `Object.create(ws, {…descriptors})`. Taking the transport as a
 * constructor argument instead removes both the inheritance and the hack.
 */
export class JsonConnection<TIn = any, TOut = any> {
  private readonly emitMessage = emitter<TIn>();
  readonly onMessage = this.emitMessage.subscribe;

  private readonly emitClose = emitter<void>();
  readonly onClose = this.emitClose.subscribe;

  constructor(private readonly transport: SocketTransport) {
    transport.onMessage(data => this.processMessage(data));
    transport.onClose(() => this.emitClose());
  }

  send(value: TOut) {
    this.transport.send(JSON.stringify(value));
  }

  close() {
    this.transport.close();
  }

  private processMessage(data: string) {
    let message: TIn;

    try {
      message = JSON.parse(data) as TIn;
    } catch (error) {
      console.warn('Invalid JSON:', data);
      return;
    }

    this.emitMessage(message);
  }
}