// @ts-check
/**
 * The connection to the relay.  It knows nothing about pages or encryption:
 * it delivers bytes to peers and reports who is present.  It reconnects by
 * itself when the connection drops.
 */

const RETRY_DELAYS_MS = [500, 1000, 2000, 5000];

/** Close codes after which retrying is pointless (see the relay). */
const FINAL_CLOSE_CODES = new Map([
  [4001, 'The session is full.'],
  [4002, 'The relay is full.'],
]);

/**
 * @typedef {object} RelayHandlers
 * @property {(peer: number, peers: number[]) => void} onWelcome
 *     Connected (or reconnected): our peer number and the peers present.
 * @property {(peer: number) => void} onJoin
 * @property {(peer: number) => void} onLeave
 * @property {(peer: number, body: Uint8Array<ArrayBuffer>) => void} onMessage
 * @property {(status: 'connecting' | 'connected' | 'failed', detail?: string) => void} onStatus
 */

export class RelayConnection {
  /**
   * @param {string} relay    Address of the relay, ws:// or wss://.
   * @param {string} roomId
   * @param {RelayHandlers} handlers
   */
  constructor(relay, roomId, handlers) {
    this.url = `${relay}/room/${roomId}`;
    this.handlers = handlers;
    /** @type {WebSocket | null} */
    this.socket = null;
    this.attempt = 0;
    this.closed = false;
  }

  connect() {
    if (this.closed) return;
    this.handlers.onStatus('connecting');
    const socket = new WebSocket(this.url);
    socket.binaryType = 'arraybuffer';
    this.socket = socket;

    socket.onmessage = (event) => {
      if (socket !== this.socket) return;
      if (typeof event.data === 'string') {
        const control = JSON.parse(event.data);
        if (control.type === 'welcome') {
          this.attempt = 0;
          this.handlers.onStatus('connected');
          this.handlers.onWelcome(control.peer, control.peers);
        } else if (control.type === 'join') {
          this.handlers.onJoin(control.peer);
        } else if (control.type === 'leave') {
          this.handlers.onLeave(control.peer);
        }
      } else {
        const bytes = new Uint8Array(event.data);
        if (bytes.length < 4) return;
        const peer = new DataView(event.data).getUint32(0);
        this.handlers.onMessage(peer, bytes.subarray(4));
      }
    };

    socket.onclose = (event) => {
      if (socket !== this.socket) return;
      this.socket = null;
      if (this.closed) return;
      const final = FINAL_CLOSE_CODES.get(event.code);
      if (final) {
        this.closed = true;
        this.handlers.onStatus('failed', final);
        return;
      }
      this.handlers.onStatus('connecting');
      const delay = RETRY_DELAYS_MS[Math.min(this.attempt, RETRY_DELAYS_MS.length - 1)];
      this.attempt += 1;
      setTimeout(() => this.connect(), delay);
    };
  }

  /** @returns {boolean} */
  get connected() {
    return this.socket !== null && this.socket.readyState === WebSocket.OPEN;
  }

  /**
   * @param {number} destination  A peer number, or 0 for everyone else.
   * @param {Uint8Array} body
   */
  send(destination, body) {
    if (!this.socket || this.socket.readyState !== WebSocket.OPEN) return;
    const message = new Uint8Array(4 + body.length);
    new DataView(message.buffer).setUint32(0, destination);
    message.set(body, 4);
    this.socket.send(message);
  }

  close() {
    this.closed = true;
    if (this.socket) this.socket.close();
  }
}