src/utils/protocol.ts

import WebSocket from 'ws';

// ── Inbound message types (client → server) ──────────────────────────────────
export type ClientMessageType =
  | 'heartbeat'
  | 'offer'
  | 'answer'
  | 'ice-candidate'
  | 'message'
  | 'get-upload-url'
  | 'relay'
  | 'friend';

// ── Outbound message types (server → client) ──────────────────────────────────
export type ServerMessageType =
  | 'connected'
  | 'ice-servers'
  | 'offer'
  | 'answer'
  | 'ice-candidate'
  | 'message'
  | 'upload-url'
  | 'relay'
  | 'peer-online'
  | 'peer-offline'
  | 'offline-flush'
  | 'error';

export interface ClientMessage {
  type: ClientMessageType;
  payload: Record<string, unknown>;
  // requestId allows client to correlate responses
  requestId?: string;
}

export interface ServerMessage {
  type: ServerMessageType;
  payload: Record<string, unknown>;
  requestId?: string;
  ts: number; // epoch ms
}

/**
 * Parse and validate an incoming raw WS message.
 * Returns null if the data is malformed — caller should silently drop.
 */
export function parseClientMessage(raw: WebSocket.RawData): ClientMessage | null {
  try {
    const str = raw.toString('utf8');
    if (str.length > 65536) return null; // 64 KB hard cap — protects against flood

    const obj = JSON.parse(str) as unknown;

    if (
      typeof obj !== 'object' ||
      obj === null ||
      typeof (obj as Record<string, unknown>).type !== 'string'
    ) {
      return null;
    }

    return obj as ClientMessage;
  } catch {
    return null;
  }
}

/**
 * Serialize a server message.
 * Using a single Buffer allocation avoids repeated JSON.stringify on hot paths.
 */
export function buildServerMessage(
  type: ServerMessageType,
  payload: Record<string, unknown>,
  requestId?: string
): Buffer {
  const msg: ServerMessage = { type, payload, requestId, ts: Date.now() };
  return Buffer.from(JSON.stringify(msg), 'utf8');
}

/**
 * Send a message to a WebSocket, catching send errors silently.
 * Avoids crashing the process when a socket closes mid-send.
 */
export function safeSend(
  ws: WebSocket,
  type: ServerMessageType,
  payload: Record<string, unknown>,
  requestId?: string
): void {
  if (ws.readyState !== WebSocket.OPEN) return;

  try {
    ws.send(buildServerMessage(type, payload, requestId));
  } catch {
    // Socket probably closed between the readyState check and send — ignore
  }
}