import { BufferReader, BufferWriter } from '@node-dlc/bufio';

import { MessageType } from '../MessageType';
import { IWireMessage } from './IWireMessage';

export class PongMessage implements IWireMessage {
  /**
   * Deserializes a pong message from a Buffer into a PongMessage
   * instance.
   */
  public static deserialize(payload: Buffer): PongMessage {
    const instance = new PongMessage();

    const reader = new BufferReader(payload);
    reader.readUInt16BE(); // read off type

    const byteslen = reader.readUInt16BE();
    instance.ignored = reader.readBytes(byteslen);
    return instance;
  }

  /**
   * Message type = 19
   */
  public type: MessageType = MessageType.Pong;

  /**
   * Should be set to zeros of length specified in a ping message's
   * num_pong_bytes. Must not set ignored to sensitive data such as
   * secrets or portions of initialized memory.
   */
  public ignored: Buffer;

  /**
   * In order to allow for the existence of long-lived TCP
   * connections, at times it may be required that both ends keep
   * alive the TCP connection at the application level.
   *
   * The pong message is a reply to a ping message and must
   * reply with the specify number of bytes when the num_pong_bytes
   * value is less than 65532.
   * for the number of pong bytes it expects to receive as
   * a reply. The ignored bits should be set to 0.
   */
  constructor(numPongBytes = 0) {
    this.ignored = Buffer.alloc(numPongBytes);
  }

  /**
   * Serializes a PongMessage into a Buffer that can be
   * streamed on the wire.
   */
  public serialize(): Buffer {
    const len =
      2 + // type
      2 + // byteslen
      +this.ignored.length;

    const writer = new BufferWriter(Buffer.alloc(len));
    writer.writeUInt16BE(this.type);
    writer.writeUInt16BE(this.ignored.length);
    writer.writeBytes(this.ignored);
    return writer.toBuffer();
  }
}