import { MAX_DATA_LENGTH } from "../common";
import { numberToUint16BE } from "../utilities/number";
import { SmartBuffer } from "../utilities/smart-buffer";

export interface IncomingPacket {
  messageType: number;
  senderId: number;
  data: Uint8Array;
}

export interface OutgoingPacket {
  messageType: Uint8Array;
  data?: Uint8Array;
}

/**
 * Create an outgoing packet ready-to-send over a WebSocket in line with the BENNC basic message strucure specification.
 * @param outgoingPacket The message type and data to send.
 * @returns A buffer containing the ready-to-send packet.
 */
export function packOutgoingPacket(outgoingPacket: OutgoingPacket): Uint8Array {
  // Default to empty data if not provided
  const data = outgoingPacket.data ?? new Uint8Array(0);

  // Verify that the data does not exceed the maximum data length.
  if (data.length > MAX_DATA_LENGTH) {
    throw RangeError(
      `Specified data of length ${data.length} exceeds max data length ${MAX_DATA_LENGTH}.`,
    );
  }

  // Prepare the outgoing packet.
  const buffer = new SmartBuffer();
  buffer.writeBytes(outgoingPacket.messageType);
  buffer.writeBytes(numberToUint16BE(data.length));
  buffer.writeBytes(data);

  return buffer.data;
}

/**
 * Unpack an incoming packet coming from a WebSocket in line with the BENNC basic message strucure specification.
 * @param incomingPacket The incoming buffer from a WebSocket to unpack.
 * @returns The unpacked data.
 */
export function unpackIncomingPacket(
  incomingPacket: ArrayBuffer,
): IncomingPacket {
  const buffer = SmartBuffer.from(incomingPacket);

  const messageType = buffer.readUInt16();
  const senderId = buffer.readUInt32();
  const length = buffer.readUInt16();
  const data = buffer.readBytes(length);

  return {
    messageType: messageType,
    senderId: senderId,
    data: data,
  };
}