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

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