/**
 * Functions for managing packets used by the RCON protocol
 */
class Packet {
  /**
   * Generate a unique max 32 bit ID integer
   * @return {Number} Generated ID
   */
  static id () {
    return Number.parseInt(Math.random().toString(2).substring(2, 32), 2);
  }
  /**
   * Create a new packet buffer with given ID, type and payload
   * @param  {Number} id A unique max 32 bit client generated request ID
   * @param  {[type]} type Type of the packet
   * @param  {String} payload Data to be sent encoded in 'ASCII'
   * @return {Buffer} Created packet
   */
  static write (id, type, payload) {
    // Length of payload in bytes when encoded in ASCII
    const length = Buffer.byteLength(payload, 'ascii');
    // 14 bytes for the length, ID, type and 2-byte padding
    const buffer = Buffer.allocUnsafe(14 + length);
    // Offsets are hardcoded for speed
    buffer.writeInt32LE(10 + length, 0); // Length
    buffer.writeInt32LE(id, 4); // Request ID
    buffer.writeInt32LE(type, 8); // Type
    buffer.write(payload, 12, 'ascii'); // Payload
    buffer.writeInt16LE(0, 12 + length); // Two null bytes of padding
    return buffer;
  }
  /**
   * Parse the given packet into a JSON object
   * @param  {Buffer} packet
   * @return {Object} Parsed packet
   */
  static read (packet) {
    // Length of the rest of the packet
    const length = packet.readInt32LE(0);
    // Check if we have a valid packet with 2 null bytes of padding in the end
    if (packet.length === 4 + length && !packet.readInt16LE(packet.length - 2)) {
      // Offsets are hardcoded for speed
      return {
        length: length,
        id: packet.readInt32LE(4),
        type: packet.readInt32LE(8),
        payload: packet.toString('ascii', 12, packet.length - 2)
      };
    } else {
      throw new Error(`Invalid packet! [${packet}]`);
    }
  }
}
/**
 * RCON packet type Integers understood by the Mineccraft Server
 * https://wiki.vg/RCON#Packets
 * @type {Object}
 */
Packet.type = {
  AUTH: 3,
  AUTH_RES: 2,
  COMMAND: 2,
  COMMAND_RES: 0,
  // Invalid type that can be used to detect when the full response has been received
  COMMAND_END: 255
};
/**
 * Predefined responses the Minecraft Server can send
 * @type {Object}
 */
Packet.payload = {
  // Response the server sends after receiving a packet with above invalid type
  COMMAND_END: `Unknown request ${Packet.type['COMMAND_END'].toString(16)}`
};

module.exports = Packet;