/**
 * @module net/crypto
 */
/**
 * An inline-based implementation of the RC4 stream cipher.
 */
export class RC4 {

  private state: Buffer;
  private key: Buffer;
  private i: number;
  private j: number;

  /**
   * Constructs a new RC4 cipher object and initializes
   * the Keystream State with the given key.
   * @param key The key to use in the Keystream.
   */
  constructor(key: Buffer) {
    if (!Buffer.isBuffer(key)) {
      throw new TypeError(`Parameter "key" must be a Buffer, not ${typeof key}`);
    }
    this.key = key;
    this.reset();
  }

  /**
   * Performs an inline cipher on the entire contents of the `data` buffer.
   * @param data A stream of data to cipher using the Keystream.
   */
  cipher(data: Buffer): void {
    for (let n = 0; n < data.length; n++) {
      this.i = (this.i + 1) % 256;
      this.j = (this.j + this.state[this.i]) % 256;
      const tmp = this.state[this.i];
      this.state[this.i] = this.state[this.j];
      this.state[this.j] = tmp;
      const k = this.state[(this.state[this.i] + this.state[this.j]) % 256];
      /* tslint:disable no-bitwise */
      data[n] = (data[n] ^ k);
      /* tslint:enable no-bitwise */
    }
  }

  /**
   * Initializes the Keystream State.
   */
  reset(): void {
    this.state = Buffer.alloc(256);
    this.i = 0;
    this.j = 0;
    for (let i = 0; i < 256; i++) {
      this.state[i] = i;
    }

    let j = 0;
    for (let i = 0; i < 256; i++) {
      j = (j + this.state[i] + this.key[i % this.key.length]) % 256;
      const tmp = this.state[i];
      this.state[i] = this.state[j];
      this.state[j] = tmp;
    }
  }
}

/**
 * The RC4 Private Key used to encrypt outgoing packet.
 * This key is a Hex String, so should be converted to
 * a Buffer for use.
 * @example
 * const key = Buffer.from(OUTGOING_KEY, 'hex');
 */
export const OUTGOING_KEY = '6a39570cc9de4ec71d64821894';
/**
 * The RC4 Private Key to decrypt incoming packet data.
 * This key is a Hex String, so should be converted to
 * a Buffer for use.
 * @example
 * const key = Buffer.from(INCOMING_KEY, 'hex');
 */
export const INCOMING_KEY = 'c79332b197f92ba85ed281a023';