import {
  BlockCipherMode,
} from './cipher-core.js';

function generateKeystreamAndEncrypt(words, offset, blockSize, cipher) {
  const _words = words;
  let keystream;

  // Shortcut
  const iv = this._iv;

  // Generate keystream
  if (iv) {
    keystream = iv.slice(0);

    // Remove IV for subsequent blocks
    this._iv = undefined;
  } else {
    keystream = this._prevBlock;
  }
  cipher.encryptBlock(keystream, 0);

  // Encrypt
  for (let i = 0; i < blockSize; i += 1) {
    _words[offset + i] ^= keystream[i];
  }
}

/**
 * Cipher Feedback block mode.
 */
export class CFB extends BlockCipherMode {
}
CFB.Encryptor = class extends CFB {
  processBlock(words, offset) {
    // Shortcuts
    const cipher = this._cipher;
    const { blockSize } = cipher;

    generateKeystreamAndEncrypt.call(this, words, offset, blockSize, cipher);

    // Remember this block to use with next block
    this._prevBlock = words.slice(offset, offset + blockSize);
  }
};
CFB.Decryptor = class extends CFB {
  processBlock(words, offset) {
    // Shortcuts
    const cipher = this._cipher;
    const { blockSize } = cipher;

    // Remember this block to use with next block
    const thisBlock = words.slice(offset, offset + blockSize);

    generateKeystreamAndEncrypt.call(this, words, offset, blockSize, cipher);

    // This block becomes the previous block
    this._prevBlock = thisBlock;
  }
};