/*
 *
 * This file contains an adaptation of the AES decryption algorithm
 * from the Standford Javascript Cryptography Library. That work is
 * covered by the following copyright and permissions notice:
 *
 * Copyright 2009-2010 Emily Stark, Mike Hamburg, Dan Boneh.
 * All rights reserved.
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions are
 * met:
 *
 * 1. Redistributions of source code must retain the above copyright
 *    notice, this list of conditions and the following disclaimer.
 *
 * 2. Redistributions in binary form must reproduce the above
 *    copyright notice, this list of conditions and the following
 *    disclaimer in the documentation and/or other materials provided
 *    with the distribution.
 *
 * THIS SOFTWARE IS PROVIDED BY THE AUTHORS ``AS IS'' AND ANY EXPRESS OR
 * IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED
 * WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE
 * DISCLAIMED. IN NO EVENT SHALL <COPYRIGHT HOLDER> OR CONTRIBUTORS BE
 * LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
 * CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF
 * SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR
 * BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY,
 * WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE
 * OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN
 * IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
 *
 * The views and conclusions contained in the software and documentation
 * are those of the authors and should not be interpreted as representing
 * official policies, either expressed or implied, of the authors.
 */
import Stream from './stream';
import {unpad} from 'pkcs7';

/**
 * Convert network-order (big-endian) bytes into their little-endian
 * representation.
 */
const ntoh = function(word) {
  return (word << 24) |
    ((word & 0xff00) << 8) |
    ((word & 0xff0000) >> 8) |
    (word >>> 24);
};

/**
 * Expand the S-box tables.
 *
 * @private
 */
const precompute = function() {
  let _tables = [[[], [], [], [], []], [[], [], [], [], []]];
  let encTable = _tables[0];
  let decTable = _tables[1];
  let sbox = encTable[4];
  let sboxInv = decTable[4];
  let i;
  let x;
  let xInv;
  let d = [];
  let th = [];
  let x2;
  let x4;
  let x8;
  let s;
  let tEnc;
  let tDec;

  // Compute double and third tables
  for (i = 0; i < 256; i++) {
    th[(d[i] = i << 1 ^ (i >> 7) * 283) ^ i] = i;
  }

  for (x = xInv = 0; !sbox[x]; x ^= x2 || 1, xInv = th[xInv] || 1) {
    // Compute sbox
    s = xInv ^ xInv << 1 ^ xInv << 2 ^ xInv << 3 ^ xInv << 4;
    s = s >> 8 ^ s & 255 ^ 99;
    sbox[x] = s;
    sboxInv[s] = x;

    // Compute MixColumns
    x8 = d[x4 = d[x2 = d[x]]];
    tDec = x8 * 0x1010101 ^ x4 * 0x10001 ^ x2 * 0x101 ^ x * 0x1010100;
    tEnc = d[s] * 0x101 ^ s * 0x1010100;

    for (i = 0; i < 4; i++) {
      encTable[i][x] = tEnc = tEnc << 24 ^ tEnc >>> 8;
      decTable[i][s] = tDec = tDec << 24 ^ tDec >>> 8;
    }
  }

  // Compactify. Considerable speedup on Firefox.
  for (i = 0; i < 5; i++) {
    encTable[i] = encTable[i].slice(0);
    decTable[i] = decTable[i].slice(0);
  }
  return _tables;
}

let tables;

/**
 * Schedule out an AES key for both encryption and decryption. This
 * is a low-level class. Use a cipher mode to do bulk encryption.
 *
 * @constructor
 * @param key {Array} The key as an array of 4, 6 or 8 words.
 */
class AES {
  constructor(key) {
   /**
    * The expanded S-box and inverse S-box tables. These will be computed
    * on the client so that we don't have to send them down the wire.
    *
    * There are two tables, _tables[0] is for encryption and
    * _tables[1] is for decryption.
    *
    * The first 4 sub-tables are the expanded S-box with MixColumns. The
    * last (_tables[01][4]) is the S-box itself.
    *
    * @private
    */
    if (!tables) {
      tables = precompute();
    }
    this._tables = tables;
    let i;
    let j;
    let tmp;
    let encKey;
    let decKey;
    let sbox = this._tables[0][4];
    let decTable = this._tables[1];
    let keyLen = key.length;
    let rcon = 1;

    if (keyLen !== 4 && keyLen !== 6 && keyLen !== 8) {
      throw new Error('Invalid aes key size');
    }

    encKey = key.slice(0);
    decKey = [];
    this._key = [encKey, decKey];

    // schedule encryption keys
    for (i = keyLen; i < 4 * keyLen + 28; i++) {
      tmp = encKey[i - 1];

      // apply sbox
      if (i % keyLen === 0 || (keyLen === 8 && i % keyLen === 4)) {
        tmp = sbox[tmp >>> 24] << 24 ^
          sbox[tmp >> 16 & 255] << 16 ^
          sbox[tmp >> 8 & 255] << 8 ^
          sbox[tmp & 255];

        // shift rows and add rcon
        if (i % keyLen === 0) {
          tmp = tmp << 8 ^ tmp >>> 24 ^ rcon << 24;
          rcon = rcon << 1 ^ (rcon >> 7) * 283;
        }
      }

      encKey[i] = encKey[i - keyLen] ^ tmp;
    }

    // schedule decryption keys
    for (j = 0; i; j++, i--) {
      tmp = encKey[j & 3 ? i : i - 4];
      if (i <= 4 || j < 4) {
        decKey[j] = tmp;
      } else {
        decKey[j] = decTable[0][sbox[tmp >>> 24 ]] ^
          decTable[1][sbox[tmp >> 16 & 255]] ^
          decTable[2][sbox[tmp >> 8 & 255]] ^
          decTable[3][sbox[tmp & 255]];
      }
    }
  }

  /**
   * Decrypt 16 bytes, specified as four 32-bit words.
   * @param encrypted0 {number} the first word to decrypt
   * @param encrypted1 {number} the second word to decrypt
   * @param encrypted2 {number} the third word to decrypt
   * @param encrypted3 {number} the fourth word to decrypt
   * @param out {Int32Array} the array to write the decrypted words
   * into
   * @param offset {number} the offset into the output array to start
   * writing results
   * @return {Array} The plaintext.
   */
  decrypt(encrypted0, encrypted1, encrypted2, encrypted3, out, offset) {
    let key = this._key[1];
    // state variables a,b,c,d are loaded with pre-whitened data
    let a = encrypted0 ^ key[0];
    let b = encrypted3 ^ key[1];
    let c = encrypted2 ^ key[2];
    let d = encrypted1 ^ key[3];
    let a2;
    let b2;
    let c2;

    // key.length === 2 ?
    let nInnerRounds = key.length / 4 - 2;
    let i;
    let kIndex = 4;
    let table = this._tables[1];

    // load up the tables
    let table0 = table[0];
    let table1 = table[1];
    let table2 = table[2];
    let table3 = table[3];
    let sbox = table[4];

    // Inner rounds. Cribbed from OpenSSL.
    for (i = 0; i < nInnerRounds; i++) {
      a2 = table0[a >>> 24] ^
        table1[b >> 16 & 255] ^
        table2[c >> 8 & 255] ^
        table3[d & 255] ^
        key[kIndex];
      b2 = table0[b >>> 24] ^
        table1[c >> 16 & 255] ^
        table2[d >> 8 & 255] ^
        table3[a & 255] ^
        key[kIndex + 1];
      c2 = table0[c >>> 24] ^
        table1[d >> 16 & 255] ^
        table2[a >> 8 & 255] ^
        table3[b & 255] ^
        key[kIndex + 2];
      d = table0[d >>> 24] ^
        table1[a >> 16 & 255] ^
        table2[b >> 8 & 255] ^
        table3[c & 255] ^
        key[kIndex + 3];
      kIndex += 4;
      a = a2; b = b2; c = c2;
    }

    // Last round.
    for (i = 0; i < 4; i++) {
      out[(3 & -i) + offset] =
        sbox[a >>> 24] << 24 ^
        sbox[b >> 16 & 255] << 16 ^
        sbox[c >> 8 & 255] << 8 ^
        sbox[d & 255] ^
        key[kIndex++];
      a2 = a; a = b; b = c; c = d; d = a2;
    }
  }

}

/* eslint-disable max-len */
/**
 * Decrypt bytes using AES-128 with CBC and PKCS#7 padding.
 * @param encrypted {Uint8Array} the encrypted bytes
 * @param key {Uint32Array} the bytes of the decryption key
 * @param initVector {Uint32Array} the initialization vector (IV) to
 * use for the first round of CBC.
 * @return {Uint8Array} the decrypted bytes
 *
 * @see http://en.wikipedia.org/wiki/Advanced_Encryption_Standard
 * @see http://en.wikipedia.org/wiki/Block_cipher_mode_of_operation#Cipher_Block_Chaining_.28CBC.29
 * @see https://tools.ietf.org/html/rfc2315
 */
/* eslint-enable max-len */
export const decrypt = function(encrypted, key, initVector) {
  // word-level access to the encrypted bytes
  let encrypted32 = new Int32Array(encrypted.buffer,
                                   encrypted.byteOffset,
                                   encrypted.byteLength >> 2);

  let decipher = new AES(Array.prototype.slice.call(key));

  // byte and word-level access for the decrypted output
  let decrypted = new Uint8Array(encrypted.byteLength);
  let decrypted32 = new Int32Array(decrypted.buffer);

  // temporary variables for working with the IV, encrypted, and
  // decrypted data
  let init0;
  let init1;
  let init2;
  let init3;
  let encrypted0;
  let encrypted1;
  let encrypted2;
  let encrypted3;

  // iteration variable
  let wordIx;

  // pull out the words of the IV to ensure we don't modify the
  // passed-in reference and easier access
  init0 = initVector[0];
  init1 = initVector[1];
  init2 = initVector[2];
  init3 = initVector[3];

  // decrypt four word sequences, applying cipher-block chaining (CBC)
  // to each decrypted block
  for (wordIx = 0; wordIx < encrypted32.length; wordIx += 4) {
    // convert big-endian (network order) words into little-endian
    // (javascript order)
    encrypted0 = ntoh(encrypted32[wordIx]);
    encrypted1 = ntoh(encrypted32[wordIx + 1]);
    encrypted2 = ntoh(encrypted32[wordIx + 2]);
    encrypted3 = ntoh(encrypted32[wordIx + 3]);

    // decrypt the block
    decipher.decrypt(
      encrypted0,
      encrypted1,
      encrypted2,
      encrypted3,
      decrypted32,
      wordIx
    );

    // XOR with the IV, and restore network byte-order to obtain the
    // plaintext
    decrypted32[wordIx] = ntoh(decrypted32[wordIx] ^ init0);
    decrypted32[wordIx + 1] = ntoh(decrypted32[wordIx + 1] ^ init1);
    decrypted32[wordIx + 2] = ntoh(decrypted32[wordIx + 2] ^ init2);
    decrypted32[wordIx + 3] = ntoh(decrypted32[wordIx + 3] ^ init3);

    // setup the IV for the next round
    init0 = encrypted0;
    init1 = encrypted1;
    init2 = encrypted2;
    init3 = encrypted3;
  }

  return decrypted;
};

export class AsyncStream extends Stream {
  constructor() {
    super(Stream);
    this.jobs = [];
    this.delay = 1;
    this.timeout_ = null;
  }
  processJob_() {
    this.jobs.shift()();
    if (this.jobs.length) {
      this.timeout_ = setTimeout(this.processJob_.bind(this),
                                 this.delay);
    } else {
      this.timeout_ = null;
    }
  }
  push(job) {
    this.jobs.push(job);
    if (!this.timeout_) {
      this.timeout_ = setTimeout(this.processJob_.bind(this),
                                 this.delay);
    }
  }
}

// the maximum number of bytes to process at one time
const decrypterStep = 4 * 8000;

export class Decrypter extends Stream {
  constructor(encrypted, key, initVector, done) {
    super(Stream);
    let step = decrypterStep;
    let encrypted32 = new Int32Array(encrypted.buffer);
    let decrypted = new Uint8Array(encrypted.byteLength);
    let i = 0;

    this.asyncStream_ = new AsyncStream();

    // split up the encryption job and do the individual chunks asynchronously
    this.asyncStream_.push(this.decryptChunk_(encrypted32.subarray(i, i + step),
                                              key,
                                              initVector,
                                              decrypted));
    for (i = step; i < encrypted32.length; i += step) {
      initVector = new Uint32Array([ntoh(encrypted32[i - 4]),
                                    ntoh(encrypted32[i - 3]),
                                    ntoh(encrypted32[i - 2]),
                                    ntoh(encrypted32[i - 1])]);
      this.asyncStream_.push(this.decryptChunk_(encrypted32.subarray(i, i + step),
                                                key,
                                                initVector,
                                                decrypted));
    }
    // invoke the done() callback when everything is finished
    this.asyncStream_.push(function() {
      // remove pkcs#7 padding from the decrypted bytes
      done(null, unpad(decrypted));
    });
  }
  decryptChunk_(encrypted, key, initVector, decrypted) {
    return function() {
      let bytes = decrypt(encrypted, key, initVector);

      decrypted.set(bytes, encrypted.byteOffset);
    };
  }
}

Decrypter.STEP = decrypterStep;

export default {
  decrypt,
  Decrypter,
  AsyncStream
};