import HKDF from 'hkdf';
import srp from 'srp-js';
import * as forge from 'node-forge';

const DEFAULT_BYTE_LENGTH = 32;
const DEFAULT_PBKDF2_ITERATIONS = 1E5; // 100,000

/**
 * Generate hex signing key used for AES encryption
 *
 * @param pass
 * @param email
 * @param salt
 */
export async function deriveKey (pass, email, salt) {
  const combinedSalt = await _hkdfSalt(salt, email);
  return _pbkdf2Passphrase(pass, combinedSalt);
}

/**
 * Encrypt with RSA256 public key
 *
 * @param publicKeyJWK
 * @param plaintext
 * @return String
 */
export function encryptRSAWithJWK (publicKeyJWK, plaintext) {
  if (publicKeyJWK.alg !== 'RSA-OAEP-256') {
    throw new Error('Public key algorithm was not RSA-OAEP-256');
  } else if (publicKeyJWK.kty !== 'RSA') {
    throw new Error('Public key type was not RSA');
  } else if (!publicKeyJWK.key_ops.find(o => o === 'encrypt')) {
    throw new Error('Public key does not have "encrypt" op');
  }

  const encodedPlaintext = encodeURIComponent(plaintext);

  const n = _b64UrlToBigInt(publicKeyJWK.n);
  const e = _b64UrlToBigInt(publicKeyJWK.e);
  const publicKey = forge.rsa.setPublicKey(n, e);

  const encrypted = publicKey.encrypt(encodedPlaintext, 'RSA-OAEP', {
    md: forge.md.sha256.create()
  });
  return forge.util.bytesToHex(encrypted);
}

export function decryptRSAWithJWK (privateJWK, encryptedBlob) {
  const n = _b64UrlToBigInt(privateJWK.n);
  const e = _b64UrlToBigInt(privateJWK.e);
  const d = _b64UrlToBigInt(privateJWK.d);
  const p = _b64UrlToBigInt(privateJWK.p);
  const q = _b64UrlToBigInt(privateJWK.q);
  const dP = _b64UrlToBigInt(privateJWK.dp);
  const dQ = _b64UrlToBigInt(privateJWK.dq);
  const qInv = _b64UrlToBigInt(privateJWK.qi);

  const privateKey = forge.rsa.setPrivateKey(n, e, d, p, q, dP, dQ, qInv);
  const bytes = forge.util.hexToBytes(encryptedBlob);
  const decrypted = privateKey.decrypt(bytes, 'RSA-OAEP', {
    md: forge.md.sha256.create()
  });

  return decodeURIComponent(decrypted);
}

export function recryptRSAWithJWK (privateJWK, publicJWK, encryptedBlob) {
  const decrypted = decryptRSAWithJWK(privateJWK, encryptedBlob);
  return encryptRSAWithJWK(publicJWK, decrypted);
}

/**
 * Encrypt data using symmetric key
 *
 * @param jwkOrKey JWK or string representing symmetric key
 * @param plaintext string of data to encrypt
 * @param additionalData any additional public data to attach
 * @returns {{iv, t, d, ad}}
 */
export function encryptAES (jwkOrKey, plaintext, additionalData = '') {
  // TODO: Add assertion checks for JWK
  const rawKey = typeof jwkOrKey === 'string' ? jwkOrKey : _b64UrlToHex(jwkOrKey.k);
  const key = forge.util.hexToBytes(rawKey);

  const iv = forge.random.getBytesSync(12);
  const cipher = forge.cipher.createCipher('AES-GCM', key);

  // Plaintext could contain weird unicode, so we have to encode that
  const encodedPlaintext = encodeURIComponent(plaintext);

  cipher.start({additionalData, iv, tagLength: 128});
  cipher.update(forge.util.createBuffer(encodedPlaintext));
  cipher.finish();

  return {
    iv: forge.util.bytesToHex(iv),
    t: forge.util.bytesToHex(cipher.mode.tag),
    d: forge.util.bytesToHex(cipher.output),
    ad: forge.util.bytesToHex(additionalData)
  };
}

/**
 * Decrypt AES using a key
 *
 * @param jwkOrKey JWK or string representing symmetric key
 * @param message
 * @returns String
 */
export function decryptAES (jwkOrKey, message) {
  // TODO: Add assertion checks for JWK
  const rawKey = typeof jwkOrKey === 'string' ? jwkOrKey : _b64UrlToHex(jwkOrKey.k);
  const key = forge.util.hexToBytes(rawKey);

  // ~~~~~~~~~~~~~~~~~~~~ //
  // Decrypt with AES-GCM //
  // ~~~~~~~~~~~~~~~~~~~~ //

  const decipher = forge.cipher.createDecipher('AES-GCM', key);
  decipher.start({
    iv: forge.util.hexToBytes(message.iv),
    tagLength: message.t.length * 4,
    tag: forge.util.hexToBytes(message.t),
    additionalData: forge.util.hexToBytes(message.ad)
  });

  decipher.update(forge.util.createBuffer(forge.util.hexToBytes(message.d)));

  if (decipher.finish()) {
    return decodeURIComponent(decipher.output.toString());
  } else {
    throw new Error('Failed to decrypt data');
  }
}

/**
 * Generate a random salt in hex
 *
 * @returns {string}
 */
export function getRandomHex (bytes = DEFAULT_BYTE_LENGTH) {
  return forge.util.bytesToHex(forge.random.getBytesSync(bytes));
}

/**
 * Generate a random account Id
 *
 * @returns {string}
 */
export function generateAccountId () {
  return `act_${getRandomHex(DEFAULT_BYTE_LENGTH)}`;
}

/**
 * Generate a random key
 *
 * @returns {Promise}
 */
export function srpGenKey () {
  return new Promise((resolve, reject) => {
    srp.genKey((err, secret1Buffer) => {
      if (err) {
        reject(err);
      } else {
        resolve(secret1Buffer.toString('hex'));
      }
    });
  });
}

/**
 * Generate a random AES256 key for use with symmetric encryption
 */
export async function generateAES256Key () {
  const c = window.crypto;
  const subtle = c ? c.subtle || c.webkitSubtle : null;

  if (subtle) {
    // console.log('-- Using Native AES Key Generation --');
    const key = await subtle.generateKey(
      {name: 'AES-GCM', length: 256},
      true,
      ['encrypt', 'decrypt']
    );
    return subtle.exportKey('jwk', key);
  } else {
    // console.log('-- Using Fallback Forge AES Key Generation --');
    const key = forge.util.bytesToHex(forge.random.getBytesSync(32));
    return {
      kty: 'oct',
      alg: 'A256GCM',
      ext: true,
      key_ops: ['encrypt', 'decrypt'],
      k: _hexToB64Url(key)
    };
  }
}

/**
 * Generate RSA keypair JWK with 2048 bits and exponent 0x10001
 *
 * @returns Object
 */
export async function generateKeyPairJWK () {
  // NOTE: Safari has crypto.webkitSubtle, but it does not support RSA-OAEP-SHA256
  const subtle = window.crypto && window.crypto.subtle;

  if (subtle) {
    // console.log('-- Using Native RSA Generation --');

    const pair = await subtle.generateKey({
      name: 'RSA-OAEP',
      publicExponent: new Uint8Array([1, 0, 1]),
      modulusLength: 2048,
      hash: 'SHA-256'
    },
      true,
      ['encrypt', 'decrypt']
    );

    return {
      publicKey: await subtle.exportKey('jwk', pair.publicKey),
      privateKey: await subtle.exportKey('jwk', pair.privateKey)
    };
  } else {
    // console.log('-- Using Forge RSA Generation --');

    const pair = forge.pki.rsa.generateKeyPair({bits: 2048, e: 0x10001});
    const privateKey = {
      alg: 'RSA-OAEP-256',
      kty: 'RSA',
      key_ops: ['decrypt'],
      ext: true,
      d: _bigIntToB64Url(pair.privateKey.d),
      dp: _bigIntToB64Url(pair.privateKey.dP),
      dq: _bigIntToB64Url(pair.privateKey.dQ),
      e: _bigIntToB64Url(pair.privateKey.e),
      n: _bigIntToB64Url(pair.privateKey.n),
      p: _bigIntToB64Url(pair.privateKey.p),
      q: _bigIntToB64Url(pair.privateKey.q),
      qi: _bigIntToB64Url(pair.privateKey.qInv)
    };

    const publicKey = {
      alg: 'RSA-OAEP-256',
      kty: 'RSA',
      key_ops: ['encrypt'],
      e: _bigIntToB64Url(pair.publicKey.e),
      n: _bigIntToB64Url(pair.publicKey.n)
    };

    return {privateKey, publicKey};
  }
}

// ~~~~~~~~~~~~~~~~ //
// Helper Functions //
// ~~~~~~~~~~~~~~~~ //

/**
 * Combine email and raw salt into usable salt
 *
 * @param rawSalt
 * @param rawEmail
 * @returns {Promise}
 */
function _hkdfSalt (rawSalt, rawEmail) {
  return new Promise(resolve => {
    const hkdf = new HKDF('sha256', rawSalt, rawEmail);
    hkdf.derive('', DEFAULT_BYTE_LENGTH, buffer => resolve(buffer.toString('hex')));
  });
}

/**
 * Convert a JSBN BigInteger to a URL-safe version of base64 encoding. This
 * should only be used for encoding JWKs
 *
 * @param n BigInteger
 * @returns {string}
 */
function _bigIntToB64Url (n) {
  return _hexToB64Url(n.toString(16));
}

function _hexToB64Url (h) {
  const bytes = forge.util.hexToBytes(h);
  return window.btoa(bytes)
    .replace(/=/g, '')
    .replace(/\+/g, '-')
    .replace(/\//g, '_');
}

function _b64UrlToBigInt (s) {
  return new forge.jsbn.BigInteger(_b64UrlToHex(s), 16);
}

function _b64UrlToHex (s) {
  const b64 = s.replace(/-/g, '+').replace(/_/g, '/');
  return forge.util.bytesToHex(window.atob(b64));
}

/**
 * Derive key from password
 *
 * @param passphrase
 * @param salt hex representation of salt
 */
async function _pbkdf2Passphrase (passphrase, salt) {
  if (window.crypto && window.crypto.subtle) {
    // console.log('-- Using native PBKDF2 --');

    const k = await window.crypto.subtle.importKey(
      'raw',
      Buffer.from(passphrase, 'utf8'),
      {name: 'PBKDF2'},
      true,
      ['deriveBits']
    );

    const algo = {
      name: 'PBKDF2',
      salt: new Buffer(salt, 'hex'),
      iterations: DEFAULT_PBKDF2_ITERATIONS,
      hash: 'SHA-256'
    };

    const derivedKeyRaw = await window.crypto.subtle.deriveBits(algo, k, DEFAULT_BYTE_LENGTH * 8);
    return new Buffer(derivedKeyRaw).toString('hex');
  } else {
    // console.log('-- Using Forge PBKDF2 --');
    const derivedKeyRaw = forge.pkcs5.pbkdf2(
      passphrase,
      forge.util.hexToBytes(salt),
      DEFAULT_PBKDF2_ITERATIONS,
      DEFAULT_BYTE_LENGTH,
      forge.md.sha256.create()
    );

    return forge.util.bytesToHex(derivedKeyRaw);
  }
}