'use strict';

var utils = require('./utils');
var assert = require('minimalistic-assert');

function Hmac(hash, key, enc) {
  if (!(this instanceof Hmac))
    return new Hmac(hash, key, enc);
  this.Hash = hash;
  this.blockSize = hash.blockSize / 8;
  this.outSize = hash.outSize / 8;
  this.inner = null;
  this.outer = null;

  this._init(utils.toArray(key, enc));
}
module.exports = Hmac;

Hmac.prototype._init = function init(key) {
  // Shorten key, if needed
  if (key.length > this.blockSize)
    key = new this.Hash().update(key).digest();
  assert(key.length <= this.blockSize);

  // Add padding to key
  for (var i = key.length; i < this.blockSize; i++)
    key.push(0);

  for (i = 0; i < key.length; i++)
    key[i] ^= 0x36;
  this.inner = new this.Hash().update(key);

  // 0x36 ^ 0x5c = 0x6a
  for (i = 0; i < key.length; i++)
    key[i] ^= 0x6a;
  this.outer = new this.Hash().update(key);
};

Hmac.prototype.update = function update(msg, enc) {
  this.inner.update(msg, enc);
  return this;
};

Hmac.prototype.digest = function digest(enc) {
  this.outer.update(this.inner.digest());
  return this.outer.digest(enc);
};