var crypto = require('crypto');

// NOTE: slower than 'bcrypt' but is pure JS and has no dependencies.
// for server side, consider using 'bcrypt' (C++), has the same API.
var bcrypt = require('bcryptjs');

/* Applies SHA256 to the given data, returns encoded as base64 string.
 *
 * Parameters:
 *  - data: any value usable by crypto's update() method, i.e: String
 *    or buffer.
 *
 * Returns: String encoded as base64 of the sha256
 */
function sha256AsBase64(data) {
  return crypto.createHash('sha256')
    .update(data)
    .digest('base64');
}

/* Get bcrypt salt from username.
 *
 * Parameters:
 *  - `username`: string with username.
 *  - `rounds` (optional): use bcrypt rounds, or 12 if omitted.
 *  - `prefix` (optional): use bcrypt prefix, or `2a` if omitted.
 *
 * Returns: String encoded as bcrypt salt format. Example:
 * `$2a$12$N9qo8uLOickgx2ZMRZoMye`
 */
function bcryptSaltFromUsername(username, rounds, prefix) {
  var hash = crypto.createHash('sha256').update(username).digest();
  return ('$' + (prefix || '2a') +
          '$' + (rounds || 12) +
          '$' + bcrypt.encodeBase64(hash, 16));
}

/* Hash the given password using the given salt.
 *
 * This basically calls bcrypt on the `sha256AsBase64(password)`.
 *
 * Parameters:
 *  - `password`: string with clear text password.
 *  - `salt`: salt encoded using bcrypt's standard format.
 *
 * Return: 60 characters string encoded with the standard bcrypt
 * format, ie:
 * `$2a$12$N9qo8uLOickgx2ZMRZoMyeIjZAgcfl7p92ldGxad68LJZdL17lhWy`
 */
function bcryptPasswordSaltSync(password, salt) {
  return bcrypt.hashSync(sha256AsBase64(password), salt);
}

/* Create a `challenge` using the bcryptPassword and the given salt.
 *
 * This basically calls bcrypt on the `bcryptPassword`.
 *
 * Parameters:
 *  - `bcryptPassword`: string with hashed password, see
 *     `bcryptUserPasswordSync()`. Must be 60 characters in length.
 *  - `salt`: salt encoded using bcrypt's standard format.
 *
 * Return: 60 characters string encoded with the standard bcrypt
 * format, ie:
 * `$2a$12$N9qo8uLOickgx2ZMRZoMyeIjZAgcfl7p92ldGxad68LJZdL17lhWy`
 */
function bcryptChallengePasswordSync(bcryptPassword, salt) {
  if (bcryptPassword.length !== 60) {
    throw new Error('invalid bcryptPassword length!');
  }
  return bcrypt.hashSync(bcryptPassword, salt);
}

/* Given an username and its password, create the bcrypt hash expected
 * by Elo API.
 *
 * The Elo API demands 12 salt-rounds (2^12 operations = 4096
 * iterations) using the first 16 bytes of `salt16Bytes =
 * sha256(username)` encoded as `bcrypt.encodeBase64(salt16Bytes,
 * 16)`. **NOTE: bcrypt uses a custom base64 alphabet!**.
 *
 * Since bcrypt limits its hashed payload to 72 characters and
 * passwords are of an unknown size we apply `sha256AsBase64(password)`
 * so we're fixed to 44 characters resulting from the Base64 encode of
 * the 256 bits from sha256.
 *
 * The resulting string is a 60 characters string encoded with the
 * standard bcrypt format: a prefix, the salt-rounds, the salt and the
 * actual hash, Example:
 *
 *  - Prefix: `2a` (bcrypt version)
 *  - Rounds: `12`
 *  - Salt: `N9qo8uLOickgx2ZMRZoMye`
 *  - Hash: `IjZAgcfl7p92ldGxad68LJZdL17lhW`
 *  - Encoded: `$2a$12$N9qo8uLOickgx2ZMRZoMyeIjZAgcfl7p92ldGxad68LJZdL17lhWy`
 *
 * Parameters:
 *  - `username`: string with username.
 *  - `password`: string with clear text password.
 *
 * Return: 60 characters string encoded with the standard bcrypt
 * format, ie:
 * `$2a$12$N9qo8uLOickgx2ZMRZoMyeIjZAgcfl7p92ldGxad68LJZdL17lhWy`
 */
function bcryptUserPasswordSync(username, password) {
  var salt = bcryptSaltFromUsername(username);
  return bcryptPasswordSaltSync(password, salt);
}

/* Hash the given password using the given salt.
 *
 * This basically calls bcrypt on the `sha256AsBase64(password)`.
 *
 * Parameters:
 *  - `password`: string with clear text password.
 *  - `salt`: salt encoded using bcrypt's standard format.
 *  - `cb`: the callback function that receives 2 parameters: error and
 *    hash. It's called when the computation is done.
 *
 * Return: if no `cb` is provided, returns a `Promise`.
 */
function bcryptPasswordSalt(password, salt, cb) {
  return bcrypt.hash(sha256AsBase64(password), salt, cb);
}


/* Create a `challenge` using the bcryptPassword and the given salt.
 *
 * This basically calls bcrypt on the `bcryptPassword`.
 *
 * Parameters:
 *  - `bcryptPassword`: string with hashed password, see
 *     `bcryptUserPassword()`. Must be 60 characters in length.
 *  - `salt`: salt encoded using bcrypt's standard format.
 *  - `cb`: the callback function that receives 2 parameters: error and
 *    hash. It's called when the computation is done.
 *
 * Return: if no `cb` is provided, returns a `Promise`.
 */
function bcryptChallengePassword(bcryptPassword, salt) {
  if (bcryptPassword.length !== 60) {
    throw new Error('invalid bcryptPassword length!');
  }
  return bcrypt.hash(bcryptPassword, salt);
}

/* Given an username and its password, create the bcrypt hash expected
 * by Elo API.
 *
 * The Elo API demands 12 salt-rounds (2^12 operations = 4096
 * iterations) using the first 16 bytes of `salt16Bytes =
 * sha256(username)` encoded as `bcrypt.encodeBase64(salt16Bytes,
 * 16)`. **NOTE: bcrypt uses a custom base64 alphabet!**.
 *
 * Since bcrypt limits its hashed payload to 72 characters and
 * passwords are of an unknown size we apply `sha256AsBase64(password)`
 * so we're fixed to 44 characters resulting from the Base64 encode of
 * the 256 bits from sha256.
 *
 * The resulting string is a 60 characters string encoded with the
 * standard bcrypt format: a prefix, the salt-rounds, the salt and the
 * actual hash, Example:
 *
 *  - Prefix: `2a` (bcrypt version)
 *  - Rounds: `12`
 *  - Salt: `N9qo8uLOickgx2ZMRZoMye`
 *  - Hash: `IjZAgcfl7p92ldGxad68LJZdL17lhW`
 *  - Encoded: `$2a$12$N9qo8uLOickgx2ZMRZoMyeIjZAgcfl7p92ldGxad68LJZdL17lhWy`
 *
 * Parameters:
 *  - `username`: string with username.
 *  - `password`: string with clear text password.
 *  - `cb`: the callback function that receives 2 parameters: error and
 *    hash. It's called when the computation is done.
 *
 * Return: if no `cb` is provided, returns a `Promise`.
 */
function bcryptUserPassword(username, password, cb) {
  var salt = bcryptSaltFromUsername(username);
  return bcryptPasswordSalt(password, salt, cb);
}

module.exports = {
  sha256AsBase64: sha256AsBase64,
  bcryptSaltFromUsername: bcryptSaltFromUsername,
  bcryptUserPasswordSync: bcryptUserPasswordSync,
  bcryptPasswordSaltSync: bcryptPasswordSaltSync,
  bcryptChallengePasswordSync: bcryptChallengePasswordSync,
  bcryptUserPassword: bcryptUserPassword,
  bcryptPasswordSalt: bcryptPasswordSalt,
  bcryptChallengePassword: bcryptChallengePassword,
  bcrypt: bcrypt,
};