# user.rb

require 'digest/sha1'

class User < ActiveRecord::Base
  # Constants
  SCREEN_NAME_MINIMUM_LENGTH = 2
  SCREEN_NAME_MAXIMUM_LENGTH = 20

  EMAIL_MAXIMUM_LENGTH = 50

  PASSWORD_MINIMUM_LENGTH = 6
  PASSWORD_MAXIMUM_LENGTH = 20

  # Ranges
  SCREEN_NAME_RANGE = SCREEN_NAME_MINIMUM_LENGTH..SCREEN_NAME_MAXIMUM_LENGTH
  PASSWORD_RANGE = PASSWORD_MINIMUM_LENGTH..PASSWORD_MAXIMUM_LENGTH

  # Unique validations
  validates_uniqueness_of :screen_name, :email
  # Length validations
  validates_length_of     :screen_name, :within => SCREEN_NAME_RANGE
  validates_length_of     :password, :within => PASSWORD_RANGE
  validates_length_of     :email, :maximum => EMAIL_MAXIMUM_LENGTH
  # Presence validations
  validates_presence_of   :screen_name, :email, :password
  # Format validations
  validates_format_of     :email,
                          :with => /^\S+\@(\[?)[a-zA-Z0-9\-\.]+\.([a-zA-Z]{2,4}|[0-9]{1,4})(\]?)$/ix,
                          :message => "not a valid email address!"
  # Exclusion validations
  validates_exclusion_of  :screen_name,
                          :in => %w( admin Admin guest Guest administrator Administrator ),
                          :message => "is reserved and cannot be registered."

  def self.authenticate(name, password)
    @user = self.find_by_name(name)
    if @user
      expected_password = encrypted_password(password, @user.salt)
      if @user.hashed_password != expected_password
        @user = nil
      end
    end
    @user
  end

  def password
    @password
  end

  def password=(pwd)
    @password = pwd
    return if pwd.blank?
    create_new_salt
    self.hashed_password = User.encrypted_password(self.password, self.salt)
  end

  def after_destroy
    if User.count.zero?
      raise "Can't delete last user"
    end
  end

  private

  def self.encrypted_password(password, salt)
    string_to_hash = password + "somethingrandom" + salt
    Digest::SHA1.hexdigest(string_to_hash)
  end

  def create_new_salt
    self.salt = self.object_id.to_s + rand.to_s
  end
end

# user_test.rb

require File.dirname(__FILE__) + '/../test_helper'

class UserTest < Test::Unit::TestCase
  fixtures :users

  def setup
    @valid_user = users(:valid_user)
    @invalid_user = users(:invalid_user)
  end

  def test_user_validity
    assert @valid_user.valid?
  end

  def test_user_invalidity
    assert !@invalid_user.valid?
    attributes = [:screen_name, :email, :hashed_password, :salt]
    attributes.each do |attribute|
      assert @invalid_user.errors.invalid?(attribute)
    end
  end
end

# users.yaml

valid_user:
    id: 1
    screen_name: testing
    email: blah@blah.com
    hashed_password: 4a10675pff47c4e298ae7a368bbd60f6bc59f7ed
    salt: 284601900.605789

invalid_user:
    id: 2
    screen_name: a
    email: a/a.com
    hashed_password: 4a10675pff47c4e298ae7a368bbd60f6bc59f7ed
    salt: 284601900.605789

# errors

Started
.FF
Finished in 0.099934 seconds.

  1) Failure:
test_user_invalidity(UserTest)
    [./test/unit/user_test.rb:19:in `test_user_invalidity'
     ./test/unit/user_test.rb:18:in `each'
     ./test/unit/user_test.rb:18:in `test_user_invalidity']:
<false> is not true.

  2) Failure:
test_user_validity(UserTest) [./test/unit/user_test.rb:12]:
<false> is not true.

3 tests, 6 assertions, 2 failures, 0 errors
rake aborted!
Command failed with status (1): [/opt/local/bin/ruby -Ilib:test "/opt/local...]

(See full trace by running task with --trace)