require 'encrypted_strings/no_key_error'

module PluginAWeek #:nodoc:
  module EncryptedStrings
    # Symmetric encryption uses a key and a specific algorithm to encrypt the
    # string.  As long as the key and algorithm are known, the string can be
    # decrypted.
    # 
    # Source: http://support.microsoft.com/kb/246071
    # 
    # == Encrypting 
    # 
    # To encrypt a string using a symmetric algorithm, the type of algorithm and
    # key must be specified.  You can define the defaults for these values like
    # so:
    # 
    #   PluginAWeek::EncryptedStrings::SymmetricEncryptor.default_algorithm = 'des-ecb'
    #   PluginAWeek::EncryptedStrings::SymmetricEncryptor.default_key = 'secret'
    # 
    # If these configuration options are not passed in to #encrypt, then the
    # default values will be used.  You can override the default values like so:
    # 
    #   password = 'shhhh'
    #   password.encrypt(:symmetric, :algorithm => 'des-ecb', :key => 'secret')  # => "sUG6tYSn0mI=\n"
    # 
    # An exception will be raised if no key is specified.
    # 
    # == Decrypting
    # 
    # To decrypt a string using an symmetric algorithm, the type of algorithm
    # and key must also be specified.  Defaults for these values can be defined
    # as show above.
    # 
    # If these configuration options are not passed in to #decrypt, then the
    # default values will be used.  You can override the default values like so:
    # 
    #   password = "sUG6tYSn0mI=\n"
    #   password.decrypt(:symmetric, :algorithm => 'des-ecb', :key => 'secret') # => "shhhh"
    # 
    # An exception will be raised if no key is specified.
    class SymmetricEncryptor < Encryptor
      # The default algorithm to use for encryption.  Default is DES
      @@default_algorithm = 'DES-EDE3-CBC'
      cattr_accessor :default_algorithm
      
      # The default key to use.  Default is nil
      @@default_key = nil
      cattr_accessor :default_key
      
      # The algorithm to use for encryption/decryption
      attr_accessor :algorithm
      
      # The private key that seeds the algorithm
      attr_accessor :key
      
      # Configuration options:
      # * +key+ - Private key
      # * +algorithm+ - Algorithm to use
      def initialize(options = {})
        options = options.symbolize_keys
        options.assert_valid_keys(
          :key,
          :algorithm
        )
        options.reverse_merge!(:key => self.class.default_key)
        options[:algorithm] ||= self.class.default_algorithm
        
        self.key = options[:key]
        raise NoKeyError if key.nil?
        
        self.algorithm = options[:algorithm]
        
        super()
      end
      
      # Decrypts the current string using the current key and algorithm specified
      def decrypt(data)
        cipher.decrypt(key)
        decrypted_data = cipher.update(Base64.decode64(data))
        decrypted_data << cipher.final
      end
      
      # Encrypts the current string using the current key and algorithm specified
      def encrypt(data)
        cipher.encrypt(key)
        encrypted_data = cipher.update(data)
        encrypted_data << cipher.final
        
        Base64.encode64(encrypted_data)
      end
      
      private
        def cipher #:nodoc:
          @cipher ||= OpenSSL::Cipher::Cipher.new(algorithm)
        end
    end
  end
end