require 'openssl'

module Net; module SSH; module Transport; module HMAC

  # The base class of all OpenSSL-based HMAC algorithm wrappers.
  class Abstract

    class <<self
      def key_length(*v)
        @key_length = nil if !defined?(@key_length)
        if v.empty?
          @key_length = superclass.key_length if @key_length.nil? && superclass.respond_to?(:key_length)
          return @key_length
        elsif v.length == 1
          @key_length = v.first
        else
          raise ArgumentError, "wrong number of arguments (#{v.length} for 1)"
        end
      end

      def mac_length(*v)
        @mac_length = nil if !defined?(@mac_length)
        if v.empty?
          @mac_length = superclass.mac_length if @mac_length.nil? && superclass.respond_to?(:mac_length)
          return @mac_length
        elsif v.length == 1
          @mac_length = v.first
        else
          raise ArgumentError, "wrong number of arguments (#{v.length} for 1)"
        end
      end

      def digest_class(*v)
        @digest_class = nil if !defined?(@digest_class)
        if v.empty?
          @digest_class = superclass.digest_class if @digest_class.nil? && superclass.respond_to?(:digest_class)
          return @digest_class
        elsif v.length == 1
          @digest_class = v.first
        else
          raise ArgumentError, "wrong number of arguments (#{v.length} for 1)"
        end
      end
    end

    def key_length
      self.class.key_length
    end

    def mac_length
      self.class.mac_length
    end

    def digest_class
      self.class.digest_class
    end

    # The key in use for this instance.
    attr_reader :key

    def initialize(key=nil)
      self.key = key
    end

    # Sets the key to the given value, truncating it so that it is the correct
    # length.
    def key=(value)
      @key = value ? value.to_s[0,key_length] : nil
    end

    # Compute the HMAC digest for the given data string.
    def digest(data)
      OpenSSL::HMAC.digest(digest_class.new, key, data)[0,mac_length]
    end

  end

end; end; end; end
