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# -*- coding: binary -*-
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module Rex
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  module Proto
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    module Kerberos
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      module Model
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        # This class provides a representation of a Kerberos Checksum definition.
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        class Checksum < Element
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          # @!attribute type
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          #   @return [Integer] The algorithm used to generate the checksum
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          attr_accessor :type
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          # @!attribute checksum
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          #   @return [String] The checksum itself
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          attr_accessor :checksum
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          # Decodes the Rex::Proto::Kerberos::Model::Checksum from an input
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          #
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          # @param input [String, OpenSSL::ASN1::ASN1Data] the input to decode from
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          # @return [self] if decoding succeeds
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          # @raise [Rex::Proto::Kerberos::Model::Error::KerberosDecodingError] if decoding doesn't succeed
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          def decode(input)
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            case input
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            when String
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              decode_string(input)
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            when OpenSSL::ASN1::ASN1Data
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              decode_asn1(input)
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            else
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              raise ::Rex::Proto::Kerberos::Model::Error::KerberosDecodingError, 'Failed to decode Checksum, invalid input'
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            end
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            self
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          end
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          # Encodes a Rex::Proto::Kerberos::Model::Checksum into an ASN.1 String
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          #
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          # @return [String]
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          def encode
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            elems = []
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            elems << OpenSSL::ASN1::ASN1Data.new([encode_type], 0, :CONTEXT_SPECIFIC)
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            elems << OpenSSL::ASN1::ASN1Data.new([encode_checksum], 1, :CONTEXT_SPECIFIC)
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            seq = OpenSSL::ASN1::Sequence.new(elems)
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            seq.to_der
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          end
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          private
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          # Encodes the type field
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          #
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          # @return [OpenSSL::ASN1::Integer]
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          def encode_type
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            bn = OpenSSL::BN.new(type.to_s)
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            int = OpenSSL::ASN1::Integer.new(bn)
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            int
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          end
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          # Encodes the checksum field
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          #
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          # @return [OpenSSL::ASN1::OctetString]
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          def encode_checksum
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            OpenSSL::ASN1::OctetString.new(checksum)
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          end
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          # Decodes a Rex::Proto::Kerberos::Model::Checksum from an String
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          #
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          # @param input [String] the input to decode from
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          # @raise [Rex::Proto::Kerberos::Model::Error::KerberosDecodingError] if decoding doesn't succeed
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          def decode_string(input)
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            asn1 = OpenSSL::ASN1.decode(input)
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            decode_asn1(asn1)
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          rescue OpenSSL::ASN1::ASN1Error
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            raise Rex::Proto::Kerberos::Model::Error::KerberosDecodingError
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          end
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          # Decodes a Rex::Proto::Kerberos::Model::Checksum from an
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          # OpenSSL::ASN1::Sequence
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          #
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          # @param input [OpenSSL::ASN1::Sequence] the input to decode from
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          # @raise [Rex::Proto::Kerberos::Model::Error::KerberosDecodingError] if decoding doesn't succeed
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          def decode_asn1(input)
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            seq_values = input.value
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            seq_values.each do |val|
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              case val.tag
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              when 0
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                self.type = decode_type(val)
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              when 1
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                self.checksum = decode_checksum(val)
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              else
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                raise ::Rex::Proto::Kerberos::Model::Error::KerberosDecodingError, 'Failed to decode KdcRequestBody SEQUENCE'
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              end
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            end
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          end
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          # Decodes the type field
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          #
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          # @param input [OpenSSL::ASN1::ASN1Data] the input to decode from
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          # @return [Integer]
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          def decode_type(input)
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            input.value[0].value.to_i
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          end
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          # Decodes the checksum field
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          #
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          # @param input [OpenSSL::ASN1::ASN1Data] the input to decode from
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          # @return [String]
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          def decode_checksum(input)
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            input.value[0].value
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          end
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        end
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      end
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    end
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  end
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end
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