module RASN1
  module Types

    # @abstract This is base class for all ASN.1 types.
    #   
    #   Subclasses SHOULD define:
    #   * a TAG constant defining ASN.1 tag number,
    #   * a private method {#value_to_der} converting its {#value} to DER,
    #   * a private method {#der_to_value} converting DER into {#value}.
    #
    # ==Define an optional value
    # An optional value may be defined using +:optional+ key from {#initialize}:
    #   Integer.new(:int, optional: true)
    # An optional value implies:
    # * while parsing, if decoded tag is not optional expected tag, no {ASN1Error}
    #   is raised, and parser tries net tag,
    # * while encoding, if {#value} is +nil+, this value is not encoded.
    # ==Define a default value
    # A default value may be defined using +:default+ key from {#initialize}:
    #  Integer.new(:int, default: 0)
    # A default value implies:
    # * while parsing, if decoded tag is not expected tag, no {ASN1Error} is raised
    #   and parser sets default value to this tag. Then parser tries nex tag,
    # * while encoding, if {#value} is equal to default value, this value is not
    #   encoded.
    # ==Define a tagged value
    # ASN.1 permits to define tagged values.
    # By example:
    #  -- context specific tag
    #  CType ::= [0] EXPLICIT INTEGER
    #  -- application specific tag
    #  AType ::= [APPLICATION 1] EXPLICIT INTEGER
    #  -- private tag
    #  PType ::= [PRIVATE 2] EXPLICIT INTEGER
    # These types may be defined as:
    #  ctype = RASN1::Types::Integer.new(:ctype, explicit: 0)                      # with explicit, default #asn1_class is :context
    #  atype = RASN1::Types::Integer.new(:atype, explicit: 1, class: :application)
    #  ptype = RASN1::Types::Integer.new(:ptype, explicit: 2, class: :private)
    #
    # Implicit tagged values may also be defined:
    #  ctype_implicit = RASN1::Types::Integer.new(:ctype, implicit: 0)
    # @author Sylvain Daubert
    class Base
      # Allowed ASN.1 tag classes
      CLASSES = {
                 universal:   0x00,
                 application: 0x40,
                 context:     0x80,
                 private:     0xc0
                }

      # Maximum ASN.1 tag number
      MAX_TAG = 0x1e

      # Length value for indefinite length
      INDEFINITE_LENGTH = 0x80

      # @return [Symbol, String]
      attr_reader :name
      # @return [Symbol]
      attr_reader :asn1_class
      # @return [Object,nil] default value, if defined
      attr_reader :default
      # @return [Object]
      attr_writer :value

      # Get ASN.1 type
      # @return [String]
      def self.type
        return @type if @type
        @type = self.to_s.gsub(/.*::/, '').gsub(/([a-z0-9])([A-Z])/, '\1 \2').upcase
      end


      # @param [Symbol, String] name name for this tag in grammar
      # @param [Hash] options
      # @option options [Symbol] :class ASN.1 tag class. Default value is +:universal+
      # @option options [::Boolean] :optional define this tag as optional. Default
      #   is +false+
      # @option options [Object] :default default value for DEFAULT tag
      # @option options [Object] :value value to set
      def initialize(name, options={})
        @name = name

        set_options options
      end

      # Used by +#dup+ and +#clone+. Deep copy @value.
      def initialize_copy(other)
        @value = @value.nil? ? nil : @value.dup
      end

      # Get value or default value
      def value
        if @value.nil?
          @default
        else
          @value
        end
      end

      # @return [::Boolean]
      def optional?
        @optional
      end

      # Say if this type is tagged or not
      # @return [::Boolean]
      def tagged?
        !@tag.nil?
      end

      # Say if a tagged type is explicit
      # @return [::Boolean,nil] return +nil+ if not tagged, return +true+
      #   if explicit, else +false+
      def explicit?
        @tag.nil? ? @tag : @tag == :explicit
      end

      # Say if a tagged type is implicit
      # @return [::Boolean,nil] return +nil+ if not tagged, return +true+
      #   if implicit, else +false+
      def implicit?
        @tag.nil? ? @tag : @tag == :implicit
      end

      # @abstract This method SHOULD be partly implemented by subclasses, which
      #   SHOULD respond to +#value_to_der+.
      # @return [String] DER-formated string
      def to_der
        if self.class.const_defined?('TAG')
          build_tag
        else
          raise NotImplementedError, 'should be implemented by subclasses'
        end
      end

      # @return [::Boolean] +true+ if this is a primitive type
      def primitive?
        if self.class < Primitive
          true
        else
          false
        end
      end

      # @return [::Boolean] +true+ if this is a constructed type
      def constructed?
        if self.class < Constructed
          true
        else
          false
        end
      end

      # Get ASN.1 type
      # @return [String]
      def type
        self.class.type
      end

      # Get tag value
      # @return [Integer]
      def tag
        (@tag_value || self.class::TAG) | CLASSES[@asn1_class] | self.class::ASN1_PC
      end

      # @abstract This method SHOULD be partly implemented by subclasses to parse
      #  data. Subclasses SHOULD respond to +#der_to_value+.
      # Parse a DER string. This method updates object.
      # @param [String] der DER string
      # @param [Boolean] ber if +true+, accept BER encoding
      # @return [Integer] total number of parsed bytes
      # @raise [ASN1Error] error on parsing
      def parse!(der, ber: false)
        return 0 unless check_tag(der)

        total_length, data = get_data(der, ber)
        if explicit?
          type = self.class.new(@name)
          type.parse!(data)
          @value = type.value
        else
          der_to_value(data, ber: ber)
        end

        total_length
      end


      private

      def set_options(options)
        set_class options[:class]
        set_optional options[:optional]
        set_default options[:default]
        set_tag options
        @value = options[:value]
      end

      def set_class(asn1_class)
        case asn1_class
        when nil
          @asn1_class = :universal
        when Symbol
          if CLASSES.keys.include? asn1_class
            @asn1_class = asn1_class
          else
            raise ClassError
          end
        else
          raise ClassError
        end
      end

      def set_optional(optional)
        @optional = !!optional
      end

      def set_default(default)
        @default = default
      end

      def set_tag(options)
        if options[:explicit]
          @tag = :explicit
          @tag_value = options[:explicit]
        elsif options[:implicit]
          @tag = :implicit
          @tag_value = options[:implicit]
        end

        @asn1_class = :context if @tag and @asn1_class == :universal
      end

      def build_tag?
        !(!@default.nil? and (@value.nil? or @value == @default)) and
          !(optional? and @value.nil?)
      end

      def build_tag
        if build_tag?
          if explicit?
            v = self.class.new(nil)
            v.value = @value
            encoded_value = v.to_der
          else
            encoded_value = value_to_der
          end
          encode_tag << encode_size(encoded_value.size) << encoded_value
        else
          ''
        end
      end

      def encode_tag
        if (@tag_value || self.class::TAG) <= MAX_TAG
          [tag].pack('C')
        else
          raise ASN1Error, 'multi-byte tag value are not supported'
        end
      end

      def encode_size(size)
        if size >= INDEFINITE_LENGTH
          bytes = []
          while size > 255
            bytes << (size & 0xff)
            size >>= 8
          end
          bytes << size
          bytes.reverse!
          bytes.unshift(INDEFINITE_LENGTH | bytes.size)
          bytes.pack('C*')
        else
          [size].pack('C')
        end
      end

      def check_tag(der)
        tag = der[0, 1]
        if tag != encode_tag
          if optional?
            @value = nil
          elsif !@default.nil?
            @value = @default
          else
            raise_tag_error(encode_tag, tag)
          end
          false
        else
          true
        end
      end

      def get_data(der, ber)
        length = der[1, 1].unpack('C').first
        length_length = 0

        if length == INDEFINITE_LENGTH
          if primitive?
            raise ASN1Error, "malformed #{type} TAG (#@name): indefinite length " \
              "forbidden for primitive types"
          else
            if ber
              raise NotImplementedError, "TAG #@name: indefinite length not " \
                "supported yet"
            else
              raise ASN1Error, "TAG #@name: indefinite length forbidden in DER " \
                "encoding"
            end
          end
        elsif length < INDEFINITE_LENGTH
          data = der[2, length]
        else
          length_length = length & 0x7f
          length = der[2, length_length].unpack('C*').
            reduce(0) { |len, b| (len << 8) | b }
          data = der[2 + length_length, length]
        end

        total_length = 2 + length
        total_length += length_length if length_length > 0

        [total_length, data]
      end

      def raise_tag_error(expected_tag, tag)
        msg = "Expected tag #{tag2name(expected_tag)} but get #{tag2name(tag)}"
        msg << " for #@name"
        raise ASN1Error, msg
      end

      def tag2name(tag)
        return 'no tag' if tag.nil? or tag.empty?

        itag = tag.unpack('C').first
        name = CLASSES.key(itag & 0xc0).to_s.upcase
        name << " #{itag & Constructed::ASN1_PC > 0 ? 'CONSTRUCTED' : 'PRIMITIVE'}"
        type =  Types.constants.map { |c| Types.const_get(c) }.
                  select { |klass| klass < Primitive || klass < Constructed }.
                  find { |klass| klass::TAG == itag & 0x1f }
        name << " #{type.nil? ? "0x%02X" % (itag & 0x1f) : type.type }"
      end
    end
  end
end