petervandenabeele/dbd

module Dbd
  class Fact
    module Factory

      class << self

        ##
        # @return [Class] the top class for which instances are created here.
        def top_class
          Fact
        end

        ##
        # @return [String] A new subject string.
        def new_subject
          top_class::Subject.new_subject
        end

        ##
        # @return [String] A new id string.
        def new_id
          top_class::ID.new_id
        end

        ##
        # Constructs a Fact or ContextFact from a string values array
        # (e.g. pulled from a CSV row).
        #
        # @param [Array] string_values Required : the array with values, organized as in attributes
        # @return [Fact, Context] the constructed fact
        def from_string_values(string_values, options={})
          string_hash = string_hash_from_values(string_values)
          validate_string_hash(string_hash) if options[:validate]
          fact_from_values_hash(values_hash(string_hash))
        end

        ##
        # Formats for checking CSV fields
        # the predicate, object_type and object are tested in the initializer
        def attribute_formats
          {
            id: [true, Fact::ID.valid_regexp],
            time_stamp: [true, TimeStamp.valid_regexp],
            context_subject: [false, Fact::Subject.valid_regexp],
            subject: [true, Fact::Subject.valid_regexp]
          }
        end

      private

        def unescaped_string_values(string_values)
          string_values.map{ |string_value| unescaped_string(string_value) }
        end

        def unescaped_string(string)
          r = %r{(\\\\|\\n)}
          repl = {
            "\\\\" => "\\",  # double backslash => single backslash
            "\\n" => "\n"}   # backslash n => newline
          string.gsub(r, repl)
        end

        def string_hash_from_values(string_values)
          unescaped_values = unescaped_string_values(string_values)
          attributes_strings_array = [top_class.attributes, unescaped_values].transpose
          # Remove empty values (e.g. the context_subject for a ContextFact).
          attributes_strings_array.delete_if{ |_, v| v == '' }
          Hash[attributes_strings_array]
        end

        def values_hash(string_hash)
          string_hash.tap do |h|
            h[:time_stamp] = TimeStamp.new(time: h[:time_stamp])
          end
        end

        def fact_from_values_hash(values_hash)
          if values_hash[:context_subject]
            Fact.new(values_hash)
          else
            ContextFact.new(values_hash)
          end
        end

        def validate_string_hash(string_hash)
          attribute_formats.each do |attr, validation|
            string = string_hash[attr]
            mandatory, format = validation
            validate_string_by_regexp(mandatory, string, format)
          end

        end

        def validate_string_by_regexp(mandatory, string, format)
          if (mandatory || string) && (string !~ format)
            report_invalid_entry(string)
          end
        end

        def report_invalid_entry(string)
          raise FactError, "invalid entry found : #{string}"
        end

      end
    end
  end
end