require 'marc'
require 'traject/ndj_reader'

# `Traject::MarcReader` uses pure ruby marc gem to parse MARC records. It
# can read MARC ISO 2709 ('binary'), MARC-XML, and Marc-in-json (newline-delimited-json).
#
# MarcReader can not currently read binary MARC in the MARC8 encoding, see
# the Traject::Marc4JReader instead.
#
# By default assumes binary MARC encoding, please set marc_source.type setting
# for XML or json.
#
# ## Settings

# * "marc_source.type":  serialization type. default 'binary'
#       * "binary". standard ISO 2709 "binary" MARC format.
#       * "xml", MarcXML
#       * "json" The "marc-in-json" format, encoded as newline-separated
#         json. (synonym 'ndj'). A simplistic newline-separated json, with no comments
#         allowed, and no unescpaed internal newlines allowed in the json
#         objects -- we just read line by line, and assume each line is a
#         marc-in-json. http://dilettantes.code4lib.org/blog/2010/09/a-proposal-to-serialize-marc-in-json/
# * "marc_reader.xml_parser": For XML type, which XML parser to tell Marc::Reader
#         to use. Anything recognized by [Marc::Reader :parser
#         argument](http://rdoc.info/github/ruby-marc/ruby-marc/MARC/XMLReader).
#         By default, asks Marc::Reader to take
#         it's best guess as to highest performance available
#         installed option. Probably best to leave as default.
#
# ## Example
#
# In a configuration file:
#
#     require 'traject/marc_reader'
#
#     settings do
#       provide "reader_class_name", "Traject::MarcReader"
#       provide "marc_source.type", "xml"
#     end
#
class Traject::MarcReader
  include Enumerable

  attr_reader :settings, :input_stream

  @@best_xml_parser = MARC::XMLReader.best_available

  def initialize(input_stream, settings)
    @settings = Traject::Indexer::Settings.new settings
    @input_stream = input_stream
  end

  # Creates proper kind of ruby MARC reader, depending
  # on settings or guesses.
  def internal_reader
    unless defined? @internal_reader
      @internal_reader =
        case settings["marc_source.type"]
        when "xml"
          parser = settings["marc_reader.xml_parser"] || @@best_xml_parser
          MARC::XMLReader.new(self.input_stream, :parser=> parser)
        when 'json'
          Traject::NDJReader.new(self.input_stream, settings)
        else
          MARC::Reader.new(self.input_stream)
        end
    end
    return @internal_reader
  end

  def each(*args, &block)
    self.internal_reader.each(*args, &block)
  end

end