module Traject
  # MarcExtractor is a class for extracting lists of strings from a MARC::Record,
  # according to specifications. See #parse_string_spec for description of string
  # string arguments used to specify extraction. See #initialize for options
  # that can be set controlling extraction.
  #
  # Examples:
  #
  #     array_of_stuff   = MarcExtractor.new("001:245abc:700a").extract(marc_record)
  #     values           = MarcExtractor.new("245a:245abc").extract_marc(marc_record)
  #     seperated_values = MarcExtractor.new("020a:020z").extract(marc_record)
  #     bytes            = MarcExtractor.new("008[35-37]")
  #
  # ## String extraction specifications
  #
  # Extraction directions are supplied in strings, usually as the first
  # parameter to MarcExtractor.new or MarcExtractor.cached. These specifications
  # are also the first parameter to the #marc_extract macro.
  #
  # A String specification is a string (or array of strings) which consists
  # of one or more Data and Control Field Specifications seperated by colons.
  #
  # A Data Field Specification is of the form:
  #
  # * `{tag}{|indicators|}{subfields}`
  # * {tag} is three chars (usually but not neccesarily numeric)
  # * {indicators} are optional two chars enclosed in pipe ('|') characters,
  # * {subfields} are optional list of chars (alphanumeric)
  #
  # indicator spec must be two chars, but one can be * meaning "don't care".
  # space to mean 'blank'
  #
  #     "245|01|abc65:345abc:700|*5|:800"
  #
  # A Control Field Specification is used with tags for control (fixed) fields (ordinarily fields 001-010)
  # and includes a tag and a a byte slice specification.
  #
  #      "008[35-37]:007[5]""
  #      => bytes 35-37 inclusive of any field 008, and byte 5 of any field 007 (TODO: Should we support
  #      "LDR" as a pseudo-tag to take byte slices of leader?)
  #
  # * subfields and indicators can only be provided for marc data/variable fields
  # * byte slice can only be provided for marc control fields (generally tags less than 010)
  #
  # ## Subfield concatenation
  #
  # Normally, for a spec including multiple subfield codes, multiple subfields
  # from the same MARC field will be concatenated into one string separated by spaces:
  #
  #     600 a| Chomsky, Noam x| Philosophy.
  #     600 a| Chomsky, Noam x| Political and social views.
  #     MarcExtractor.new("600ax").extract(record)
  #     # results in two values sent to Solr:
  #     "Chomsky, Noam Philosophy."
  #     "Chomsky, Noam Political and social views."
  #
  # You can turn off this concatenation and leave individual subfields in seperate
  # strings by setting the `separator` option to nil:
  #
  #     MarcExtractor.new("600ax", :separator => nil).extract(record)
  #     # Results in four values being sent to Solr (or 3 if you de-dup):
  #     "Chomksy, Noam"
  #     "Philosophy."
  #     "Chomsky, Noam"
  #     "Political and social views."
  #
  # However, **the default is different for specifications with only a single
  # subfield**, these are by default kept seperated:
  #
  #     020 a| 285197145X a| 9782851971456
  #     MarcExtractor.new("020a:020z").extract(record)
  #     # two seperate strings sent to Solr:
  #     "285197145X"
  #     "9782851971456"
  #
  # For single subfield specifications, you force concatenation by
  # repeating the subfield specification:
  #
  #     MarcExtractor.new("020aa:020zz").extract(record)
  #     # would result in a single string sent to solr for
  #     # the single field, by default space-separated:
  #     "285197145X 9782851971456"
  #
  # ## Note on Performance and MarcExtractor creation and reuse
  #
  # A MarcExtractor is somewhat expensive to create, and has been shown in profiling/
  # benchmarking to be a bottleneck if you end up creating one for each marc record
  # processed.  Instead, a single MarcExtractor should be created, and re-used
  # per MARC record.
  #
  # If you are creating a traject 'macro' method, here's one way to do that,
  # capturing the MarcExtractor under closure:
  #
  #     def some_macro(spec, other_args, whatever)
  #       extractor = MarcExtractor.new( spec )
  #       # ...
  #       return lambda do |record, accumulator, context|
  #          #...
  #          accumulator.concat extractor.extract(record)
  #          #...
  #       end
  #     end
  #
  # In other cases, you may find it convenient to improve performance by
  # using the MarcExtractor#cached method, instead of MarcExtractor#new, to
  # lazily create and then re-use a MarcExtractor object with
  # particular initialization arguments.
  class MarcExtractor
    attr_accessor :options, :spec_hash

    # First arg is a specification for extraction of data from a MARC record.
    # Specification can be given in two forms:
    #
    #  * a string specification like "008[35]:020a:245abc", see top of class
    #    for examples. A string specification is most typical argument.
    #  * The output of a previous call to MarcExtractor.parse_string_spec(string_spec),
    #    a 'pre-parsed' specification.
    #
    # Second arg is options:
    #
    # [:separator]  default ' ' (space), what to use to separate
    #               subfield values when joining strings
    #
    # [:alternate_script] default :include, include linked 880s for tags
    #                     that match spec. Also:
    #                     * false => do not include.
    #                     * :only => only include linked 880s, not original
    def initialize(spec, options = {})
      self.options = {
        :separator => ' ',
        :alternate_script => :include
      }.merge(options)

      self.spec_hash = spec.kind_of?(Hash) ? spec : self.class.parse_string_spec(spec)


      # Tags are "interesting" if we have a spec that might cover it
      @interesting_tags_hash = {}

      # By default, interesting tags are those represented by keys in spec_hash.
      # Add them unless we only care about alternate scripts.
      unless options[:alternate_script] == :only
        self.spec_hash.keys.each {|tag| @interesting_tags_hash[tag] = true}
      end

      # If we *are* interested in alternate scripts, add the 880
      if options[:alternate_script] != false
        @interesting_tags_hash['880'] = true
      end

      self.freeze
    end

    # Takes the same arguments as MarcExtractor.new, but will re-use an existing
    # cached MarcExtractor already created with given initialization arguments,
    # if available.
    #
    # This can be used to increase performance of indexing routines, as
    # MarcExtractor creation has been shown via profiling/benchmarking
    # to be expensive.
    #
    # Cache is thread-local, so should be thread-safe.
    #
    # You should _not_ modify the state of any MarcExtractor retrieved
    # via cached, as the MarcExtractor will be re-used and shared (possibly
    # between threads even!). We try to use ruby #freeze to keep you from doing so,
    # although if you try hard enough you can surely find a way to do something
    # you shouldn't.
    #
    #     extractor = MarcExtractor.cached("245abc:700a", :separator => nil)
    def self.cached(*args)
      cache = (Thread.current[:marc_extractor_cached] ||= Hash.new)
      return ( cache[args] ||= Traject::MarcExtractor.new(*args).freeze )
    end

    # Check to see if a tag is interesting (meaning it may be covered by a spec
    # and the passed-in options about alternate scripts)
    def interesting_tag?(tag)
      return @interesting_tags_hash.include?(tag)
    end


    # Converts from a string marc spec like "008[35]:245abc:700a" to a hash used internally
    # to represent the specification. See comments at head of class for
    # documentation of string specification format.
    #
    #
    # ## Return value
    #
    # The hash returned is keyed by tag, and has as values an array of 0 or
    # or more MarcExtractor::Spec objects representing the specified extraction
    # operations for that tag.
    #
    # It's an array of possibly more than one, because you can specify
    # multiple extractions on the same tag: for instance "245a:245abc"
    #
    # See tests for more examples.
    def self.parse_string_spec(spec_string)
      # hash defaults to []
      hash = Hash.new

      spec_strings = spec_string.is_a?(Array) ? spec_string.map{|s| s.split(/\s*:\s*/)}.flatten : spec_string.split(/s*:\s*/)

      spec_strings.each do |part|
        if (part =~ /\A([a-zA-Z0-9]{3})(\|([a-z0-9\ \*]{2})\|)?([a-z0-9]*)?\Z/)
          # variable field
          tag, indicators, subfields = $1, $3, $4

          spec = Spec.new(:tag => tag)

          if subfields and !subfields.empty?
            spec.subfields = subfields.split('')
          end

          if indicators
           # if specified as '*', leave nil
           spec.indicator1 = indicators[0] if indicators[0] != "*"
           spec.indicator2 = indicators[1] if indicators[1] != "*"
          end

          hash[spec.tag] ||= []
          hash[spec.tag] << spec

        elsif (part =~ /\A([a-zA-Z0-9]{3})(\[(\d+)(-(\d+))?\])\Z/) # control field, "005[4-5]"
          tag, byte1, byte2 = $1, $3, $5

          spec = Spec.new(:tag => tag)

          if byte1 && byte2
            spec.bytes = ((byte1.to_i)..(byte2.to_i))
          elsif byte1
           spec.bytes = byte1.to_i
          end

          hash[spec.tag] ||= []
          hash[spec.tag] << spec
        else
          raise ArgumentError.new("Unrecognized marc extract specification: #{part}")
        end
      end

      return hash
    end


    # Returns array of strings, extracted values. Maybe empty array.
    def extract(marc_record)
      results = []

      self.each_matching_line(marc_record) do |field, spec|
        if control_field?(field)
          results << (spec.bytes ? field.value.byteslice(spec.bytes) : field.value)
        else
          results.concat collect_subfields(field, spec)
        end
      end

      return results
    end

    # Yields a block for every line in source record that matches
    # spec. First arg to block is MARC::DataField or ControlField, second
    # is the MarcExtractor::Spec that it matched on. May take account
    # of options such as :alternate_script
    #
    # Third (optional) arg to block is self, the MarcExtractor object, useful for custom
    # implementations.
    def each_matching_line(marc_record)
      marc_record.fields(@interesting_tags_hash.keys).each do |field|

        # Make sure it matches indicators too, specs_covering_field
        # doesn't check that.
        specs_covering_field(field).each do |spec|
          if spec.matches_indicators?(field)
            yield(field, spec, self)
          end
        end

      end
    end

    # line each_matching_line, takes a block to process each matching line,
    # but collects results of block into an array -- flattens any subarrays for you!
    #
    # Useful for re-use of this class for custom processing
    #
    # yields the MARC Field, the MarcExtractor::Spec object, the MarcExtractor object.
    def collect_matching_lines(marc_record)
      results = []
      self.each_matching_line(marc_record) do |field, spec, extractor|
        results.concat [yield(field, spec, extractor)].flatten
      end
      return results
    end


    # Pass in a marc data field and a Spec object with extraction
    # instructions, returns an ARRAY of one or more strings, subfields extracted
    # and processed per spec. Takes account of options such
    # as :separator
    #
    # Always returns array, sometimes empty array.
    def collect_subfields(field, spec)
      subfields = field.subfields.collect do |subfield|
        subfield.value if spec.includes_subfield_code?(subfield.code)
      end.compact

      return subfields if subfields.empty? # empty array, just return it.

      if options[:separator] && spec.joinable?
        subfields = [subfields.join(options[:separator])]
      end

      return subfields
    end



    # Find Spec objects, if any, covering extraction from this field.
    # Returns an array of 0 or more MarcExtractor::Spec objects
    #
    # When given an 880, will return the spec (if any) for the linked tag iff
    # we have a $6 and we want the alternate script.
    #
    # Returns an empty array in case of no matching extraction specs.
    def specs_covering_field(field)
      tag = field.tag

      # Short-circuit the unintersting stuff
      return [] unless interesting_tag?(tag)

      # Due to bug in jruby https://github.com/jruby/jruby/issues/886 , we need
      # to do this weird encode gymnastics, which fixes it for mysterious reasons.

      if tag == "880" && field['6']
        tag = field["6"].encode(field["6"].encoding).byteslice(0,3)
      end

      # Take the resulting tag and get the spec from it (or the default nil if there isn't a spec for this tag)
      spec = self.spec_hash[tag] || []
    end


    def control_field?(field)
      # should the MARC gem have a more efficient way to do this,
      # define #control_field? on both ControlField and DataField?
      return field.kind_of? MARC::ControlField
    end

    def freeze
      self.options.freeze
      self.spec_hash.freeze
      super
    end


    # Represents a single specification for extracting data
    # from a marc field, like "600abc" or "600|1*|x".
    #
    # Includes the tag for reference, although this is redundant and not actually used
    # in logic, since the tag is also implicit in the overall spec_hash
    # with tag => [spec1, spec2]
    class Spec
      attr_accessor :tag, :subfields, :indicator1, :indicator2, :bytes

      def initialize(hash = {})
        hash.each_pair do |key, value|
          self.send("#{key}=", value)
        end
      end


      #  Should subfields extracted by joined, if we have a seperator?
      #  * '630' no subfields specified => join all subfields
      #  * '630abc' multiple subfields specified = join all subfields
      #  * '633a' one subfield => do not join, return one value for each $a in the field
      #  * '633aa' one subfield, doubled => do join after all, will return a single string joining all the values of all the $a's.
      #
      # Last case is handled implicitly at the moment when subfields == ['a', 'a']
      def joinable?
        (self.subfields.nil? || self.subfields.size != 1)
      end

      # Pass in a MARC field, do it's indicators match indicators
      # in this spec? nil indicators in spec mean we don't care, everything
      # matches.
      def matches_indicators?(field)
        return (self.indicator1.nil? || self.indicator1 == field.indicator1) &&
          (self.indicator2.nil? || self.indicator2 == field.indicator2)
      end

      # Pass in a string subfield code like 'a'; does this
      # spec include it?
      def includes_subfield_code?(code)
        # subfields nil means include them all
        self.subfields.nil? || self.subfields.include?(code)
      end

      def ==(spec)
        return false unless spec.kind_of?(Spec)

        return (self.tag == spec.tag) &&
          (self.subfields == spec.subfields) &&
          (self.indicator1 == spec.indicator1) &&
          (self.indicator1 == spec.indicator2) &&
          (self.bytes == spec.bytes)
      end
    end

  end
end