module Company
  module Mapping

#TFIDF class implements Term Frequency Inverse Document Frequency statistic.
    class TFIDF
      attr_accessor :tf, :idf

      def initialize(corpus)
        @corpus = corpus
      end

      #Calculates the tf-idf weights in the given corpus
      def calculate
        @tfidf = Hash.new

        if (@idf==nil)
          @idf = InverseDocumentFrequency.new(@corpus)
        end

        if (@tf==nil)
          _tokenizer = BasicTokenizer.new
          @tf = NormalizedTermFrequency.new(_tokenizer)
        end

        @idf_weights = @idf.calculate

        @corpus.each {
            |doc|

          _termfreq = @tf.calculate(doc.contents)

          _tfidf_weights = Hash.new

          _termfreq.each do |term, tf|
            _weight = tf * @idf_weights[term]
            _tfidf_weights[term] = _weight
          end

          @tfidf[doc.id] = _tfidf_weights
        }
        return @tfidf
      end

      #Calculates tfidf weights of new incoming document without importing the document in the corpus and re-calculating the tf-idf weights for the entire corpus
      def calculate_tfidf_weights_of_new_document(new_doc)
        _termfreq = @tf.calculate(new_doc.contents)

        _tfidf_weights = Hash.new

        _termfreq.each do |term, tf|
          if (@idf_weights.has_key? term)
            _weight = tf * @idf_weights[term]
          else
            _weight = tf * @idf.maxIDF
          end
          _tfidf_weights[term] = _weight
        end
        @tfidf[new_doc.id] = _tfidf_weights
        return @tfidf
      end

      #Calculates tf-idf similarity between two given documents. It is actually
      #the calculated Cosine Similarity by using tf*idf weights.
      def similarity(doc1_id, doc2_id)
        if (@tfidf==nil)
          calculate
        end

        _cosine_similarity = CosineSimilarity.new
        return _cosine_similarity.calculate(@tfidf[doc1_id], @tfidf[doc2_id])
      end

      def info
        " term frequency–inverse document frequency, is a numerical "
        +"statistic that is intended to reflect how important a word "
        +"is to a document in a collection or corpus"
      end
    end

  end
end