best_match.rb

Tags = %w[ruby haskell c++ scala java c# js php agda idris julia ocaml]

module BestMatch
  module_function
  def distance_tags a, b
    sum(a & b) / sum(a)
  end

  def sum tags
    tags.inject(0.0){ |r, t| r + tag_score(t) }
  end

  def tag_score tag
    (1.0 / count(tag)) ** 0.5
  end

  def count tag
    Tags.index(tag) + 1
  end
end

if $PROGRAM_NAME == __FILE__
  require 'pork'
  require 'rubyqc'
  RubyQC.default_times = 20
  Pork.report_at_exit
  Pork::API.describe BestMatch do
    include BestMatch
    extend RubyQC::API
    check(1..5, 1..12, 1..12) do |x, y, z|
      check(someof(x, Tags), someof(y, Tags), someof(z, Tags)) do |*abc|
        would 'distance_tags' do
          a, b, c = abc
          ab = distance_tags(a, b)
          ac = distance_tags(a, c)
          abs = (a & b).size
          acs = (a & c).size
          if    abs > acs
            ab.should(abc).gte ac
          elsif abs < acs
            ab.should(abc).lte ac
          end
          (0..1.0).should.include? ab
          (0..1.0).should.include? ac
        end
      end
    end
  end
end