module Sterile

def titlecase(string)
  lsquo = [8216].pack("U")
  rsquo = [8217].pack("U")
  ldquo = [8220].pack("U")
  rdquo = [8221].pack("U")
  ndash = [8211].pack("U")
  string.strip!
  string.gsub!(/\s+/, " ")
  string.downcase! unless string =~ /[[:lower:]]/
  small_words = %w{ a an and as at(?!&t) but by en for if in nor of on or the to v[.]? via vs[.]? }.join("|")
  apos = / (?: ['#{rsquo}] [[:lower:]]* )? /xu
  string.gsub!(
    /
      \b
      ([_\*]*)
      (?:
        ( [-\+\w]+ [@.\:\/] [-\w@.\:\/]+ #{apos} )      # URL, domain, or email
        |
        ( (?i: #{small_words} ) #{apos} )               # or small word, case-insensitive
        |
        ( [[:alpha:]] [[:lower:]'#{rsquo}()\[\]{}]* #{apos} )  # or word without internal caps
        |
        ( [[:alpha:]] [[:alpha:]'#{rsquo}()\[\]{}]* #{apos} )  # or some other word
      )
      ([_\*]*)
      \b
    /xu
  ) do
    ($1 ? $1 : "") +
    ($2 ? $2 : ($3 ? $3.downcase : ($4 ? $4.downcase.capitalize : $5))) +
    ($6 ? $6 : "")
  end
  if RUBY_VERSION < "1.9.0"
    string.gsub!(
      /
        \b
        ([:alpha:]+)
        (#{ndash})
        ([:alpha:]+)
        \b
      /xu
    ) do
      $1.downcase.capitalize + $2 + $1.downcase.capitalize
    end
  end
  string.gsub!(
    /
      (
        \A [[:punct:]]*     # start of title
        | [:.;?!][ ]+       # or of subsentence
        | [ ]['"#{ldquo}#{lsquo}(\[][ ]*  # or of inserted subphrase
      )
      ( #{small_words} )    # followed by a small-word
      \b
    /xiu
  ) do
    $1 + $2.downcase.capitalize
  end
  string.gsub!(
    /
      \b
      ( #{small_words} )    # small-word
      (?=
        [[:punct:]]* \Z     # at the end of the title
        |
        ['"#{rsquo}#{rdquo})\]] [ ]       # or of an inserted subphrase
      )
    /xu
  ) do
    $1.downcase.capitalize
  end
  string.gsub!(
    /
      (
        \b
        [[:alpha:]]         # single first letter
        [\-#{ndash}]               # followed by a dash
      )
      ( [[:alpha:]] )       # followed by a letter
    /xu
  ) do
    $1 + $2.downcase
  end
  string.gsub!(/q&a/i, 'Q&A')
  string
end