require 'unicode'
 
# Normalizes token text to lower case.
class UnicodeLowerCaseFilter
  def initialize(token_stream)
    @input = token_stream
  end
 
  def text=(text)
    @input.text = text   
  end
 
  def next()
    t = @input.next()
 
    if (t == nil)
      return nil
    end
 
    t.text = Unicode.downcase(t.text)
    return t
  end
end
 
class VietnameseAnalyzer < Ferret::Analysis::Analyzer
  include Ferret::Analysis
 
  # Standard Character mappings to remove all special characters
  # so only default ASCII characters get indexed
  CHARACTER_MAPPINGS = {
    ['á','à','ạ','ả','ã','ă','ắ','ằ','ặ','ẳ','ẵ','â','ấ','ầ','ậ','ẩ','ẫ'] => 'a',
    ['Ä‘'] => 'd',
    ['é','è','ẹ','ẻ','ẽ','ê','ế','ề','ệ','ể','ễ'] => 'e',
    ['í','ì','ị','ỉ','ĩ'] => 'i',
    ['ó','ò','ọ','ủ','õ','ơ','ớ','ờ','ợ','ở','ỡ','ô','ố','ồ','ộ','ổ','ỗ'] => 'o',
    ['ú','ù','ụ','ů','ũ','ư','ứ','ừ','ự','ử','ữ'] => 'u',
    ['ý','ỳ','ỵ','ỷ','ỹ'] => 'y',
  } unless defined?(CHARACTER_MAPPINGS)
 
  def token_stream(field, str)
    ts = StandardTokenizer.new(str)
    ts = UnicodeLowerCaseFilter.new(ts)
    ts = MappingFilter.new(ts, CHARACTER_MAPPINGS)
  end
end