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# encoding: utf-8
#
module Picky
# Defines tokenizing processes used both in indexing and querying.
#
class Tokenizer
def self.index_default= new_default
@index_default = new_default
end
def self.index_default
@index_default ||= new
end
def self.query_default= new_default
@query_default = new_default
end
def self.query_default
@query_default ||= new
end
# TODO Move EMPTY_STRING top level.
#
EMPTY_STRING = ''.freeze
def to_s
reject_condition_location = @reject_condition.to_s[/:(\d+) \(lambda\)/, 1]
<<-TOKENIZER
Removes characters: #{@removes_characters_regexp ? "/#{@removes_characters_regexp.source}/" : '-'}
Stopwords: #{@remove_stopwords_regexp ? "/#{@remove_stopwords_regexp.source}/" : '-'}
Splits text on: #{@splits_text_on.respond_to?(:source) ? "/#{@splits_text_on.source}/" : (@splits_text_on ? @splits_text_on : '-')}
Normalizes words: #{@normalizes_words_regexp_replaces ? @normalizes_words_regexp_replaces : '-'}
Rejects tokens? #{reject_condition_location ? "Yes, see line #{reject_condition_location} in app/application.rb" : '-'}
Substitutes chars? #{@substituter ? "Yes, using #{@substituter}." : '-' }
Case sensitive? #{@case_sensitive ? "Yes." : "-"}
TOKENIZER
end
# Stopwords.
#
# We only allow regexps (even if string would be okay
# too for gsub! - it's too hard to understand)
#
def stopwords regexp
check_argument_in __method__, Regexp, regexp
@remove_stopwords_regexp = regexp
end
def remove_stopwords text
text.gsub! @remove_stopwords_regexp, EMPTY_STRING if @remove_stopwords_regexp
text
end
@@non_single_stopword_regexp = /^\b[\w:]+?\b[\.\*\~]?\s?$/
def remove_non_single_stopwords text
return text unless @remove_stopwords_regexp
return text if text.match @@non_single_stopword_regexp
remove_stopwords text
end
# Illegals.
#
# We only allow regexps (even if string would be okay
# too for gsub! - it's too hard to understand)
#
def removes_characters regexp
check_argument_in __method__, Regexp, regexp
@removes_characters_regexp = regexp
end
def remove_illegals text
text.gsub! @removes_characters_regexp, EMPTY_STRING if @removes_characters_regexp
text
end
# Splitting.
#
# We allow Strings and Regexps.
# Note: We do not test against to_str since symbols do not work with String#split.
#
def splits_text_on regexp_or_string
raise ArgumentError.new "#{__method__} takes a Regexp or String as argument, not a #{regexp_or_string.class}." unless Regexp === regexp_or_string || String === regexp_or_string
@splits_text_on = regexp_or_string
end
def split text
text.split @splits_text_on
end
# Normalizing.
#
# We only allow arrays.
#
def normalizes_words regexp_replaces
raise ArgumentError.new "#{__method__} takes an Array of replaces as argument, not a #{regexp_replaces.class}." unless regexp_replaces.respond_to?(:to_ary)
@normalizes_words_regexp_replaces = regexp_replaces
end
def normalize_with_patterns text
return text unless @normalizes_words_regexp_replaces
@normalizes_words_regexp_replaces.each do |regex, replace|
# This should be sufficient
#
text.gsub!(regex, replace) and break
end
text
end
def normalize_with_patterns?
@normalizes_words_regexp_replaces
end
# Substitute Characters with this substituter.
#
# Default is European Character substitution.
#
def substitutes_characters_with substituter = CharacterSubstituters::WestEuropean.new
raise ArgumentError.new "The substitutes_characters_with option needs a character substituter, which responds to #substitute." unless substituter.respond_to?(:substitute)
@substituter = substituter
end
def substitute_characters text
substituter?? substituter.substitute(text) : text
end
# Reject tokens after tokenizing based on the given criteria.
#
def rejects_token_if &condition
@reject_condition = condition
end
def reject tokens
tokens.reject! &@reject_condition
end
def case_sensitive case_sensitive
@case_sensitive = case_sensitive
end
def downcase?
!@case_sensitive
end
def maximum_tokens amount
@maximum_tokens = amount
end
def cap words
words.slice!(@maximum_tokens..-1) if cap?(words)
end
def cap? words
@maximum_tokens && words.size > @maximum_tokens
end
# Checks if the right argument type has been given.
#
def check_argument_in method, type, argument, &condition
raise ArgumentError.new "Application##{method} takes a #{type} as argument, not a #{argument.class}." unless type === argument
end
attr_reader :substituter
alias substituter? substituter
def initialize options = {}
substitutes_characters_with options[:substitutes_characters_with] if options[:substitutes_characters_with]
removes_characters options[:removes_characters] if options[:removes_characters]
stopwords options[:stopwords] if options[:stopwords]
splits_text_on options[:splits_text_on] || /\s/
normalizes_words options[:normalizes_words] if options[:normalizes_words]
maximum_tokens options[:maximum_tokens]
rejects_token_if &(options[:rejects_token_if] || :blank?)
case_sensitive options[:case_sensitive] unless options[:case_sensitive].nil?
end
# Returns a number of tokens, generated from the given text,
# based on the parameters given.
#
# Returns:
# [[:token1, :token2], ["Original1", "Original2"]]
#
def tokenize text
text = preprocess text # processing the text
return empty_tokens if text.blank?
words = pretokenize text # splitting and preparations for tokenizing
return empty_tokens if words.empty?
tokens = tokens_for words # creating tokens / strings
[tokens, words]
end
# Default preprocessing hook.
#
# Does:
# 1. Character substitution.
# 2. Remove illegal expressions.
# 3. Remove non-single stopwords. (Stopwords that occur with other words)
#
def preprocess text
text = substitute_characters text
remove_illegals text
# We do not remove single stopwords e.g. in the indexer for
# an entirely different reason than in the query tokenizer.
# An indexed thing with just name "UND" (a possible stopword)
# should not lose its name.
#
remove_non_single_stopwords text
text
end
# Pretokenizing.
#
# Does:
# * Split the text into words.
# * Cap the amount of tokens if maximum_tokens is set.
#
def pretokenize text
words = split text
words.collect! { |word| normalize_with_patterns word } if normalize_with_patterns?
reject words
cap words if cap?(words)
words
end
# Downcases.
#
def tokens_for words
words.collect! { |word| word.downcase!; word } if downcase?
words
end
# Returns empty tokens.
#
def empty_tokens
[[], []]
end
end
end
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