discourse/app/services/word_watcher.rb

# frozen_string_literal: true

class WordWatcher
  REPLACEMENT_LETTER ||= CGI.unescape_html("■")

  def initialize(raw)
    @raw = raw
  end

  @cache_enabled = true

  def self.disable_cache
    @cache_enabled = false
  end

  def self.cache_enabled?
    @cache_enabled
  end

  def self.words_for_action(action)
    words = WatchedWord
      .where(action: WatchedWord.actions[action.to_sym])
      .limit(WatchedWord::MAX_WORDS_PER_ACTION)
      .order(:id)

    if WatchedWord.has_replacement?(action.to_sym)
      words.pluck(:word, :replacement).to_h
    else
      words.pluck(:word)
    end
  end

  def self.words_for_action_exists?(action)
    WatchedWord.where(action: WatchedWord.actions[action.to_sym]).exists?
  end

  def self.get_cached_words(action)
    if cache_enabled?
      Discourse.cache.fetch(word_matcher_regexp_key(action), expires_in: 1.day) do
        words_for_action(action).presence
      end
    else
      words_for_action(action).presence
    end
  end

  # This regexp is run in miniracer, and the client JS app
  # Make sure it is compatible with major browsers when changing
  # hint: non-chrome browsers do not support 'lookbehind'
  def self.word_matcher_regexp(action, raise_errors: false)
    words = get_cached_words(action)
    if words
      if WatchedWord.has_replacement?(action.to_sym)
        words = words.keys
      end
      words = words.map do |w|
        word = word_to_regexp(w)
        word = "(#{word})" if SiteSetting.watched_words_regular_expressions?
        word
      end
      regexp = words.join('|')
      if !SiteSetting.watched_words_regular_expressions?
        regexp = "(#{regexp})"
        regexp = "(?:\\W|^)#{regexp}(?=\\W|$)"
      end
      Regexp.new(regexp, Regexp::IGNORECASE)
    end
  rescue RegexpError
    raise if raise_errors
    nil # Admin will be alerted via admin_dashboard_data.rb
  end

  def self.word_matcher_regexps(action)
    if words = get_cached_words(action)
      words.map { |w, r| [word_to_regexp(w, whole: true), r] }.to_h
    end
  end

  def self.word_to_regexp(word, whole: false)
    if SiteSetting.watched_words_regular_expressions?
      # Strip ruby regexp format if present, we're going to make the whole thing
      # case insensitive anyway
      regexp = word.start_with?("(?-mix:") ? word[7..-2] : word
      regexp = "(#{regexp})" if whole
      return regexp
    end

    regexp = Regexp.escape(word).gsub("\\*", '\S*')

    if whole && !SiteSetting.watched_words_regular_expressions?
      regexp = "(?:\\W|^)(#{regexp})(?=\\W|$)"
    end

    regexp
  end

  def self.word_matcher_regexp_key(action)
    "watched-words-list:#{action}"
  end

  def self.censor(html)
    regexp = word_matcher_regexp(:censor)
    return html if regexp.blank?

    doc = Nokogiri::HTML5::fragment(html)
    doc.traverse do |node|
      node.content = censor_text_with_regexp(node.content, regexp) if node.text?
    end
    doc.to_s
  end

  def self.censor_text(text)
    regexp = word_matcher_regexp(:censor)
    return text if regexp.blank?

    censor_text_with_regexp(text, regexp)
  end

  def self.apply_to_text(text)
    if regexp = word_matcher_regexp(:censor)
      text = censor_text_with_regexp(text, regexp)
    end

    %i[replace link]
      .flat_map { |type| word_matcher_regexps(type).to_a }
      .reduce(text) do |t, (word_regexp, replacement)|
        t.gsub(Regexp.new(word_regexp)) { |match| "#{match[0]}#{replacement}" }
      end
  end

  def self.clear_cache!
    WatchedWord.actions.each do |a, i|
      Discourse.cache.delete word_matcher_regexp_key(a)
    end
  end

  def requires_approval?
    word_matches_for_action?(:require_approval)
  end

  def should_flag?
    word_matches_for_action?(:flag)
  end

  def should_block?
    word_matches_for_action?(:block, all_matches: true)
  end

  def should_silence?
    word_matches_for_action?(:silence)
  end

  def word_matches_for_action?(action, all_matches: false)
    regexp = self.class.word_matcher_regexp(action)
    if regexp
      match = regexp.match(@raw)
      return match if !all_matches || !match

      if SiteSetting.watched_words_regular_expressions?
        set = Set.new
        @raw.scan(regexp).each do |m|
          if Array === m
            set.add(m.find(&:present?))
          elsif String === m
            set.add(m)
          end
        end
        matches = set.to_a
      else
        matches = @raw.scan(regexp)
        matches.flatten!
        matches.uniq!
      end
      matches.compact!
      matches.sort!
      matches
    else
      false
    end
  end

  def word_matches?(word)
    Regexp.new(WordWatcher.word_to_regexp(word, whole: true), Regexp::IGNORECASE).match?(@raw)
  end

  private

  def self.censor_text_with_regexp(text, regexp)
    text.gsub(regexp) do |match|
      # the regex captures leading whitespaces
      padding = match.size - match.lstrip.size
      if padding > 0
        match[0..padding - 1] + REPLACEMENT_LETTER * (match.size - padding)
      else
        REPLACEMENT_LETTER * match.size
      end
    end
  end
end