module Banzai
  module Filter
    # HTML filter that replaces :emoji: and unicode with images.
    #
    # Based on HTML::Pipeline::EmojiFilter
    #
    # Context options:
    #   :asset_root
    #   :asset_host
    class EmojiFilter < HTML::Pipeline::Filter
      IGNORED_ANCESTOR_TAGS = %w(pre code tt).to_set

      def call
        search_text_nodes(doc).each do |node|
          content = node.to_html
          next if has_ancestor?(node, IGNORED_ANCESTOR_TAGS)

          next unless content.include?(':') || node.text.match(emoji_unicode_pattern)

          html = emoji_unicode_element_unicode_filter(content)
          html = emoji_name_element_unicode_filter(html)

          next if html == content

          node.replace(html)
        end
        doc
      end

      # Replace :emoji: with corresponding gl-emoji unicode.
      #
      # text - String text to replace :emoji: in.
      #
      # Returns a String with :emoji: replaced with gl-emoji unicode.
      def emoji_name_element_unicode_filter(text)
        text.gsub(emoji_pattern) do |match|
          name = $1
          Gitlab::Emoji.gl_emoji_tag(name)
        end
      end

      # Replace unicode emoji with corresponding gl-emoji unicode.
      #
      # text - String text to replace unicode emoji in.
      #
      # Returns a String with unicode emoji replaced with gl-emoji unicode.
      def emoji_unicode_element_unicode_filter(text)
        text.gsub(emoji_unicode_pattern) do |moji|
          emoji_info = Gitlab::Emoji.emojis_by_moji[moji]
          Gitlab::Emoji.gl_emoji_tag(emoji_info['name'])
        end
      end

      # Build a regexp that matches all valid :emoji: names.
      def self.emoji_pattern
        @emoji_pattern ||=
          /(?<=[^[:alnum:]:]|\n|^)
          :(#{Gitlab::Emoji.emojis_names.map { |name| Regexp.escape(name) }.join('|')}):
          (?=[^[:alnum:]:]|$)/x
      end

      # Build a regexp that matches all valid unicode emojis names.
      def self.emoji_unicode_pattern
        @emoji_unicode_pattern ||= /(#{Gitlab::Emoji.emojis_unicodes.map { |moji| Regexp.escape(moji) }.join('|')})/
      end

      private

      def emoji_pattern
        self.class.emoji_pattern
      end

      def emoji_unicode_pattern
        self.class.emoji_unicode_pattern
      end
    end
  end
end
