module ActsAsTaggableOn
  ##
  # Returns a new TagList using the given tag string.
  #
  # Example:
  #   tag_list = ActsAsTaggableOn::TagListParser.parse("One , Two,  Three")
  #   tag_list # ["One", "Two", "Three"]
  module TagListParser
    class << self
      def parse(string)
        string = string.join(ActsAsTaggableOn.glue) if string.respond_to?(:join)
        TagList.new.tap do |tag_list|
          string = string.to_s.dup


          string.gsub!(double_quote_pattern) {
            # Append the matched tag to the tag list
            tag_list << Regexp.last_match[2]
            # Return the matched delimiter ($3) to replace the matched items
            ''
          }

          string.gsub!(single_quote_pattern) {
            # Append the matched tag ($2) to the tag list
            tag_list << Regexp.last_match[2]
            # Return an empty string to replace the matched items
            ''
          }

          # split the string by the delimiter
          # and add to the tag_list
          tag_list.add(string.split(Regexp.new delimiter))
        end
      end


      # private
      def delimiter
        # Parse the quoted tags
        d = ActsAsTaggableOn.delimiter
        # Separate multiple delimiters by bitwise operator
        d = d.join('|') if d.kind_of?(Array)
        d
      end

      # (             # Tag start delimiter ($1)
      # \A       |  # Either string start or
      # #{delimiter}        # a delimiter
      # )
      # \s*"          # quote (") optionally preceded by whitespace
      # (.*?)         # Tag ($2)
      # "\s*          # quote (") optionally followed by whitespace
      # (?=           # Tag end delimiter (not consumed; is zero-length lookahead)
      # #{delimiter}\s*  |  # Either a delimiter optionally followed by whitespace or
      # \z          # string end
      # )
      def double_quote_pattern
        /(\A|#{delimiter})\s*"(.*?)"\s*(?=#{delimiter}\s*|\z)/
      end

      # (             # Tag start delimiter ($1)
      # \A       |  # Either string start or
      # #{delimiter}        # a delimiter
      # )
      # \s*'          # quote (') optionally preceded by whitespace
      # (.*?)         # Tag ($2)
      # '\s*          # quote (') optionally followed by whitespace
      # (?=           # Tag end delimiter (not consumed; is zero-length lookahead)
      # #{delimiter}\s*  | d # Either a delimiter optionally followed by whitespace or
      # \z          # string end
      # )
      def single_quote_pattern
        /(\A|#{delimiter})\s*'(.*?)'\s*(?=#{delimiter}\s*|\z)/
      end

    end
  end
end