class for extracting arguments from a string

template_method_arguments.rb

  # This class is solely used for extracting arguments from a string
  # It is used to process the arguments input to template_methods in the CMS content areas
  # It handles arguments that are comma separated, inside or outside of quotes
  # Like normal arguments to a programming function if something is inside a quote it will
  # all be part of the same argument and commas inside of quotes are part of that argument
  # rather than used to separate it from another argument.  It also takes into account backslashes
  # so 'I\'m an argument' will properly be processed
  #
  # For example link("http://google.com", 'Google is fun to use, really it is')
  # It will result in the arguments:
  # [
  #   "http://google.com",
  #   'Google is fun to use, really it is, isn\'t it?'
  # ]
  class TemplateMethodArguments
    def self.extract(str)
      new(str).extract
    end

    def initialize(str)
      @str = strip_parens(str)
    end

    def extract
      @quotation_start = nil
      @args = []
      @current_arg = ''

      @str.each_char.with_index do |char, i|
        if @quotation_start.nil?
          handle_non_quoted_argument(char, i)
        else
          handle_quoted_argument(char, i)
        end
      end
      add_current_arg
      @args
    end

    private

    def strip_parens(str)
      str = str.strip
      str = str[1..-1] if str[0] == '('
      str = str[0..-2] if str[-1] == ')'
      str
    end

    def handle_non_quoted_argument(char, i)
      if non_escaped_quote?(char, i)
        begin_quoted_argument(char)
      else
        handle_non_quoted_char(char, i)
      end
    end

    def handle_non_quoted_char(char, i)
      if char == ','
        add_current_arg(strip_arg: true)
      elsif char != '\\' || escaped_char?(i)
        @current_arg << char
      end
    end

    def begin_quoted_argument(char)
      @current_arg = ''
      @quotation_start = char
    end

    def end_quoted_argument
      add_current_arg(add_empty: true)
      @quotation_start = nil
    end

    def handle_quoted_argument(char, i)
      if char == @quotation_start && non_escaped_char?(i)
        end_quoted_argument
      elsif char != '\\' || escaped_char?(i)
        @current_arg << char
      end
    end

    def add_current_arg(strip_arg: false, add_empty: false)
      @current_arg = @current_arg.strip if strip_arg
      @args << @current_arg if @current_arg.present? || add_empty
      @current_arg = ''
    end

    def non_escaped_quote?(char, i)
      ['\'', '"'].include?(char) && non_escaped_char?(i)
    end

    def non_escaped_char?(i)
      i.zero? || @str[i - 1] != '\\'
    end

    def escaped_char?(i)
      !i.zero? && @str[i - 1] == '\\'
    end
  end