class Chronic::Handler

def match(tokens, definitions)
  token_index = 0
  @pattern.each do |elements|
    was_optional = false
    elements = [elements] unless elements.is_a?(Array)
    elements.each_index do |i|
      name = elements[i].to_s
      optional = name[-1, 1] == '?'
      name = name.chop if optional
      case elements[i]
      when Symbol
        if tags_match?(name, tokens, token_index)
          token_index += 1
          break
        else
          if optional
            was_optional = true
            next
          elsif i + 1 < elements.count
            next
          else
            return false unless was_optional
          end
        end
      when String
        return true if optional && token_index == tokens.size
        if definitions.key?(name.to_sym)
          sub_handlers = definitions[name.to_sym]
        else
          raise "Invalid subset #{name} specified"
        end
        sub_handlers.each do |sub_handler|
          return true if sub_handler.match(tokens[token_index..tokens.size], definitions)
        end
      else
        raise "Invalid match type: #{elements[i].class}"
      end
    end
  end
  return false if token_index != tokens.size
  return true
end