class Liquid::RangeLookup

def self.parse(start_markup, end_markup)
  start_obj = Expression.parse(start_markup)
  end_obj   = Expression.parse(end_markup)
  if start_obj.respond_to?(:evaluate) || end_obj.respond_to?(:evaluate)
    new(start_obj, end_obj)
  else
    begin
      start_obj.to_i..end_obj.to_i
    rescue NoMethodError
      invalid_expr = start_markup unless start_obj.respond_to?(:to_i)
      invalid_expr ||= end_markup unless end_obj.respond_to?(:to_i)
      if invalid_expr
        raise Liquid::SyntaxError, "Invalid expression type '#{invalid_expr}' in range expression"
      end
      raise
    end
  end
end

def evaluate(context)
  start_int = to_integer(context.evaluate(@start_obj))
  end_int   = to_integer(context.evaluate(@end_obj))
  start_int..end_int
end

def initialize(start_obj, end_obj)
  @start_obj = start_obj
  @end_obj   = end_obj
end

def to_integer(input)
  case input
  when Integer
    input
  when NilClass, String
    input.to_i
  else
    Utils.to_integer(input)
  end
end