input: Write a python function to generate a diamond shape pattern based on the size provided.
  assert diamond_shape(3) == '  *  *  *  *  *\n *  *  *  *\n  *  *\n *  *  *  *\n  *'
  assert diamond_shape(1) == '*'
  assert diamond_shape(4) == '   *   *   *   *   *\n  *  *  *  *  *  *\n *  *  *  *  *\n*  *   *  *  *\n *  *  *  *\n  *'
output: def diamond_shape(size):
      if size < 1:
          return ""
      
      result = []
      for i in range(size):
          result.append(' ' * (size - i - 1) + '* ' * (i + 1) + ' ' * (size - i - 1))
  
      for i in range(size - 1):
          result.append(' ' * (i + 1) + '* ' * (size - i - 1) + ' ' * (i + 1))
      
      return '\n'.join(result).strip()