挺难懂的解决方法

挺难懂的
下面这段代码如何理解呢，最好在关节点上给与解释

 * 行为模型实例<br /> *<br /> * @param string $model 模型名称<br /> * @return obj 对象形式的返回结果<br /> */<br />function Logic($model = null, $base_path = null){<br />    static $_cache = array();<br />    $cache_key = $model.'.'.$base_path;<br />    if (!is_null($model) && isset($_cache[$cache_key])) return $_cache[$cache_key];<br />    $base_path = $base_path == null ? BASE_DATA_PATH : $base_path;<br />    $file_name = $base_path.'/logic/'.$model.'.logic.php';<br />    $class_name = $model.'Logic';<br />    if (!file_exists($file_name)){<br />        return $_cache[$cache_key] =  new Model($model);<br />    }else{<br />        require_once($file_name);<br />        if (!class_exists($class_name)){<br />            $error = 'Logic Error:  Class '.$class_name.' is not exists!';<br />            throw_exception($error);<br />        }else{<br />            return $_cache[$cache_key] = new $class_name();<br />        }<br />    }<br />}

------解决思路----------------------

<br />function Logic($model = null, $base_path = null){<br />	//定义静态变量<br />    static $_cache = array();<br />	//定义缓存key值<br />    $cache_key = $model.'.'.$base_path;<br />	//若是静态变量中有这个模型的实例就直接返回<br />    if (!is_null($model) && isset($_cache[$cache_key])) return $_cache[$cache_key];<br />	//组织类文件路径<br />    $base_path = $base_path == null ? BASE_DATA_PATH : $base_path;<br />    $file_name = $base_path.'/logic/'.$model.'.logic.php';<br />    $class_name = $model.'Logic';<br />	//类文件是否存在<br />    if (!file_exists($file_name)){<br />		//不存在就实例一个model<br />        return $_cache[$cache_key] =  new Model($model);<br />    }else{<br />		//存在就引入<br />        require_once($file_name);<br />		//判断是否存在 该类<br />        if (!class_exists($class_name)){<br />			//不存在就抛出异常<br />            $error = 'Logic Error:  Class '.$class_name.' is not exists!';<br />            throw_exception($error);<br />        }else{<br />			//存在就实例化它，存入静态数组中并返回<br />            return $_cache[$cache_key] = new $class_name();<br />        }<br />    }<br />}<br />