外观/门面facade模式可以将应用与一个复杂的第三方库简单地连接起来，尤其是应用只依赖于复杂第三方库的一小部分功能的时候。它有四个部分

  • Facade
  • Additional Facade: 继承Facade并为Facade添加一些其他功能，而不改变Facade这一简单接口本身
  • The Complex system
  • client
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// a complex 3rd party video conversion framework
class VideoFile {
  // ...
}

class OggCompressionCodec {
  // ...
}

class MPEG4CompressionCodec {
  // ...
}

class CodecFactory {
  // ...
}

class BitrateReader {
  // ...
}

class AudioMixer {
  // ...
}

// here is the facade class
class VideoConverter {
  public:
    File convert(std::string& filename, std::string& format) {
      // 返回裸指针不是一个好习惯，文档中必须清晰说明谁拥有这个指针并负责其生命周期
      // 直接返回File(result)将使用编译器的返回值优化功能，安全且高效
      VideoFile file = VideoFile(filename);
      CodecFactory codecfactory = CodecFactory();
      Codec* sourceCodec = codecfactory.extract(file);
      Codec* destinationCodec = nullptr;
      if (format == "mp4") destinationCodec = MPEG4CompressionCodec();
      else destinationCodec = OggCompressionCodec();
      Buffer buffer = BitrateReader::read(filename, sourceCodec);
      Buffer result = BitrateReader::convert(buffer, destinationCodec);
      AutoMixer mixer = AutoMixer();
      result = mixer.fix(result);
      
      delete destinationCodec;
      delete sourceCodec;
      return File(result)
    }
}

int main(int argc, char* argv[]) {
  VideoConverter converter = VideoConverter();
  File mp4 = converter->convert("some.ogg", "mp4");
  mp4.save();

  return 0;
}