class MetaMBConvBlock(MetaModule):


    def __init__(self, block_args, global_params, image_size=None):
        super().__init__()
        self._block_args = block_args
        self._bn_mom = 1 - global_params.batch_norm_momentum # pytorch's difference from tensorflow
        self._bn_eps = global_params.batch_norm_epsilon
        self.has_se = (self._block_args.se_ratio is not None) and (0 < self._block_args.se_ratio <= 1)
        self.id_skip = block_args.id_skip  # whether to use skip connection and drop connect

        # Expansion phase (Inverted Bottleneck)
        inp = self._block_args.input_filters  # number of input channels
        oup = self._block_args.input_filters * self._block_args.expand_ratio  # number of output channels
        if self._block_args.expand_ratio != 1:
            Conv2d = get_same_padding_conv2d_meta(image_size=image_size)
            self._expand_conv = Conv2d(in_channels=inp, out_channels=oup, kernel_size=1, bias=False)
            self._bn0 = MetaBatchNorm2d(num_features=oup, momentum=self._bn_mom, eps=self._bn_eps)
            # image_size = calculate_output_image_size(image_size, 1) <-- this wouldn't modify image_size

        # Depthwise convolution phase
        k = self._block_args.kernel_size
        s = self._block_args.stride
        Conv2d = get_same_padding_conv2d_meta(image_size=image_size)
        self._depthwise_conv = Conv2d(
            in_channels=oup, out_channels=oup, groups=oup,  # groups makes it depthwise
            kernel_size=k, stride=s, bias=False)
        self._bn1 = MetaBatchNorm2d(num_features=oup, momentum=self._bn_mom, eps=self._bn_eps)
        
        image_size = calculate_output_image_size(image_size, s)

        # Squeeze and Excitation layer, if desired
        if self.has_se:
            Conv2d = get_same_padding_conv2d_meta(image_size=(1,1))
            num_squeezed_channels = max(1, int(self._block_args.input_filters * self._block_args.se_ratio))
            self._se_reduce = Conv2d(in_channels=oup, out_channels=num_squeezed_channels, kernel_size=1)
            self._se_expand = Conv2d(in_channels=num_squeezed_channels, out_channels=oup, kernel_size=1)

        # Pointwise convolution phase
        final_oup = self._block_args.output_filters
        Conv2d = get_same_padding_conv2d_meta(image_size=image_size)
        self._project_conv = Conv2d(in_channels=oup, out_channels=final_oup, kernel_size=1, bias=False)
        self._bn2 = MetaBatchNorm2d(num_features=final_oup, momentum=self._bn_mom, eps=self._bn_eps)
        

        self._swish = MemoryEfficientSwish()

    def forward(self, inputs, drop_connect_rate=None):
        """MBConvBlock's forward function.

        Args:
            inputs (tensor): Input tensor.
            drop_connect_rate (bool): Drop connect rate (float, between 0 and 1).

        Returns:
            Output of this block after processing.
        """

        # Expansion and Depthwise Convolution
        x = inputs
        if self._block_args.expand_ratio != 1:
            x = self._expand_conv(inputs)
            x = self._bn0(x)
            x = self._swish(x)

        x = self._depthwise_conv(x)
        x = self._bn1(x)
        
        x = self._swish(x)

        # Squeeze and Excitation
        if self.has_se:
            x_squeezed = F.adaptive_avg_pool2d(x, 1)
            x_squeezed = self._se_reduce(x_squeezed)
            x_squeezed = self._swish(x_squeezed)
            x_squeezed = self._se_expand(x_squeezed)
            x = torch.sigmoid(x_squeezed) * x

        # Pointwise Convolution
        x = self._project_conv(x)
        x = self._bn2(x)
        
        # Skip connection and drop connect
        input_filters, output_filters = self._block_args.input_filters, self._block_args.output_filters
        if self.id_skip and self._block_args.stride == 1 and input_filters == output_filters:
            # The combination of skip connection and drop connect brings about stochastic depth.
            if drop_connect_rate:
                x = drop_connect(x, p=drop_connect_rate, training=self.training)
            x = x + inputs  # skip connection
        return x

    def set_swish(self, memory_efficient=True):
        """Sets swish function as memory efficient (for training) or standard (for export).

        Args:
            memory_efficient (bool): Whether to use memory-efficient version of swish.
        """
        self._swish = MemoryEfficientSwish() if memory_efficient else Swish()


class MetaEfficientNet(MetaModule):

    def __init__(self, blocks_args=None, global_params=None,in_channels=3):
        super().__init__()

        assert isinstance(blocks_args, list), 'blocks_args should be a list'
        assert len(blocks_args) > 0, 'block args must be greater than 0'
        self._global_params = global_params
        self._blocks_args = blocks_args

        # Batch norm parameters
        bn_mom = 1 - self._global_params.batch_norm_momentum
        bn_eps = self._global_params.batch_norm_epsilon

        # Get stem static or dynamic convolution depending on image size
        image_size = global_params.image_size
        Conv2d = get_same_padding_conv2d_meta(image_size=image_size)

        # Stem
        in_channels = in_channels  # rgb
        out_channels = round_filters(32, self._global_params)  # number of output channels
        self._conv_stem = Conv2d(in_channels, out_channels, kernel_size=3, stride=2, bias=False)
        self._bn0 = MetaBatchNorm2d(num_features=out_channels, momentum=bn_mom, eps=bn_eps)
        image_size = calculate_output_image_size(image_size, 2)

        # Build blocks
        num_block = len(self._blocks_args)
        self._blocks = nn.ModuleList([])
        
        for i,block_args in enumerate(self._blocks_args):

            # Update block input and output filters based on depth multiplier.
            block_args = block_args._replace(
                input_filters=round_filters(block_args.input_filters, self._global_params),
                output_filters=round_filters(block_args.output_filters, self._global_params),
                num_repeat=round_repeats(block_args.num_repeat, self._global_params)
            )

            # The first block needs to take care of stride and filter size increase.

            self._blocks.append(MetaMBConvBlock(block_args, self._global_params, image_size=image_size))
            #self._blocks.append(MBConvBlockIN(block_args, self._global_params, image_size=image_size))
            image_size = calculate_output_image_size(image_size, block_args.stride)
            if block_args.num_repeat > 1: # modify block_args to keep same output size
                block_args = block_args._replace(input_filters=block_args.output_filters, stride=1)
            for _ in range(block_args.num_repeat - 1):
                self._blocks.append(MetaMBConvBlock(block_args, self._global_params, image_size=image_size))
        # Head
        in_channels = block_args.output_filters  # output of final block
        out_channels = round_filters(1280, self._global_params)
        Conv2d = get_same_padding_conv2d_meta(image_size=image_size)
        self._conv_head = Conv2d(in_channels, out_channels, kernel_size=1, bias=False)
        self._bn1 = MetaBatchNorm2d(num_features=out_channels, momentum=bn_mom, eps=bn_eps)

        # Final linear layer
        self._avg_pooling = nn.AdaptiveAvgPool2d(1)
        self._dropout = nn.Dropout(self._global_params.dropout_rate)
        self._fc = MetaLinear(out_channels, self._global_params.num_classes)
        self._swish = MemoryEfficientSwish()

    def set_swish(self, memory_efficient=True):
        """Sets swish function as memory efficient (for training) or standard (for export).

        Args:
            memory_efficient (bool): Whether to use memory-efficient version of swish.

        """
        self._swish = MemoryEfficientSwish() if memory_efficient else Swish()
        for block in self._blocks:
            block.set_swish(memory_efficient)


    def extract_features(self, inputs):
        """use convolution layer to extract feature .

        Args:
            inputs (tensor): Input tensor.

        Returns:
            Output of the final convolution 
            layer in the efficientnet model.
        """
        # Stem
        x = self._swish(self._bn0(self._conv_stem(inputs)))

        # Blocks
        for idx, block in enumerate(self._blocks):
            drop_connect_rate = self._global_params.drop_connect_rate
            if drop_connect_rate:
                drop_connect_rate *= float(idx) / len(self._blocks) # scale drop connect_rate
            x = block(x, drop_connect_rate=drop_connect_rate)
        
        # Head
        x = self._swish(self._bn1(self._conv_head(x)))

        return x
    

    def forward(self, inputs):
        """EfficientNet's forward function.
           Calls extract_features to extract features, applies final linear layer, and returns logits.

        Args:
            inputs (tensor): Input tensor.

        Returns:
            Output of this model after processing.
        """
        bs = inputs.size(0)

        # Convolution layers
        feature = self.extract_features(inputs)

        # Pooling and final linear layer
        x = self._avg_pooling(feature)
        x = x.view(bs, -1)
        x = self._dropout(x)
        x = self._fc(x)


        return x,feature

    @classmethod
    def from_name(cls, model_name, in_channels=3, **override_params):
        """create an efficientnet model according to name.

        Args:
            model_name (str): Name for efficientnet.
            in_channels (int): Input data's channel number.
            override_params (other key word params): 
                Params to override model's global_params.
                Optional key:
                    'width_coefficient', 'depth_coefficient',
                    'image_size', 'dropout_rate',
                    'num_classes', 'batch_norm_momentum',
                    'batch_norm_epsilon', 'drop_connect_rate',
                    'depth_divisor', 'min_depth'

        Returns:
            An efficientnet model.
        """
        cls._check_model_name_is_valid(model_name)
        blocks_args, global_params = get_model_params(model_name, override_params)
        model = cls(blocks_args, global_params)
        model._change_in_channels(in_channels)
        return model

    @classmethod
    def from_pretrained(cls, model_name, weights_path=None, advprop=False, 
                        in_channels=3, num_classes=1000, **override_params):
        """create an efficientnet model according to name.

        Args:
            model_name (str): Name for efficientnet.
            weights_path (None or str): 
                str: path to pretrained weights file on the local disk.
                None: use pretrained weights downloaded from the Internet.
            advprop (bool): 
                Whether to load pretrained weights
                trained with advprop (valid when weights_path is None).
            in_channels (int): Input data's channel number.
            num_classes (int): 
                Number of categories for classification.
                It controls the output size for final linear layer.
            override_params (other key word params): 
                Params to override model's global_params.
                Optional key:
                    'width_coefficient', 'depth_coefficient',
                    'image_size', 'dropout_rate',
                    'num_classes', 'batch_norm_momentum',
                    'batch_norm_epsilon', 'drop_connect_rate',
                    'depth_divisor', 'min_depth'

        Returns:
            A pretrained efficientnet model.
        """
        model = cls.from_name(model_name, num_classes = num_classes, **override_params)
        load_pretrained_weights(model, model_name, weights_path=weights_path, load_fc=(num_classes == 1000), advprop=advprop)
        model._change_in_channels(in_channels)
        return model

    @classmethod
    def get_image_size(cls, model_name):
        """Get the input image size for a given efficientnet model.

        Args:
            model_name (str): Name for efficientnet.

        Returns:
            Input image size (resolution).
        """
        cls._check_model_name_is_valid(model_name)
        _, _, res, _ = efficientnet_params(model_name)
        return res

    @classmethod
    def _check_model_name_is_valid(cls, model_name):
        """Validates model name. 

        Args:
            model_name (str): Name for efficientnet.

        Returns:
            bool: Is a valid name or not.
        """
        valid_models = ['efficientnet-b'+str(i) for i in range(9)]

        # Support the construction of 'efficientnet-l2' without pretrained weights
        valid_models += ['efficientnet-l2']

        if model_name not in valid_models:
            raise ValueError('model_name should be one of: ' + ', '.join(valid_models))
    
    def _change_in_channels(self, in_channels):
        """Adjust model's first convolution layer to in_channels, if in_channels not equals 3.

        Args:
            in_channels (int): Input data's channel number.
        """
        if in_channels != 3:
            Conv2d = get_same_padding_conv2d(image_size = self._global_params.image_size)
            out_channels = round_filters(32, self._global_params)
            self._conv_stem = Conv2d(in_channels, out_channels, kernel_size=3, stride=2, bias=False)用中文详细解释这段代码