# Copyright 2018 The TensorFlow Authors. All Rights Reserved.
#
# Licensed under the Apache License, Version 2.0 (the "License");
# you may not use this file except in compliance with the License.
# You may obtain a copy of the License at
#
#     http://www.apache.org/licenses/LICENSE-2.0
#
# Unless required by applicable law or agreed to in writing, software
# distributed under the License is distributed on an "AS IS" BASIS,
# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
# See the License for the specific language governing permissions and
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# ==============================================================================

"""DenseNet models for Keras.

Reference:
  - [Densely Connected Convolutional Networks](
      https://arxiv.org/abs/1608.06993) (CVPR 2017)
"""

import tensorflow.compat.v2 as tf

from keras import backend
from keras.applications import imagenet_utils
from keras.engine import training
from keras.layers import VersionAwareLayers
from keras.utils import data_utils
from keras.utils import layer_utils

# isort: off
from tensorflow.python.util.tf_export import keras_export

BASE_WEIGHTS_PATH = (
    "https://storage.googleapis.com/tensorflow/keras-applications/densenet/"
)
DENSENET121_WEIGHT_PATH = (
    BASE_WEIGHTS_PATH + "densenet121_weights_tf_dim_ordering_tf_kernels.h5"
)
DENSENET121_WEIGHT_PATH_NO_TOP = (
    BASE_WEIGHTS_PATH
    + "densenet121_weights_tf_dim_ordering_tf_kernels_notop.h5"
)
DENSENET169_WEIGHT_PATH = (
    BASE_WEIGHTS_PATH + "densenet169_weights_tf_dim_ordering_tf_kernels.h5"
)
DENSENET169_WEIGHT_PATH_NO_TOP = (
    BASE_WEIGHTS_PATH
    + "densenet169_weights_tf_dim_ordering_tf_kernels_notop.h5"
)
DENSENET201_WEIGHT_PATH = (
    BASE_WEIGHTS_PATH + "densenet201_weights_tf_dim_ordering_tf_kernels.h5"
)
DENSENET201_WEIGHT_PATH_NO_TOP = (
    BASE_WEIGHTS_PATH
    + "densenet201_weights_tf_dim_ordering_tf_kernels_notop.h5"
)

layers = VersionAwareLayers()


def dense_block(x, blocks, name):
    """A dense block.

    Args:
      x: input tensor.
      blocks: integer, the number of building blocks.
      name: string, block label.

    Returns:
      Output tensor for the block.
    """
    for i in range(blocks):
        x = conv_block(x, 32, name=name + "_block" + str(i + 1))
    return x


def transition_block(x, reduction, name):
    """A transition block.

    Args:
      x: input tensor.
      reduction: float, compression rate at transition layers.
      name: string, block label.

    Returns:
      output tensor for the block.
    """
    bn_axis = 3 if backend.image_data_format() == "channels_last" else 1
    x = layers.BatchNormalization(
        axis=bn_axis, epsilon=1.001e-5, name=name + "_bn"
    )(x)
    x = layers.Activation("relu", name=name + "_relu")(x)
    x = layers.Conv2D(
        int(backend.int_shape(x)[bn_axis] * reduction),
        1,
        use_bias=False,
        name=name + "_conv",
    )(x)
    x = layers.AveragePooling2D(2, strides=2, name=name + "_pool")(x)
    return x


def conv_block(x, growth_rate, name):
    """A building block for a dense block.

    Args:
      x: input tensor.
      growth_rate: float, growth rate at dense layers.
      name: string, block label.

    Returns:
      Output tensor for the block.
    """
    bn_axis = 3 if backend.image_data_format() == "channels_last" else 1
    x1 = layers.BatchNormalization(
        axis=bn_axis, epsilon=1.001e-5, name=name + "_0_bn"
    )(x)
    x1 = layers.Activation("relu", name=name + "_0_relu")(x1)
    x1 = layers.Conv2D(
        4 * growth_rate, 1, use_bias=False, name=name + "_1_conv"
    )(x1)
    x1 = layers.BatchNormalization(
        axis=bn_axis, epsilon=1.001e-5, name=name + "_1_bn"
    )(x1)
    x1 = layers.Activation("relu", name=name + "_1_relu")(x1)
    x1 = layers.Conv2D(
        growth_rate, 3, padding="same", use_bias=False, name=name + "_2_conv"
    )(x1)
    x = layers.Concatenate(axis=bn_axis, name=name + "_concat")([x, x1])
    return x


def DenseNet(
    blocks,
    include_top=True,
    weights="imagenet",
    input_tensor=None,
    input_shape=None,
    pooling=None,
    classes=1000,
    classifier_activation="softmax",
):
    """Instantiates the DenseNet architecture.

    Reference:
    - [Densely Connected Convolutional Networks](
        https://arxiv.org/abs/1608.06993) (CVPR 2017)

    This function returns a Keras image classification model,
    optionally loaded with weights pre-trained on ImageNet.

    For image classification use cases, see
    [this page for detailed examples](
      https://keras.io/api/applications/#usage-examples-for-image-classification-models).

    For transfer learning use cases, make sure to read the
    [guide to transfer learning & fine-tuning](
      https://keras.io/guides/transfer_learning/).

    Note: each Keras Application expects a specific kind of input preprocessing.
    For DenseNet, call `tf.keras.applications.densenet.preprocess_input` on your
    inputs before passing them to the model.
    `densenet.preprocess_input` will scale pixels between 0 and 1 and then
    will normalize each channel with respect to the ImageNet dataset statistics.

    Args:
      blocks: numbers of building blocks for the four dense layers.
      include_top: whether to include the fully-connected
        layer at the top of the network.
      weights: one of `None` (random initialization),
        'imagenet' (pre-training on ImageNet),
        or the path to the weights file to be loaded.
      input_tensor: optional Keras tensor
        (i.e. output of `layers.Input()`)
        to use as image input for the model.
      input_shape: optional shape tuple, only to be specified
        if `include_top` is False (otherwise the input shape
        has to be `(224, 224, 3)` (with `'channels_last'` data format)
        or `(3, 224, 224)` (with `'channels_first'` data format).
        It should have exactly 3 inputs channels,
        and width and height should be no smaller than 32.
        E.g. `(200, 200, 3)` would be one valid value.
      pooling: optional pooling mode for feature extraction
        when `include_top` is `False`.
        - `None` means that the output of the model will be
            the 4D tensor output of the
            last convolutional block.
        - `avg` means that global average pooling
            will be applied to the output of the
            last convolutional block, and thus
            the output of the model will be a 2D tensor.
        - `max` means that global max pooling will
            be applied.
      classes: optional number of classes to classify images
        into, only to be specified if `include_top` is True, and
        if no `weights` argument is specified.
      classifier_activation: A `str` or callable. The activation function to use
        on the "top" layer. Ignored unless `include_top=True`. Set
        `classifier_activation=None` to return the logits of the "top" layer.
        When loading pretrained weights, `classifier_activation` can only
        be `None` or `"softmax"`.

    Returns:
      A `keras.Model` instance.
    """
    if not (weights in {"imagenet", None} or tf.io.gfile.exists(weights)):
        raise ValueError(
            "The `weights` argument should be either "
            "`None` (random initialization), `imagenet` "
            "(pre-training on ImageNet), "
            "or the path to the weights file to be loaded."
        )

    if weights == "imagenet" and include_top and classes != 1000:
        raise ValueError(
            'If using `weights` as `"imagenet"` with `include_top`'
            " as true, `classes` should be 1000"
        )

    # Determine proper input shape
    input_shape = imagenet_utils.obtain_input_shape(
        input_shape,
        default_size=224,
        min_size=32,
        data_format=backend.image_data_format(),
        require_flatten=include_top,
        weights=weights,
    )

    if input_tensor is None:
        img_input = layers.Input(shape=input_shape)
    else:
        if not backend.is_keras_tensor(input_tensor):
            img_input = layers.Input(tensor=input_tensor, shape=input_shape)
        else:
            img_input = input_tensor

    bn_axis = 3 if backend.image_data_format() == "channels_last" else 1

    x = layers.ZeroPadding2D(padding=((3, 3), (3, 3)))(img_input)
    x = layers.Conv2D(64, 7, strides=2, use_bias=False, name="conv1/conv")(x)
    x = layers.BatchNormalization(
        axis=bn_axis, epsilon=1.001e-5, name="conv1/bn"
    )(x)
    x = layers.Activation("relu", name="conv1/relu")(x)
    x = layers.ZeroPadding2D(padding=((1, 1), (1, 1)))(x)
    x = layers.MaxPooling2D(3, strides=2, name="pool1")(x)

    x = dense_block(x, blocks[0], name="conv2")
    x = transition_block(x, 0.5, name="pool2")
    x = dense_block(x, blocks[1], name="conv3")
    x = transition_block(x, 0.5, name="pool3")
    x = dense_block(x, blocks[2], name="conv4")
    x = transition_block(x, 0.5, name="pool4")
    x = dense_block(x, blocks[3], name="conv5")

    x = layers.BatchNormalization(axis=bn_axis, epsilon=1.001e-5, name="bn")(x)
    x = layers.Activation("relu", name="relu")(x)

    if include_top:
        x = layers.GlobalAveragePooling2D(name="avg_pool")(x)

        imagenet_utils.validate_activation(classifier_activation, weights)
        x = layers.Dense(
            classes, activation=classifier_activation, name="predictions"
        )(x)
    else:
        if pooling == "avg":
            x = layers.GlobalAveragePooling2D(name="avg_pool")(x)
        elif pooling == "max":
            x = layers.GlobalMaxPooling2D(name="max_pool")(x)

    # Ensure that the model takes into account
    # any potential predecessors of `input_tensor`.
    if input_tensor is not None:
        inputs = layer_utils.get_source_inputs(input_tensor)
    else:
        inputs = img_input

    # Create model.
    if blocks == [6, 12, 24, 16]:
        model = training.Model(inputs, x, name="densenet121")
    elif blocks == [6, 12, 32, 32]:
        model = training.Model(inputs, x, name="densenet169")
    elif blocks == [6, 12, 48, 32]:
        model = training.Model(inputs, x, name="densenet201")
    else:
        model = training.Model(inputs, x, name="densenet")

    # Load weights.
    if weights == "imagenet":
        if include_top:
            if blocks == [6, 12, 24, 16]:
                weights_path = data_utils.get_file(
                    "densenet121_weights_tf_dim_ordering_tf_kernels.h5",
                    DENSENET121_WEIGHT_PATH,
                    cache_subdir="models",
                    file_hash="9d60b8095a5708f2dcce2bca79d332c7",
                )
            elif blocks == [6, 12, 32, 32]:
                weights_path = data_utils.get_file(
                    "densenet169_weights_tf_dim_ordering_tf_kernels.h5",
                    DENSENET169_WEIGHT_PATH,
                    cache_subdir="models",
                    file_hash="d699b8f76981ab1b30698df4c175e90b",
                )
            elif blocks == [6, 12, 48, 32]:
                weights_path = data_utils.get_file(
                    "densenet201_weights_tf_dim_ordering_tf_kernels.h5",
                    DENSENET201_WEIGHT_PATH,
                    cache_subdir="models",
                    file_hash="1ceb130c1ea1b78c3bf6114dbdfd8807",
                )
        else:
            if blocks == [6, 12, 24, 16]:
                weights_path = data_utils.get_file(
                    "densenet121_weights_tf_dim_ordering_tf_kernels_notop.h5",
                    DENSENET121_WEIGHT_PATH_NO_TOP,
                    cache_subdir="models",
                    file_hash="30ee3e1110167f948a6b9946edeeb738",
                )
            elif blocks == [6, 12, 32, 32]:
                weights_path = data_utils.get_file(
                    "densenet169_weights_tf_dim_ordering_tf_kernels_notop.h5",
                    DENSENET169_WEIGHT_PATH_NO_TOP,
                    cache_subdir="models",
                    file_hash="b8c4d4c20dd625c148057b9ff1c1176b",
                )
            elif blocks == [6, 12, 48, 32]:
                weights_path = data_utils.get_file(
                    "densenet201_weights_tf_dim_ordering_tf_kernels_notop.h5",
                    DENSENET201_WEIGHT_PATH_NO_TOP,
                    cache_subdir="models",
                    file_hash="c13680b51ded0fb44dff2d8f86ac8bb1",
                )
        model.load_weights(weights_path)
    elif weights is not None:
        model.load_weights(weights)

    return model


@keras_export(
    "keras.applications.densenet.DenseNet121", "keras.applications.DenseNet121"
)
def DenseNet121(
    include_top=True,
    weights="imagenet",
    input_tensor=None,
    input_shape=None,
    pooling=None,
    classes=1000,
    classifier_activation="softmax",
):
    """Instantiates the Densenet121 architecture."""
    return DenseNet(
        [6, 12, 24, 16],
        include_top,
        weights,
        input_tensor,
        input_shape,
        pooling,
        classes,
        classifier_activation,
    )


@keras_export(
    "keras.applications.densenet.DenseNet169", "keras.applications.DenseNet169"
)
def DenseNet169(
    include_top=True,
    weights="imagenet",
    input_tensor=None,
    input_shape=None,
    pooling=None,
    classes=1000,
    classifier_activation="softmax",
):
    """Instantiates the Densenet169 architecture."""
    return DenseNet(
        [6, 12, 32, 32],
        include_top,
        weights,
        input_tensor,
        input_shape,
        pooling,
        classes,
        classifier_activation,
    )


@keras_export(
    "keras.applications.densenet.DenseNet201", "keras.applications.DenseNet201"
)
def DenseNet201(
    include_top=True,
    weights="imagenet",
    input_tensor=None,
    input_shape=None,
    pooling=None,
    classes=1000,
    classifier_activation="softmax",
):
    """Instantiates the Densenet201 architecture."""
    return DenseNet(
        [6, 12, 48, 32],
        include_top,
        weights,
        input_tensor,
        input_shape,
        pooling,
        classes,
        classifier_activation,
    )


@keras_export("keras.applications.densenet.preprocess_input")
def preprocess_input(x, data_format=None):
    return imagenet_utils.preprocess_input(
        x, data_format=data_format, mode="torch"
    )


@keras_export("keras.applications.densenet.decode_predictions")
def decode_predictions(preds, top=5):
    return imagenet_utils.decode_predictions(preds, top=top)


preprocess_input.__doc__ = imagenet_utils.PREPROCESS_INPUT_DOC.format(
    mode="",
    ret=imagenet_utils.PREPROCESS_INPUT_RET_DOC_TORCH,
    error=imagenet_utils.PREPROCESS_INPUT_ERROR_DOC,
)
decode_predictions.__doc__ = imagenet_utils.decode_predictions.__doc__

DOC = """

  Reference:
  - [Densely Connected Convolutional Networks](
      https://arxiv.org/abs/1608.06993) (CVPR 2017)

  Optionally loads weights pre-trained on ImageNet.
  Note that the data format convention used by the model is
  the one specified in your Keras config at `~/.keras/keras.json`.

  Note: each Keras Application expects a specific kind of input preprocessing.
  For DenseNet, call `tf.keras.applications.densenet.preprocess_input` on your
  inputs before passing them to the model.

  Args:
    include_top: whether to include the fully-connected
      layer at the top of the network.
    weights: one of `None` (random initialization),
      'imagenet' (pre-training on ImageNet),
      or the path to the weights file to be loaded.
    input_tensor: optional Keras tensor (i.e. output of `layers.Input()`)
      to use as image input for the model.
    input_shape: optional shape tuple, only to be specified
      if `include_top` is False (otherwise the input shape
      has to be `(224, 224, 3)` (with `'channels_last'` data format)
      or `(3, 224, 224)` (with `'channels_first'` data format).
      It should have exactly 3 inputs channels,
      and width and height should be no smaller than 32.
      E.g. `(200, 200, 3)` would be one valid value.
    pooling: Optional pooling mode for feature extraction
      when `include_top` is `False`.
      - `None` means that the output of the model will be
          the 4D tensor output of the
          last convolutional block.
      - `avg` means that global average pooling
          will be applied to the output of the
          last convolutional block, and thus
          the output of the model will be a 2D tensor.
      - `max` means that global max pooling will
          be applied.
    classes: optional number of classes to classify images
      into, only to be specified if `include_top` is True, and
      if no `weights` argument is specified.
    classifier_activation: A `str` or callable. The activation function to use
      on the "top" layer. Ignored unless `include_top=True`. Set
      `classifier_activation=None` to return the logits of the "top" layer.
      When loading pretrained weights, `classifier_activation` can only
      be `None` or `"softmax"`.

  Returns:
    A Keras model instance.
"""

setattr(DenseNet121, "__doc__", DenseNet121.__doc__ + DOC)
setattr(DenseNet169, "__doc__", DenseNet169.__doc__ + DOC)
setattr(DenseNet201, "__doc__", DenseNet201.__doc__ + DOC)
