# Copyright 2023 The KerasCV Authors
#
# 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
#
#     https://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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from keras_cv.api_export import keras_cv_export
from keras_cv.backend import keras
from keras_cv.backend import ops


@keras_cv_export("keras_cv.layers.OverlappingPatchingAndEmbedding")
class OverlappingPatchingAndEmbedding(keras.layers.Layer):
    def __init__(self, project_dim=32, patch_size=7, stride=4, **kwargs):
        """
        Overlapping Patching and Embedding layer. Differs from `PatchingAndEmbedding`
        in that the patch size does not affect the sequence length. It's fully derived
        from the `stride` parameter. Additionally, no positional embedding is done
        as part of the layer - only a projection using a `Conv2D` layer.

        References:
            - [SegFormer: Simple and Efficient Design for Semantic Segmentation with Transformers](https://arxiv.org/abs/2105.15203) (CVPR 2021) # noqa: E501
            - [Official PyTorch implementation](https://github.com/NVlabs/SegFormer/blob/master/mmseg/models/backbones/mix_transformer.py) # noqa: E501
            - [Ported from the TensorFlow implementation from DeepVision](https://github.com/DavidLandup0/deepvision/blob/main/deepvision/layers/hierarchical_transformer_encoder.py) # noqa: E501

        Args:
            project_dim: integer, the dimensionality of the projection.
                Defaults to `32`.
            patch_size: integer, the size of the patches to encode.
                Defaults to `7`.
            stride: integer, the stride to use for the patching before
                projection. Defaults to `5`.

        Basic usage:

        ```
        project_dim = 1024
        patch_size = 16

        encoded_patches = keras_cv.layers.OverlappingPatchingAndEmbedding(
        project_dim=project_dim, patch_size=patch_size)(img_batch)

        print(encoded_patches.shape) # (1, 3136, 1024)
        ```
        """
        super().__init__(**kwargs)

        self.project_dim = project_dim
        self.patch_size = patch_size
        self.stride = stride

        self.proj = keras.layers.Conv2D(
            filters=project_dim,
            kernel_size=patch_size,
            strides=stride,
            padding="same",
        )
        self.norm = keras.layers.LayerNormalization()

    def call(self, x):
        x = self.proj(x)
        # B, H, W, C
        shape = x.shape
        x = ops.reshape(x, (-1, shape[1] * shape[2], shape[3]))
        x = self.norm(x)
        return x

    def get_config(self):
        config = super().get_config()
        config.update(
            {
                "project_dim": self.project_dim,
                "patch_size": self.patch_size,
                "stride": self.stride,
            }
        )
        return config
