"""
Copyright 2020 The OneFlow 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
limitations under the License.
"""
import oneflow as flow
from oneflow.framework.tensor import register_tensor_op
from oneflow.nn.module import Module


class Flatten(Module):
    """Flattens a contiguous range of dims into a tensor. For use with: nn.Sequential.

    Args:
        start_dim: first dim to flatten (default = 1).
        end_dim: last dim to flatten (default = -1).
    

    For example: 

    .. code-block:: python 

        >>> import oneflow as flow
        >>> input = flow.Tensor(32, 1, 5, 5)
        >>> m = flow.nn.Flatten()
        >>> output = m(input)
        >>> output.shape
        oneflow.Size([32, 25])

    """

    def __init__(self, start_dim: int = 1, end_dim: int = -1) -> None:
        super().__init__()
        self.start_dim = start_dim
        self.end_dim = end_dim

    def forward(self, input):
        return flow._C.flatten(input, start_dim=self.start_dim, end_dim=self.end_dim)

    def extra_repr(self) -> str:
        return "start_dim={}, end_dim={}".format(self.start_dim, self.end_dim)


if __name__ == "__main__":
    import doctest

    doctest.testmod(raise_on_error=True)
