import torch.nn.functional as F


class InputPadder:
    """Pads images such that dimensions are divisible by 8"""

    # TODO: Ideally, this should be part of the eval transforms preset, instead
    # of being part of the validation code. It's not obvious what a good
    # solution would be, because we need to unpad the predicted flows according
    # to the input images' size, and in some datasets (Kitti) images can have
    # variable sizes.

    def __init__(self, dims, mode="sintel"):
        self.ht, self.wd = dims[-2:]
        pad_ht = (((self.ht // 8) + 1) * 8 - self.ht) % 8
        pad_wd = (((self.wd // 8) + 1) * 8 - self.wd) % 8
        if mode == "sintel":
            self._pad = [pad_wd // 2, pad_wd - pad_wd // 2, pad_ht // 2, pad_ht - pad_ht // 2]
        else:
            self._pad = [pad_wd // 2, pad_wd - pad_wd // 2, 0, pad_ht]

    def pad(self, *inputs):
        return [F.pad(x, self._pad, mode="replicate") for x in inputs]

    def unpad(self, x):
        ht, wd = x.shape[-2:]
        c = [self._pad[2], ht - self._pad[3], self._pad[0], wd - self._pad[1]]
        return x[..., c[0] : c[1], c[2] : c[3]]