import torch

from util import datapoints

from ._utils import is_simple_tensor


def uniform_temporal_subsample_video(video: torch.Tensor, num_samples: int) -> torch.Tensor:
    # Reference: https://github.com/facebookresearch/pytorchvideo/blob/a0a131e/pytorchvideo/transforms/functional.py#L19
    t_max = video.shape[-4] - 1
    indices = torch.linspace(0, t_max, num_samples, device=video.device).long()
    return torch.index_select(video, -4, indices)


def uniform_temporal_subsample(inpt: datapoints._VideoTypeJIT, num_samples: int) -> datapoints._VideoTypeJIT:
    if torch.jit.is_scripting() or is_simple_tensor(inpt):
        return uniform_temporal_subsample_video(inpt, num_samples)
    elif isinstance(inpt, datapoints.Video):
        output = uniform_temporal_subsample_video(inpt.as_subclass(torch.Tensor), num_samples)
        return datapoints.Video.wrap_like(inpt, output)
    else:
        raise TypeError(f"Input can either be a plain tensor or a `Video` datapoint, but got {type(inpt)} instead.")
