# Shifts src_tf dim to dest dim
# i.e. shift_dim(x, 1, -1) would be (b, c, t, h, w) -> (b, t, h, w, c)
def shift_dim(x, src_dim=-1, dest_dim=-1, make_contiguous=True):
    n_dims = len(x.shape)
    if src_dim < 0:
        src_dim = n_dims + src_dim
    if dest_dim < 0:
        dest_dim = n_dims + dest_dim

    assert 0 <= src_dim < n_dims and 0 <= dest_dim < n_dims

    dims = list(range(n_dims))
    del dims[src_dim]

    permutation = []
    ctr = 0
    for i in range(n_dims):
        if i == dest_dim:
            permutation.append(src_dim)
        else:
            permutation.append(dims[ctr])
            ctr += 1
    x = x.permute(permutation)
    if make_contiguous:
        x = x.contiguous()
    return x

# reshapes tensor start from dim i (inclusive)
# to dim j (exclusive) to the desired shape
# e.g. if x.shape = (b, thw, c) then
# view_range(x, 1, 2, (t, h, w)) returns
# x of shape (b, t, h, w, c)
def view_range(x, i, j, shape):
    shape = tuple(shape)

    n_dims = len(x.shape)
    if i < 0:
        i = n_dims + i

    if j is None:
        j = n_dims
    elif j < 0:
        j = n_dims + j

    assert 0 <= i < j <= n_dims

    x_shape = x.shape
    target_shape = x_shape[:i] + shape + x_shape[j:]
    return x.view(target_shape)

    
def tensor_slice(x, begin, size):
    assert all([b >= 0 for b in begin])
    size = [l - b if s == -1 else s
            for s, b, l in zip(size, begin, x.shape)]
    assert all([s >= 0 for s in size])

    slices = [slice(b, b + s) for b, s in zip(begin, size)]
    return x[slices]


import math
import numpy as np
import skvideo.io
def save_video_grid(video, fname, nrow=None):
    b, c, t, h, w = video.shape
    video = video.permute(0, 2, 3, 4, 1)
    video = (video.cpu().numpy() * 255).astype('uint8')

    if nrow is None:
        nrow = math.ceil(math.sqrt(b))
    ncol = math.ceil(b / nrow)
    padding = 1
    video_grid = np.zeros((t, (padding + h) * nrow + padding,
                           (padding + w) * ncol + padding, c), dtype='uint8')
    for i in range(b):
        r = i // ncol
        c = i % ncol

        start_r = (padding + h) * r
        start_c = (padding + w) * c
        video_grid[:, start_r:start_r + h, start_c:start_c + w] = video[i]

    skvideo.io.vwrite(fname, video_grid, inputdict={'-r': '5'})
    print('saved videos to', fname)


