import torch
import utils.basic
import torch.nn.functional as F

def bilinear_sampler(input, coords, align_corners=True, padding_mode="border"):
    r"""Sample a tensor using bilinear interpolation

    `bilinear_sampler(input, coords)` samples a tensor :attr:`input` at
    coordinates :attr:`coords` using bilinear interpolation. It is the same
    as `torch.nn.functional.grid_sample()` but with a different coordinate
    convention.

    The input tensor is assumed to be of shape :math:`(B, C, H, W)`, where
    :math:`B` is the batch size, :math:`C` is the number of channels,
    :math:`H` is the height of the image, and :math:`W` is the width of the
    image. The tensor :attr:`coords` of shape :math:`(B, H_o, W_o, 2)` is
    interpreted as an array of 2D point coordinates :math:`(x_i,y_i)`.

    Alternatively, the input tensor can be of size :math:`(B, C, T, H, W)`,
    in which case sample points are triplets :math:`(t_i,x_i,y_i)`. Note
    that in this case the order of the components is slightly different
    from `grid_sample()`, which would expect :math:`(x_i,y_i,t_i)`.

    If `align_corners` is `True`, the coordinate :math:`x` is assumed to be
    in the range :math:`[0,W-1]`, with 0 corresponding to the center of the
    left-most image pixel :math:`W-1` to the center of the right-most
    pixel.

    If `align_corners` is `False`, the coordinate :math:`x` is assumed to
    be in the range :math:`[0,W]`, with 0 corresponding to the left edge of
    the left-most pixel :math:`W` to the right edge of the right-most
    pixel.

    Similar conventions apply to the :math:`y` for the range
    :math:`[0,H-1]` and :math:`[0,H]` and to :math:`t` for the range
    :math:`[0,T-1]` and :math:`[0,T]`.

    Args:
        input (Tensor): batch of input images.
        coords (Tensor): batch of coordinates.
        align_corners (bool, optional): Coordinate convention. Defaults to `True`.
        padding_mode (str, optional): Padding mode. Defaults to `"border"`.

    Returns:
        Tensor: sampled points.
    """

    sizes = input.shape[2:]

    assert len(sizes) in [2, 3]

    if len(sizes) == 3:
        # t x y -> x y t to match dimensions T H W in grid_sample
        coords = coords[..., [1, 2, 0]]

    if align_corners:
        coords = coords * torch.tensor(
            [2 / max(size - 1, 1) for size in reversed(sizes)], device=coords.device
        )
    else:
        coords = coords * torch.tensor(
            [2 / size for size in reversed(sizes)], device=coords.device
        )

    coords -= 1

    return F.grid_sample(
        input, coords, align_corners=align_corners, padding_mode=padding_mode
    )


def sample_features4d(input, coords):
    r"""Sample spatial features

    `sample_features4d(input, coords)` samples the spatial features
    :attr:`input` represented by a 4D tensor :math:`(B, C, H, W)`.

    The field is sampled at coordinates :attr:`coords` using bilinear
    interpolation. :attr:`coords` is assumed to be of shape :math:`(B, R,
    3)`, where each sample has the format :math:`(x_i, y_i)`. This uses the
    same convention as :func:`bilinear_sampler` with `align_corners=True`.

    The output tensor has one feature per point, and has shape :math:`(B,
    R, C)`.

    Args:
        input (Tensor): spatial features.
        coords (Tensor): points.

    Returns:
        Tensor: sampled features.
    """

    B, _, _, _ = input.shape

    # B R 2 -> B R 1 2
    coords = coords.unsqueeze(2)

    # B C R 1
    feats = bilinear_sampler(input, coords)

    return feats.permute(0, 2, 1, 3).view(
        B, -1, feats.shape[1] * feats.shape[3]
    )  # B C R 1 -> B R C


def sample_features5d(input, coords):
    r"""Sample spatio-temporal features

    `sample_features5d(input, coords)` works in the same way as
    :func:`sample_features4d` but for spatio-temporal features and points:
    :attr:`input` is a 5D tensor :math:`(B, T, C, H, W)`, :attr:`coords` is
    a :math:`(B, R1, R2, 3)` tensor of spatio-temporal point :math:`(t_i,
    x_i, y_i)`. The output tensor has shape :math:`(B, R1, R2, C)`.

    Args:
        input (Tensor): spatio-temporal features.
        coords (Tensor): spatio-temporal points.

    Returns:
        Tensor: sampled features.
    """

    B, T, _, _, _ = input.shape

    # B T C H W -> B C T H W
    input = input.permute(0, 2, 1, 3, 4)

    # B R1 R2 3 -> B R1 R2 1 3
    coords = coords.unsqueeze(3)

    # B C R1 R2 1
    feats = bilinear_sampler(input, coords)

    return feats.permute(0, 2, 3, 1, 4).view(
        B, feats.shape[2], feats.shape[3], feats.shape[1]
    )  # B C R1 R2 1 -> B R1 R2 C


def bilinear_sample2d(im, x, y, return_inbounds=False):
    # x and y are each B, N
    # output is B, C, N
    B, C, H, W = list(im.shape)
    N = list(x.shape)[1]

    x = x.float()
    y = y.float()
    H_f = torch.tensor(H, dtype=torch.float32)
    W_f = torch.tensor(W, dtype=torch.float32)
    
    # inbound_mask = (x>-0.5).float()*(y>-0.5).float()*(x<W_f+0.5).float()*(y<H_f+0.5).float()

    max_y = (H_f - 1).int()
    max_x = (W_f - 1).int()

    x0 = torch.floor(x).int()
    x1 = x0 + 1
    y0 = torch.floor(y).int()
    y1 = y0 + 1
    
    x0_clip = torch.clamp(x0, 0, max_x)
    x1_clip = torch.clamp(x1, 0, max_x)
    y0_clip = torch.clamp(y0, 0, max_y)
    y1_clip = torch.clamp(y1, 0, max_y)
    dim2 = W
    dim1 = W * H

    base = torch.arange(0, B, dtype=torch.int64, device=x.device)*dim1
    base = torch.reshape(base, [B, 1]).repeat([1, N])

    base_y0 = base + y0_clip * dim2
    base_y1 = base + y1_clip * dim2

    idx_y0_x0 = base_y0 + x0_clip
    idx_y0_x1 = base_y0 + x1_clip
    idx_y1_x0 = base_y1 + x0_clip
    idx_y1_x1 = base_y1 + x1_clip

    # use the indices to lookup pixels in the flat image
    # im is B x C x H x W
    # move C out to last dim
    im_flat = (im.permute(0, 2, 3, 1)).reshape(B*H*W, C)
    i_y0_x0 = im_flat[idx_y0_x0.long()]
    i_y0_x1 = im_flat[idx_y0_x1.long()]
    i_y1_x0 = im_flat[idx_y1_x0.long()]
    i_y1_x1 = im_flat[idx_y1_x1.long()]

    # Finally calculate interpolated values.
    x0_f = x0.float()
    x1_f = x1.float()
    y0_f = y0.float()
    y1_f = y1.float()

    w_y0_x0 = ((x1_f - x) * (y1_f - y)).unsqueeze(2)
    w_y0_x1 = ((x - x0_f) * (y1_f - y)).unsqueeze(2)
    w_y1_x0 = ((x1_f - x) * (y - y0_f)).unsqueeze(2)
    w_y1_x1 = ((x - x0_f) * (y - y0_f)).unsqueeze(2)

    output = w_y0_x0 * i_y0_x0 + w_y0_x1 * i_y0_x1 + \
             w_y1_x0 * i_y1_x0 + w_y1_x1 * i_y1_x1
    # output is B*N x C
    output = output.view(B, -1, C)
    output = output.permute(0, 2, 1)
    # output is B x C x N

    if return_inbounds:
        x_valid = (x > -0.5).byte() & (x < float(W_f - 0.5)).byte()
        y_valid = (y > -0.5).byte() & (y < float(H_f - 0.5)).byte()
        inbounds = (x_valid & y_valid).float()
        inbounds = inbounds.reshape(B, N) # something seems wrong here for B>1; i'm getting an error here (or downstream if i put -1)
        return output, inbounds

    return output # B, C, N