# Copyright 2025 Lightricks and The HuggingFace Team. 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 math

import torch
import torch.nn.functional as F

from ...configuration_utils import ConfigMixin, register_to_config
from ...models.modeling_utils import ModelMixin


RATIONAL_RESAMPLER_SCALE_MAPPING = {
    0.75: (3, 4),
    1.5: (3, 2),
    2.0: (2, 1),
    4.0: (4, 1),
}


# Copied from diffusers.pipelines.ltx.modeling_latent_upsampler.ResBlock
class ResBlock(torch.nn.Module):
    def __init__(self, channels: int, mid_channels: int | None = None, dims: int = 3):
        super().__init__()
        if mid_channels is None:
            mid_channels = channels

        Conv = torch.nn.Conv2d if dims == 2 else torch.nn.Conv3d

        self.conv1 = Conv(channels, mid_channels, kernel_size=3, padding=1)
        self.norm1 = torch.nn.GroupNorm(32, mid_channels)
        self.conv2 = Conv(mid_channels, channels, kernel_size=3, padding=1)
        self.norm2 = torch.nn.GroupNorm(32, channels)
        self.activation = torch.nn.SiLU()

    def forward(self, hidden_states: torch.Tensor) -> torch.Tensor:
        residual = hidden_states
        hidden_states = self.conv1(hidden_states)
        hidden_states = self.norm1(hidden_states)
        hidden_states = self.activation(hidden_states)
        hidden_states = self.conv2(hidden_states)
        hidden_states = self.norm2(hidden_states)
        hidden_states = self.activation(hidden_states + residual)
        return hidden_states


# Copied from diffusers.pipelines.ltx.modeling_latent_upsampler.PixelShuffleND
class PixelShuffleND(torch.nn.Module):
    def __init__(self, dims, upscale_factors=(2, 2, 2)):
        super().__init__()

        self.dims = dims
        self.upscale_factors = upscale_factors

        if dims not in [1, 2, 3]:
            raise ValueError("dims must be 1, 2, or 3")

    def forward(self, x):
        if self.dims == 3:
            # spatiotemporal: b (c p1 p2 p3) d h w -> b c (d p1) (h p2) (w p3)
            return (
                x.unflatten(1, (-1, *self.upscale_factors[:3]))
                .permute(0, 1, 5, 2, 6, 3, 7, 4)
                .flatten(6, 7)
                .flatten(4, 5)
                .flatten(2, 3)
            )
        elif self.dims == 2:
            # spatial: b (c p1 p2) h w -> b c (h p1) (w p2)
            return (
                x.unflatten(1, (-1, *self.upscale_factors[:2])).permute(0, 1, 4, 2, 5, 3).flatten(4, 5).flatten(2, 3)
            )
        elif self.dims == 1:
            # temporal: b (c p1) f h w -> b c (f p1) h w
            return x.unflatten(1, (-1, *self.upscale_factors[:1])).permute(0, 1, 3, 2, 4, 5).flatten(2, 3)


class BlurDownsample(torch.nn.Module):
    """
    Anti-aliased spatial downsampling by integer stride using a fixed separable binomial kernel. Applies only on H,W.
    Works for dims=2 or dims=3 (per-frame).
    """

    def __init__(self, dims: int, stride: int, kernel_size: int = 5) -> None:
        super().__init__()

        if dims not in (2, 3):
            raise ValueError(f"`dims` must be either 2 or 3 but is {dims}")
        if kernel_size < 3 or kernel_size % 2 != 1:
            raise ValueError(f"`kernel_size` must be an odd number >= 3 but is {kernel_size}")

        self.dims = dims
        self.stride = stride
        self.kernel_size = kernel_size

        # 5x5 separable binomial kernel using binomial coefficients [1, 4, 6, 4, 1] from
        # the 4th row of Pascal's triangle. This kernel is used for anti-aliasing and
        # provides a smooth approximation of a Gaussian filter (often called a "binomial filter").
        # The 2D kernel is constructed as the outer product and normalized.
        k = torch.tensor([math.comb(kernel_size - 1, k) for k in range(kernel_size)])
        k2d = k[:, None] @ k[None, :]
        k2d = (k2d / k2d.sum()).float()  # shape (kernel_size, kernel_size)
        self.register_buffer("kernel", k2d[None, None, :, :])  # (1, 1, kernel_size, kernel_size)

    def forward(self, x: torch.Tensor) -> torch.Tensor:
        if self.stride == 1:
            return x

        if self.dims == 2:
            c = x.shape[1]
            weight = self.kernel.expand(c, 1, self.kernel_size, self.kernel_size)  # depthwise
            x = F.conv2d(x, weight=weight, bias=None, stride=self.stride, padding=self.kernel_size // 2, groups=c)
        else:
            # dims == 3: apply per-frame on H,W
            b, c, f, _, _ = x.shape
            x = x.transpose(1, 2).flatten(0, 1)  # [B, C, F, H, W] --> [B * F, C, H, W]

            weight = self.kernel.expand(c, 1, self.kernel_size, self.kernel_size)  # depthwise
            x = F.conv2d(x, weight=weight, bias=None, stride=self.stride, padding=self.kernel_size // 2, groups=c)

            h2, w2 = x.shape[-2:]
            x = x.unflatten(0, (b, f)).reshape(b, -1, f, h2, w2)  # [B * F, C, H, W] --> [B, C, F, H, W]
        return x


class SpatialRationalResampler(torch.nn.Module):
    """
    Scales by the spatial size of the input by a rational number `scale`. For example, `scale = 0.75` will downsample
    by a factor of 3 / 4, while `scale = 1.5` will upsample by a factor of 3 / 2. This works by first upsampling the
    input by the (integer) numerator of `scale`, and then performing a blur + stride anti-aliased downsample by the
    (integer) denominator.
    """

    def __init__(self, mid_channels: int = 1024, scale: float = 2.0):
        super().__init__()
        self.scale = float(scale)
        num_denom = RATIONAL_RESAMPLER_SCALE_MAPPING.get(scale, None)
        if num_denom is None:
            raise ValueError(
                f"The supplied `scale` {scale} is not supported; supported scales are {list(RATIONAL_RESAMPLER_SCALE_MAPPING.keys())}"
            )
        self.num, self.den = num_denom

        self.conv = torch.nn.Conv2d(mid_channels, (self.num**2) * mid_channels, kernel_size=3, padding=1)
        self.pixel_shuffle = PixelShuffleND(2, upscale_factors=(self.num, self.num))
        self.blur_down = BlurDownsample(dims=2, stride=self.den)

    def forward(self, x: torch.Tensor) -> torch.Tensor:
        # Expected x shape: [B * F, C, H, W]
        # b, _, f, h, w = x.shape
        # x = x.transpose(1, 2).flatten(0, 1)  # [B, C, F, H, W] --> [B * F, C, H, W]
        x = self.conv(x)
        x = self.pixel_shuffle(x)
        x = self.blur_down(x)
        # x = x.unflatten(0, (b, f)).reshape(b, -1, f, h, w)  # [B * F, C, H, W] --> [B, C, F, H, W]
        return x


class LTX2LatentUpsamplerModel(ModelMixin, ConfigMixin):
    """
    Model to spatially upsample VAE latents.

    Args:
        in_channels (`int`, defaults to `128`):
            Number of channels in the input latent
        mid_channels (`int`, defaults to `512`):
            Number of channels in the middle layers
        num_blocks_per_stage (`int`, defaults to `4`):
            Number of ResBlocks to use in each stage (pre/post upsampling)
        dims (`int`, defaults to `3`):
            Number of dimensions for convolutions (2 or 3)
        spatial_upsample (`bool`, defaults to `True`):
            Whether to spatially upsample the latent
        temporal_upsample (`bool`, defaults to `False`):
            Whether to temporally upsample the latent
    """

    @register_to_config
    def __init__(
        self,
        in_channels: int = 128,
        mid_channels: int = 1024,
        num_blocks_per_stage: int = 4,
        dims: int = 3,
        spatial_upsample: bool = True,
        temporal_upsample: bool = False,
        rational_spatial_scale: float = 2.0,
        use_rational_resampler: bool = True,
    ):
        super().__init__()

        self.in_channels = in_channels
        self.mid_channels = mid_channels
        self.num_blocks_per_stage = num_blocks_per_stage
        self.dims = dims
        self.spatial_upsample = spatial_upsample
        self.temporal_upsample = temporal_upsample

        ConvNd = torch.nn.Conv2d if dims == 2 else torch.nn.Conv3d

        self.initial_conv = ConvNd(in_channels, mid_channels, kernel_size=3, padding=1)
        self.initial_norm = torch.nn.GroupNorm(32, mid_channels)
        self.initial_activation = torch.nn.SiLU()

        self.res_blocks = torch.nn.ModuleList([ResBlock(mid_channels, dims=dims) for _ in range(num_blocks_per_stage)])

        if spatial_upsample and temporal_upsample:
            self.upsampler = torch.nn.Sequential(
                torch.nn.Conv3d(mid_channels, 8 * mid_channels, kernel_size=3, padding=1),
                PixelShuffleND(3),
            )
        elif spatial_upsample:
            if use_rational_resampler:
                self.upsampler = SpatialRationalResampler(mid_channels=mid_channels, scale=rational_spatial_scale)
            else:
                self.upsampler = torch.nn.Sequential(
                    torch.nn.Conv2d(mid_channels, 4 * mid_channels, kernel_size=3, padding=1),
                    PixelShuffleND(2),
                )
        elif temporal_upsample:
            self.upsampler = torch.nn.Sequential(
                torch.nn.Conv3d(mid_channels, 2 * mid_channels, kernel_size=3, padding=1),
                PixelShuffleND(1),
            )
        else:
            raise ValueError("Either spatial_upsample or temporal_upsample must be True")

        self.post_upsample_res_blocks = torch.nn.ModuleList(
            [ResBlock(mid_channels, dims=dims) for _ in range(num_blocks_per_stage)]
        )

        self.final_conv = ConvNd(mid_channels, in_channels, kernel_size=3, padding=1)

    def forward(self, hidden_states: torch.Tensor) -> torch.Tensor:
        batch_size, num_channels, num_frames, height, width = hidden_states.shape

        if self.dims == 2:
            hidden_states = hidden_states.permute(0, 2, 1, 3, 4).flatten(0, 1)
            hidden_states = self.initial_conv(hidden_states)
            hidden_states = self.initial_norm(hidden_states)
            hidden_states = self.initial_activation(hidden_states)

            for block in self.res_blocks:
                hidden_states = block(hidden_states)

            hidden_states = self.upsampler(hidden_states)

            for block in self.post_upsample_res_blocks:
                hidden_states = block(hidden_states)

            hidden_states = self.final_conv(hidden_states)
            hidden_states = hidden_states.unflatten(0, (batch_size, -1)).permute(0, 2, 1, 3, 4)
        else:
            hidden_states = self.initial_conv(hidden_states)
            hidden_states = self.initial_norm(hidden_states)
            hidden_states = self.initial_activation(hidden_states)

            for block in self.res_blocks:
                hidden_states = block(hidden_states)

            if self.temporal_upsample:
                hidden_states = self.upsampler(hidden_states)
                hidden_states = hidden_states[:, :, 1:, :, :]
            else:
                hidden_states = hidden_states.permute(0, 2, 1, 3, 4).flatten(0, 1)
                hidden_states = self.upsampler(hidden_states)
                hidden_states = hidden_states.unflatten(0, (batch_size, -1)).permute(0, 2, 1, 3, 4)

            for block in self.post_upsample_res_blocks:
                hidden_states = block(hidden_states)

            hidden_states = self.final_conv(hidden_states)

        return hidden_states
