# Copyright (c) 2025 ByteDance Ltd. and/or its affiliates
#
# 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.

from typing import Tuple, Union
import torch
import torch.nn as nn
import torch.nn.functional as F

# -----------------------------------------------------------------------------
# Activation functions
# -----------------------------------------------------------------------------


def activate_head_gs(out, activation="norm_exp", conf_activation="expp1", conf_dim=None):
    """
    Process network output to extract GS params and density values.
    Density could be view-dependent as SH coefficient


    Args:
        out: Network output tensor (B, C, H, W)
        activation: Activation type for 3D points
        conf_activation: Activation type for confidence values

    Returns:
        Tuple of (3D points tensor, confidence tensor)
    """
    # Move channels from last dim to the 4th dimension => (B, H, W, C)
    fmap = out.permute(0, 2, 3, 1)  # B,H,W,C expected

    # Split into xyz (first C-1 channels) and confidence (last channel)
    conf_dim = 1 if conf_dim is None else conf_dim
    xyz = fmap[:, :, :, :-conf_dim]
    conf = fmap[:, :, :, -1] if conf_dim == 1 else fmap[:, :, :, -conf_dim:]

    if activation == "norm_exp":
        d = xyz.norm(dim=-1, keepdim=True).clamp(min=1e-8)
        xyz_normed = xyz / d
        pts3d = xyz_normed * torch.expm1(d)
    elif activation == "norm":
        pts3d = xyz / xyz.norm(dim=-1, keepdim=True)
    elif activation == "exp":
        pts3d = torch.exp(xyz)
    elif activation == "relu":
        pts3d = F.relu(xyz)
    elif activation == "sigmoid":
        pts3d = torch.sigmoid(xyz)
    elif activation == "linear":
        pts3d = xyz
    else:
        raise ValueError(f"Unknown activation: {activation}")

    if conf_activation == "expp1":
        conf_out = 1 + conf.exp()
    elif conf_activation == "expp0":
        conf_out = conf.exp()
    elif conf_activation == "sigmoid":
        conf_out = torch.sigmoid(conf)
    elif conf_activation == "linear":
        conf_out = conf
    else:
        raise ValueError(f"Unknown conf_activation: {conf_activation}")

    return pts3d, conf_out


# -----------------------------------------------------------------------------
# Other utilities
# -----------------------------------------------------------------------------


class Permute(nn.Module):
    """nn.Module wrapper around Tensor.permute for cleaner nn.Sequential usage."""

    dims: Tuple[int, ...]

    def __init__(self, dims: Tuple[int, ...]) -> None:
        super().__init__()
        self.dims = dims

    def forward(self, x: torch.Tensor) -> torch.Tensor:  # type: ignore[override]
        return x.permute(*self.dims)


def position_grid_to_embed(
    pos_grid: torch.Tensor, embed_dim: int, omega_0: float = 100
) -> torch.Tensor:
    """
    Convert 2D position grid (HxWx2) to sinusoidal embeddings (HxWxC)

    Args:
        pos_grid: Tensor of shape (H, W, 2) containing 2D coordinates
        embed_dim: Output channel dimension for embeddings

    Returns:
        Tensor of shape (H, W, embed_dim) with positional embeddings
    """
    H, W, grid_dim = pos_grid.shape
    assert grid_dim == 2
    pos_flat = pos_grid.reshape(-1, grid_dim)  # Flatten to (H*W, 2)

    # Process x and y coordinates separately
    emb_x = make_sincos_pos_embed(embed_dim // 2, pos_flat[:, 0], omega_0=omega_0)  # [1, H*W, D/2]
    emb_y = make_sincos_pos_embed(embed_dim // 2, pos_flat[:, 1], omega_0=omega_0)  # [1, H*W, D/2]

    # Combine and reshape
    emb = torch.cat([emb_x, emb_y], dim=-1)  # [1, H*W, D]

    return emb.view(H, W, embed_dim)  # [H, W, D]


def make_sincos_pos_embed(embed_dim: int, pos: torch.Tensor, omega_0: float = 100) -> torch.Tensor:
    """
    This function generates a 1D positional embedding from a given grid using sine and cosine functions. # noqa

    Args:
    - embed_dim: The embedding dimension.
    - pos: The position to generate the embedding from.

    Returns:
    - emb: The generated 1D positional embedding.
    """
    assert embed_dim % 2 == 0
    omega = torch.arange(embed_dim // 2, dtype=torch.double, device=pos.device)
    omega /= embed_dim / 2.0
    omega = 1.0 / omega_0**omega  # (D/2,)

    pos = pos.reshape(-1)  # (M,)
    out = torch.einsum("m,d->md", pos, omega)  # (M, D/2), outer product

    emb_sin = torch.sin(out)  # (M, D/2)
    emb_cos = torch.cos(out)  # (M, D/2)

    emb = torch.cat([emb_sin, emb_cos], dim=1)  # (M, D)
    return emb.float()


# Inspired by https://github.com/microsoft/moge


def create_uv_grid(
    width: int,
    height: int,
    aspect_ratio: float = None,
    dtype: torch.dtype = None,
    device: torch.device = None,
) -> torch.Tensor:
    """
    Create a normalized UV grid of shape (width, height, 2).

    The grid spans horizontally and vertically according to an aspect ratio,
    ensuring the top-left corner is at (-x_span, -y_span) and the bottom-right
    corner is at (x_span, y_span), normalized by the diagonal of the plane.

    Args:
        width (int): Number of points horizontally.
        height (int): Number of points vertically.
        aspect_ratio (float, optional): Width-to-height ratio. Defaults to width/height.
        dtype (torch.dtype, optional): Data type of the resulting tensor.
        device (torch.device, optional): Device on which the tensor is created.

    Returns:
        torch.Tensor: A (width, height, 2) tensor of UV coordinates.
    """
    # Derive aspect ratio if not explicitly provided
    if aspect_ratio is None:
        aspect_ratio = float(width) / float(height)

    # Compute normalized spans for X and Y
    diag_factor = (aspect_ratio**2 + 1.0) ** 0.5
    span_x = aspect_ratio / diag_factor
    span_y = 1.0 / diag_factor

    # Establish the linspace boundaries
    left_x = -span_x * (width - 1) / width
    right_x = span_x * (width - 1) / width
    top_y = -span_y * (height - 1) / height
    bottom_y = span_y * (height - 1) / height

    # Generate 1D coordinates
    x_coords = torch.linspace(left_x, right_x, steps=width, dtype=dtype, device=device)
    y_coords = torch.linspace(top_y, bottom_y, steps=height, dtype=dtype, device=device)

    # Create 2D meshgrid (width x height) and stack into UV
    uu, vv = torch.meshgrid(x_coords, y_coords, indexing="xy")
    uv_grid = torch.stack((uu, vv), dim=-1)

    return uv_grid


# -----------------------------------------------------------------------------
# Interpolation (safe interpolation, avoid INT_MAX overflow)
# -----------------------------------------------------------------------------
def custom_interpolate(
    x: torch.Tensor,
    size: Union[Tuple[int, int], None] = None,
    scale_factor: Union[float, None] = None,
    mode: str = "bilinear",
    align_corners: bool = True,
) -> torch.Tensor:
    """
    Safe interpolation implementation to avoid INT_MAX overflow in torch.nn.functional.interpolate.
    """
    if size is None:
        assert scale_factor is not None, "Either size or scale_factor must be provided."
        size = (int(x.shape[-2] * scale_factor), int(x.shape[-1] * scale_factor))

    INT_MAX = 1610612736
    total = size[0] * size[1] * x.shape[0] * x.shape[1]

    if total > INT_MAX:
        chunks = torch.chunk(x, chunks=(total // INT_MAX) + 1, dim=0)
        outs = [
            nn.functional.interpolate(c, size=size, mode=mode, align_corners=align_corners)
            for c in chunks
        ]
        return torch.cat(outs, dim=0).contiguous()

    return nn.functional.interpolate(x, size=size, mode=mode, align_corners=align_corners)
