#!/usr/bin/env python3
# Copyright (c) Meta Platforms, Inc. and affiliates.
# All rights reserved.
#
# This source code is licensed under the BSD-style license found in the
# LICENSE file in the root directory of this source tree.

from dataclasses import dataclass
from typing import NamedTuple, Optional, Tuple, Union

import torch
import torch.nn as nn
from pytorch3d.structures import Pointclouds

from .rasterize_points import rasterize_points


# Class to store the outputs of point rasterization
class PointFragments(NamedTuple):
    idx: torch.Tensor
    zbuf: torch.Tensor
    dists: torch.Tensor


@dataclass
class PointsRasterizationSettings:
    """
    Class to store the point rasterization params with defaults

    Members:
        image_size: Either common height and width or (height, width), in pixels.
        radius: The radius (in NDC units) of each disk to be rasterized.
            This can either be a float in which case the same radius is used
            for each point, or a torch.Tensor of shape (N, P) giving a radius
            per point in the batch.
        points_per_pixel: (int) Number of points to keep track of per pixel.
            We return the nearest points_per_pixel points along the z-axis.
        bin_size: Size of bins to use for coarse-to-fine rasterization. Setting
            bin_size=0 uses naive rasterization; setting bin_size=None attempts
            to set it heuristically based on the shape of the input. This should
            not affect the output, but can affect the speed of the forward pass.
        max_points_per_bin: Only applicable when using coarse-to-fine
            rasterization (bin_size != 0); this is the maximum number of points
            allowed within each bin. This should not affect the output values,
            but can affect the memory usage in the forward pass.
            Setting max_points_per_bin=None attempts to set with a heuristic.
    """

    image_size: Union[int, Tuple[int, int]] = 256
    radius: Union[float, torch.Tensor] = 0.01
    points_per_pixel: int = 8
    bin_size: Optional[int] = None
    max_points_per_bin: Optional[int] = None


class PointsRasterizer(nn.Module):
    """
    This class implements methods for rasterizing a batch of pointclouds.
    """

    def __init__(self, cameras=None, raster_settings=None) -> None:
        """
        cameras: A cameras object which has a  `transform_points` method
                which returns the transformed points after applying the
                world-to-view and view-to-ndc transformations.
            raster_settings: the parameters for rasterization. This should be a
                named tuple.

        All these initial settings can be overridden by passing keyword
        arguments to the forward function.
        """
        super().__init__()
        if raster_settings is None:
            raster_settings = PointsRasterizationSettings()

        self.cameras = cameras
        self.raster_settings = raster_settings

    def transform(self, point_clouds, **kwargs) -> Pointclouds:
        """
        Args:
            point_clouds: a set of point clouds

        Returns:
            points_proj: the points with positions projected
            in NDC space

        NOTE: keeping this as a separate function for readability but it could
        be moved into forward.
        """
        cameras = kwargs.get("cameras", self.cameras)
        if cameras is None:
            msg = "Cameras must be specified either at initialization \
                or in the forward pass of PointsRasterizer"
            raise ValueError(msg)

        pts_world = point_clouds.points_padded()
        # NOTE: Retaining view space z coordinate for now.
        # TODO: Remove this line when the convention for the z coordinate in
        # the rasterizer is decided. i.e. retain z in view space or transform
        # to a different range.
        eps = kwargs.get("eps", None)
        pts_view = cameras.get_world_to_view_transform(**kwargs).transform_points(
            pts_world, eps=eps
        )
        # view to NDC transform
        to_ndc_transform = cameras.get_ndc_camera_transform(**kwargs)
        projection_transform = cameras.get_projection_transform(**kwargs).compose(
            to_ndc_transform
        )
        pts_ndc = projection_transform.transform_points(pts_view, eps=eps)

        pts_ndc[..., 2] = pts_view[..., 2]
        point_clouds = point_clouds.update_padded(pts_ndc)
        return point_clouds

    def to(self, device):
        # Manually move to device cameras as it is not a subclass of nn.Module
        if self.cameras is not None:
            self.cameras = self.cameras.to(device)
        return self

    def forward(self, point_clouds, **kwargs) -> PointFragments:
        """
        Args:
            point_clouds: a set of point clouds with coordinates in world space.
        Returns:
            PointFragments: Rasterization outputs as a named tuple.
        """
        points_proj = self.transform(point_clouds, **kwargs)
        raster_settings = kwargs.get("raster_settings", self.raster_settings)
        idx, zbuf, dists2 = rasterize_points(
            points_proj,
            image_size=raster_settings.image_size,
            radius=raster_settings.radius,
            points_per_pixel=raster_settings.points_per_pixel,
            bin_size=raster_settings.bin_size,
            max_points_per_bin=raster_settings.max_points_per_bin,
        )
        return PointFragments(idx=idx, zbuf=zbuf, dists=dists2)
