# Copyright 2022 The Nerfstudio 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.

"""
Collection of renderers

Example:

.. code-block:: python

    field_outputs = field(ray_sampler)
    weights = ray_sampler.get_weights(field_outputs[FieldHeadNames.DENSITY])

    rgb_renderer = RGBRenderer()
    rgb = rgb_renderer(rgb=field_outputs[FieldHeadNames.RGB], weights=weights)

"""
import math
from typing import Optional, Union

import nerfacc
import torch
from torch import nn
from torchtyping import TensorType
from typing_extensions import Literal

from nerfstudio.cameras.rays import RaySamples
from nerfstudio.utils.math import components_from_spherical_harmonics


class RGBRenderer(nn.Module):
    """Standard volumetic rendering.

    Args:
        background_color: Background color as RGB. Uses random colors if None.
    """

    def __init__(self, background_color: Union[Literal["random", "last_sample"], TensorType[3]] = "random") -> None:
        super().__init__()
        self.background_color = background_color

    @classmethod
    def combine_rgb(
        cls,
        rgb: TensorType["bs":..., "num_samples", 3],
        weights: TensorType["bs":..., "num_samples", 1],
        background_color: Union[Literal["random", "last_sample"], TensorType[3]] = "random",
        ray_indices: Optional[TensorType["num_samples"]] = None,
        num_rays: Optional[int] = None,
    ) -> TensorType["bs":..., 3]:
        """Composite samples along ray and render color image

        Args:
            rgb: RGB for each sample
            weights: Weights for each sample
            background_color: Background color as RGB.
            ray_indices: Ray index for each sample, used when samples are packed.
            num_rays: Number of rays, used when samples are packed.

        Returns:
            Outputs rgb values.
        """
        if ray_indices is not None and num_rays is not None:
            # Necessary for packed samples from volumetric ray sampler
            if background_color == "last_sample":
                raise NotImplementedError("Background color 'last_sample' not implemented for packed samples.")
            comp_rgb = nerfacc.accumulate_along_rays(weights, ray_indices, rgb, num_rays)
            accumulated_weight = nerfacc.accumulate_along_rays(weights, ray_indices, None, num_rays)
        else:
            comp_rgb = torch.sum(weights * rgb, dim=-2)
            accumulated_weight = torch.sum(weights, dim=-2)

        if background_color == "last_sample":
            background_color = rgb[..., -1, :]
        if background_color == "random":
            background_color = torch.rand_like(comp_rgb).to(rgb.device)

        assert isinstance(background_color, torch.Tensor)
        comp_rgb = comp_rgb + background_color.to(weights.device) * (1.0 - accumulated_weight)

        return comp_rgb

    def forward(
        self,
        rgb: TensorType["bs":..., "num_samples", 3],
        weights: TensorType["bs":..., "num_samples", 1],
        ray_indices: Optional[TensorType["num_samples"]] = None,
        num_rays: Optional[int] = None,
    ) -> TensorType["bs":..., 3]:
        """Composite samples along ray and render color image

        Args:
            rgb: RGB for each sample
            weights: Weights for each sample
            ray_indices: Ray index for each sample, used when samples are packed.
            num_rays: Number of rays, used when samples are packed.

        Returns:
            Outputs of rgb values.
        """

        rgb = self.combine_rgb(
            rgb, weights, background_color=self.background_color, ray_indices=ray_indices, num_rays=num_rays
        )
        if not self.training:
            torch.clamp_(rgb, min=0.0, max=1.0)
        return rgb


class SHRenderer(nn.Module):
    """Render RGB value from spherical harmonics.

    Args:
        background_color: Background color as RGB. Uses random colors if None
        activation: Output activation.
    """

    def __init__(
        self,
        background_color: Union[Literal["random", "last_sample"], TensorType[3]] = "random",
        activation: Optional[nn.Module] = nn.Sigmoid(),
    ) -> None:
        super().__init__()
        self.background_color = background_color
        self.activation = activation

    def forward(
        self,
        sh: TensorType[..., "num_samples", "coeffs"],
        directions: TensorType[..., "num_samples", 3],
        weights: TensorType[..., "num_samples", 1],
    ) -> TensorType[..., 3]:
        """Composite samples along ray and render color image

        Args:
            sh: Spherical hamonics coefficients for each sample
            directions: Sample direction
            weights: Weights for each sample

        Returns:
            Outputs of rgb values.
        """

        sh = sh.view(*sh.shape[:-1], 3, sh.shape[-1] // 3)

        levels = int(math.sqrt(sh.shape[-1]))
        components = components_from_spherical_harmonics(levels=levels, directions=directions)

        rgb = sh * components[..., None, :]  # [..., num_samples, 3, sh_components]
        rgb = torch.sum(sh, dim=-1) + 0.5  # [..., num_samples, 3]

        if self.activation is not None:
            self.activation(rgb)

        rgb = RGBRenderer.combine_rgb(rgb, weights, background_color=self.background_color)

        return rgb


class AccumulationRenderer(nn.Module):
    """Accumulated value along a ray."""

    @classmethod
    def forward(
        cls,
        weights: TensorType["bs":..., "num_samples", 1],
        ray_indices: Optional[TensorType["num_samples"]] = None,
        num_rays: Optional[int] = None,
    ) -> TensorType["bs":..., 1]:
        """Composite samples along ray and calculate accumulation.

        Args:
            weights: Weights for each sample
            ray_indices: Ray index for each sample, used when samples are packed.
            num_rays: Number of rays, used when samples are packed.

        Returns:
            Outputs of accumulated values.
        """

        if ray_indices is not None and num_rays is not None:
            # Necessary for packed samples from volumetric ray sampler
            accumulation = nerfacc.accumulate_along_rays(weights, ray_indices, None, num_rays)
        else:
            accumulation = torch.sum(weights, dim=-2)
        return accumulation


class DepthRenderer(nn.Module):
    """Calculate depth along ray.

    Depth Method:
        - median: Depth is set to the distance where the accumulated weight reaches 0.5.
        - expected: Expected depth along ray. Same procedure as rendering rgb, but with depth.

    Args:
        method: Depth calculation method.
    """

    def __init__(self, method: Literal["median", "expected"] = "median") -> None:
        super().__init__()
        self.method = method

    def forward(
        self,
        weights: TensorType[..., "num_samples", 1],
        ray_samples: RaySamples,
        ray_indices: Optional[TensorType["num_samples"]] = None,
        num_rays: Optional[int] = None,
    ) -> TensorType[..., 1]:
        """Composite samples along ray and calculate depths.

        Args:
            weights: Weights for each sample.
            ray_samples: Set of ray samples.
            ray_indices: Ray index for each sample, used when samples are packed.
            num_rays: Number of rays, used when samples are packed.

        Returns:
            Outputs of depth values.
        """

        if self.method == "median":
            steps = (ray_samples.frustums.starts + ray_samples.frustums.ends) / 2

            if ray_indices is not None and num_rays is not None:
                raise NotImplementedError("Median depth calculation is not implemented for packed samples.")
            cumulative_weights = torch.cumsum(weights[..., 0], dim=-1)  # [..., num_samples]
            split = torch.ones((*weights.shape[:-2], 1), device=weights.device) * 0.5  # [..., 1]
            median_index = torch.searchsorted(cumulative_weights, split, side="left")  # [..., 1]
            median_index = torch.clamp(median_index, 0, steps.shape[-2] - 1)  # [..., 1]
            median_depth = torch.gather(steps[..., 0], dim=-1, index=median_index)  # [..., 1]
            return median_depth
        if self.method == "expected":
            eps = 1e-10
            steps = (ray_samples.frustums.starts + ray_samples.frustums.ends) / 2

            if ray_indices is not None and num_rays is not None:
                # Necessary for packed samples from volumetric ray sampler
                depth = nerfacc.accumulate_along_rays(weights, ray_indices, steps, num_rays)
                accumulation = nerfacc.accumulate_along_rays(weights, ray_indices, None, num_rays)
                depth = depth / (accumulation + eps)
            else:
                depth = torch.sum(weights * steps, dim=-2) / (torch.sum(weights, -2) + eps)

            depth = torch.clip(depth, steps.min(), steps.max())

            return depth

        raise NotImplementedError(f"Method {self.method} not implemented")


class UncertaintyRenderer(nn.Module):
    """Calculate uncertainty along the ray."""

    @classmethod
    def forward(
        cls, betas: TensorType["bs":..., "num_samples", 1], weights: TensorType["bs":..., "num_samples", 1]
    ) -> TensorType["bs":..., 1]:
        """Calculate uncertainty along the ray.

        Args:
            betas: Uncertainty betas for each sample.
            weights: Weights of each sample.

        Returns:
            Rendering of uncertainty.
        """
        uncertainty = torch.sum(weights * betas, dim=-2)
        return uncertainty


class SemanticRenderer(nn.Module):
    """Calculate semantics along the ray."""

    @classmethod
    def forward(
        cls,
        semantics: TensorType["bs":..., "num_samples", "num_classes"],
        weights: TensorType["bs":..., "num_samples", 1],
    ) -> TensorType["bs":..., "num_classes"]:
        """Calculate semantics along the ray."""
        sem = torch.sum(weights * semantics, dim=-2)
        return sem


class NormalsRenderer(nn.Module):
    """Calculate normals along the ray."""

    @classmethod
    def forward(
        cls,
        normals: TensorType["bs":..., "num_samples", 3],
        weights: TensorType["bs":..., "num_samples", 1],
    ) -> TensorType["bs":..., 3]:
        """Calculate normals along the ray."""
        n = torch.sum(weights * normals, dim=-2)
        return n