# 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.

import math
from math import isqrt
from typing import Literal, Optional
import torch
from einops import rearrange, repeat
from tqdm import tqdm

from ...specs import Gaussians
from ...utils.camera_trj_helpers import (
    interpolate_extrinsics,
    interpolate_intrinsics,
    render_dolly_zoom_path,
    render_stabilization_path,
    render_wander_path,
    render_wobble_inter_path,
)
from ...utils.geometry import affine_inverse, as_homogeneous, get_fov
from ...utils.logger import logger

try:
    from gsplat import rasterization
except ImportError:
    logger.warn(
        "Dependency `gsplat` is required for rendering 3DGS. "
        "Install via: pip install git+https://github.com/nerfstudio-project/"
        "gsplat.git@0b4dddf04cb687367602c01196913cde6a743d70"
    )


def render_3dgs(
    extrinsics: torch.Tensor,  # "batch_views 4 4", w2c
    intrinsics: torch.Tensor,  # "batch_views 3 3", normalized
    image_shape: tuple[int, int],
    gaussian: Gaussians,
    background_color: Optional[torch.Tensor] = None,  # "batch_views 3"
    use_sh: bool = True,
    num_view: int = 1,
    color_mode: Literal["RGB+D", "RGB+ED"] = "RGB+D",
    **kwargs,
) -> tuple[
    torch.Tensor,  # "batch_views 3 height width"
    torch.Tensor,  # "batch_views height width"
]:
    # extract gaussian params
    gaussian_means = gaussian.means
    gaussian_scales = gaussian.scales
    gaussian_quats = gaussian.rotations
    gaussian_opacities = gaussian.opacities
    gaussian_sh_coefficients = gaussian.harmonics
    b, _, _ = extrinsics.shape

    if background_color is None:
        background_color = repeat(torch.tensor([0.0, 0.0, 0.0]), "c -> b c", b=b).to(
            gaussian_sh_coefficients
        )

    if use_sh:
        _, _, _, n = gaussian_sh_coefficients.shape
        degree = isqrt(n) - 1
        shs = rearrange(gaussian_sh_coefficients, "b g xyz n -> b g n xyz").contiguous()
    else:  # use color
        shs = (
            gaussian_sh_coefficients.squeeze(-1).sigmoid().contiguous()
        )  # (b, g, c), normed to (0, 1)

    h, w = image_shape

    fov_x, fov_y = get_fov(intrinsics).unbind(dim=-1)
    tan_fov_x = (0.5 * fov_x).tan()
    tan_fov_y = (0.5 * fov_y).tan()
    focal_length_x = w / (2 * tan_fov_x)
    focal_length_y = h / (2 * tan_fov_y)

    view_matrix = extrinsics.float()

    all_images = []
    all_radii = []
    all_depths = []
    # render view in a batch based, each batch contains one scene
    # assume the Gaussian parameters are originally repeated along the view dim
    batch_scene = b // num_view

    def index_i_gs_attr(full_attr, idx):
        # return rearrange(full_attr, "(b v) ... -> b v ...", v=num_view)[idx, 0]
        return full_attr[idx]

    for i in range(batch_scene):
        K = repeat(
            torch.tensor(
                [
                    [0, 0, w / 2.0],
                    [0, 0, h / 2.0],
                    [0, 0, 1],
                ]
            ),
            "i j -> v i j",
            v=num_view,
        ).to(gaussian_means)
        K[:, 0, 0] = focal_length_x.reshape(batch_scene, num_view)[i]
        K[:, 1, 1] = focal_length_y.reshape(batch_scene, num_view)[i]

        i_means = index_i_gs_attr(gaussian_means, i)  # [N, 3]
        i_scales = index_i_gs_attr(gaussian_scales, i)
        i_quats = index_i_gs_attr(gaussian_quats, i)
        i_opacities = index_i_gs_attr(gaussian_opacities, i)  # [N,]
        i_colors = index_i_gs_attr(shs, i)  # [N, K, 3]
        i_viewmats = rearrange(view_matrix, "(b v) ... -> b v ...", v=num_view)[i]  # [v, 4, 4]
        i_backgrounds = rearrange(background_color, "(b v) ... -> b v ...", v=num_view)[
            i
        ]  # [v, 3]

        render_colors, render_alphas, info = rasterization(
            means=i_means,
            quats=i_quats,  # [N, 4]
            scales=i_scales,  # [N, 3]
            opacities=i_opacities,
            colors=i_colors,
            viewmats=i_viewmats,  # [v, 4, 4]
            Ks=K,  # [v, 3, 3]
            backgrounds=i_backgrounds,
            render_mode=color_mode,
            width=w,
            height=h,
            packed=False,
            sh_degree=degree if use_sh else None,
        )
        depth = render_colors[..., -1].unbind(dim=0)

        image = rearrange(render_colors[..., :3], "v h w c -> v c h w").unbind(dim=0)
        radii = info["radii"].unbind(dim=0)
        try:
            info["means2d"].retain_grad()  # [1, N, 2]
        except Exception:
            pass
        all_images.extend(image)
        all_depths.extend(depth)
        all_radii.extend(radii)

    return torch.stack(all_images), torch.stack(all_depths)


def run_renderer_in_chunk_w_trj_mode(
    gaussians: Gaussians,
    extrinsics: torch.Tensor,  # world2cam, "batch view 4 4" | "batch view 3 4"
    intrinsics: torch.Tensor,  # unnormed intrinsics, "batch view 3 3"
    image_shape: tuple[int, int],
    chunk_size: Optional[int] = 8,
    trj_mode: Literal[
        "original",
        "smooth",
        "interpolate",
        "interpolate_smooth",
        "wander",
        "dolly_zoom",
        "extend",
        "wobble_inter",
    ] = "smooth",
    input_shape: Optional[tuple[int, int]] = None,
    enable_tqdm: Optional[bool] = False,
    **kwargs,
) -> tuple[
    torch.Tensor,  # color, "batch view 3 height width"
    torch.Tensor,  # depth, "batch view height width"
]:
    cam2world = affine_inverse(as_homogeneous(extrinsics))
    if input_shape is not None:
        in_h, in_w = input_shape
    else:
        in_h, in_w = image_shape
    intr_normed = intrinsics.clone().detach()
    intr_normed[..., 0, :] /= in_w
    intr_normed[..., 1, :] /= in_h
    if extrinsics.shape[1] <= 1:
        assert trj_mode in [
            "wander",
            "dolly_zoom",
        ], "Please set trj_mode to 'wander' or 'dolly_zoom' when n_views=1"

    def _smooth_trj_fn_batch(raw_c2ws, k_size=50):
        try:
            smooth_c2ws = torch.stack(
                [render_stabilization_path(c2w_i, k_size) for c2w_i in raw_c2ws],
                dim=0,
            )
        except Exception as e:
            print(f"[DEBUG] Path smoothing failed with error: {e}.")
            smooth_c2ws = raw_c2ws
        return smooth_c2ws

    # get rendered trj
    if trj_mode == "original":
        tgt_c2w = cam2world
        tgt_intr = intr_normed
    elif trj_mode == "smooth":
        tgt_c2w = _smooth_trj_fn_batch(cam2world)
        tgt_intr = intr_normed
    elif trj_mode in ["interpolate", "interpolate_smooth", "extend"]:
        inter_len = 8
        total_len = (cam2world.shape[1] - 1) * inter_len
        if total_len > 24 * 18:  # no more than 18s
            inter_len = max(1, 24 * 10 // (cam2world.shape[1] - 1))
        if total_len < 24 * 2:  # no less than 2s
            inter_len = max(1, 24 * 2 // (cam2world.shape[1] - 1))

        if inter_len > 2:
            t = torch.linspace(0, 1, inter_len, dtype=torch.float32, device=cam2world.device)
            t = (torch.cos(torch.pi * (t + 1)) + 1) / 2
            tgt_c2w_b = []
            tgt_intr_b = []
            for b_idx in range(cam2world.shape[0]):
                tgt_c2w = []
                tgt_intr = []
                for cur_idx in range(cam2world.shape[1] - 1):
                    tgt_c2w.append(
                        interpolate_extrinsics(
                            cam2world[b_idx, cur_idx], cam2world[b_idx, cur_idx + 1], t
                        )[(0 if cur_idx == 0 else 1) :]
                    )
                    tgt_intr.append(
                        interpolate_intrinsics(
                            intr_normed[b_idx, cur_idx], intr_normed[b_idx, cur_idx + 1], t
                        )[(0 if cur_idx == 0 else 1) :]
                    )
                tgt_c2w_b.append(torch.cat(tgt_c2w))
                tgt_intr_b.append(torch.cat(tgt_intr))
            tgt_c2w = torch.stack(tgt_c2w_b)  # b v 4 4
            tgt_intr = torch.stack(tgt_intr_b)  # b v 3 3
        else:
            tgt_c2w = cam2world
            tgt_intr = intr_normed
        if trj_mode in ["interpolate_smooth", "extend"]:
            tgt_c2w = _smooth_trj_fn_batch(tgt_c2w)
        if trj_mode == "extend":
            # apply dolly_zoom and wander in the middle frame
            assert cam2world.shape[0] == 1, "extend only supports for batch_size=1 currently."
            mid_idx = tgt_c2w.shape[1] // 2
            c2w_wd, intr_wd = render_wander_path(
                tgt_c2w[0, mid_idx],
                tgt_intr[0, mid_idx],
                h=in_h,
                w=in_w,
                num_frames=max(36, min(60, mid_idx // 2)),
                max_disp=24.0,
            )
            c2w_dz, intr_dz = render_dolly_zoom_path(
                tgt_c2w[0, mid_idx],
                tgt_intr[0, mid_idx],
                h=in_h,
                w=in_w,
                num_frames=max(36, min(60, mid_idx // 2)),
            )
            tgt_c2w = torch.cat(
                [
                    tgt_c2w[:, :mid_idx],
                    c2w_wd.unsqueeze(0),
                    c2w_dz.unsqueeze(0),
                    tgt_c2w[:, mid_idx:],
                ],
                dim=1,
            )
            tgt_intr = torch.cat(
                [
                    tgt_intr[:, :mid_idx],
                    intr_wd.unsqueeze(0),
                    intr_dz.unsqueeze(0),
                    tgt_intr[:, mid_idx:],
                ],
                dim=1,
            )
    elif trj_mode in ["wander", "dolly_zoom"]:
        if trj_mode == "wander":
            render_fn = render_wander_path
            extra_kwargs = {"max_disp": 24.0}
        else:
            render_fn = render_dolly_zoom_path
            extra_kwargs = {"D_focus": 30.0, "max_disp": 2.0}
        tgt_c2w = []
        tgt_intr = []
        for b_idx in range(cam2world.shape[0]):
            c2w_i, intr_i = render_fn(
                cam2world[b_idx, 0], intr_normed[b_idx, 0], h=in_h, w=in_w, **extra_kwargs
            )
            tgt_c2w.append(c2w_i)
            tgt_intr.append(intr_i)
        tgt_c2w = torch.stack(tgt_c2w)
        tgt_intr = torch.stack(tgt_intr)
    elif trj_mode == "wobble_inter":
        tgt_c2w, tgt_intr = render_wobble_inter_path(
            cam2world=cam2world,
            intr_normed=intr_normed,
            inter_len=10,
            n_skip=3,
        )
    else:
        raise Exception(f"trj mode [{trj_mode}] is not implemented.")

    _, v = tgt_c2w.shape[:2]
    tgt_extr = affine_inverse(tgt_c2w)
    if chunk_size is None:
        chunk_size = v
    chunk_size = min(v, chunk_size)
    all_colors = []
    all_depths = []
    for chunk_idx in tqdm(
        range(math.ceil(v / chunk_size)),
        desc="Rendering novel views",
        disable=(not enable_tqdm),
        leave=False,
    ):
        s = int(chunk_idx * chunk_size)
        e = int((chunk_idx + 1) * chunk_size)
        cur_n_view = tgt_extr[:, s:e].shape[1]
        color, depth = render_3dgs(
            extrinsics=rearrange(tgt_extr[:, s:e], "b v ... -> (b v) ..."),  # w2c
            intrinsics=rearrange(tgt_intr[:, s:e], "b v ... -> (b v) ..."),  # normed
            image_shape=image_shape,
            gaussian=gaussians,
            num_view=cur_n_view,
            **kwargs,
        )
        all_colors.append(rearrange(color, "(b v) ... -> b v ...", v=cur_n_view))
        all_depths.append(rearrange(depth, "(b v) ... -> b v ...", v=cur_n_view))
    all_colors = torch.cat(all_colors, dim=1)
    all_depths = torch.cat(all_depths, dim=1)

    return all_colors, all_depths
