# Copyright (c) 2023, NVIDIA CORPORATION.  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 torch
from scipy import integrate

from nemo.collections.multimodal.parts.stable_diffusion.utils import append_dims


class NoDynamicThresholding:
    def __call__(self, uncond, cond, scale):
        return uncond + scale * (cond - uncond)


def linear_multistep_coeff(order, t, i, j, epsrel=1e-4):
    if order - 1 > i:
        raise ValueError(f"Order {order} too high for step {i}")

    def fn(tau):
        prod = 1.0
        for k in range(order):
            if j == k:
                continue
            prod *= (tau - t[i - k]) / (t[i - j] - t[i - k])
        return prod

    return integrate.quad(fn, t[i], t[i + 1], epsrel=epsrel)[0]


def get_ancestral_step(sigma_from, sigma_to, eta=1.0):
    if not eta:
        return sigma_to, 0.0
    sigma_up = torch.minimum(
        sigma_to, eta * (sigma_to ** 2 * (sigma_from ** 2 - sigma_to ** 2) / sigma_from ** 2) ** 0.5,
    )
    sigma_down = (sigma_to ** 2 - sigma_up ** 2) ** 0.5
    return sigma_down, sigma_up


def to_d(x, sigma, denoised):
    return (x - denoised) / append_dims(sigma, x.ndim)


def to_neg_log_sigma(sigma):
    return sigma.log().neg()


def to_sigma(neg_log_sigma):
    return neg_log_sigma.neg().exp()