# Copyright 2023 UC Berkeley Team and The HuggingFace 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.

# DISCLAIMER: This file is strongly influenced by https://github.com/ermongroup/ddim

from __future__ import annotations

import math
from dataclasses import dataclass
from typing import List, Optional, Tuple, Union

import numpy as np
from numpy import ndarray
import torch

from diffusers.configuration_utils import ConfigMixin, register_to_config
from diffusers.utils import BaseOutput
from diffusers.utils.torch_utils import randn_tensor
from diffusers.schedulers.scheduling_utils import (
    KarrasDiffusionSchedulers,
    SchedulerMixin,
)
from diffusers.schedulers.scheduling_ddpm import (
    DDPMSchedulerOutput,
    betas_for_alpha_bar,
    DDPMScheduler as DiffusersDDPMScheduler,
)
from ..utils.noise_util import video_fusion_noise


class DDPMScheduler(DiffusersDDPMScheduler):
    """
    `DDPMScheduler` explores the connections between denoising score matching and Langevin dynamics sampling.

    This model inherits from [`SchedulerMixin`] and [`ConfigMixin`]. Check the superclass documentation for the generic
    methods the library implements for all schedulers such as loading and saving.

    Args:
        num_train_timesteps (`int`, defaults to 1000):
            The number of diffusion steps to train the model.
        beta_start (`float`, defaults to 0.0001):
            The starting `beta` value of inference.
        beta_end (`float`, defaults to 0.02):
            The final `beta` value.
        beta_schedule (`str`, defaults to `"linear"`):
            The beta schedule, a mapping from a beta range to a sequence of betas for stepping the model. Choose from
            `linear`, `scaled_linear`, or `squaredcos_cap_v2`.
        variance_type (`str`, defaults to `"fixed_small"`):
            Clip the variance when adding noise to the denoised sample. Choose from `fixed_small`, `fixed_small_log`,
            `fixed_large`, `fixed_large_log`, `learned` or `learned_range`.
        clip_sample (`bool`, defaults to `True`):
            Clip the predicted sample for numerical stability.
        clip_sample_range (`float`, defaults to 1.0):
            The maximum magnitude for sample clipping. Valid only when `clip_sample=True`.
        prediction_type (`str`, defaults to `epsilon`, *optional*):
            Prediction type of the scheduler function; can be `epsilon` (predicts the noise of the diffusion process),
            `sample` (directly predicts the noisy sample`) or `v_prediction` (see section 2.4 of [Imagen
            Video](https://imagen.research.google/video/paper.pdf) paper).
        thresholding (`bool`, defaults to `False`):
            Whether to use the "dynamic thresholding" method. This is unsuitable for latent-space diffusion models such
            as Stable Diffusion.
        dynamic_thresholding_ratio (`float`, defaults to 0.995):
            The ratio for the dynamic thresholding method. Valid only when `thresholding=True`.
        sample_max_value (`float`, defaults to 1.0):
            The threshold value for dynamic thresholding. Valid only when `thresholding=True`.
        timestep_spacing (`str`, defaults to `"leading"`):
            The way the timesteps should be scaled. Refer to Table 2 of the [Common Diffusion Noise Schedules and
            Sample Steps are Flawed](https://huggingface.co/papers/2305.08891) for more information.
        steps_offset (`int`, defaults to 0):
            An offset added to the inference steps. You can use a combination of `offset=1` and
            `set_alpha_to_one=False` to make the last step use step 0 for the previous alpha product like in Stable
            Diffusion.
    """

    _compatibles = [e.name for e in KarrasDiffusionSchedulers]
    order = 1

    @register_to_config
    def __init__(
        self,
        num_train_timesteps: int = 1000,
        beta_start: float = 0.0001,
        beta_end: float = 0.02,
        beta_schedule: str = "linear",
        trained_betas: ndarray | List[float] | None = None,
        variance_type: str = "fixed_small",
        clip_sample: bool = True,
        prediction_type: str = "epsilon",
        thresholding: bool = False,
        dynamic_thresholding_ratio: float = 0.995,
        clip_sample_range: float = 1,
        sample_max_value: float = 1,
        timestep_spacing: str = "leading",
        steps_offset: int = 0,
    ):
        super().__init__(
            num_train_timesteps,
            beta_start,
            beta_end,
            beta_schedule,
            trained_betas,
            variance_type,
            clip_sample,
            prediction_type,
            thresholding,
            dynamic_thresholding_ratio,
            clip_sample_range,
            sample_max_value,
            timestep_spacing,
            steps_offset,
        )

    def step(
        self,
        model_output: torch.FloatTensor,
        timestep: int,
        sample: torch.FloatTensor,
        generator=None,
        return_dict: bool = True,
        w_ind_noise: float = 0.5,
        noise_type: str = "random",
    ) -> Union[DDPMSchedulerOutput, Tuple]:
        """
        Predict the sample from the previous timestep by reversing the SDE. This function propagates the diffusion
        process from the learned model outputs (most often the predicted noise).

        Args:
            model_output (`torch.FloatTensor`):
                The direct output from learned diffusion model.
            timestep (`float`):
                The current discrete timestep in the diffusion chain.
            sample (`torch.FloatTensor`):
                A current instance of a sample created by the diffusion process.
            generator (`torch.Generator`, *optional*):
                A random number generator.
            return_dict (`bool`, *optional*, defaults to `True`):
                Whether or not to return a [`~schedulers.scheduling_ddpm.DDPMSchedulerOutput`] or `tuple`.

        Returns:
            [`~schedulers.scheduling_ddpm.DDPMSchedulerOutput`] or `tuple`:
                If return_dict is `True`, [`~schedulers.scheduling_ddpm.DDPMSchedulerOutput`] is returned, otherwise a
                tuple is returned where the first element is the sample tensor.

        """
        t = timestep

        prev_t = self.previous_timestep(t)

        if model_output.shape[1] == sample.shape[1] * 2 and self.variance_type in [
            "learned",
            "learned_range",
        ]:
            model_output, predicted_variance = torch.split(
                model_output, sample.shape[1], dim=1
            )
        else:
            predicted_variance = None

        # 1. compute alphas, betas
        alpha_prod_t = self.alphas_cumprod[t]
        alpha_prod_t_prev = self.alphas_cumprod[prev_t] if prev_t >= 0 else self.one
        beta_prod_t = 1 - alpha_prod_t
        beta_prod_t_prev = 1 - alpha_prod_t_prev
        current_alpha_t = alpha_prod_t / alpha_prod_t_prev
        current_beta_t = 1 - current_alpha_t

        # 2. compute predicted original sample from predicted noise also called
        # "predicted x_0" of formula (15) from https://arxiv.org/pdf/2006.11239.pdf
        if self.config.prediction_type == "epsilon":
            pred_original_sample = (
                sample - beta_prod_t ** (0.5) * model_output
            ) / alpha_prod_t ** (0.5)
        elif self.config.prediction_type == "sample":
            pred_original_sample = model_output
        elif self.config.prediction_type == "v_prediction":
            pred_original_sample = (alpha_prod_t**0.5) * sample - (
                beta_prod_t**0.5
            ) * model_output
        else:
            raise ValueError(
                f"prediction_type given as {self.config.prediction_type} must be one of `epsilon`, `sample` or"
                " `v_prediction`  for the DDPMScheduler."
            )

        # 3. Clip or threshold "predicted x_0"
        if self.config.thresholding:
            pred_original_sample = self._threshold_sample(pred_original_sample)
        elif self.config.clip_sample:
            pred_original_sample = pred_original_sample.clamp(
                -self.config.clip_sample_range, self.config.clip_sample_range
            )

        # 4. Compute coefficients for pred_original_sample x_0 and current sample x_t
        # See formula (7) from https://arxiv.org/pdf/2006.11239.pdf
        pred_original_sample_coeff = (
            alpha_prod_t_prev ** (0.5) * current_beta_t
        ) / beta_prod_t
        current_sample_coeff = current_alpha_t ** (0.5) * beta_prod_t_prev / beta_prod_t

        # 5. Compute predicted previous sample µ_t
        # See formula (7) from https://arxiv.org/pdf/2006.11239.pdf
        pred_prev_sample = (
            pred_original_sample_coeff * pred_original_sample
            + current_sample_coeff * sample
        )

        # 6. Add noise
        variance = 0
        if t > 0:
            device = model_output.device
            # if variance_noise is None:
            #     variance_noise = randn_tensor(
            #         model_output.shape,
            #         generator=generator,
            #         device=model_output.device,
            #         dtype=model_output.dtype,
            #     )
            device = model_output.device

            if noise_type == "random":
                variance_noise = randn_tensor(
                    model_output.shape,
                    dtype=model_output.dtype,
                    device=device,
                    generator=generator,
                )
            elif noise_type == "video_fusion":
                variance_noise = video_fusion_noise(
                    model_output, w_ind_noise=w_ind_noise, generator=generator
                )
            if self.variance_type == "fixed_small_log":
                variance = (
                    self._get_variance(t, predicted_variance=predicted_variance)
                    * variance_noise
                )
            elif self.variance_type == "learned_range":
                variance = self._get_variance(t, predicted_variance=predicted_variance)
                variance = torch.exp(0.5 * variance) * variance_noise
            else:
                variance = (
                    self._get_variance(t, predicted_variance=predicted_variance) ** 0.5
                ) * variance_noise

        pred_prev_sample = pred_prev_sample + variance

        if not return_dict:
            return (pred_prev_sample,)

        return DDPMSchedulerOutput(
            prev_sample=pred_prev_sample, pred_original_sample=pred_original_sample
        )