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# Copyright 2024 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.


from typing import List, Optional, Tuple, Union

import torch

from ...utils.torch_utils import randn_tensor
from ..pipeline_utils import DiffusionPipeline, ImagePipelineOutput


class DDPMPipeline(DiffusionPipeline):
    r"""

    Pipeline for image generation.



    This model inherits from [`DiffusionPipeline`]. Check the superclass documentation for the generic methods

    implemented for all pipelines (downloading, saving, running on a particular device, etc.).



    Parameters:

        unet ([`UNet2DModel`]):

            A `UNet2DModel` to denoise the encoded image latents.

        scheduler ([`SchedulerMixin`]):

            A scheduler to be used in combination with `unet` to denoise the encoded image. Can be one of

            [`DDPMScheduler`], or [`DDIMScheduler`].

    """

    model_cpu_offload_seq = "unet"

    def __init__(self, unet, scheduler):
        super().__init__()
        self.register_modules(unet=unet, scheduler=scheduler)

    @torch.no_grad()
    def __call__(

        self,

        batch_size: int = 1,

        generator: Optional[Union[torch.Generator, List[torch.Generator]]] = None,

        num_inference_steps: int = 1000,

        output_type: Optional[str] = "pil",

        return_dict: bool = True,

    ) -> Union[ImagePipelineOutput, Tuple]:
        r"""

        The call function to the pipeline for generation.



        Args:

            batch_size (`int`, *optional*, defaults to 1):

                The number of images to generate.

            generator (`torch.Generator`, *optional*):

                A [`torch.Generator`](https://pytorch.org/docs/stable/generated/torch.Generator.html) to make

                generation deterministic.

            num_inference_steps (`int`, *optional*, defaults to 1000):

                The number of denoising steps. More denoising steps usually lead to a higher quality image at the

                expense of slower inference.

            output_type (`str`, *optional*, defaults to `"pil"`):

                The output format of the generated image. Choose between `PIL.Image` or `np.array`.

            return_dict (`bool`, *optional*, defaults to `True`):

                Whether or not to return a [`~pipelines.ImagePipelineOutput`] instead of a plain tuple.



        Example:



        ```py

        >>> from diffusers import DDPMPipeline



        >>> # load model and scheduler

        >>> pipe = DDPMPipeline.from_pretrained("google/ddpm-cat-256")



        >>> # run pipeline in inference (sample random noise and denoise)

        >>> image = pipe().images[0]



        >>> # save image

        >>> image.save("ddpm_generated_image.png")

        ```



        Returns:

            [`~pipelines.ImagePipelineOutput`] or `tuple`:

                If `return_dict` is `True`, [`~pipelines.ImagePipelineOutput`] is returned, otherwise a `tuple` is

                returned where the first element is a list with the generated images

        """
        # Sample gaussian noise to begin loop
        if isinstance(self.unet.config.sample_size, int):
            image_shape = (
                batch_size,
                self.unet.config.in_channels,
                self.unet.config.sample_size,
                self.unet.config.sample_size,
            )
        else:
            image_shape = (batch_size, self.unet.config.in_channels, *self.unet.config.sample_size)

        if self.device.type == "mps":
            # randn does not work reproducibly on mps
            image = randn_tensor(image_shape, generator=generator)
            image = image.to(self.device)
        else:
            image = randn_tensor(image_shape, generator=generator, device=self.device)

        # set step values
        self.scheduler.set_timesteps(num_inference_steps)

        for t in self.progress_bar(self.scheduler.timesteps):
            # 1. predict noise model_output
            model_output = self.unet(image, t).sample

            # 2. compute previous image: x_t -> x_t-1
            image = self.scheduler.step(model_output, t, image, generator=generator).prev_sample

        image = (image / 2 + 0.5).clamp(0, 1)
        image = image.cpu().permute(0, 2, 3, 1).numpy()
        if output_type == "pil":
            image = self.numpy_to_pil(image)

        if not return_dict:
            return (image,)

        return ImagePipelineOutput(images=image)