resnet/DDPM_ResNet.py

#!/usr/bin/env python
# coding: utf-8

# # Library

# In[1]:


import torch
import torch.nn.functional as F
from torch import nn
from torch.cuda.amp import autocast

import torchvision
from torchvision.transforms import transforms
from torch.utils.data import DataLoader

from torch.optim import Adam

from einops import rearrange, reduce, repeat
import math
from random import random

from collections import namedtuple
from functools import partial
from tqdm.auto import tqdm
import logging
import os

from PIL import Image
from torchvision import utils


# # Helper

# ### Constant

# In[2]:


ModelPrediction =  namedtuple('ModelPrediction', ['pred_noise', 'pred_x_start'])


# ### Functions

# In[3]:


def exists(x):
    return x is not None

def default(val, d):
    if exists(val):
        return val
    return d() if callable(d) else d


# In[4]:


def cast_tuple(t, length = 1):
    if isinstance(t, tuple):
        return t
    return ((t,) * length)


# In[5]:


def divisible_by(numer, denom):
    return (numer % denom) == 0


# In[6]:


def identity(t, *args, **kwargs):
    return t


# In[7]:


def cycle(dl):
    while True:
        for data in dl:
            yield data


# In[8]:


def has_int_squareroot(num):
    return (math.sqrt(num) ** 2) == num


# In[9]:


def num_to_groups(num, divisor):
    groups = num // divisor
    remainder = num % divisor
    arr = [divisor] * groups
    if remainder > 0:
        arr.append(remainder)
    return arr


# In[10]:


def convert_image_to_fn(img_type, image):
    if image.mode != img_type:
        return image.convert(img_type)
    return image


# In[11]:


def extract(a, t, x_shape):
    b, *_ = t.shape
    out = a.gather(-1, t)
    return out.reshape(b, *((1,) * (len(x_shape) - 1)))


# ### Normalization Functions

# In[12]:


def normalize_to_neg_one_to_one(img):
    return img * 2 - 1

def unnormalize_to_zero_to_one(t):
    return (t + 1) * 0.5


# ### Sinusoidal positional embeds

# In[13]:


class SinusoidalPosEmb(nn.Module):
    def __init__(self, dim, theta = 10000):
        super().__init__()
        self.dim = dim
        self.theta = theta

    def forward(self, x):
        device = x.device
        half_dim = self.dim // 2
        emb = math.log(self.theta) / (half_dim - 1)
        emb = torch.exp(torch.arange(half_dim, device=device) * -emb)
        emb = x[:, None] * emb[None, :]
        emb = torch.cat((emb.sin(), emb.cos()), dim=-1)
        return emb


# In[14]:


class RandomOrLearnedSinusoidalPosEmb(nn.Module):
    """ following @crowsonkb 's lead with random (learned optional) sinusoidal pos emb """
    """ https://github.com/crowsonkb/v-diffusion-jax/blob/master/diffusion/models/danbooru_128.py#L8 """

    def __init__(self, dim, is_random = False):
        super().__init__()
        assert divisible_by(dim, 2)
        half_dim = dim // 2
        self.weights = nn.Parameter(torch.randn(half_dim), requires_grad = not is_random)

    def forward(self, x):
        x = rearrange(x, 'b -> b 1')
        freqs = x * rearrange(self.weights, 'd -> 1 d') * 2 * math.pi
        fouriered = torch.cat((freqs.sin(), freqs.cos()), dim = -1)
        fouriered = torch.cat((x, fouriered), dim = -1)
        return fouriered


# ### Schedule

# In[15]:


def linear_beta_schedule(timesteps):
    """
    linear schedule, proposed in original ddpm paper
    """
    scale = 1000 / timesteps
    beta_start = scale * 0.0001
    beta_end = scale * 0.02
    return torch.linspace(beta_start, beta_end, timesteps, dtype = torch.float64)


# In[16]:


def cosine_beta_schedule(timesteps, s = 0.008):
    """
    cosine schedule
    as proposed in https://openreview.net/forum?id=-NEXDKk8gZ
    """
    steps = timesteps + 1
    t = torch.linspace(0, timesteps, steps, dtype = torch.float64) / timesteps
    alphas_cumprod = torch.cos((t + s) / (1 + s) * math.pi * 0.5) ** 2
    alphas_cumprod = alphas_cumprod / alphas_cumprod[0]
    betas = 1 - (alphas_cumprod[1:] / alphas_cumprod[:-1])
    return torch.clip(betas, 0, 0.999)


# In[17]:


def sigmoid_beta_schedule(timesteps, start = -3, end = 3, tau = 1, clamp_min = 1e-5):
    """
    sigmoid schedule
    proposed in https://arxiv.org/abs/2212.11972 - Figure 8
    better for images > 64x64, when used during training
    """
    steps = timesteps + 1
    t = torch.linspace(0, timesteps, steps, dtype = torch.float64) / timesteps
    v_start = torch.tensor(start / tau).sigmoid()
    v_end = torch.tensor(end / tau).sigmoid()
    alphas_cumprod = (-((t * (end - start) + start) / tau).sigmoid() + v_end) / (v_end - v_start)
    alphas_cumprod = alphas_cumprod / alphas_cumprod[0]
    betas = 1 - (alphas_cumprod[1:] / alphas_cumprod[:-1])
    return torch.clip(betas, 0, 0.999)


# # Diffusion model

# In[18]:


class GaussianDiffusion(nn.Module):
    # Copy from https://github.com/lucidrains/denoising-diffusion-pytorch/blob/main/denoising_diffusion_pytorch/denoising_diffusion_pytorch.py#L163

    def __init__(
        self,
        model,
        *,
        image_size,
        timesteps = 1000,
        sampling_timesteps = None,
        objective = 'pred_noise',
        beta_schedule = 'linear',
        schedule_fn_kwargs = dict(),
        ddim_sampling_eta = 0.,
        auto_normalize = True,
        offset_noise_strength = 0.,  # https://www.crosslabs.org/blog/diffusion-with-offset-noise
        min_snr_loss_weight = False, # https://arxiv.org/abs/2303.09556
        min_snr_gamma = 5
    ):
        super().__init__()
        assert not (type(self) == GaussianDiffusion and model.channels != model.out_dim)
        assert not hasattr(model, 'random_or_learned_sinusoidal_cond') or not model.random_or_learned_sinusoidal_cond

        self.model = model

        self.channels = self.model.channels
        self.self_condition = self.model.self_condition

        self.image_size = image_size

        self.objective = objective

        assert objective in {'pred_noise', 'pred_x0', 'pred_v'}, 'objective must be either pred_noise (predict noise) or pred_x0 (predict image start) or pred_v (predict v [v-parameterization as defined in appendix D of progressive distillation paper, used in imagen-video successfully])'

        if beta_schedule == 'linear':
            beta_schedule_fn = linear_beta_schedule
        elif beta_schedule == 'cosine':
            beta_schedule_fn = cosine_beta_schedule
        elif beta_schedule == 'sigmoid':
            beta_schedule_fn = sigmoid_beta_schedule
        else:
            raise ValueError(f'unknown beta schedule {beta_schedule}')

        betas = beta_schedule_fn(timesteps, **schedule_fn_kwargs)

        alphas = 1. - betas
        alphas_cumprod = torch.cumprod(alphas, dim=0)
        alphas_cumprod_prev = F.pad(alphas_cumprod[:-1], (1, 0), value = 1.)

        timesteps, = betas.shape
        self.num_timesteps = int(timesteps)

        # sampling related parameters

        self.sampling_timesteps = default(sampling_timesteps, timesteps) # default num sampling timesteps to number of timesteps at training

        assert self.sampling_timesteps <= timesteps
        self.is_ddim_sampling = self.sampling_timesteps < timesteps
        self.ddim_sampling_eta = ddim_sampling_eta

        # helper function to register buffer from float64 to float32

        register_buffer = lambda name, val: self.register_buffer(name, val.to(torch.float32))

        register_buffer('betas', betas)
        register_buffer('alphas_cumprod', alphas_cumprod)
        register_buffer('alphas_cumprod_prev', alphas_cumprod_prev)

        # calculations for diffusion q(x_t | x_{t-1}) and others

        register_buffer('sqrt_alphas_cumprod', torch.sqrt(alphas_cumprod))
        register_buffer('sqrt_one_minus_alphas_cumprod', torch.sqrt(1. - alphas_cumprod))
        register_buffer('log_one_minus_alphas_cumprod', torch.log(1. - alphas_cumprod))
        register_buffer('sqrt_recip_alphas_cumprod', torch.sqrt(1. / alphas_cumprod))
        register_buffer('sqrt_recipm1_alphas_cumprod', torch.sqrt(1. / alphas_cumprod - 1))

        # calculations for posterior q(x_{t-1} | x_t, x_0)

        posterior_variance = betas * (1. - alphas_cumprod_prev) / (1. - alphas_cumprod)

        # above: equal to 1. / (1. / (1. - alpha_cumprod_tm1) + alpha_t / beta_t)

        register_buffer('posterior_variance', posterior_variance)

        # below: log calculation clipped because the posterior variance is 0 at the beginning of the diffusion chain

        register_buffer('posterior_log_variance_clipped', torch.log(posterior_variance.clamp(min =1e-20)))
        register_buffer('posterior_mean_coef1', betas * torch.sqrt(alphas_cumprod_prev) / (1. - alphas_cumprod))
        register_buffer('posterior_mean_coef2', (1. - alphas_cumprod_prev) * torch.sqrt(alphas) / (1. - alphas_cumprod))

        # offset noise strength - in blogpost, they claimed 0.1 was ideal

        self.offset_noise_strength = offset_noise_strength

        # derive loss weight
        # snr - signal noise ratio

        snr = alphas_cumprod / (1 - alphas_cumprod)

        # https://arxiv.org/abs/2303.09556

        maybe_clipped_snr = snr.clone()
        if min_snr_loss_weight:
            maybe_clipped_snr.clamp_(max = min_snr_gamma)

        if objective == 'pred_noise':
            register_buffer('loss_weight', maybe_clipped_snr / snr)
        elif objective == 'pred_x0':
            register_buffer('loss_weight', maybe_clipped_snr)
        elif objective == 'pred_v':
            register_buffer('loss_weight', maybe_clipped_snr / (snr + 1))

        # auto-normalization of data [0, 1] -> [-1, 1] - can turn off by setting it to be False

        self.normalize = normalize_to_neg_one_to_one if auto_normalize else identity
        self.unnormalize = unnormalize_to_zero_to_one if auto_normalize else identity

    @property
    def device(self):
        return self.betas.device

    def predict_start_from_noise(self, x_t, t, noise):
        return (
            extract(self.sqrt_recip_alphas_cumprod, t, x_t.shape) * x_t -
            extract(self.sqrt_recipm1_alphas_cumprod, t, x_t.shape) * noise
        )

    def predict_noise_from_start(self, x_t, t, x0):
        return (
            (extract(self.sqrt_recip_alphas_cumprod, t, x_t.shape) * x_t - x0) / \
            extract(self.sqrt_recipm1_alphas_cumprod, t, x_t.shape)
        )

    def predict_v(self, x_start, t, noise):
        return (
            extract(self.sqrt_alphas_cumprod, t, x_start.shape) * noise -
            extract(self.sqrt_one_minus_alphas_cumprod, t, x_start.shape) * x_start
        )

    def predict_start_from_v(self, x_t, t, v):
        return (
            extract(self.sqrt_alphas_cumprod, t, x_t.shape) * x_t -
            extract(self.sqrt_one_minus_alphas_cumprod, t, x_t.shape) * v
        )

    def q_posterior(self, x_start, x_t, t):
        posterior_mean = (
            extract(self.posterior_mean_coef1, t, x_t.shape) * x_start +
            extract(self.posterior_mean_coef2, t, x_t.shape) * x_t
        )
        posterior_variance = extract(self.posterior_variance, t, x_t.shape)
        posterior_log_variance_clipped = extract(self.posterior_log_variance_clipped, t, x_t.shape)
        return posterior_mean, posterior_variance, posterior_log_variance_clipped

    def model_predictions(self, x, t, x_self_cond = None, clip_x_start = False, rederive_pred_noise = False):
        model_output = self.model(x, t, x_self_cond)
        maybe_clip = partial(torch.clamp, min = -1., max = 1.) if clip_x_start else identity

        if self.objective == 'pred_noise':
            pred_noise = model_output
            x_start = self.predict_start_from_noise(x, t, pred_noise)
            x_start = maybe_clip(x_start)

            if clip_x_start and rederive_pred_noise:
                pred_noise = self.predict_noise_from_start(x, t, x_start)

        elif self.objective == 'pred_x0':
            x_start = model_output
            x_start = maybe_clip(x_start)
            pred_noise = self.predict_noise_from_start(x, t, x_start)

        elif self.objective == 'pred_v':
            v = model_output
            x_start = self.predict_start_from_v(x, t, v)
            x_start = maybe_clip(x_start)
            pred_noise = self.predict_noise_from_start(x, t, x_start)

        return ModelPrediction(pred_noise, x_start)

    def p_mean_variance(self, x, t, x_self_cond = None, clip_denoised = True):
        preds = self.model_predictions(x, t, x_self_cond)
        x_start = preds.pred_x_start

        if clip_denoised:
            x_start.clamp_(-1., 1.)

        model_mean, posterior_variance, posterior_log_variance = self.q_posterior(x_start = x_start, x_t = x, t = t)
        return model_mean, posterior_variance, posterior_log_variance, x_start

    @torch.inference_mode()
    def p_sample(self, x, t: int, x_self_cond = None):
        b, *_, device = *x.shape, self.device
        batched_times = torch.full((b,), t, device = device, dtype = torch.long)
        model_mean, _, model_log_variance, x_start = self.p_mean_variance(x = x, t = batched_times, x_self_cond = x_self_cond, clip_denoised = True)
        noise = torch.randn_like(x) if t > 0 else 0. # no noise if t == 0
        pred_img = model_mean + (0.5 * model_log_variance).exp() * noise
        return pred_img, x_start

    @torch.inference_mode()
    def p_sample_loop(self, shape, return_all_timesteps = False):
        batch, device = shape[0], self.device

        img = torch.randn(shape, device = device)
        imgs = [img]

        x_start = None

        for t in tqdm(reversed(range(0, self.num_timesteps)), desc = 'sampling loop time step', total = self.num_timesteps):
            self_cond = x_start if self.self_condition else None
            img, x_start = self.p_sample(img, t, self_cond)
            imgs.append(img)

        ret = img if not return_all_timesteps else torch.stack(imgs, dim = 1)

        ret = self.unnormalize(ret)
        return ret

    @torch.inference_mode()
    def ddim_sample(self, shape, return_all_timesteps = False):
        batch, device, total_timesteps, sampling_timesteps, eta, objective = shape[0], self.device, self.num_timesteps, self.sampling_timesteps, self.ddim_sampling_eta, self.objective

        times = torch.linspace(-1, total_timesteps - 1, steps = sampling_timesteps + 1)   # [-1, 0, 1, 2, ..., T-1] when sampling_timesteps == total_timesteps
        times = list(reversed(times.int().tolist()))
        time_pairs = list(zip(times[:-1], times[1:])) # [(T-1, T-2), (T-2, T-3), ..., (1, 0), (0, -1)]

        img = torch.randn(shape, device = device)
        imgs = [img]

        x_start = None

        for time, time_next in tqdm(time_pairs, desc = 'sampling loop time step'):
            time_cond = torch.full((batch,), time, device = device, dtype = torch.long)
            self_cond = x_start if self.self_condition else None
            pred_noise, x_start, *_ = self.model_predictions(img, time_cond, self_cond, clip_x_start = True, rederive_pred_noise = True)

            if time_next < 0:
                img = x_start
                imgs.append(img)
                continue

            alpha = self.alphas_cumprod[time]
            alpha_next = self.alphas_cumprod[time_next]

            sigma = eta * ((1 - alpha / alpha_next) * (1 - alpha_next) / (1 - alpha)).sqrt()
            c = (1 - alpha_next - sigma ** 2).sqrt()

            noise = torch.randn_like(img)

            img = x_start * alpha_next.sqrt() + \
                  c * pred_noise + \
                  sigma * noise

            imgs.append(img)

        ret = img if not return_all_timesteps else torch.stack(imgs, dim = 1)

        ret = self.unnormalize(ret)
        return ret

    @torch.inference_mode()
    def sample(self, batch_size = 16, return_all_timesteps = False):
        image_size, channels = self.image_size, self.channels
        sample_fn = self.p_sample_loop if not self.is_ddim_sampling else self.ddim_sample
        return sample_fn((batch_size, channels, image_size, image_size), return_all_timesteps = return_all_timesteps)

    @torch.inference_mode()
    def interpolate(self, x1, x2, t = None, lam = 0.5):
        b, *_, device = *x1.shape, x1.device
        t = default(t, self.num_timesteps - 1)

        assert x1.shape == x2.shape

        t_batched = torch.full((b,), t, device = device)
        xt1, xt2 = map(lambda x: self.q_sample(x, t = t_batched), (x1, x2))

        img = (1 - lam) * xt1 + lam * xt2

        x_start = None

        for i in tqdm(reversed(range(0, t)), desc = 'interpolation sample time step', total = t):
            self_cond = x_start if self.self_condition else None
            img, x_start = self.p_sample(img, i, self_cond)

        return img

    @autocast(enabled = False)
    def q_sample(self, x_start, t, noise = None):
        noise = default(noise, lambda: torch.randn_like(x_start))

        return (
            extract(self.sqrt_alphas_cumprod, t, x_start.shape) * x_start +
            extract(self.sqrt_one_minus_alphas_cumprod, t, x_start.shape) * noise
        )

    def p_losses(self, x_start, t, noise = None, offset_noise_strength = None):
        b, c, h, w = x_start.shape

        noise = default(noise, lambda: torch.randn_like(x_start))

        # offset noise - https://www.crosslabs.org/blog/diffusion-with-offset-noise

        offset_noise_strength = default(offset_noise_strength, self.offset_noise_strength)

        if offset_noise_strength > 0.:
            offset_noise = torch.randn(x_start.shape[:2], device = self.device)
            noise += offset_noise_strength * rearrange(offset_noise, 'b c -> b c 1 1')

        # noise sample

        x = self.q_sample(x_start = x_start, t = t, noise = noise)

        # if doing self-conditioning, 50% of the time, predict x_start from current set of times
        # and condition with unet with that
        # this technique will slow down training by 25%, but seems to lower FID significantly

        x_self_cond = None
        if self.self_condition and random() < 0.5:
            with torch.no_grad():
                x_self_cond = self.model_predictions(x, t).pred_x_start
                x_self_cond.detach_()

        # predict and take gradient step

        model_out = self.model(x, t, x_self_cond)

        if self.objective == 'pred_noise':
            target = noise
        elif self.objective == 'pred_x0':
            target = x_start
        elif self.objective == 'pred_v':
            v = self.predict_v(x_start, t, noise)
            target = v
        else:
            raise ValueError(f'unknown objective {self.objective}')

        loss = F.mse_loss(model_out, target, reduction = 'none')
        loss = reduce(loss, 'b ... -> b', 'mean')

        loss = loss * extract(self.loss_weight, t, loss.shape)
        return loss.mean()

    def forward(self, img, *args, **kwargs):
        b, c, h, w, device, img_size, = *img.shape, img.device, self.image_size
        assert h == img_size and w == img_size, f'height and width of image must be {img_size}'
        t = torch.randint(0, self.num_timesteps, (b,), device=device).long()

        img = self.normalize(img)
        return self.p_losses(img, t, *args, **kwargs)


# # Resnet Model

# In[19]:


def default_conv(in_channels, out_channels, kernel_size, bias=True):
    return nn.Conv2d(
        in_channels, out_channels, kernel_size,
        padding=(kernel_size//2), bias=bias)


# In[20]:


class Swish(nn.Module):
    def forward(self, x):
        return x * torch.sigmoid(x)


# In[21]:


class AttnBlock(nn.Module):
    def __init__(self, in_ch):
        super().__init__()
        self.group_norm = nn.GroupNorm(32, in_ch)
        self.proj_q = nn.Conv2d(in_ch, in_ch, 1, stride=1, padding=0)
        self.proj_k = nn.Conv2d(in_ch, in_ch, 1, stride=1, padding=0)
        self.proj_v = nn.Conv2d(in_ch, in_ch, 1, stride=1, padding=0)
        self.proj = nn.Conv2d(in_ch, in_ch, 1, stride=1, padding=0)

    def forward(self, x):
        B, C, H, W = x.shape
        h = self.group_norm(x)
        q = self.proj_q(h)
        k = self.proj_k(h)
        v = self.proj_v(h)

        q = q.permute(0, 2, 3, 1).view(B, H * W, C)
        k = k.view(B, C, H * W)
        w = torch.bmm(q, k) * (int(C) ** (-0.5))
        assert list(w.shape) == [B, H * W, H * W]
        w = F.softmax(w, dim=-1)

        v = v.permute(0, 2, 3, 1).view(B, H * W, C)
        h = torch.bmm(w, v)
        assert list(h.shape) == [B, H * W, C]
        h = h.view(B, H, W, C).permute(0, 3, 1, 2)
        h = self.proj(h)

        return x + h


# In[22]:


class ResBlock(nn.Module):
    def __init__(self, in_ch, out_ch, tdim, dropout, attn=False):
        super().__init__()
        self.block1 = nn.Sequential(
            nn.GroupNorm(32, in_ch),
            Swish(),
            nn.Conv2d(in_ch, out_ch, 3, stride=1, padding=1),
        )
        self.temb_proj = nn.Sequential(
            Swish(),
            nn.Linear(tdim, out_ch),
        )
        self.block2 = nn.Sequential(
            nn.GroupNorm(32, out_ch),
            Swish(),
            nn.Dropout(dropout),
            nn.Conv2d(out_ch, out_ch, 3, stride=1, padding=1),
        )
        if in_ch != out_ch:
            self.shortcut = nn.Conv2d(in_ch, out_ch, 1, stride=1, padding=0)
        else:
            self.shortcut = nn.Identity()
        if attn:
            self.attn = AttnBlock(out_ch)
        else:
            self.attn = nn.Identity()

    def forward(self, x, temb):
        h = self.block1(x)
        h += self.temb_proj(temb)[:, :, None, None]
        h = self.block2(h)

        h = h + self.shortcut(x)
        h = self.attn(h)
        return h


# In[23]:


class EDSR(nn.Module):
    # Modified from https://github.com/sanghyun-son/EDSR-PyTorch/blob/master/src/model/edsr.py#L31

    def __init__(self,
                 resblocks=['ResBlock', 'ResBlock', 'ResBlock', 'AttnBlock', 'AttnBlock', 'ResBlock', 'ResBlock', 'ResBlock'],
                 n_feats=128,
                 t_dim=256,
                 dropout=0.1,
                 channels=1,
                 out_dim=1,
                 self_condition = False,
                 learned_sinusoidal_cond=False,
                 random_fourier_features=False,
                 learned_sinusoidal_dim=16,
                 sinusoidal_pos_emb_theta=10000,
                 conv=default_conv):
        super(EDSR, self).__init__()

        self.resblocks = resblocks
        self.n_feats = n_feats
        self.t_dim = t_dim
        self.dropout = dropout
        self.channels = channels
        self.out_dim = out_dim
        self.self_condition = self_condition
        self.kernel_size = 3

        # define time embedding
        if learned_sinusoidal_cond:
            sinu_pos_emb = RandomOrLearnedSinusoidalPosEmb(learned_sinusoidal_dim, random_fourier_features)
            fourier_dim = learned_sinusoidal_dim + 1
        else:
            sinu_pos_emb = SinusoidalPosEmb(dim=self.n_feats, theta=sinusoidal_pos_emb_theta)
            fourier_dim = self.n_feats

        self.time_mlp = nn.Sequential(
            sinu_pos_emb,
            nn.Linear(fourier_dim, self.t_dim),
            nn.GELU(),
            nn.Linear(self.t_dim, self.t_dim)
        )

        # define head module
        self.head = conv(self.channels, self.n_feats, self.kernel_size)

        # define body module
        self.body = nn.ModuleList()
        for block in resblocks:
            if block == "ResBlock":
                self.body.append(
                    ResBlock(in_ch=self.n_feats,
                             out_ch=self.n_feats,
                             tdim=self.t_dim,
                             dropout=self.dropout,
                             attn=False))
            elif block == "AttnBlock":
                self.body.append(
                    ResBlock(in_ch=self.n_feats,
                             out_ch=self.n_feats,
                             tdim=self.t_dim,
                             dropout=self.dropout,
                             attn=True))
            else:
                raise NotImplementedError("Model currently doesn't support this kind of block!")
        self.body.append(conv(self.n_feats, self.n_feats, self.kernel_size))

        # define tail module
        self.tail = conv(self.n_feats, self.out_dim, self.kernel_size)


    def forward(self, x, t, cond=None):
        t = self.time_mlp(t)

        x = self.head(x)

        res = x
        for block in self.body:
            if isinstance(block, ResBlock):
                res = block(res, t)
            else:
                res = block(res)
                res += x

        x = self.tail(res)

        return x


# # Train

# In[24]:


# output dir
save_path = '/content/DDPM_ResNet_Unet/resnet/model'
log_path = '/content/DDPM_ResNet_Unet/resnet/log'

if not os.path.exists(log_path):
    os.mkdir(log_path)
if not os.path.exists(save_path):
    os.mkdir(save_path)


# In[25]:


# setup logging

# Setup logging to file
logging.basicConfig(
     filename=os.path.join(log_path, 'info.log'),
     filemode="w",
     level=logging.DEBUG,
     format= '[%(asctime)s] %(levelname)s - %(message)s',
     datefmt='%H:%M:%S',
     force=True
 )


# Stop PIL from printing to file
pil_logger = logging.getLogger('PIL')
pil_logger.setLevel(logging.INFO)

# write and print at the same time
console = logging.StreamHandler()
console.setLevel(logging.INFO)
logging.getLogger().addHandler(console)

logger = logging.getLogger('Diffusion_Resnet')


# In[26]:


# define model
model = EDSR(
    resblocks=['ResBlock', 'ResBlock', 'ResBlock', 'AttnBlock', 'AttnBlock', 
               'AttnBlock', 'AttnBlock', 'ResBlock', 'ResBlock', 'ResBlock',],
    n_feats=256,
    t_dim=512,
    dropout=0.1,
    channels=1, # MNIST
    out_dim=1, # MNIST
    learned_sinusoidal_cond=False,
    random_fourier_features=False,
    learned_sinusoidal_dim=16,
    sinusoidal_pos_emb_theta=10000,)

diffusion_model = GaussianDiffusion(
        model,
        image_size=28, # MNIST
        timesteps=1000,
        sampling_timesteps=None,
        objective ='pred_noise',
        beta_schedule ='linear',
        schedule_fn_kwargs=dict(),
        ddim_sampling_eta= 0.,
        auto_normalize = True,
        offset_noise_strength = 0.,  # https://www.crosslabs.org/blog/diffusion-with-offset-noise
        min_snr_loss_weight = False, # https://arxiv.org/abs/2303.09556
        min_snr_gamma = 5)


# In[27]:


# define dataset
transform = transforms.Compose([
    transforms.ToTensor(),
    # v2.Normalize((0.1307,), (0.3081,)), # https://stackoverflow.com/questions/70892017/normalize-mnist-in-pytorch
])

train_dataset = torchvision.datasets.MNIST(root='.', train=True,
                                     download=True, transform=transform)
# test_dataset = torchvision.datasets.MNIST(root='.', train=True,
#                                      download=True, transform=transform)

train_dataloader = DataLoader(train_dataset, batch_size=32, shuffle=True)
# test_dataloader = DataLoader(test_dataset, batch_size=32, shuffle=True)


# In[28]:


# define optimizer
train_lr = 1e-4
adam_betas = (0.9, 0.99)

optimizer = Adam(diffusion_model.parameters(),
                 lr=train_lr,
                 betas=adam_betas)


# In[29]:


# device
device = torch.device('cuda' if torch.cuda.is_available() else 'cpu')


# In[30]:


# trainer
max_epoches = 50
iter_print = 100
iter_sample = 1000
save_each = 1

diffusion_model = diffusion_model.to(device)

last_trained_path = None
if last_trained_path:
    data = torch.load(os.path.join(last_trained_path))
    diffusion_model.load_state_dict(data['model'])
    optimizer.load_state_dict(data['opt'])
    count = data['step']
    start_epoch = data['epoch']
    log_loss = data['loss']
else:
    count = 0
    start_epoch = 1
    log_loss = []

for epoch in range(start_epoch, max_epoches+1):
    diffusion_model.train()
    for img, _ in train_dataloader:
        img = img.to(device)

        loss = diffusion_model(img)

        optimizer.zero_grad()
        loss.backward()
        optimizer.step()

        if count % iter_print == 0 or count == 0:
            logger.info('Epoch {}/{}, Iter {}: Loss = {}, lr = {}'.format(
                epoch,
                max_epoches,
                count,
                loss.mean().item(),
                train_lr,
            ))

        log_loss.append(loss.mean().item())

        loss = None

        count += 1

        if count % iter_sample == 0:
            diffusion_model.eval()

            sample_imgs = diffusion_model.sample(batch_size=16)

            utils.save_image(sample_imgs,
                            os.path.join(log_path, f"iter_{count}.png"),
                            nrow = int(math.sqrt(16)))


    if epoch % save_each == 0:
        data = {
            'model': diffusion_model.state_dict(),
            'opt': optimizer.state_dict(),
            'step': count,
            'epoch': epoch,
            'loss': log_loss,
        }

        torch.save(data, os.path.join(save_path, f"epoch_{epoch}.pth"))